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Magnetic measurements of a three-dimensional (3D) molecular magnet built of Mn9[W(CN)8]6 clusters have been carried out to study its static and dynamic properties. Measurements of ac susceptibility in the presence of static magnetic field revealed slow magnetic relaxations. It was found that for the 120 Hz wave frequency the optimal static field which maximizes the imaginary component of the ac susceptibility is about 500 Oe. [ABSTRACT FROM AUTHOR]

The bistability of multiple physical properties driven by external stimuli in a solid is a desired prerequisite for its application in memory devices with convenient data readout. We present a pathway for thermal bistability detectable in four physical properties: magnetic, light absorption, second-harmonic generation (SHG), and dielectric. We report a novel heterometallic (TBA){[Fe II (phIN) 4 ][Re V (CN) 8 ]} ⋅ (phIN) (1) (TBA=tetrabutylammonium cation, phIN=phenyl isonicotinate) cyanido-bridged chain material. Owing to an appropriate {N 6 } coordination sphere of Fe(II) centers, 1 reveals a thermal spin crossover (SCO) effect which is complete and cooperative providing a distinct thermal hysteresis loop in magnetic measurements. Moreover, it exhibits simultaneous thermal bistability in (a) visible-light absorption due to the presence of efficient d-d electronic transitions in the low-spin (LS) state, (b) SHG activity as it crystallizes in a polar Cc space group due to the bulky substituent on phIN ligands, and (c) dielectric parameters, including dielectric constant, which can be correlated with subtle changes in polarity between LS and HS (high spin) phases. Thus, we present a remarkable thermally controlled hysteretic behavior in four physical functionalities realized by properly functionalizing an SCO-active coordination compound., (© 2024 Wiley-VCH GmbH.)

We present a synergistic experimental-theoretical methodology for the investigation of lanthanide-based single-molecule magnets (SMMs), demonstrated using the example of novel heterometallic molecules incorporating Nd 3+ /Ce 3+ ions combined with three different, rarely explored, pentacyanidocobaltate(III) metalloligands, [Co III (CN) 5 (azido/nitrito- N /iodido)] 3- . The theoretical part of our approach broadens the exploration of ab initio calculations for lanthanide(III) complexes toward the convenient simulations of such physical characteristics as directional dependences of Helmholtz energy, magnetization, susceptibility, and their thermal and field evolution, as well as light absorption and emission bands. This work was conducted using newly designed SlothPy software (https://slothpy.org). It is introduced as an open-source Python library for simulating various physical properties from first-principles based on results of electronic structure calculations obtained within popular quantum chemistry packages. The computational results were confronted with spectroscopic and ac / dc -magnetic data, the latter analyzed using previously designed relACs software. The combination of experimental and computational methods gave insight into phonon-assisted magnetic relaxation mechanisms, disentangling them from the temperature-independent quantum tunneling of magnetization and emphasizing the role of local-mode processes. This study provides an understanding of the changes in lanthanide(III) magnetic anisotropy introduced with pentacyanidocobaltates(III) modifications, theoretically exploring also potential applications of reported compounds as anisotropy switches or optical thermometers.

We present an efficient strategy for obtaining red-emissive molecular nanomagnets by exploring a heterometallic approach. We report the {[Dy III (4-pyridone) 5 ] 2 [Ru II (CN) 2 (phen) 2 ] 2 }·(CF 3 SO 3 ) 6 ·2MeOH (phen = 1,10-phenanthroline) compound composed of exchange-coupled {DyIII2} single-molecule magnets functionalized by Ru(II)-cyanido units. The latter makes the resulting {DyIII2RuII2} 6+ cations a unique example of a soluble lanthanide SMM exhibiting red charge-transfer photoluminescence in the solution and solid state, well enhanced when compared with the cyanido precursor.

The design of high-performance optical materials can be realized using coordination polymers (CPs) often supported by non-covalent interactions, such as metallophilicity. The challenge is to control two or more optical effects, e.g. , non-linear optics (NLO) and photoluminescence (PL). We present a new strategy for the combination of the NLO effect of second-harmonic generation (SHG) and the visible PL achieved by linking dicyanidoaurate(i) ions, which form luminescent metallophilic stacks, with cadmium(ii) complexes bearing chiral amine ligands, used to break the crystal's symmetry. We report a family of NLO- and PL-active materials based on heterometallic Cd(ii)-Au(i) coordination systems incorporating enantiopure propane-1,2-diamine (pda) ligands (1- S , 1- R ), their racemate (2), and enantiopure trans -cyclopentane-1,2-diamine (cpda) ligands (3- S , 3- R ). Due to acentric space groups, they exhibit the SHG signal, tunable within the range of 11-24% of the KDP reference, which was correlated with the dipole moments of Cd(ii) units. They show efficient blue PL whose energy and quantum yield, the latter ranging from 0.40 to 0.83, are controlled by Cd(ii) complexes affecting the Au-Au distances and vibrational modes. We prove that chiral Cd(ii)-amine complexes play the role of molecular agents for the stimulation of both the NLO and PL of the materials based on aurophilic stacks., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Since the last century, we have witnessed the development of molecular magnetism which deals with magnetic materials based on molecular species, i.e., organic radicals and metal complexes. Among them, the broadest attention was devoted to molecule-based ferro-/ferrimagnets, spin transition materials, including those exploring electron transfer, molecular nanomagnets, such as single-molecule magnets (SMMs), molecular qubits, and stimuli-responsive magnetic materials. Their physical properties open the application horizons in sensors, data storage, spintronics, and quantum computation. It was found that various optical phenomena, such as thermochromism, photoswitching of magnetic and optical characteristics, luminescence, nonlinear optical and chiroptical effects, as well as optical responsivity to external stimuli, can be implemented into molecule-based magnetic materials. Moreover, the fruitful interactions of these optical effects with magnetism in molecule-based materials can provide new physical cross-effects and multifunctionality, enriching the applications in optical, electronic, and magnetic devices. This Review aims to show the scope of optical phenomena generated in molecule-based magnetic materials, including the recent advances in such areas as high-temperature photomagnetism, optical thermometry utilizing SMMs, optical addressability of molecular qubits, magneto-chiral dichroism, and opto-magneto-electric multifunctionality. These findings are discussed in the context of the types of optical phenomena accessible for various classes of molecule-based magnetic materials.

Multifunctional optical materials can be realized by combining stimuli-responsive photoluminescence (PL), e.g. , optical thermometry, with non-linear optical (NLO) effects, such as second-harmonic generation (SHG). We report a novel approach towards SHG-active luminescent thermometers achieved by constructing unique iridium(iii) complexes, cis -[Ir III (CN) 2 ( R , R -pinppy) 2 ] - ( R , R -pinppy = ( R , R )-2-phenyl-4,5-pinenopyridine), bearing both a chiral 2-phenylpyridine derivative and cyanido ligands, the latter enabling the formation of a series of molecular materials: (TBA)[Ir III (CN) 2 ( R , R -pinppy) 2 ]·2MeCN (1) (TBA + = tetrabutylammonium) and ( n Bu-DABCO) 2 [Ir III (CN) 2 ( R , R -pinppy) 2 ](i)·MeCN (2) ( n Bu-DABCO + = 1-( n -butyl)-1,4-diazabicyclo-[2.2.2]octan-1-ium) hybrid salts, (TBA) 2 {[La III (NO 3 ) 3 (H 2 O) 0.5 ] 2 [Ir III (CN) 2 ( R , R -pinppy) 2 ] 2 } (3) square molecules, and {[La III (NO 3 ) 2 (dmf) 3 ][Ir III (CN) 2 ( R , R -pinppy) 2 ]}·MeCN (4) coordination chains. Thanks to the chiral pinene group, 1-4 crystallize in non-centrosymmetric space groups leading to SHG activity, while the N,C-coordination of ppy-type ligands to Ir(iii) centers generates visible charge-transfer (CT) photoluminescence. The PL characteristics are distinctly temperature-dependent which was utilized in achieving ratiometric optical thermometry below 220 K. The PL phenomena were rationalized by DFT/TD-DFT calculations indicating an MLCT-type of the emission in obtained Ir(iii) complexes with the rich vibronic structure providing a few emission bands that variously depend on temperature due to the role of thermally activated vibrations. As these crucial vibrational modes depend on the crystal lattice, the thermometry performance differs within 1-4 being the most efficient in 4 while the SHG is by far the best also for 4. This proves that pinene-functionalized cyclometalated dicyanidoiridates(iii) are great prerequisites for tunable PL-NLO conjunction with the most effective multifunctionality ensured by the insertion of these anions into bimetallic frameworks., Competing Interests: There are no conflicts to declare., (This journal is © the Partner Organisations.)

Switching of multiple physical properties by external stimuli in dynamic materials enables applications in, e.g., smart sensors, biomedical tools, as well as data-storage devices. Among stimuli-responsive materials, inorganic-organic molecular hybrids exhibiting thermal order-disorder phase transitions were tested as promising molecular switches of electrical characteristics, including dielectric constant. We aimed at broadening the multifunctional potential of such hybrid materials towards the switching of not only electrical but also other physical properties, e.g., light emission. We report two ionic salts based on luminescent tetracyanidonitridorhenate(V) anions bearing two different diamine ligands, 1,2-diaminoethane (1) and 1,3-diaminopropane (2), both crystallizing with polar N-methyl-dabconium cations. They exhibit an order-disorder phase transition related to the heating-induced turning-on of the rotation of polar cations. This leads to a unique synchronous switching of the dielectric constant as well as metal-complex-centered photoluminescence, as demonstrated by changes in, e.g., emission lifetime. The roles of organic cations, non-trivial Re(V) complexes, and their interaction in achieving the coupled thermal switching of electrical and optical properties are discussed utilizing experimental and theoretical approaches., (© 2023 Wiley-VCH GmbH.)

The triphenylmethane (trityl) group has been recognized as a supramolecular synthon in crystal engineering, molecular machine rotors and stereochemical chirality inductors in materials science. Herein we demonstrate for the first time how it can be utilized in the domain of molecular magnetic materials through shaping of single molecule magnet (SMM) properties within the lanthanide complexes in tandem with other non-covalent interactions. Trityl-appended mono- (HL 1 ) and bis-compartmental (HL 2 ) hydrazone ligands were synthesized and complexated with Dy(III) and Er(III) triflate and nitrate salts to generate four monometallic (1-4) and two bimetallic (5, 6) complexes. The static and dynamic magnetic properties of 1-6 were investigated, revealing that only ligand HL 1 induces assemblies (1-4) capable of showing SMM behaviour, with Dy(III) congeners (1, 2) able to exhibit the phenomenon also under zero field conditions. Theoretical ab initio studies helped in determination of Dy(III) energetic levels, magnetic anisotropic axes and corroborated magnetic relaxation mechanisms to be a combination of Raman and quantum tunnelling in zero dc field, the latter being cancelled in the optimum non-zero dc field. Our work represents the first study of magneto-structural correlations within the trityl Ln-SMMs, leading to generation of slowly relaxing zero-field dysprosium complexes within the hydrogen-bonded assemblies., (© 2023 Wiley-VCH GmbH.)

A conjunction of Single-Molecule Magnet (SMM) behavior and luminescence thermometry is an emerging research line aiming at contactless read-out of temperature in future SMM-based devices. The shared working range between slow magnetic relaxation and the thermometric response is typically narrow or absent. We report Tb III -based emissive SMMs formed in a cyanido-bridged framework whose properties are governed by the reversible structural transformation from [Tb III (H 2 O) 2 ][Co III (CN) 6 ] ⋅ 2.7H 2 O (1) to its dehydrated phase, Tb III [Co III (CN) 6 ] (2). The 8-coordinated complexes in 1 show the moderate SMM effect but it is enhanced for trigonal-prismatic Tb III complexes in 2, showing the SMM features up to 42 K. They are governed by the combination of QTM, Raman, and Orbach relaxation with the energy barrier of 594(18) cm -1 (854(26) K), one of the highest among the Tb III -based molecular nanomagnets. Both systems exhibit emission related to the f-f electronic transitions, with the temperature variations resulting in the optical thermometry below 100 K. The dehydration leads to a wide temperature overlap between the SMM behavior and thermometry, from 6 K to 42 K. These functionalities are further enriched after the magnetic dilution. The role of post-synthetic formation of high-symmetry Tb III complexes in achieving the SMM effect and hot-bands-based optical thermometry is discussed., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

A series of four new Dy 12 dodecanuclear clusters based on azobenzene derivative ligands of salicylic acid ( L1 - L4 ) has been synthesized and characterized in the crystalline phase using X-ray diffraction on single crystal and powder, IR spectroscopy, elemental analysis, and DSC-TGA methods. It was revealed that all obtained clusters exhibit the formation of the similar metallic cluster nodes, as vertex-sharing heterocubanes, obtained from four Dy 3+ cations, three bridging hydroxyl groups, and O atoms from the salicylic ligands. The coordination geometry around the Dy(III) centers has been carefully analyzed. Whereas Dy 12 -L1 and Dy 12 -L2 with L1 and L2 containing Me and OMe groups in para positions of the phenyl rings, respectively, form similar porous 3D diamond-like molecular networks due to CH-π interactions, for Dy 12 -L3 with L3 bearing NO 2 -electron-withdrawing group, the generation of 2D molecular grids assembled by π-π staking is observed, and for Dy 12 -L4 with L4 bearing phenyl substituent, 3D hexagonal channels have been generated. The complexes Dy 12 -L1 , Dy 12 -L2 , and Dy 12 -L3 exhibit a zero-field slow magnetic relaxation effect. After UV irradiation of Dy 12 -L1 , a decrease of the magnetic anisotropy energy barrier displaying the possibility of control over magnetic properties by the external stimulus has been observed.

Covalent linker transformations in metal-organic frameworks (MOFs) enable their functionalization but often suffer from low conversions or require harsh conditions, including heating, corrosive reactants and solvents, or catalysts. In this work, using solvent-free mechanochemistry for the first time for such conversions, we demonstrate the systematic MOF pore modification with pendant hydroxyl groups and the resulting effects on the network rigidity, its luminescent properties, as well as adsorption of CO 2 and vapors of methanol, ethanol, isopropanol, D 2 O, and H 2 O. A new zinc-based heterolinker MOF (JUK-20) containing both protic luminescent units and reactive tetrazine cores was used as a model and subjected to an inverse electron-demand Diels-Alder (iEDDA) click reaction with a series of dienophiles (x) of different lengths having OH groups. From the obtained series of JUK-20(Zn)-x MOFs, a flexible material capable of luminescent humidity sensing was identified, and the influence of water on the luminescence of the material was explained by analogy with the excited-state intramolecular proton transfer (ESIPT) model. In general, our results provide guidance for designing and tuning MOFs for luminescence-based detection using a stepwise synthetic approach.

Multifunctional materials, which exhibit diverse physical properties, are candidates for the new generation of smart devices that realize many tasks simultaneously. Particular attention is given to single-phase multifunctional materials that offer the new physical effects induced by the coupling between introduced properties. Complexes of lanthanide(3+) ions are an attractive source of multifunctionality since they combine luminescent functionalities related to their f-f or d-f electronic transitions with magnetic anisotropy that originates from spin-orbit coupling and crystal-field effects. The resulting luminescent single-molecule magnets (SMMs) link the area of functional luminophores, applicable in light-emitting diodes or sensing, with the field of molecular magnets, applicable for high-density data storage, and offer additional advantages, e.g. , fruitful magneto-optical correlations and the switching of emission by a magnetic field. It was recently shown that luminescent lanthanide SMMs can provide multifunctionality that is richly expanded towards their sensitivity to solvent exchange, temperature, or light, as well as the generation of electrical properties, such as super-ionic conductivity and ferroelectricity, or non-centrosymmetricity- and chirality-related effects, e.g. , second-harmonic generation and circularly polarized luminescence. Here, we discuss the pioneering reports on multifunctional materials that use luminescent lanthanide SMMs, with the emphasis of our contribution relying on the functionalization of 4f metal complexes through their insertion into heterometallic d-f coordination compounds.

We report an effective strategy toward tunable room-temperature multicolor to white-light emission realized by mixing three different lanthanide ions (Sm 3+ , Tb 3+ , and Ce 3+ ) in three-dimensional (3D) coordination frameworks based on hexacyanidoruthenate(II) metalloligands. Mono-lanthanide compounds, K{Ln III (H 2 O) n [Ru II (CN) 6 ]}· m H 2 O ( 1 , Ln = La, n = 3, m = 1.2; 2 , Ln = Ce, n = 3, m = 1.3; 3 , Ln = Sm, n = 2, m = 2.4; 4 , Ln = Tb, n = 2, m = 2.4) are 3D cyanido-bridged networks based on the Ln-NC-Ru linkages, with cavities occupied by K + ions and water molecules. They crystallize differently for larger ( 1 , 2 ) and smaller ( 3 , 4 ) lanthanides, in the hexagonal P 6 3 /m or the orthorhombic C mcm space groups, respectively. All exhibit luminescence under the UV excitation, including weak blue emission in 1 due to the d-d 3 T 1g → 1 A 1g electronic transition of Ru II , as well as much stronger blue emission in 2 related to the d-f 2 D 3/2 → 2 F 5/2,7/2 transitions of Ce III , red emission in 3 due to the f-f 4 G 5/2 → 6 H 5/2,7/2,9/2,11/2 transitions of Sm III , and green emission in 4 related to the f-f 5 D 4 → 7 F 6,5,4,3 transitions of Tb III . The lanthanide emissions, especially those of Sm III , take advantage of the Ru II -to-Ln III energy transfer. The Ce III and Tb III emissions are also supported by the excitation of the d-f electronic states. Exploring emission features of the Ln III -Ru II networks, two series of heterobi-lanthanide systems, K{Sm x Ce 1- x (H 2 O) n [Ru(CN) 6 ]}· m H 2 O ( x = 0.47, 0.88, 0.88, 0.99, 0.998; 5 - 9 ) and K{Tb x Ce 1- x (H 2 O) n [Ru(CN) 6 ]}· m H 2 O ( x = 0.56, 0.65, 0.93, 0.99, 0.997; 10 - 14 ) were prepared. They exhibit the composition- and excitation-dependent tuning of emission from blue to red and blue to green, respectively. Finally, the heterotri-lanthanide system of the K{Sm 0.4 Tb 0.599 Ce 0.001 (H 2 O) 2 [Ru(CN) 6 ]}·2.5H 2 O ( 15 ) composition shows the rich emission spectrum consisting of the peaks related to Ce III , Tb III , and Sm III centers, which gives the emission color tuning from blue to orange and white-light emission of the CIE 1931 xy parameters of 0.325, 0.333.

Diamagnetic cis -dicyanidoferrate(II) complexes bearing blocking aromatic diimines, cis -[Fe II (CN) 2 (L NN ) 2 ] 0 (L NN = 2,2'-bipyridine, 1,10'-phenanthroline) serve as metalloligands to Dy III centres leading to a rigid cyanido-bridged chain of vertex-sharing {Dy III 2 Fe II 2 } squares which constrains the equatorial plane of embedded 4f metal ions. This results in a novel convenient route to rationally designed single-molecule magnets as the magnetic anisotropy of Dy III centres can be efficiently generated by inserting aromatic N -oxide ligands on labile axial positions.

Gold complexes can generate excimers ([Au 2 ]→[Au 2 ]*) and exciplexes ([Au 3 ]→[Au 3 ]*) with light excitation. Four Gd III and Y III complexes were assembled with dimeric {[Au(SCN) 2 ] - } 2 and trimeric {[Au(SCN) 2 ] - } 3 bis(thiocyanato)gold(I) counterions. The vibrational signature associated with the Au⋅⋅⋅Au vibrational mode was probed with ultralow frequency (ULF) Raman spectroscopy as a function of temperature. Emission spectroscopy was used to explore photophysical properties. Two broad features in the high- and low-energy regions were associated with the fluorescence and phosphorescence of the gold entities, respectively. Temperature-dependent luminescence measurements showed that the emission color can be tuned from blue to green via cyan and white. Hence, these complexes can act as colorimetric thermometers. Additionally, a ratiometric thermal sensing ability was incorporated with high sensitivity up to 5 % K -1 in the cryogenic temperature range., (© 2022 Wiley-VCH GmbH.)

The interest in the generation of photoluminescence in lanthanide(III) single-molecule magnets (SMMs) is driven by valuable magneto-optical correlations as well as perspectives toward magnetic switching of emission and opto-magnetic devices linking SMMs with optical thermometry. In the pursuit of enhanced magnetic anisotropy and optical features, the key role is played by suitable ligands attached to the 4f metal ion. In this context, cyanido complexes of d-block metal ions, serving as expanded metalloligands, are promising. We report two novel discrete coordination systems serving as emissive SMMs, {[Dy III (H 2 O) 3 (tmpo) 3 ] 2 [Pt IV Br 2 (CN) 4 ] 3 }·2H 2 O (1) and {[Dy III (H 2 O)(tmpo) 4 ] 2 [Pt IV Br 2 (CN) 4 ] 3 }·2CH 3 CN (2) (tmpo = trimethylphosphine oxide), obtained by combining Dy III complexes with uncommon dibromotetracyanidoplatinate(IV) ions, [Pt IV Br 2 (CN) 4 ] 2- . They are built of analogous Z-shaped cyanido-bridged {Dy 2 Pt 3 } molecules but differ in the coordination number of Dy III (C.N. = 8 in 1, C.N. = 7 in 2) and the number of coordinated tmpo ligands (three in 1, four in 2) which is related to the applied solvents. As a result, both compounds reveal Dy III -centred slow magnetic relaxation but only 1 shows SMM character at zero dc field, while 2 is a field-induced SMM. The relaxation dynamics in both systems is governed by the Raman relaxation mechanism. These effects were analysed using ac magnetic data and the results of the ab initio calculations with the support of magneto-optical correlations based on low-temperature high-resolution emission spectra. Our findings indicate that heteroligand halogeno-cyanido Pt IV complexes are promising precursors for emissive SMMs with the further potential of sensitivity to external stimuli that may be related to the lability of the axially positioned halogeno ligands.

The ab initio calculations were correlated with magnetic and emission characteristics to understand the modulation of properties of NIR-emissive [Yb III (2,2'-bipyridine-1,1'-dioxide) 4 ] 3+ single-molecule magnets by cyanido/thiocyanidometallate counterions, [Ag I (CN) 2 ] - ( 1 ), [Au I (SCN) 2 ] - ( 2 ), [Cd II (CN) 4 ] 2- /[Cd II 2 (CN) 7 ] 3- ( 3 ), and [M III (CN) 6 ] 3- [M III = Co ( 4 ), Ir ( 5 ), Fe ( 6 ), Cr ( 7 )]. Theoretical studies indicate easy-axis-type ground doublets for all Yb III centers. They differ in the magnetic axiality; however, transversal g -tensor components are always large enough to explain the lack of zero-dc-field relaxation. The excited doublets lie more than 120 cm -1 above the ground one for all Yb III centers. It was confirmed by high-resolution emission spectra reproduced from the ab initio calculations that give reliable insight into energies and oscillator strengths of optical transitions. These findings indicate the dominance of Raman relaxation with the power n varying from 2.93(4) to 6.9(2) in the 4 - 3 - 5 - 1 - 2 series. This trend partially follows the magnetic axiality, being deeper correlated with the phonon modes schemes of (thio)cyanido matrices.

Luminescent single-molecule magnets (SMMs) constitute a class of molecular materials offering optical insight into magnetic anisotropy, magnetic switching of emission, and magnetic luminescent thermometry. They are accessible using lanthanide(III) complexes with advanced organic ligands or metalloligands. We present a simple route to luminescent SMMs realized by the insertion of well-known organic cations, tetrabutylammonium and tetraphenylphosphonium, into dysprosium(III) borohydrides, the representatives of metal borohydrides investigated due to their hydrogen storage properties. We report two novel compounds, [n-Bu 4 N][Dy III (BH 4 ) 4 ] (1) and [Ph 4 P][Dy III (BH 4 ) 4 ] (2), involving Dy III centers surrounded by four pseudo-tetrahedrally arranged BH 4 - ions. While 2 has higher symmetry and adopts a tetragonal unit cell (I4 1 /a), 1 crystallizes in a less symmetric monoclinic unit cell (P2 1 /c). They exhibit yellow room-temperature photoluminescence related to the f-f electronic transitions. Moreover, they reveal Dy III -centered magnetic anisotropy generated by the distorted arrangement of four borohydride anions. It leads to field-induced slow magnetic relaxation, well-observed for the magnetically diluted samples, [n-Bu 4 N][Y III 0.9 Dy III 0.1 (BH 4 ) 4 ] (1@Y) and [Ph 4 P][Y III 0.9 Dy III 0.1 (BH 4 ) 4 ] (2@Y). 1@Y exhibits an Orbach-type relaxation with an energy barrier of 26.4(5) K while only the onset of SMM features was found in 2@Y. The more pronounced single-ion anisotropy of Dy III complexes of 1 was confirmed by the results of the ab initio calculations performed for both 1-2 and the highly symmetrical inorganic Dy III borohydrides, α/β-Dy(BH 4 ) 3 , 3 and 4. The magneto-luminescent character was achieved by the implementation of large organic cations that lower the symmetry of Dy III centers inducing single-ion anisotropy and separate them in the crystal lattice enabling the emission property. These findings are supported by the comparison with 3 and 4, crystalizing in cubic unit cells, which are not emissive and do not exhibit SMM behavior.

A unique family of three-dimensional (3D) luminescent Sr II -Re V metal-organic frameworks (MOFs), {[Sr II (MeOH) 5 ][Re V (CN) 4 (N)(bpen) 0.5 ]·MeOH} n [ 1·MeOH ; N 3- = nitrido ligand, bpen = 1,2-bis(4-pyridyl)ethane, and MeOH = methanol], {[Sr II (MeOH) 4 ][Re V (CN) 4 (N)(bpee) 0.5 ]·2MeOH} n [ 2·MeOH ; bpee = 1,2-bis(4-pyridyl)ethylene], and {[Sr II (bpy) 0.5 (MeOH) 2 ][Re V (CN) 4 (N)(bpy) 0.5 ]} n ( 3·MeOH ; bpy = 4,4'-bipyridine), is reported. They are obtained by the molecular self-assembly of Sr 2+ ions with tetracyanidonitridorhenate(V) metalloligands, [Re V (CN) 4 (N)] 2- , and pyridine-based organic spacers (L = bpen, bpee, bpy). Such a combination of molecular precursors results in bimetallic Sr II -Re V cyanido-bridged layers further bonded by organic ligands into pillared Hofmann-type coordination skeletons. Because of the formation of {Re V -(L)-Re V } moieties providing emissive metal-to-ligand charge-transfer states, 1·MeOH - 3·MeOH exhibit solid-state room-temperature photoluminescence tunable from green to orange by the applied organic ligand. The most stable MOF of 3·MeOH , based on the alternating {Re V -(bpy)-Re V } and {Sr II -(bpy)-Sr II } linkages, exhibits three interconvertible, variously solvated phases, methanol-solvated 3·MeOH , hydrated {[Sr II (bpy) 0.5 (H 2 O) 2 ][Re V (CN) 4 (N)(bpy) 0.5 ]·0.6H 2 O} n ( 3·H 2 O ), and desolvated {[Sr II (bpy) 0.5 ][Re V (CN) 4 (N)(bpy) 0.5 ]} n ( 3 ). Their formation was correlated with water and methanol vapor sorption properties investigated for 3·H 2 O . The solvent content affects the luminescence mainly by tuning the emission energy within the series of 3·MeOH , 3·H 2 O , and 3 . All of the obtained compounds exhibit temperature-driven modulation of luminescence, including the shift of the emission maximum and lifetime. The thermochromic luminescent response was found to be sensitive to the presence and type of solvent in the crystal lattice. This work shows that the construction of [Re V (CN) 4 (N)] 2- -based MOFs is an efficient route toward advanced solid luminophores tunable by external stimuli such as solvent or temperature.

Functional molecule-based solids built of metal complexes can reveal a great impact of external stimuli upon their optical, magnetic, electric, and mechanical properties. We report a novel molecular material, {[Eu III (H 2 O) 3 (pyrone) 4 ][Co III (CN) 6 ]}· n H 2 O ( 1 , n = 2; 2 , n = 1), which was obtained by the self-assembly of Eu 3+ and [Co(CN) 6 ] 3- ions in the presence of a small 2-pyrrolidinone (pyrone) ligand in an aqueous medium. The as-synthesized material, 1 , consists of dinuclear cyanido-bridged {EuCo} molecules accompanied by two H-bonded water molecules. By lowering the relative humidity (RH) below 30% at room temperature, 1 undergoes a single-crystal-to-single-crystal transformation related to the partial removal of crystallization water molecules which results in the new crystalline phase, 2 . Both 1 and 2 solvates exhibit pronounced Eu III -centered visible photoluminescence. However, they differ in the energy splitting of the main emission band of a 5 D 0 → 7 F 2 origin, and the emission lifetime, which is longer in the partially dehydrated 2 . As the 1 ↔ 2 structural transformation can be repeatedly reversed by changing the RH value, the reported material shows a room-temperature switching of detailed luminescent features including the ratio between emission components and the emission lifetime values.

Coordination complexes of lanthanide(3+) ions can combine Single-Molecule Magnetism (SMM) with thermally modulated luminescence applicable in optical thermometry. We report an innovative approach towards high performance SMM-based optical thermometers which explores tunable anisotropy and the luminescence re-absorption effect of Ho III complexes. Our concept is shown in dinuclear cyanido-bridged molecules, {[Ho III (4-pyridone) 4 (H 2 O) 2 ][M III (CN) 6 ]}· n H 2 O (M = Co, 1 ; Rh, 2 ; Ir, 3 ) and their magnetically diluted analogues, {[Ho III x Y III 1- x (4-pyridone) 4 (H 2 O) 2 ][M III (CN) 6 ]}· n H 2 O (M = Co, x = 0.11, 1@Y ; Rh, x = 0.12, 2@Y ; Ir, x = 0.10, 3@Y ). They are built of pentagonal bipyramidal Ho III complexes revealing the zero-dc-field SMM effect. Experimental studies and the ab initio calculations indicate an Orbach magnetic relaxation with energy barriers varying from 89.8 to 86.7 and 78.7 cm -1 K for 1 , 2 , and 3 , respectively. 1-3 also differ in the strength of quantum tunnelling of magnetization which is suppressed by hyperfine interactions, and, further, by the magnetic dilution. The Y III -based dilution governs the optical properties as 1-3 exhibit poor emission due to the dominant re-absorption from Ho III while 1@Y-3@Y show room-temperature blue emission of 4-pyridone. Within ligand emission bands, the sharp re-absorption lines of the Ho III electronic transitions were observed. Their strong thermal variation was used in achieving highly sensitive ratiometric optical thermometers whose good performance ranges, lying between 25 and 205 K, are adjustable by using hexacyanidometallates. This work shows that Ho III complexes are great prerequisites for advanced opto-magnetic systems linking slow magnetic relaxation with unique optical thermometry exploiting a luminescence re-absorption phenomenon., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A two-step hysteretic Fe II spin crossover (SCO) effect was achieved in programmed layered Cs{[Fe(3-CNpy) 2 ][Re(CN) 8 ]}⋅H 2 O (1) (3-CNpy=3-cyanopyridine) assembly consisting of cyanido-bridged Fe II -Re V square grid sheets bonded by Cs + ions. The presence of two non-equivalent Fe II sites and the conjunction of 2D bimetallic coordination network with non-covalent interlayer interactions involving Cs + , [Re V (CN) 8 ] 3- ions, and 3-CNpy ligands, leads to the occurrence of two steps of thermal SCO with strong cooperativity giving a double thermal hysteresis loop. The resulting spin-transition phenomenon could be tuned by an external pressure giving the room-temperature range of SCO, as well as by visible-light irradiation, inducing an efficient recovery of the high-spin Fe II state at low temperatures. We prove that octacyanidorhenate(V) ion is an outstanding metalloligand for induction of a cooperative multistep, multiswitchable Fe II SCO effect., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Discrete molecular species that can perform certain functions in response to multiple external stimuli constitute a special class of multifunctional molecular materials called smart molecules. Herein, cyanido-bridged coordination clusters {[Fe II (2-pyrpy) 2 ] 4 [M IV (CN) 8 ] 2 }⋅4 MeOH⋅6 H 2 O (M=Mo (1 solv), M=W (2 solv) and 2-pyrpy=2-(1-pyrazolyl)pyridine are presented, which show persistent solvent driven single-crystal-to-single-crystal transformations upon sorption/desorption of water and methanol molecules. Three full desolvation-resolvation cycles with the concomitant change of the host molecules do not damage the single crystals. More importantly, the Fe 4 M 2 molecules constitute a unique example where the presence of the guests directly affects the pressure-induced thermal spin crossover (SCO) phenomenon occurring at the Fe II centres. The hydrated phases show a partial SCO with approximately two out-of-four Fe II centres undergoing a gradual thermal SCO at 1 GPa, while in the anhydrous form the pressure-induced SCO effect is almost quenched with only 15 % of the Fe II centres undergoing high-spin to low-spin transition at 1 GPa., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Octacyanidometallates have been successfully employed in the design of heterometallic coordination systems offering a spectacular range of desired physical properties with great potential for technological applications. The [M(CN)8]n- ions comprise a series of complexes of heavy transition metals in high oxidation states, including NbIV, MoIV/V, WIV/V, and ReV. Since the discovery of the pioneering bimetallic {MnII4[MIV(CN)8]2} and {MnII9[MV(CN)8]6} (M = Mo, W) molecules in 2000, octacyanidometallates were fruitfully explored as precursors for the construction of diverse d-d or d-f coordination clusters and frameworks which could be obtained in the crystalline form under mild synthetic conditions. The primary interest in [M(CN)8]n--based networks was focused on their application as molecule-based magnets exhibiting long-range magnetic ordering resulting from the efficient intermetallic exchange coupling mediated by cyanido bridges. However, in the last few years, octacyanidometallate-based materials proved to offer varied and remarkable functionalities, becoming efficient building blocks for the construction of molecular nanomagnets, magnetic coolers, spin transition materials, photomagnets, solvato-magnetic materials, including molecular magnetic sponges, luminescent magnets, chiral magnets and photomagnets, SHG-active magnetic materials, pyro- and ferroelectrics, ionic conductors as well as electrochemical containers. Some of these materials can be processed into the nanoscale opening the route towards the development of magnetic, optical and electronic devices. In this review, we summarise all important achievements in the field of octacyanidometallate-based functional materials, with the particular attention to the most recent advances, and present a thorough discussion on non-trivial structural and electronic features of [M(CN)8]n- ions, which are purposefully explored to introduce desired physical properties and their combinations towards advanced multifunctional materials.

Lanthanide(III)-based coordination complexes have been explored as a source of bifunctional molecular materials combining Single-Molecule Magnet (SMM) behavior with visible-to-near-infrared photoluminescence. In pursuit of more advanced multifunctionality, the next target is to functionalize crystalline solids based on emissive molecular nanomagnets toward high proton conductivity and an efficient luminescent thermometric effect. Here, a unique multifunctional molecule-based material, (H 5 O 2 ) 2 (H)[Yb III (hmpa) 4 ][Co III (CN) 6 ] 2 ·0.2H 2 O ( 1 , hmpa = hexamethylphosphoramide), composed of molecular {YbCo 2 } 3- anions noncovalently bonded to acidic H 5 O 2 + and H + ions, is reported. The resulting Yb III complexes present a slow magnetic relaxation below 6 K and room temperature NIR 4f-centered photoluminescence sensitized by [Co(CN) 6 ] 3- S·cm -4 S·cm -1 at 97% relative humidity, which classifies 1 as a superionic conductor. Moreover, the emission pattern is strongly temperature-dependent which was utilized in achieving a highly sensitive single-center luminescent thermometer with a relative thermal sensitivity, S r > 1% K -1 in the 50-175 K range. This work shows an unprecedented combination of magnetic, optical, and electrical functionalities in a single phase working as a proton conductive NIR-emissive thermometer based on Single-Molecule Magnets.

We report an efficient pathway toward sensitization of red room temperature Eu III emission by the charge-transfer (CT) states related to d 8 -d 10 heterometallophilic interactions achieved by the simultaneous application of tetracyanidometallates of Pt II /Pd II and dicyanidometallates of Au I /Ag I in the construction of a trimetallic d-d-f assembly. The combination of Eu 3+ , [M II (CN) 4 ] 2- (M = Pt, Pd), and [M I (CN) 2 ] - (M = Au, Ag) ions along with 4,4'-bipyridine N , N '-dioxide (4,4'-bpdo) results in four novel isostructural 2D {[Eu III (4,4'-bpdo)(H 2 O) 2 ][M II (CN) 4 ]}·[M I (CN) 2 ]·H 2 O (M II /M I = Pt/Au, 1 ; Pt/Ag, 2 ; Pd/Au, 3 ; Pd/Ag, 4 ) coordination networks. They are built of hybrid coordination layers, based on cyanido-bridged {Eu III [M II (CN) 4 ]} n square grids coexisting with metal-organic {Eu III (4,4'-bpdo)} n chains, with the further attachment of [M I (CN) 2 ] - ions through metallophilic {M II -M I } interactions. This results in dinuclear {M II M I } units generating an orange emissive metal-to-metal-to-ligand charge-transfer (MMLCT) state, whose energy is tuned by the applied d 8 -d 10 metal centers. Thanks to these CT states, 1 - 4 exhibit room temperature red Eu III photoluminescence enhanced by energy transfer from {M II M I } units, with the additional role of 4,4'-bpdo also transferring the energy to lanthanides. These donor CT states lying in the visible range successfully broaden the available efficient excitation range up to 500 nm. The overall emission quantum yield ranges from 8(1)% for 4 to 15(2)% for 1 , with the intermediate values for 2 and 3 relatively high among the reported Eu III -based compounds with tetracyanido- and dicyanidometallates. We found that the sensitization efficiency is equally high for all compounds because of the similar energies of the CT states, while the main differences are related to the observed emission lifetimes ranging from ca. 80 μs for 4 to 120-130 μs for 2 and 3 to ca. 180 μs for 1 . This phenomenon was correlated with the energies of the vibrational states, e.g., cyanide stretching vibrations, responsible for nonradiative deactivation of Eu III excited states, which are the highest for the Pd/Ag pair of 4 and the lowest for the Pt/Au pair in 1 . Thus, the heaviest pair of Pt II /Au I cyanide metal complexes is proven to be the best candidate for the sensitization of room temperature Eu III luminescence.

Microporous magnets compose a class of multifunctional molecule-based materials where desolvation-driven structural transformation leads to the switching of magnetic properties. Herein, we present a special type of microporous magnet where a dehydration-hydration process within a bimetal coordination framework results in the switching of emissive Dy III single-molecule magnets (SMMs). We report a three-dimensional (3-D) cyanido-bridged coordination polymer, {[Dy III (H 2 O) 2 ][Co III (CN) 6 ]}·2.2H 2 O ( 1 ), and its dehydrated form of {Dy III [Co III (CN) 6 ]} ( 2 ), which was obtained through a reversible single-crystal-to-single-crystal transformation. Both phases are composed of paramagnetic Dy III centers alternately arranged with diamagnetic hexacyanidocobaltates(III). The hydrated phase contains eight-coordinated [Dy III (μ-NC) 6 (H 2 O) 2 ] 3- complexes of a square antiprism geometry, while the dehydrated form contains six-coordinated [Dy III (μ-NC) 6 ] 3- moieties of a trigonal prism geometry. This change in coordination geometry results in the generation of Dy III single-molecule magnets in 2 , whereas slow magnetic relaxation effect is not observed for Dy III sites in 1 . The D 4d -to- D 3h symmetry change of Dy III complexes produces also the shift of photoluminescent color from nearly white to deep yellow thanks to the modulation of emission bands of f-f electronic transitions. A combined approach utilizing dc magnetic data and low-temperature emission spectra confirmed an axial crystal field of trigonal prismatic Dy III complexes in 2 , which produces an Orbach type of slow magnetic relaxation. Therefore, we present a unique route to the efficient switching of SMM behavior and photoluminescence of Dy III complexes embedded in a 3-D cyanido-bridged framework.

Three-dimensional bimetallic cyanido-bridged frameworks, [Ln III (2,2'-bipyridine N,N'-dioxide) 2 (H 2 O)][Cu I 2 (CN) 5 ]⋅5 H 2 O (Ln=Dy, 1; Yb, 2), are reported. They exhibit the effect of slow relaxation of magnetization, leading to a magnetic hysteresis loop, and sensitized visible-to-near-infrared photoluminescence. Both physical properties are related to the eight-coordinated lanthanide(III) complexes embedded in the unprecedented coordination skeleton composed of symmetry-breaking polycyanidocuprate linkers. The three-dimensional d-f cyanido-bridged network was shown to serve as an efficient coordination scaffold to achieve emissive lanthanide single-molecule magnets., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report a unique synthetic route toward the multistep spin crossover (SCO) effect induced by utilizing the partial ligand transformation during the crystallization process, which leads to the incorporation of three different Fe II complexes into a single coordination framework. The 3-acetoxypyridine (3-OAcpy) molecules were introduced to the self-assembled Fe II -[M IV (CN) 8 ] 4- (M = Mo, Nb) system in the aqueous solution which results in the partial hydrolysis of the ligand into 3-hydroxypyridine (3-OHpy). It gives two novel isostructural three-dimensional {Fe II 2 (3-OAcpy) 5 (3-OHpy) 3 [M IV (CN) 8 ]}· nH 2 O (M = Mo, n = 0, FeMo; M = Nb, n = 1, FeNb) coordination frameworks. They exhibit an unprecedented cyanido-bridged skeleton composed of {Fe 3 M 2 } n coordination nanotubes bonded by additional Fe complexes. These frameworks contain three types of Fe sites differing in the attached organic ligands, [Fe1(3-OAcpy) 4 (μ-NC) 2 ], [Fe2(3-OHpy) 4 (μ-NC) 2 ], and [Fe3(3-OAcpy) 3 (3-OHpy)(μ-NC) 2 ], which lead to the thermal two-step Fe II SCO, as proven by X-ray diffraction, magnetic susceptibility, UV-vis-NIR optical absorption, and 57 Fe Mössbauer spectroscopy studies. The first step of SCO, going from room temperature to the 150-170 K range with transition temperatures of 245(5) and 283(5) K for FeMo and FeNb, respectively, is related to Fe1 sites, while the second step, occurring at the 50-140 K range with transition temperatures of 70(5) and 80(5) K for FeMo and FeNb, respectively, is related to Fe2 sites. The Fe3 site with both 3-OAcpy and 3-OHpy ligands does not undergo the SCO at all. The observed two-step SCO phenomenon is explained by the differences in the ligand field strength of the Fe complexes and the role of their alignment in the coordination framework. The simultaneous application of two related pyridine derivatives is the efficient synthetic route for the multistep Fe II SCO in the cyanido-bridged framework which is a promising step toward rational design of advanced spin transition molecular switches.

Self-assembly of lanthanide(III) complexes of 2,2':6',2″-terpyridine (terpy) with dicyanidoargentate(I) and dicyanidoaurate(I) anions in water results in the formation of six isostructural dinuclear systems [Ln III (terpy)(H 2 O)(NO 3 ) 2 ][M I (CN) 2 ] (Ln III /M I = Dy/Ag, 1; Dy/Au, 2; Yb/Ag, 3; Yb/Au, 4; Er/Ag, 5; Er/Au, 6). They form three-dimensional supramolecular networks based on dinuclear molecules linked by hydrogen bonds, π-π interactions, and argentophilic (Ag···Ag) or aurophilic (Au···Au) interactions. All of the assemblies show complex solid-state strong UV and weak vis-NIR absorption due to overlapping contributions from 2,2':6',2″-terpyridine, dicyanidoargentate(I), dicyanidoaurate(I), and lanthanide(III) ions. Moreover, they exhibit excitation-wavelength-dependent multicolor photoluminescence ranging from bright white to blue via yellow, green, and cyan colors due to variable contributions from the dicyanidometalate and ligand. Assemblies 3-6 show NIR emission originating from Yb III and Er III metal centers. Furthermore, compounds 1-6 and their magnetically diluted samples are magnetic-field-induced single-molecule magnets with energy barriers of up to 35 K. The effect of noble metal substitution on the magnetic properties of particular lanthanide ions is described. The influence on the thermal anisotropic energy barrier, which relates to the strength of the magnetic anisotropy, depends on the type of lanthanide used. The Ag-to-Au substitution enhances the anisotropy of the prolate Yb III ion and decreases it for the oblate Dy III ion. It also modifies the strength of dipolar interactions affecting the slow magnetic relaxation processes.

Unique hybrid organic-inorganic coordination networks, three-dimensional [(UO2)2(OH)(4,4'-bpdo)2][M(CN)6]·nH2O (M = Co, 1; Rh, 2; Ir, 3) and layered [(UO2)2(OH)2(4,4'-bpdo)2][Pt(CN)6]·H2O (4), employing cyanide, hydroxide and 4,4'-bpdo bridges, are reported. They exhibit vibronically coupled charge transfer emission of uranyl ions, whose colour is tunable from green to orange by the implemented hexacyanidometallates.

Trivalent lanthanide ions combined with two molecular linkers, organic 4,4'-azopyridine-1,1'-dioxide (apdo), and inorganic hexacyanidocobaltate(III), gave a series of magnetoluminescent coordination polymers, [{Ln III (apdo)(H 2 O) 4 }{Co III (CN) 6 }]·2H 2 O (Ln = Nd, 1; Tb, 2; Dy, 3; Er, 4; Tm, 5; Yb, 6). They are hybrid organic-inorganic layered frameworks composed of cyanido-bridged {Ln 2 (μ-NC) 4 Co 2 } squares linked by Ln-apdo-Ln bridges into a coordination network of a mixed 4- and 8-metal ring topology. Lanthanide(III) complexes, [Ln III (μ-apdo) 2 (H 2 O) 4 (μ-NC) 2 ] + , of a distorted dodecahedral geometry are isolated by diamagnetic [Co III (CN) 6 ] 3- and apdo linkers. As a result, 1-6 reveal field-induced slow relaxation of magnetization, with typical temperature-dependent relaxation of a single-ion origin for Nd III -containing 1, Dy III -containing 3, and Yb III -containing 6. The related alternate-current magnetic data were precisely analyzed, indicating the multiple magnetic relaxation pathways, including a direct process, strong quantum tunneling of magnetization, non-negligible Raman processes, and crucial two-phonon Orbach thermal relaxation. The thermal energy barriers of the Orbach process, Δ E/ k B , are 15.1(9) K with τ 0 = 9.8(9) × 10 -6 s at H dc = 4500 Oe, 16.1(8) K with τ 0 = 9.0(9) × 10 -5 s at H dc = 1500 Oe, and 17.3(6) K with τ 0 = 3.2(7) × 10 -6 s at H dc = 700 Oe, for 1, 3, and 6, respectively, proving the single-molecule magnet (SMM) behavior. Because of the presence of [Co(CN) 6 ] 3- , 1-6 show strong UV absorption, while the chromophoric apdo leads to the strong absorption in the visible range. As a result, the visible 4f/3d metal-centered emission is quenched, but the near-infrared luminescence from Nd III and Yb III is observed in 1 and 6, respectively. It is realized by Co-to-Ln metal-to-metal, and apdo-to-Ln ligand-to-metal energy transfers; thus, broad UV-to-visible excitation can be explored. Compounds 1-6 form a novel family of functional bimetallic assemblies, incorporating NIR-emissive SMMs as presented for NdCo (1) and YbCo (6) derivatives.

Functional crystalline materials based on bimetallic cyanido-bridged {[Dy III (4-Mephen)(dmf) 4 ][M V (CN) 8 ]}·0.5H 2 O (M = Re, 1; Mo, 2; W, 3; 4-Mephen = 4-methyl-1,10-phenanthroline) helices have been prepared. 1 is the first heterometallic coordination polymer incorporating an unexplored [Re V (CN) 8 ] 3- ion. Implementation of the Re V -based diamagnetic analogue of broadly investigated paramagnetic [Mo V (CN) 8 ] 3- and [W V (CN) 8 ] 3- ions into the d-f coordination framework results in yellow photoluminescence originating from 4 F 9/2 → 6 H J f-f electronic transitions of Dy III sensitized by 4-Mephen, and field-induced slow magnetic relaxation related to the single-ion anisotropy of the dysprosium(III) complexes. We prove that [Re V (CN) 8 ] 3- can work as a noninnocent metalloligand in the preparation of emissive 4f-metal-based single-molecule magnets.

Two series of trimetallic {Ni II x Co II 9-x [W V (CN) 8 ] 6 } (NiCoW) and {Mn II x Co II 9-x [W V (CN) 8 ] 6 } (MnCoW) (x=1-8) crystalline solid-solutions were constructed and systematically studied by SEM EDX, single-crystal X-ray diffraction (SC XRD), and magnetic measurements. The atomic Ni:Co:W and Mn:Co:W ratios in the solid state follow the stoichiometric concentration in the mother MeOH solutions fairly well. The structural studies revealed a definite strong tendency of smaller 3d ions to locate in the central [M(μ-NC) 6 ] moiety of the skeleton: Ni II over the Co II ] are consecutively occupied by the mixture of 3d metal ions, accessible according to the stoichiometry of the mother solutions. The DC magnetic χT(T) and M(H) curves illustrate the continuous tendency of change with x along both series, nicely reproducing the changes of the theoretical high spin in the ground state S II over Mn II . In contrast, the external fac-[M(μ-NC) 3 (MeOH) 3 ] are consecutively occupied by the mixture of 3d metal ions, accessible according to the stoichiometry of the mother solutions. The DC magnetic χT(T) and M(H) curves illustrate the continuous tendency of change with x along both series, nicely reproducing the changes of the theoretical high spin in the ground state S gr , assuming the ferromagnetic HS Co II -NC-W V and antiferromagnetic Mn II -NC-W V interactions established by numerous literature reports. The AC magnetic measurements indicate the occurrence of slow magnetic relaxation, with the highest energy barrier ΔE/k B of 26 K for the Ni 6 Co 3 W 6 congener and of 17 K for the Mn 6 Co 3 W 6 congener, and relatively large values of distribution parameter α. The values of ΔE are correlated with possible anisotropy of distribution of fac-[Co II (μ-NC) 3 (MeOH) 3 ] moieties at the external corners of the cube substructure., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A near-infrared emissive and magnetically anisotropic Nd(iii) complex is formed within a hybrid organic-inorganic {[NdIII(pzdo)(H2O)4][CoIII(CN)6]}·0.5(pzdo)·4H2O (1) (pzdo = pyrazine-N,N'-dioxide) ladder chain built of coexisting Nd-pzdo-Nd and Nd-NC-Co molecular bridges. 1 reveals two NdIII-centered properties, a field-induced slow magnetic relaxation of a single-ion origin with a thermal energy barrier of ΔE/kB = 51(2) K at Hdc = 1 kOe, and a near-infrared fluorescence sensitized by organic and inorganic linkers.

Solid-state functional luminescent materials arouse an enormous scientific interest due to their diverse applications in lighting, display devices, photonics, optical communication, low energy scintillation, optical storage, light conversion, or photovoltaics. Among all types of solid luminophors, the emissive coordination polymers, especially those based on luminescent trivalent lanthanide ions, exhibit a particularly large scope of light-emitting functionalities, fruitfully investigated in the aspects of chemical sensing, display devices, and bioimaging. Here, we present the complete overview of one of the promising families of photoluminescent coordination compounds, that are heterometallic d-f cyanido-bridged networks composed of lanthanide(3+) ions connected through cyanide bridges with polycyanidometallates of d-block metal ions. We are showing that the combination of cationic lanthanide complexes of selected inorganic and organic ligands with anionic homoligand [M(CN)x] n- (x = 2, 4, 6 and 8) or heteroligand [M(L)(CN)4] 2- (L = bidentate organic ligand, M = transition metal ions) anions is the efficient route towards the emissive coordination networks revealing important optical properties, including 4f-metal-centred visible and near-infrared emission sensitized through metal-to-metal and/or ligand-to-metal energy transfer processes, and multi-coloured photoluminescence switchable by external stimuli such as excitation wavelength, temperature, or pressure., Competing Interests: The authors declare no conflict of interest.

Ytterbium (3+) ions combined with 3-pyridone and hexacyanido-cobaltate(iii) anions in a concentrated aqueous solution produce cyanido-bridged {[Yb III (3-pyridone) 2 (H 2 O) 2 ][Co III (CN) 6 ]} (1) chains. The resulting Yb III complexes of an elongated octahedral geometry reveal two coexisting functionalities: a field-induced slow magnetic relaxation with an energy barrier of ΔE/k B = 45(1) K at H dc = 1 kOe, and an Yb III -centered near-infrared fluorescence in the 950-1100 nm range sensitized by 3-pyridone and [Co III (CN) 6 ] 3- .

Spin crossover (SCO) materials, revealing the externally tunable transition between two different spin states, arouse great scientific interest due to their perspective application in information storage, display devices and sensing. Of special importance are the molecular systems offering the possibility of multimodal switching within many spin centers. This is achievable in polynuclear clusters consisting of several SCO-active complexes, however, such molecules are very rare. Herein, we report a unique pair of nanometric pentadecanuclear {Fe 9 [M(CN) 8 ] 6 (Me 3 tacn) 8 }·14MeOH (Me 3 tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane, M = Re, 1; M = W, 2) clusters exhibiting a thermally induced spin crossover effect on Fe(ii) complexes, that is on both central and external Fe sites embedded in the cyanido-bridged cluster core. The spin transition occurs gradually in the 120-300 K range, and it is not fully completed even at room temperature. We show that facial coordination of an N,N,N-tridentate Me 3 tacn ligand dramatically modifies the character of the spin transition phenomenon when confronted with the previously reported {Fe 9 [M(CN) 8 ] 6 (MeOH) 24 }·nMeOH (M = Re, W) clusters by (i) engaging, for the first time, not only central but also external Fe intracluster units in the SCO effect, (ii) cancelling the Fe-W charge transfer pathway, and (iii) decreasing the cooperativity within the supramolecular network.

Cyanide-bridged {Mn II 9 [W V (CN) 8 } clusters with the ground state spin S 6 } clusters with the ground state spin S SG = 39/2 were connected by a 4,4'-dipyridyl disulfide (4,4'-dpds) linker into 2-D double-connected coordination layers of the I 0 O 2 type, {Mn II 9 (4,4'-dpds) 4 (MeOH) 16 [W V (CN) 8 ] 6 }·12MeOH (1). The intercluster contacts are controlled by the bridging Mn II -(4,4'-dpds)-Mn II coordination modes and direct hydrogen bonds W-CN···HO MeOH -Mn in three crystallographic directions, with the vertex-to-vertex contact unprecedented in {Mn 9 W 6 }-based networks dominating over the typical edge-to-edge contacts. The resulting 3D supramolecular network of high-spin clusters was subjected to a thorough magnetic characterization in context of two critical issues. First, the intracluster W V -CN-Mn II exchange coupling and intercluster interaction were successfully modeled through the combination of dc measurements, Quantum Monte Carlo simulations, and mean-field calculations, yielding a reasonable J ap = -8.0 cm -1 (related to apical and equatorial CN bridges, depending on the angle they form with the S eq = -19.2 cm -1 (related to apical and equatorial CN bridges, depending on the angle they form with the S 4 axis of dodecahedral [W(CN) 8 ] 3- units, respectively), and zJ' = 0.014 cm -1 with the average g W = g Mn = 2.0 parameter set. Continuing this approach, we simulated the magnetocaloric effect (MCE) and compared it to the experimental result of ΔS max = 7.31 J kg -1 K -1 for fields >5.0 T. Second, two relaxation processes were induced by a relatively weak magnetic field, H dc = 500 Oe, at an H ac field frequency range of up to 10 kHz, which are related to dipole-dipole interactions between high-spin (39/2) moieties. The observed relaxation times significantly differ from each other, the slow process with τ slow at tenths of a second being temperature independent and the faster process being 3-5 orders of magnitude faster with the effective energy barrier Δ eff = 17.6 K. These dynamic properties are surprising, since the compound is made up of isotropic high-spin molecules.

Coordination compounds built of trivalent lanthanide ions have been demonstrated as promising solid-state materials for diverse photoluminescent applications and as attractive magnetic objects with the prospective application in information storage and spintronics. We present a synthetic methodology in which both luminescent and magnetic functionalities are induced within lanthanide-based coordination polymers by the application of hexacyanocobaltate(III) anions and 3-hydroxypyridine (3-OHpy), both coordinated to 4f-metal ions modulating the lanthanide-centered properties. We report a series of trimetallic cyanido-bridged chains {[Eu III x Tb III 1-x (3-OHpy) 2 (H 2 O) 4 ][Co III (CN) 6 ]}·H 2 O (x = 1, 0.8, 0.5, 0.4, 0.3, 0.2, 0.1, 0; compounds 1, 2, ..., 7, 8). They reveal tunable visible photoluminescence ranging from green, through yellow and orange, to red color depending on the composition of material and the wavelength of UV excitation light. Such multicolored emission is realized by the adjusted ratio between red emissive Eu 3+ and green emissive Tb 3+ and by the selection of wavelengths of UV light controlling the intensities of Eu- and Tb-based components of visible luminescence. The photoluminescence is enhanced by the energy-transfer (ET) process from [Co III (CN) 6 ] 3- and 3-OHpy to lanthanides, and the efficiencies of ET to Eu and Tb play an important role in the switchable emission. The whole family, 1-8, exhibits temperature-dependent paramagnetism due to the intrinsic property of lanthanide(3+) ions. Tb-containing 2-8 reveal the field-induced slow relaxation of magnetization due to the magnetic anisotropy of Tb 3+ . Moreover, the compounds built of large amounts of Tb reveal the double relaxation, the faster of a typical Tb III single-ion origin, and the slower originating from the magnetic dipole-magnetic dipole interactions between neighboring Tb III centers. Compound 2, which can be considered as a magnetically diluted sample, exhibits almost single relaxation process with the thermal energy barrier ΔE/k B s at H 0 = 1.1(2) × 10 -8 s at H dc = 1500 Oe, indicating a single-molecule magnet behavior.

The rotating magnetocaloric effect (RMCE) is a new issue in the field of magnetic refrigeration. We have explored this subject on the two-dimensional (2D) enantiopure {[Mn II (R-mpm) 2 ] 2 [Nb IV (CN) 8 ]}·4H 2 O (where mpm = α-methyl-2-pyridinemethanol) coordination ferrimagnet. In this study, the magnetic and magnetocaloric properties of single crystals were investigated along the bc//H easy plane and the a*//H hard axis. The observed small easy plane anisotropy is due to the dipole-dipole interactions. For fields higher than 0.5 T, no significant difference in the magnetocaloric effect between both geometries was noticed. The maximal magnetic entropy change for conventional effect was observed at 32 K and the magnetic field change μ 0 ΔH = 5.0 T attaining the value of ∼5 J mol -1 K -1 . The obtained maximal value of -ΔS m is comparable to previously reported results for polycrystalline octacyanidoniobate-based bimetallic coordination polymers. A substantial anisotropy of magnetocaloric effect between the easy plane and hard axis appears in low fields. This includes the presence of inverse magnetocaloric effect only for the a*//H direction. The difference between both geometries was used to study the rotating magnetocaloric effect. We show that the inverse part of magnetocaloric effect can be used to enhance the rotating magnetic entropy change up to 51%. This finding is of key importance for searching efficient materials for RMCE.

An inorganic three-dimensional [Ni II (H 2 O) 2 ] 2 [W IV (CN) 8 ]·4H 2 O (1) framework undergoes a single-crystal-to-single-crystal transformation upon thermal dehydration, producing a fully anhydrous phase Ni II 2 [W IV (CN) 8 ] (1d). The dehydration process induces changes in optical, magnetic, and thermal expansion properties. While 1 reveals typical positive thermal expansion of the crystal lattice, greenish-yellow color, and paramagnetic behavior, 1d is the first ever reported octacyanido-based solid revealing negative thermal expansion, also exhibiting a deep red color and diamagnetism. Such drastic shift in the physical properties is explained by the removal of water molecules, leaving the exclusively cyanido-bridged bimetallic network, which is accompanied by the transformation of the octahedral paramagnetic [Ni II (H 2 O) 2 (NC) 4 ] 2- to the square-planar diamagnetic [Ni II (NC) 4 ] 2- moieties.

A cyanido-bridged layered {[Dy(III)(4-OHpy)2(H2O)3][Co(III)(CN)6]}·0.5H2O (1) (4-OHpy = 4-hydroxypyridine) framework with dual photo-luminescence and magnetic properties was prepared. 1 exhibits visible emission whose color, yellow to greenish-blue, is switchable by selected wavelengths of UV excitation light. Magnetic data revealed that 1 shows not only the slow magnetic relaxation of a typical Dy(III) single-ion origin but also the relaxation process caused by the magnetic dipole-magnetic dipole interactions between the neighbouring Dy(III) centers.

The self-assembly of Dy(III) -3-hydroxypyridine (3-OHpy) complexes with hexacyanidocobaltate(III) anions in water produces cyanido-bridged {[Dy(III) (3-OHpy)2 (H2 O)4 ] [Co(III) (CN)6 ]}⋅H2 O (1) chains. They reveal a single-molecule magnet (SMM) behavior with a large zero direct current (dc) field energy barrier, ΔE=266(12) cm(-1) (≈385 K), originating from the single-ion property of eight-coordinated Dy(III) of an elongated dodecahedral geometry, which are embedded with diamagnetic [Co(III) (CN)6 ](3-) ions into zig-zag coordination chains. The SMM character is enhanced by the external dc magnetic field, which results in the ΔE of 320(23) cm(-1) (≈460 K) at Hdc =1 kOe, and the opening of a butterfly hysteresis loop below 6 K. Complex 1 exhibits white Dy(III) -based emission realized by energy transfer from Co(III) and 3-OHpy to Dy(III) . Low temperature emission spectra were correlated with SMM property giving the estimation of the zero field ΔE. 1 is a unique example of bifunctional magneto-luminescent material combining white emission and slow magnetic relaxation with a large energy barrier, both controlled by rich structural and electronic interplay between Dy(III) , 3-OHpy, and [Co(III) (CN)6 ](3-) ., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Pentadecanuclear {CII9[W(V)(CN)8]6} clusters were combined with bidentate 2,2'-bipyridine N,N'-dioxide (2,2'-bpdo) ligands resulting in two distinct molecules, {Co9W6(2,2'-bpdo)7} (cluster A) and {Co9W6(2,2'-bpdo)6} (cluster B), capped by seven and six 2,2'-bpdo ligands, respectively. They crystallize within a single {Co9W6(2,2'-bpdo)7}·{Co9W6(2,2'-bpdo)6}·solvent (1) supramolecular network, and reveal single-molecule magnet behaviour with an enhanced energy barrier, a ΔE/kB of 30.0(8) K, which was tentatively ascribed to seven-capped axially deformed cluster A.

Precisely controlled stoichiometric mixtures of Co(2+) and Fe(2+) metal ions were combined with the [W(V)(CN)8](3-) metalloligand in a methanolic solution to produce a series of trimetallic cyanido-bridged {Fe(9-x)Co(x)[W(CN)8]6(MeOH)24}·12MeOH (x = 0, 1, ..., 8, 9; compounds 0, 1, ..., 8, 9) clusters. All the compounds, 0-9, are isostructural, and consist of pentadecanuclear clusters of a six-capped body-centered cube topology, capped by methanol molecules which are coordinated to 3d metal centers. Thus, they can be considered as a unique type of a cluster-based molecular solid solution in which different Co/Fe metal ratios can be introduced while preserving the coordination skeleton and the overall molecular architecture. Depending on the Co/Fe ratio, 0-9 exhibit an unprecedented tuning of magnetic functionalities which relate to charge transfer assisted phase transition effects and slow magnetic relaxation effects. The iron rich 0-5 phases exhibit thermally induced reversible structural phase transitions in the 180-220 K range with the critical temperatures being linearly dependent on the value of x. The phase transition in 0 is accompanied by (HS)Fe(II) W(V) ↔ (HS)Fe(III) W(IV) charge transfer (CT) and the additional minor contribution of a Fe-based spin crossover (SCO) effect. The Co-containing 1-5 phases reveal two simultaneous electron transfer processes which explore (HS)Fe(II) W(V) ↔ (HS)Fe(III) W(IV) CT and the more complex (HS)Co(II) W(V) ↔ (LS)Co(III) W(IV) charge transfer induced spin transition (CTIST). Detailed structural, spectroscopic, and magnetic studies help explain the specific role of both types of CN(-)-bridged moieties: the Fe-NC-W linkages activate the molecular network toward a phase transition, while the subsequent Co-W CTIST enhances structural changes and enlarges thermal hysteresis of the magnetic susceptibility. On the second side of the 0-9 series, the vanishing phase transition in the cobalt rich 6-9 phases results in the high-spin ground state, and in the occurrence of a slow magnetic relaxation process at low temperatures. The energy barrier of the magnetic relaxation gradually increases with the increasing value of x, reaching up to ΔE/kB = 22.3(3) K for compound 9.

The unique enantiopure {[Λ-Co(II)((R)-mpm)2]3[W(V)(CN)8]2}·9H2O [(R)-1] and {[Δ-Co(II)((S)-mpm)2]3[W(V)(CN)8]2}·9H2O [(S)-1], where mpm = α-methylpyridinemethanol, magnetic spongelike materials, crystallizing in the chiral P21 space group, are constructed of cyanido-bridged {Co3W2} trigonal bipyramids with three cis-[Co(II)(mpm)2(μ-NC)2] moieties in equatorial sites and two [W(V)(CN)8](3-) units in apical positions. The arrangement of {Co3W2} clusters in the crystal lattice is controlled by interactions with crystallization H2O molecules, resulting in two independent hydrogen-bonding systems: the first weaving along open channels in the a direction (weakly bonded H2O) and the second closed in the cages formed by the surrounding [W(CN)8](3-) and mpm fragments (strongly bonded H2O). The strong optical activity of (R)- and (S)-1 together with continuous chirality measure (CCM) analysis confirms the chirality transfer from enantiopure (R)- and (S)-mpm to [Co(mpm)2(μ-NC)2] units, a cyanido-bridged skeleton, and to the whole crystal lattice. Magnetic properties confronted with ab initio calculations prove the ferromagnetic couplings within Co(II)-NC-W(V) linkages inside {Co3W2} molecules, accompanied by weak antiferromagnetic intermolecular interactions. The reversible removal of weakly bonded H2O above 50 °C induces the structural phase transition 1 ⇄ 1deh and strongly affects the magnetic characteristics. The observed changes can be interpreted in terms of the combined effects of the decreasing strength of ferromagnetic Co(II)-W(V) coupling and the increasing role of antiferromagnetic intermolecular correlation, both connected with dehydration-induced structural modifications in the clusters' core and supramolecular network of 1.