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In this paper magnetic properties of hybrid inorganic-organic compound {[FeII(pyrazole)4]2[NbIV(CN)8]∙4H2O}n are presented. This is a three dimensional molecular magnet with well localized magnetic moments, which make it a suitable candidate for testing magnetic models. In order to characterize the magnetic properties of the above compound we performed the AC/DC magnetometry in the range 0-5 T. The special attention was paid to the phase transition at 7.9 K. The study in magnetic field supports magnetic ordering below 7.9 K.

In this paper, the general analysis of powder sample magnetic susceptibility of single ion magnets displaying axial (D) and rhombic (E) local anisotropy, and characterized by the isotropic spectroscopic tensor g, is conducted. The aim is to obtain exact expressions for the temperature dependence of magnetic susceptibility to extract both anisotropy parameters D and E from the powder susceptibility data. Two cases are considered, with integer (S = 1) and half-integer (S = 3=2) spin. In the former, the procedure based on the low-temperature behavior of the susceptibility signal, which effectively reduces the number of fitting parameters, is proposed. By contrast, in the case of the SIM with S = 3=2, it is explicitly demonstrated that the powder susceptibility depends on the combined anisotropy parameter Δ = √ D² + 3E², precluding the full resolution of the axial and rhombic anisotropy constants. [ABSTRACT FROM AUTHOR]

Motivated by the rapid development in the synthesis of novel molecule-based magnets, we have investigated magnetic and thermodynamic properties of mixed spin (s-S) exchange coupled chains displaying a simple linear AB or a knotted AB2 arrangement. Approximate approach for s = 1/2 and S ≥ 5/2, treating at an intermediate step spin S operator as a commuting variable and using the transfer matrix technique, is used. Susceptibility, magnetization and heat capacity of both spin systems are evaluated numerically from the corresponding free energy for S = 5/2. Uniform: ferromagnetic and antiferromagnetic couplings are discussed. The procedure reproduces the right values of saturation magnetization and the entropy content of the systems, corroborating its correctness. χT curves are shown to depend crucially on the μBH/J ratio. For zero-field heat capacity a double-peak structure is revealed for the AB chain, whereas for the AB2 chain only one broad anomaly is observed. [ABSTRACT FROM AUTHOR]

Complementary experimental methods such as &mgr;SR spectroscopy, ac magnetometry, and relaxation calorimetry have been employed as a probe of critical behavior of a unique ferrimagnetic molecular magnet {[MnII(pydz)(H2O)2][MnII(H2O)2][NbIV(CN)8]-2H2O}n with Tc ≈ 42 K. A full set of critical exponents is determined. Static exponents α, &bgr;, &ggr;, and the dynamic exponent &ohgr; are extracted directly from the measurements. Further critical exponents &ngr;, &eegr;, and z are derived on the basis of scaling or hyperscaling relations. The knowledge of the thermal dependence of the order parameter combined with the results of the calorimetric measurements allowed for the determination of two further static critical exponents &kgr; and &kgr;′. The system shows a close affinity to the three-dimensional (3D) Heisenberg model. Ferrimagnetism of the compound leads to a coexistence of typically ferro- and antiferromagnetic characteristics. [ABSTRACT FROM AUTHOR]

Spin crossover (SCO) and light-induced excited spin state trapping (LIESST) effects were studied using high pressure X-ray diffraction at cryogenic temperatures on a single crystal of the {[Fe II (pyrazole) 4 ] 2 [Nb IV (CN) 8 ]·4H 2 O} n (FeNb) coordination polymer. The studied compound does not show SCO or LIESST at ambient pressure, but these effects can be enforced by a mechanical stimulus. The obtained results demonstrate the manipulation of the spin state via the appropriate combination of multiple stimuli simultaneously.

Multifunctional molecules responsive to light are highly desired as components for the construction of remotely controlled nanodevices. Here we present a Dy III single molecule magnet (SMM) comprising dithienylethene (dte) photochromic bridging ligands in the form of a pyridine (py) derivative: 1,2-bis((2-methyl-5-pyridyl)thie-3-yl)perfluorocyclo-pentene (dtepy). The title trinuclear compound {[Dy III (BHT) 3 ] 3 (dtepy) 2 }·4C 5 H 12 (1) was synthesized by combining the low-coordinate dysprosium complexes Dy III (BHT) 3 (BHT = 2,6-di- tert -butyl-4-methylphenolate) with dtepy bridging ligands in the 'open' form using n -pentane as a completely inert solvent. The trinuclear molecule comprises two different Dy III centers due to its quasi-linear geometry: a central trigonal bipyramidal Dy III ion and two peripheral ones with an approximate trigonal pyramidal geometry. Thanks to that, 1 shows two types of SMM behavior which is slightly affected by the photoisomerization of the photochromic dtepy bridges. The impact of the photoisomerization on the magnetization dynamics was studied by means of alternating current (AC) magnetic susceptibility measurements for the 'open' and 'closed' forms of the molecules. The changes between the 'open' and 'closed' isomers were further investigated by IR and UV-vis spectroscopy, suggesting the co-existence of the ligand-related photochromism and single-molecule magnet behavior in 1. However, the powder X-ray diffraction studies indicate loss of structural order in the first photoisomerization step preventing in-depth studies., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Iron(II) can show a very rich coordination chemistry with concomitant modulation of its properties as promising functional materials. Metalation of the neutral tridentate nitrogen-donor mer -coordinating ligand 2,6-bis(2-(methyl)-2 H -tetrazol-5-yl)pyridine (Me 2 btp) with Fe(ClO 4 ) 2 ·6H 2 O through accurate solvent polarity control enables the selective crystallization of [Fe HS/LS (Me 2 btp) 2 ](ClO 4 ) 2 ·MeCN·2.75H 2 O (2 HS/LS ·MeCN·2.75H 2 O) as red rods, where half of the iron(II) centres resides in the low spin (LS, S = 0) state and the other half is in the high spin (HS, S = 2) state. The red rods spontaneously convert into yellow crystals once removed from the mother liquor and exposed to air due to solvent rearrangement within the crystal packing; these new crystals can be assigned to [Fe HS (Me 2 btp) 2 ](ClO 4 ) 2 ·solvent (2 HS ·solvent) where all the iron(II) centres are now blocked in the HS state, as confirmed by magnetic measurements. The polarity of the crystallization solvent, together with the maintenance of the crystals within the mother liquor, are pivotal for the reactivity and interconversion of different species. Indeed, upon long standing in solution, 2 HS/LS ·MeCN·2.75H 2 O converts to another form of red crystals belonging to [Fe LS (Me 2 btp) 2 ][Fe HS (Me 2 btp)(MeCN) 2 (H 2 O)](ClO 4 ) 4 ·MeCN (2 LS ·3 HS ·MeCN), as confirmed by single crystal X-ray diffraction data. In this co-crystal, the iron(II) in 2 resides in the LS state at all temperatures while the iron(II) in 3 is blocked in the HS state. Well-formed yellow crystals could be also isolated among the red crystals of 2 HS/LS ·MeCN·2.75H 2 O, and they could be identified as the unprecedented octacoordinated species [Fe(Me 2 btp) 2 (MeCN)(H 2 O)](ClO 4 ) 2 ·H 2 O (1·H 2 O) by single-crystal X-ray diffraction. These yellow crystals are stable in the air, but slowly convert into 2 LS ·3 HS ·MeCN if kept in the mother liquor for about one week. 1·H 2 O can be considered the trapped intermediate in the solid state during the conversion of [Fe HS (Me 2 btp) 2 ] 2+ into [Fe HS (Me 2 btp)(MeCN) 2 (H 2 O)] 2+ in solution, where the two tridentate ligands in the starting species can unfold to accommodate coordinated MeCN and H 2 O molecules, as confirmed by theoretical calculations, and eventually one of the two Me 2 btp is completely replaced by the solvent.

Iron(ii) spin cross-over (SCO) compounds combine a thermally driven transition from the diamagnetic low-spin (LS) state to the paramagnetic high-spin (HS) state with a distinct change in the crystal lattice volume. Inversely, if the crystal lattice volume was modulated post-synthetically, the spin state of the compound could be tunable, resulting in the inverse effect for SCO. Herein, we demonstrate such a spin-state tuning in a breathing cyanido-bridged porous coordination polymer (PCP), where the volume change resulting from guest-induced gate-opening and -closing directly affects its spin state. We report the synthesis of a three-dimensional coordination framework {[Fe II (4-CNpy) 4 ] 2 [W IV (CN) 8 ]·4H 2 O} n (1·4H 2 O; 4-CNpy = 4-cyanopyridine), which demonstrates a SCO phenomenon characterized by strong elastic frustration. This leads to a 48 K wide hysteresis loop above 140 K, but below this temperature results in a very gradual and incomplete SCO transition. 1·4H 2 O was activated under mild conditions, producing the nonporous {[Fe II (4-CNpy) 4 ] 2 [W IV (CN) 8 ]} n (1) via a single-crystal-to-single-crystal process involving a 7.3% volume decrease, which shows complete and nonhysteretic SCO at T 1/2 = 93 K. The low-temperature photoswitching behavior in 1 and 1·4H 2 O manifested the characteristic elasticity of the frameworks; 1 can be quantitatively converted into a metastable HS state after 638 nm light irradiation, while the photoactivation of 1·4H 2 O is only partial. Furthermore, nonporous 1 adsorbed CO 2 molecules in a gated process, leading to {[Fe II (4-CNpy) 4 ] 2 [W IV (CN) 8 ]·4CO 2 } n (1·4CO 2 ), which resulted in a 15% volume increase and stabilization of the HS state in the whole temperature range down to 2 K. The demonstrated post-synthetic guest-exchange employing common gases is an efficient approach for tuning the spin state in breathing SCO-PCPs., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The extreme sensitivity of trivalent lanthanide ions to crystal field variations led to the emergence of single-molecule magnetic switching under various stimuli. The use of pressure as an external stimulus instead of classic light irradiation, oxidation or any chemical reactions allows a fine tuning of the magnetic modulation. Here the well-known pure isotopically enriched [ 162 Dy(tta) 3 (L)]⋅C 6 H 14 ( 162 Dy) Single-Molecule Magnet (SMM) (tta - =2-2-thenoyltrifluoroacetonate and L=4,5-bis(propylthio)-tetrathiafulvalene-2-(2-pyridyl)benzimidazole-methyl-2-pyridine) was experimentally investigated by single-crystal diffraction and squid magnetometry under high applied pressures. Both reversible piezochromic properties and pressure modulation of the slow magnetic relaxation behavior were demonstrated and supported by ab initio calculations. The magnetic study of the diluted sample [ 162 Dy 0.05 Y 0.95 (tta) 3 (L)]⋅C 6 H 14 ( 162 Dy@Y) indicated that variations in the electronic structure have mainly intermolecular origin with weak intramolecular contribution. Quantitative magnetic interpretation concludes to a deterioration of the Orbach process for the benefit of both Raman and QTM mechanisms under applied pressure., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The structures and magnetic properties of photoresponsive magnets can be controlled or fine-tuned by visible light irradiation, which makes them appealing as candidates for ternary memory devices: photochromic and photomagnetic at the same time. One of the strategies for photoresponsive magnetic systems is the use of photochromic/photoswitchable molecules coordinated to paramagnetic metal centers to indirectly influence their magnetic properties. Herein, we present two erbium(III)-based coordination systems: a trinuclear molecule {[Er III (BHT) 3 ] 3 (dtepy) 2 } . 4C 5 H 12 ( 1 ) and a 1D coordination chain {[Er III (BHT) 3 (azopy)} n ·2C 5 H 12 ( 2 ), where the bridging photochromic ligands belong to the class of diarylethenes: 1,2-bis((2-methyl-5-pyridyl)thie-3-yl)perfluorocyclopentene (dtepy) and 4,4'-azopyridine (azopy), respectively (BHT = 2,6-di- tert -butyl-4-methylphenolate). Both compounds show slow dynamics of magnetization, typical for single-molecule magnets (SMMs) as revealed by alternating current (AC) magnetic susceptibility measurements. The trinuclear compound 1 also shows an immediate color change from yellow to dark blue in response to near-UV irradiation. Such behavior is typical for the photoisomerization of the open form of the ligand into its closed form. The color change can be reversed by exposing the closed form to visible light. The chain-like compound 2 , on the other hand, does not show significant signs of the expected trans - cis photoisomerization of the azopyridine in response to UV irradiation and does not appear to show photoswitching behavior.

A single crystal of [Co(NCS) 2 (4-methoxypyridine) 2 ] n was obtained and investigated. The magnetic measurements performed along three perpendicular crystallographic directions are compared to the results obtained previously for a powder sample. The magnetic inter- and intrachain interactions do not differ, however, a change of the energy barrier of magnetic relaxations is obtained. For the single crystal sample the relaxation is much slower, which is attributed to the presence of longer chains, and show that below the ordering temperature the spin chains relax by the process that involves a single domain wall. Above the ordering temperature, a second relaxation process is observed, for which the relaxation time is temperature independent, indicating a negligible energy barrier. Such phenomenon was previously not observed for any of the powder samples of compounds from the [Co(NCS) 2 (ligand) 2 ] n family.

A series of new CN-bridged coordination networks of different dimensionality and topology was obtained through the modification of reaction conditions between [Ni(cyclam)] 2+ (cyclam = 1,4,8,11-tetraazacyclotetradecane) and [W(CN) 8 ] 4- . The factors determining the reaction pathway are temperature and addition of the LiCl electrolyte. The products include three negatively charged frameworks incorporating Li + guests: the 1D Li 2 [Ni(cyclam)][W(CN) 8 ]·6H 2 O ( 1 ) straight chain, the 1D Li 2 [Ni(cyclam)][W(CN) 8 ]·2H 2 O ( 2 ) zigzag chain, and the 2D Li 2 [Ni(cyclam)] 3 [W(CN) 8 ] 2 ·24H 2 O ( 3 ) honeycomb-like network, as well as the 3D two-fold interpenetrating [Ni(cyclam)] 5 [Ni(CN) 4 ][W(CN) 8 ] 2 ·11H 2 O ( 4 ) network and the 1D [Ni(cyclam)][Ni(CN) 4 ]·2H 2 O ( 5 ) chain, which result from partial decomposition of the starting complexes. Together with the previously characterized 3D [Ni(cyclam)] 2 [W(CN) 8 ]·16H 2 O ( 6 ) network, they constitute the largest family of CN-bridged coordination polymers obtained from the same pair of building blocks. All compounds exhibit paramagnetic behavior because of the separation of paramagnetic nickel(II) centers through the diamagnetic polycyanidometallates. However, the presence of the photomagnetically active octacyanidotungstate(IV) ions allowed observation of the magnetic superexchange after the violet light excitation (405 nm) for compound 3 , which constitutes the first example of the photomagnetic effect in a Ni II -[W IV (CN) 8 ] system. The photomagnetic investigations for fully hydrated and dehydrated sample of 3 , as well as for the isostructural octacyanidomolybdate(IV)-based network are discussed.

Paddlewheel-type binuclear complexes featuring metal-metal bonding have been the subject of widespread interest due to fundamental concern in their electronic structures and potential applications. Here, we explore the molecular and electronic structures of diiron(II,II) complexes with N,N'-diarylformamidinate ligands. While a paddlewheel-type diiron(II,II) complex with N,N'-diphenylformamidinate ligands (DPhF) exhibits the centrosymmetric [Fe 2 (μ-DPhF) 4 ] structure, a minor alteration in the ligand system, i. e., switching from phenyl to p-tolyl N-substituted formamidinate ligand (DTolF), resulted in the isolation of an unprecedented non-centrosymmetric [Fe(μ-DTolF) 3 Fe(κ 2 -DTolF)] complex. Both complexes were characterized using single-crystal X-ray diffraction, magnetic measurements, 57 Fe Mössbauer spectroscopy, and cyclic voltammetry along with high-level ab-initio calculations. The results provide a new view on a range of factors controlling the ground-state electronic configuration and structural diversity of homoleptic diiron(II,II) complexes. Model calculations determined that the Mayer bond orders for Fe-Fe interactions are significantly lower than 1 and equal to 0.15 and 0.28 for [Fe 2 (μ-DPhF) 4 ] and [Fe(μ-DTolF) 3 Fe(κ 2 -DTolF)], respectively., (© 2022 Wiley-VCH GmbH.)

Three new hybrid organic-inorganic frameworks employing octacyanidometallates and 4,4'-bypiridine dioxide (4,4'-bpdo) as bridging molecules were prepared and characterized. The three-dimensional coordination frameworks {[Fe II (μ-4,4'-bpdo)(H 2 O) 2 ] 2 [M IV (CN) 8 ]·9H 2 O} n (Fe2Mo, Fe2W and Fe2Nb; M = Mo, W and Nb) are composed of cyanido-bridged chains, which are interconnected by the organic linkers. Magnetic measurements for Fe2Nb show a two-step transition to the antiferromagnetic state, which results from the cooperation of antiferromagnetic intra- and inter-chain interactions. Fe2Mo and Fe2W, on the other hand, behave as paramagnets at 2 K because of the diamagnetic character of the corresponding octacyanidometallate(IV) building units. However, after 450 nm light irradiation they show transition to the metastable high spin Mo IV or W IV states, respectively, with distinct ferromagnetic intrachain spin interactions, as opposed to the antiferromagnetic ones observed in the Fe2Nb framework.

Magnetic molecules known as molecular nanomagnets (MNMs) may be the key to ultra-high density data storage. Thus, novel strategies on how to design MNMs are desirable. Here, inspired by the hexagonal structure of the hardest intermetallic magnet SmCo 5 , we have synthesized a nanomagnetic molecule where the central lanthanide (Ln) Er III is coordinated solely by three transition metal ions (TM) in a perfectly trigonal planar fashion. This intermetallic molecule [Er III (Re I Cp 2 ) 3 ] (ErRe 3 ) starts a family of molecular nanomagnets (MNM) with unsupported Ln-TM bonds and paves the way towards molecular intermetallics with strong direct magnetic exchange interactions-a promising route towards high-performance single-molecule magnets., (© 2022. The Author(s).)

A chiral porous cyanide-bridged framework {[Mn II (L)] 2 [W IV (CN) 8 ]·10H 2 O} n (1; L = 2,6-bis[1-(2-( N -methylamino)ethylimino)ethyl]-pyridine) showing a strong structural similarity to MOF-74 has been prepared and characterised. The crystallised water molecules can be easily removed below 60 °C, leading to a distinct crystal colour change and the activation of its photomagnetic properties - constituting the so called photomagnetic sponge behaviour of this system. The complete dehydration of 1 proceeds through a single-crystal-to-single-crystal transformation and the resulting anhydrous framework {[Mn II (L)] 2 [W IV (CN) 8 ]} n (1anh) was studied using single-crystal X-ray diffraction.

Solution-based syntheses are omnipresent in chemistry but are often associated with obvious disadvantages, and the search for new mild and green synthetic methods continues to be a hot topic. Here, comparative studies in four different reaction media were conducted, that is, the solid-state mechano- and slow-chemistry synthesis, melted phase, and solution protocols, and the impact of the employed solvent-free solid-state versus liquid-phase synthetic approaches was highlighted on a pool of products. A moderately exothermic model reaction system was chosen based on bis(pentafluorophenyl)zinc, (C 6 F 5 ) 2 Zn, and 2,2,6,6-tetramethylpiperidinyl oxide (TEMPO) as a stable nitroxyl radical, anticipating that these reagents may offer a unique landscape for addressing kinetic and thermodynamic aspects of wet and solvent-free solid-state processes. In a toluene solution two distinct paramagnetic Lewis acid-base adducts (C 6 F 5 ) 2 Zn(η 1 -TEMPO) (1) and (C 6 F 5 ) 2 Zn(η 1 -TEMPO) 2 (2) equilibrated, but only 2 was affordable by crystallization. In turn, crystallization from the melt was the only method yielding single crystals of 1. Moreover, the solid-state approaches were stoichiometry sensitive and allowed for the selective synthesis of both adducts by simple stoichiometric control over the substrates. Density functional theory (DFT) calculations were carried out to examine selected structural and thermodynamic features of the adducts 1 and 2. Compound 2 is a unique non-redox active metal complex supported by two nitroxide radicals, and the magnetic studies revealed weak-to-moderate intramolecular antiferromagnetic interactions between the two coordinated TEMPO molecules., (© 2021 Wiley-VCH GmbH.)

This work provides a summary of the preparation, structure, reactivity, physicochemical properties, and main uses of 1,2,5-thiadiazole 1,1-dioxides in chemistry and material sciences. An overview of all currently known structures containing the 1,2,5-thiadiazole 1,1-dioxide motif (including the anions radical species) is provided according to the Cambridge Structural Database search. The analysis of the bond lengths typical for neutral and anion radical species is performed, providing a useful tool for unambiguous assessment of the valence state of the dioxothiadiazole-based compounds based solely on the structural data. Theoretical methodologies used in the literature to describe the dioxothiadiazoles are also shortly discussed, together with the typical 'fingerprint' of the dioxothiadiazole ring reported by means of various spectroscopic techniques (NMR, IR, UV-Vis). The second part describes the synthetic strategies leading to 1,2,5-thiadiazole 1,1-dioxides followed by the discussion of their electrochemistry and reactivity including mainly the chemical methods for the successful reduction of dioxothiadiazoles to their anion radical forms and the ability to form coordination compounds. Finally, the magnetic properties of dioxothiadiazole radical anions and the metal complexes involving dioxothiadiazoles as ligands are discussed, including simple alkali metal salts and d -block coordination compounds. The last section is a prospect of other uses of dioxothiadiazole-containing molecules reported in the literature followed by the perspectives and possible future research directions involving these compounds.

While metal-organic frameworks (MOFs) are at the forefront of cutting-edge porous materials, extraordinary sorption properties can also be observed in Prussian Blue Analogs (PBAs) and related materials comprising extremely short bridging ligands. Herein, we present a bimetallic nonporous cyanide-bridged coordination polymer (CP) {[Mn(imH)] 2 [Mo(CN) 8 ]} n ( 1Mn ; imH = imidazole) that can efficiently and reversibly capture and release water molecules over tens of cycles without any fatigue despite being based on one of the shortest bridging ligands known - the cyanide. The sorption performance of {[Mn(imH)] 2 [Mo(CN) 8 ]} n matches or even outperforms MOFs that are typically selected for water harvesting applications with perfect sorption reversibility and very low desorption temperatures. Water sorption in 1Mn is possible due to the breathing effect (accompanied by a dramatic cyanide-framework transformation) occurring in three well-defined steps between four different crystal phases studied structurally by X-ray diffraction structural analysis. Moreover, the capture of H 2 O by 1Mn switches the EPR signal intensity of the Mn II centres, which has been demonstrated by in situ EPR measurements and enables monitoring of the hydration level of 1Mn by EPR. The sorption of water in 1Mn controls also its photomagnetic behavior at the cryogenic regime, thanks to the presence of the [Mo IV (CN) 8 ] 4- photomagnetic chromophore in the structure. These observations demonstrate the extraordinary sorption potential of cyanide-bridged CPs and the possibility to merge it with the unique physical properties of this class of compounds arising from their bimetallic character ( e.g. photomagnetism and long-range magnetic ordering)., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Bistable and stimuli-responsive molecule-based materials are promising candidates for the development of molecular switches and sensors for future technologies. The CN-bridged {NH 4 [Ni(cyclam)][Fe(CN) 6 ]⋅5 H 2 O} n chain exists in two valence states: Ni II -Fe III (1 HT ) and Ni III -Fe II (1 LT ) and shows unique multiresponsivity under ambient conditions to various stimuli, including temperature, pressure, light, and humidity, which generate measurable response in the form of significant changes in magnetic susceptibility and color. The electron-transfer phase transition 1 LT ↔1 HT shows room-temperature thermal hysteresis, can be induced by irradiation, and shows high sensitivity to small applied pressure, which shifts it to higher temperatures. Additionally, it can be reversibly turned off by dehydration to the {NH 4 [Ni II (cyclam)][Fe III (CN) 6 ]} n (1 d) phase, which features the Ni II -Fe III valence state over the whole temperature range, but responds to pressure by yielding Ni III -Fe II above 1.06 GPa., (© 2020 Wiley-VCH GmbH.)

The preparation, structures, and electrochemical and magnetic properties supported by density functional theory (DFT) calculations of three new copper(II) compounds with [1,2,5]thiadiazolo[3,4- f ][1,10]phenanthroline 1,1-dioxide (td) and its radical anion (td ·- ) are reported: {[Cu II Cl(td)](μ-Cl) 2 [Cu II Cl(td)]} ( 1 ), which incorporates only neutral td ligands; [Cu II Cl(td ·- )(td)]·2MeCN ( 2 ), which comprises one neutral td and one radical td ·- ; and PPN[Cu II Cl(td ·- ) 2 ]·2DMA ( 3 ), where Cu II ions are coordinated by two radical anions td ·- (DMA, dimethylacetamide; PPN + , the bis(triphenylphosphine)iminium cation). All three compounds show interesting paramagnetic behavior with low-temperature features indicating significant antiferromagnetic coupling. The magnetic properties of 1 are dominated by Cu II ···Cu II interactions ( J CuCu ) mediated through the Cl - bridges, while the magnetic properties of 2 and 3 are governed mainly by the td ·- ···td ·- ( J tdtd ) and Cu II -td ·- ( J Cutd ) exchange interactions. The structure of 2 features only two major magnetic coupling pathways enabling the fitting of experimental data with J tdtd = -36.0(5) cm -1 and J Cutd = -12.6(2) cm -1 only. Compound 3 exhibits a complex network of magnetic contacts. Attempt to approximate its magnetic behavior using only a local magnetic contacts model resulted in J tdtd = -5.6(1) cm -1 and two J Cutd constants, -12.4(2) and -22.6(4) cm -1 . The experimental fitting is critically compared with the results of broken symmetry density functional theory (BS DFT) calculations for inter- and intramolecular contacts. More consistent results were obtained with the M06 functional as opposed to popular B3LYP, which encountered problems reproducing some of the experimental intermolecular exchange interactions. Electrochemical measurements of 2 and 3 in MeCN showed three reversible nearly overlapping redox peaks appearing in a narrow potential range of -600 to -100 mV vs Fc/Fc + . Small differences between the redox events suggest that such compounds may be good candidates for new switchable materials, where the electron transfer between the metal and the ligand center is triggered by temperature, pressure, or light (valence tautomerism).

Propeller-like lanthanide complexes with suitable chiral ligand scaffolds are highly desired as they combine chirality with possible magnetic bistability. However, the library of relevant chiral lanthanide-based molecules is quite limited. Herein we present the preparation, structures, magnetic behavior as well as EPR studies of a series of propeller-shaped lanthanide Single Ion Magnets (SIMs). Coordination of the smallest helicene-type molecule 1,10-phenanthroline-N,N'-dioxide (phendo) to Ln III ions results in the formation of homoleptic complexes [Ln III (phendo) 4 ](NO 3 ) 3 ·xMeOH (Ln = Gd, Er, Yb) Gd, Er and Yb, where four phendos encircle the metal center equatorially in a four-bladed propeller fashion. The magnetization dynamics in these systems is studied by magnetic measurements and EPR spectroscopy for non-diluted as well as solid state dilutions of Er and Yb in a diamagnetic [Y III (phendo) 4 ](NO 3 ) 3 ·xMeOH (Y) matrix. Careful analysis of the slow magnetic relaxation in the diluted samples can be described by a combination of Raman and Orbach relaxation mechanisms. The most important finding concerns the identical power law τ≈T -3 describing the anomalous Raman relaxation for all three reported compounds diluted in the Y matrix. This identical power law strongly suggests that the exponent of the Raman relaxation process in the series of solid-state diluted isostructural compounds is practically independent of the metal ion (as long as the molar mass changes are negligible) and highlights a possible experimental strategy towards reliable Raman relaxation determination.

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.

Over recent years, investigations of coordination polymer thin films have been initiated due to their unique properties, which are expected to be strongly enhanced in the thin film form. In this work, a crystalline [Fe II (H 2 O) 2 ] 2 [Nb IV (CN) 8 ]∙4H 2 O (1) film on a transparent Nafion membrane was obtained, for the first time, via ion-exchange synthesis. The proper film formation and its composition was confirmed with the use of energy dispersive X-ray spectroscopy and infrared spectroscopy, as well as in situ Ultraviolet-Visible (UV-Vis) spectroscopy. The obtained film were also characterized by scanning electron microscopy, X-ray diffraction, and magnetic measurements. The [Fe II (H 2 O) 2 ] 2 [Nb IV (CN) 8 ]∙4H 2 O film shows a sharp phase transition to a long-range magnetically ordered state at T c = 40 K. The 1 film is a soft ferromagnet with the coercive field H c = 1.2 kOe. Compared to the bulk counterpart, a decrease in critical temperature and a significant increase in the coercive field were observed in the films indicating a distinct size effect. The decrease in T c could also have been related to the possible partial oxidation of Fe II ions to Fe III , which could be efficient, due to the large surface of the thin film sample.

The rational design of coordination frameworks combining more than two different metal ions using a self-assembly approach is challenging because it rarely offers sufficient control over the building blocks at the actual self-assembly stage. In this work, we present a successful two-step strategy toward heterotrimetallic coordination frameworks by employing a new bimetallic [(NC) 7 Mo IV -CN-Pt IV (NH 3 ) 4 -NC-Mo IV (CN) 7 ] 4- secondary building unit (SBU). This anionic moiety has been isolated and characterized as a simple salt with an organic dppipH 2 2+ cation (dppipH 2 ) 2 [(NC) 7 Mo IV -CN-Pt IV (NH 3 ) 4 -NC-Mo IV (CN) 7 ]·15H 2 O ( 1 ) (dppip = 1,4-di(4-pyridinyl)piperazine). The salt presents a second-order phase transition related to cation conformational change around 250 K and a photomagnetic effect after irradiation with 450 nm light at 10 K. When combined with aqueous solutions of Mn II or Cu II complexes, it forms either a one-dimensional chain [Mn II (dpop)][Mn II (dpop)(H 2 O)][(NC) 7 Mo IV -CN-Pt IV (NH 3 ) 4 -NC-Mo IV (CN) 7 ]·36H 2 O ( 2 ) (dpop = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo-[12.3.1]octadeca-1(18),2,12,14,16-pentaene) or a photomagnetic two-dimensional honeycomb network [Cu II (cyclam)] 2 [(NC) 7 Mo IV -CN-Pt IV (NH 3 ) 4 -NC-Mo IV (CN) 7 ]·40.89H 2 O ( 3 ) (cyclam = 1,4,8,11-tetraazacyclotetradecane), both characterized by very large cavities in their structure filled with solvent molecules. Both 2 and 3 incorporate three different transition-metal ions and constitute a new family of 3d-4d-5d coordination frameworks. Moreover, compound 3 inherits the photomagnetic properties of the MoPtMo SBU.

Chiral photomagnets compose a class of multifunctional molecule-based materials with light-induced alteration of magnetization and chiral properties. The rational design and synthesis of such assemblies is a challenge, and only few such systems are known. Herein, the remarkable octacyanide-bridged enantiomeric pair of 1-D chains [Cu(( R,R )-chxn) 2 ] 2 [Mo(CN) 8 ]·H 2 O ( 1R ) and [Cu(( S,S )-chxn) 2 ] 2 [Mo(CN) 8 ]·H 2 O ( 1S ) exhibiting enantiopure structural helicity, which results in optical activity in the 350-800 nm range as confirmed by natural circular dichroism (NCD) spectra, is reported. The photomagnetic effects of 1R , 1S , and 1rac result from the blue light excitation (436 nm) of the photomagnetically active octacyanidomolybdate(IV) ions. In the excited state Mo IV HS centers with S = 1 couple antiferromagnetically with the neighboring Cu II centers with J CuMo values of -1.3, -1.0, and -1.1 cm -1 for 1R , 1S , and 1rac , respectively. The values of thermal relaxation energy barriers have been estimated as 142 and 356 K for 1R and 1S , being comparable with the energy range of the thermal bath. The value for 1rac reveals a significantly lower value of 75 K. On the basis of these results the value of g Mo HS has been estimated to be in the range 4.8-5.8.