Search

Dicyanidobis(aromatic α,α′-diimine) Fe(ii) complexes efficiently constrain the equatorial plane of the Dy(iii) centre which opens a pathway for controlling the lanthanide magnetic anisotropy by placing organic N-oxides at axial positions.

The change of the oxidation state from WIV to WV in isotopological CoII–[W(CN)8]n− chains leads to the appearence of pronounced single-chain magnet behaviour.

We discuss the advances in employing the magneto-luminescent lanthanide complexes as a source of multifunctionality that covers the sensitivity to external stimuli, as well as their electrical, non-linear, and chirality-related optical properties.

Uncommon lanthanides are used to construct luminescent molecular nanomagnets and a pioneering SMM-based optical thermometer utilizing Sm(iii) centres.

This study represents the first explorative investigation on the supramolecular structural diversity in Hg(II) coordination chemistry with triazole-thiourea ligands leading to a variety of mononuclear, binuclear, and coordination polymers: {[Hg(L1)2(L1–)2]} (1), {[Hg2(L1)2(μ2-I)2I2]·DMSO} (2), {[Hg(L2)(μ2-I)I]·MeOH}∝ (3), {[Hg2(μ-L3–)4]}∝ (4), {[HgCl(L4–)L4]·MeOH} (5), {[Hg2(L4)2(μ2-I)2(I)2]·2MeOH} (6), {[Hg2(μ2-L5–)4]}∝ (7), {[Hg2(μ2-Cl)2(L6–)2(L6)2]} (8), {[Hg2(μ2-Br)2(L6–)2(L6)2]} (9), and {[Hg2(μ2-I)2(L6–)2(L6)2]} (10). A reaction mechanism was suggested for the unexpected ligand rearrangement occurring in {[Hg2I3(μ3-L5′)]}∝ (11). The ligands were fully characterized including by X-ray crystallography and computational means. This includes six new triazole-thiourea based ligands, namely, 1-R-3-(4H-1,2,4-triazol-4-yl)thiourea (where R = methyl (L1), ethyl (L2), propyl (L3), isopropyl (L4), and its polymorph (L4-poly), allyl (L5), ethyl acetate (L6), and its solvate (L6_MeOH)). Under UV light excitation, 7, 10, and 11 exhibit visible photoluminescence of wide origin, ranging from ligand-centered (LC) fluorescence combined with organic-ligand-to-metal charge transfer (LMCT) emissive states in 7 and 10, up to halide-to-metal charge transfer (XMCT) combined with halide-to-ligand charge transfer (XLCT) emissive states in 11. The variable emission mechanisms in the obtained coordination polymers were elucidated by experimental proofs confronted with theoretical calculations of the electronic densities of states, proving that Hg(II) halide coordination polymers involving flexible 1,2,4-triazole-based ligands form a promising class of luminescent molecular materials.

A unique family of three-dimensional (3D) luminescent SrII-ReV metal-organic frameworks (MOFs), {[SrII(MeOH)5][ReV(CN)4(N)(bpen)0.5]·MeOH}n [1·MeOH; N3- = nitrido ligand, bpen = 1,2-bis(4-pyridyl)ethane, and MeOH = methanol], {[SrII(MeOH)4][ReV(CN)4(N)(bpee)0.5]·2MeOH}n [2·MeOH; bpee = 1,2-bis(4-pyridyl)ethylene], and {[SrII(bpy)0.5(MeOH)2][ReV(CN)4(N)(bpy)0.5]}n (3·MeOH; bpy = 4,4'-bipyridine), is reported. They are obtained by the molecular self-assembly of Sr2+ ions with tetracyanidonitridorhenate(V) metalloligands, [ReV(CN)4(N)]2-, and pyridine-based organic spacers (L = bpen, bpee, bpy). Such a combination of molecular precursors results in bimetallic SrII-ReV cyanido-bridged layers further bonded by organic ligands into pillared Hofmann-type coordination skeletons. Because of the formation of {ReV-(L)-ReV} 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 {ReV-(bpy)-ReV} and {SrII-(bpy)-SrII} linkages, exhibits three interconvertible, variously solvated phases, methanol-solvated 3·MeOH, hydrated {[SrII(bpy)0.5(H2O)2][ReV(CN)4(N)(bpy)0.5]·0.6H2O}n (3·H2O), and desolvated {[SrII(bpy)0.5][ReV(CN)4(N)(bpy)0.5]}n (3). Their formation was correlated with water and methanol vapor sorption properties investigated for 3·H2O. The solvent content affects the luminescence mainly by tuning the emission energy within the series of 3·MeOH, 3·H2O, 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 [ReV(CN)4(N)]2--based MOFs is an efficient route toward advanced solid luminophores tunable by external stimuli such as solvent or temperature.

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 HoIII complexes. Our concept is shown in dinuclear cyanido-bridged molecules, {[HoIII(4-pyridone)4(H2O)2][MIII(CN)6]}·nH2O (M = Co, 1; Rh, 2; Ir, 3) and their magnetically diluted analogues, {[HoIIIxYIII1–x(4-pyridone)4(H2O)2][MIII(CN)6]}·nH2O (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 HoIII 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 YIII-based dilution governs the optical properties as 1–3 exhibit poor emission due to the dominant re-absorption from HoIII while 1@Y–3@Y show room-temperature blue emission of 4-pyridone. Within ligand emission bands, the sharp re-absorption lines of the HoIII 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 HoIII complexes are great prerequisites for advanced opto-magnetic systems linking slow magnetic relaxation with unique optical thermometry exploiting a luminescence re-absorption phenomenon., HoIII complexes bearing organic luminophores and inorganic metalloligands are an effective tool for achieving the unique conjunction of single-molecule magnetism and thermometric luminescence re-absorption phenomenon.

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 {[FeII (2-pyrpy)2 ]4 [MIV (CN)8 ]2 }⋅4 MeOH⋅6 H2 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 Fe4 M2 molecules constitute a unique example where the presence of the guests directly affects the pressure-induced thermal spin crossover (SCO) phenomenon occurring at the FeII centres. The hydrated phases show a partial SCO with approximately two out-of-four FeII 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 FeII centres undergoing high-spin to low-spin transition at 1 GPa.

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

The ab initio calculations were correlated with magnetic and emission characteristics to understand the modulation of properties of NIR-emissive [YbIII(2,2′-bipyridine-1,1′-dioxide)4]3+ single-molecule magnets by cyanido/thiocyanidometallate counterions, [AgI(CN)2]− (1), [AuI(SCN)2]− (2), [CdII(CN)4]2–/[CdII2(CN)7]3– (3), and [MIII(CN)6]3– [MIII = Co (4), Ir (5), Fe (6), Cr (7)]. Theoretical studies indicate easy-axis-type ground doublets for all YbIII 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 YbIII 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.

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 inc...

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

One of the pathways toward luminescent single-molecule magnets (SMMs) is realized by the self-assembly of lanthanide(3+) ions with cyanido transition metal complexes. We report a novel family of emissive SMMs, {YbIII(4-pyridone)4[FeII(phen)2(CN)2]2}(CF3SO3)3·solv (solv = 2MeCN, 1·MeCN; 2AcrCN, 1·AcrCN; 2PrCN, 1·PrCN; 2MalCN·1MeOH; 1·MalCN; MeCN = acetonitrile, AcrCN = acrylonitrile, PrCN = propionitrile, MalCN = malononitrile). They are based on paramagnetic YbIII centers coordinating diamagnetic [FeII(phen)2(CN)2] metalloligands but differ in the nitrile solvents of crystallization. They exhibit a field-induced slow magnetic relaxation dominated by a Raman process, without an Orbach relaxation as indicated by AC magnetic data and the ab initio calculations. The Raman relaxation is solvent-dependent as represented by the power “n” of the BRamanTn contribution varying from 3.07(1), to 2.61(1), 2.37(1), and 1.68(4) for 1·MeCN, 1·PrCN, 1·AcrCN, and 1·MalCN, respectively, while the BRaman parameter adopts the opposite trend. This was correlated with the variation of phonon modes schemes, including the number of available vibrational modes and their energies, dependent on the increasing complexity of the applied nitrile. 1·MeCN and 1·MalCN show the additional T-independent relaxation assignable to dipole-dipole interactions as confirmed by its suppression in 1·AcrCN and 1·PrCN revealing longer Yb–Yb distances and the disappearance in the LuIII-diluted 1·MeCN@Lu. All compounds exhibit YbIII–centered near-infrared photoluminescence sensitized by organic ligands.

A unique family of three-dimensional (3D) luminescent Sr

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, {[EuIII(H2O)3(pyrone)4][CoIII(CN)6]}·nH2O (1, n = 2, 2, n = 1), which was obtained by the self-assembly of Eu3+ 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 EuIII-centered visible photoluminescence. However, they differ in the energy splitting of the main emission band of a 5D0 → 7F2 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.

Lanthanide(III) single-molecule magnets (Ln-SMMs) offer the fruitful conjunction of magnetic and photoluminescent properties originating from their single-ion anisotropy and emissive f–f electronic transitions. The flexibility of lanthanide(III)-based coordination systems is the most significant prerequisite for the generation of additional physical phenomena, including non-linear optical effects related to the lack of inversion centre. In the quest towards multifunctional molecular nanomagnets, we report heterometallic d–f layered coordination polymers, {[NdIII4(H2O)17(pzdo)5][MIV(CN)8]3}·9H2O (M = Mo (1), W (2); pzdo = pyrazine-N,N′-dioxide). They crystallize in the non-centrosymmetric C2 space group due to the spontaneous resolution process, confirmed by the observation of second harmonic generation (SHG) activity. These materials exhibit UV-to-vis-light-induced near-infrared (NIR) NdIII-centred luminescence sensitized by octacyanidometallates and organic ligand, and slow relaxation of magnetization of NdIII complexes which was investigated by alternate-current (ac) magnetic measurements and the ab initio calculations. The observed magnetic and optical properties are sensitive to the nature of the d-transition metal centre, namely most of their features are improved upon the replacement of MoIV with WIV centres. In this work, we show the generation of SHG-active NIR-emissive SMMs realized by Nd3+ ions inserted into hybrid layers built of inorganic [M(CN)8]4− and organic pzdo linkers.

Rare-earth (RE) metal complexes exhibit attractive magnetic and optical properties related to their strong magnetic anisotropy and efficient photoluminescence. Due to the accessibility of high coordination numbers, they are useful molecular building blocks for the construction of bimetallic coordination systems. Therefore, they can be readily combined with hexacyanidometallate ions of transition metals into the d–f cyanido-bridged frameworks. This leads to the rich family of molecule-based materials varying from purely inorganic 3-D REIII–[MII/III(CN)6]4−/3− (RE = La–Lu, Y; M = Cr, Fe, Ru, Co) networks, through coordination polymers of lower dimensionality obtained with supporting organic ligands, up to strictly molecular species. The past decade brought intensive interest in the design and synthesis of rare-earth hexacyanidometallate frameworks with particular attention paid to their magnetic, optical, electronic, and mechanical properties. In this review, we discuss the most important results of this research area, including remarkable thermal expansion properties, magnetic ordering effects, single-molecule magnetism, luminescent functionalities, electrochemical activity for applications in alkali ion batteries and electroanalytical sensing, and efficient NMR relaxivity for magnetic resonance imaging, as well as photo- and pressure-induced switching of magnetic and optical characteristics. We focus on the recent advances, emphasizing also the general advantages and the future perspectives in the combination of RE(III) complexes and hexacyanidometallates within the d–f coordination frameworks towards the generation of diverse physical functionalities.

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-Bu4N][DyIII(BH4)4] (1) and [Ph4P][DyIII(BH4)4] (2), involving DyIII centers surrounded by four pseudo-tetrahedrally arranged BH4– ions. While 2 has higher symmetry and adopts a tetragonal unit cell (I41/a), 1 crystallizes in a less symmetric monoclinic unit cell (P21/c). They exhibit yellow room-temperature photoluminescence related to the f–f electronic transitions. Moreover, they reveal DyIII-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-Bu4N][YIII0.9DyIII0.1(BH4)4] (1@Y) and [Ph4P][YIII0.9DyIII0.1(BH4)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 DyIII complexes of 1 was confirmed by the results of the ab initio calculations performed for both 1–2 and the highly symmetrical inorganic DyIII borohydrides, α/β-Dy(BH4)3, 3 and 4. The magneto-luminescent character was achieved by the implementation of large organic cations that lower the symmetry of DyIII 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.

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, {[DyIII(H2O)3(tmpo)3]2[PtIVBr2(CN)4]3}·2H2O (1) and {[DyIII(H2O)(tmpo)4]2[PtIVBr2(CN)4]3}·2CH3CN (2) (tmpo = trimethylphosphine oxide), obtained by combining DyIII complexes with uncommon dibromotetracyanidoplatinate(IV) ions, [PtIVBr2(CN)4]2−. They are built of analogous Z-shaped cyanido-bridged {Dy2Pt3} molecules but differ in the coordination number of DyIII (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 DyIII-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 PtIV 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 [YbIII(2,2'-bipyridine-1,1'-dioxide)4]3+ single-molecule magnets by cyanido/thiocyanidometallate counterions, [AgI(CN)2]- (1), [AuI(SCN)2]- (2), [CdII(CN)4]2-/[CdII2(CN)7]3- (3), and [MIII(CN)6]3- [MIII = Co (4), Ir (5), Fe (6), Cr (7)]. Theoretical studies indicate easy-axis-type ground doublets for all YbIII 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 YbIII 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.

A two-step hysteretic FeII spin crossover (SCO) effect was achieved in programmed layered Cs{[Fe(3-CNpy)2 ][Re(CN)8 ]}⋅H2 O (1) (3-CNpy=3-cyanopyridine) assembly consisting of cyanido-bridged FeII -ReV square grid sheets bonded by Cs+ ions. The presence of two non-equivalent FeII sites and the conjunction of 2D bimetallic coordination network with non-covalent interlayer interactions involving Cs+ , [ReV (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 FeII state at low temperatures. We prove that octacyanidorhenate(V) ion is an outstanding metalloligand for induction of a cooperative multistep, multiswitchable FeII SCO effect.

The self-assembly of lanthanide(3+) ions with pyrazine N,N′-dioxide (pzdo) and bis(triphenylphosphine)iminium (PPN+) salts of diamagnetic octacyanidometallates of MoIV and WIV results in one-dimensional (PPN)[LnIII(pzdo)2(MeOH)0.3(H2O)3.7][MIV(CN)8]·7.7H2O·2MeOH (Ln = Er and Yb; M = Mo and W) coordination networks. They are constructed of zigzag metal–organic {LnIII(μ-pzdo)}n chains with terminal [MIV(CN)8]4− metalloligands attached to the LnIII centres. Both Er- and Yb-containing frameworks exhibit field-induced slow magnetic relaxation originating from the field-dependent equilibrium between quantum tunnelling of magnetization and the direct process along with the temperature-dependent Raman and Orbach relaxation processes. Transition metal substitution on [MIV(CN)8]4− sites modifies the intrinsic magnetic anisotropy of lanthanides, as depicted by the subtle change of thermal energy barriers of Orbach relaxation in Er-based systems, while it significantly affects Raman relaxation due to the modulated phonon mode scheme. All reported compounds exhibit strong visible light absorption due to a series of electronic transitions of pzdo ligands and [M(CN)8]4− ions and the appearance of low energy anion–π charge transfer band involving pzdo and octacyanidometallates. These charge transfer states were utilized in achieving the sensitized near-infrared photoluminescence of ErIII and YbIII centers; thus, the energy transfer process is strongly dependent on the nature of the metal centre in the [MIV(CN)8]4− ion. The W(IV)-pzdo system is a good sensitizer for ErIII, while the Mo(IV)-pzdo unit is better for YbIII emission which can be rationalized in terms of the positions of energy levels of their respective donor states. Therefore, we report NIR emissive ErIII and YbIII single-molecule magnets with tunable magnetic and optical properties, uncovering the crucial role of octacyanidometallates and their anion–π interactions with pzdo ligands.

Two series of trimetallic {NiII x CoII 9-x [WV (CN)8 ]6 } (NiCoW) and {MnII x CoII 9-x [WV (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: NiII over the CoII and CoII over MnII . 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 Sgr , assuming the ferromagnetic HS CoII -NC-WV and antiferromagnetic MnII -NC-WV interactions established by numerous literature reports. The AC magnetic measurements indicate the occurrence of slow magnetic relaxation, with the highest energy barrier ΔE/kB of 26 K for the Ni6 Co3 W6 congener and of 17 K for the Mn6 Co3 W6 congener, and relatively large values of distribution parameter α. The values of ΔE are correlated with possible anisotropy of distribution of fac-[CoII (μ-NC)3 (MeOH)3 ] moieties at the external corners of the cube substructure.

The combination of [WV(CN)8]3– anions with 3d metal cations MII in MeOH leads to the formation of pentadecanuclear spherical cyanido-bridged clusters {M[M(solv)3]8[M′(CN)8]6}, M9M′6. By decorating their surface with organic ligands or/and by installation of different ions in their coordination skeleton, one could tune high spin in the ground state, slow relaxation of magnetization, or structural/spin phase transition. In this work we present the extended molecular high spin (SGS = 15/2, geff = 3.4) clusters or chains of clusters {Co9W6(N,O-L)x} (N,O-L – pyrazine mono-N-oxide, pzmo; 4,4-bipyridine mono-N-oxide – 4,4′-bpmo) equipped with the structurally ordered remote (2–2.5 nm) N-oxide functions, as a result of deliberate combination of solvated Co9W6 supercomplexes with asymmetric N,O-donor linkers L. The systematic occurrence of such motifs in the series 1–3 is a result of preference for the Co–NL coordination over the Co–OL coordination, controlled also by strongly competing supramolecular interactions...

Heterometallic cyanido-bridged networks are versatile molecular platforms for diverse optical, magnetic and electronic functionalities. We present a pioneering synthetic route which employs polycyanidometallates in the preparation of unique d–f coordination systems revealing multi-stimuli responsive multi-coloured photoluminescence with potential application in colorimetric and ratiometric temperature sensing. We report two layered cyanido-bridged frameworks, bimetallic {[TbIII(4-OHpy)2(H2O)3][CoIII(CN)6]}·0.5H2O (1) (4-OHpy = 4-hydroxypyridine), and trimetallic {[TbIII0.5DyIII0.5(4-OHpy)2(H2O)3][CoIII(CN)6]}·0.5H2O (2), along with their structural and full physicochemical characterization. They exhibit room temperature visible photoluminescence within an extensive colour range, including white light emission, tunable through the applied lanthanide ions, and switchable by excitation with light through selective excitation of the green emissive TbIII, yellow emissive DyIII, blue luminescent 4-OHpy, and red luminescent [Co(CN)6]3− components. The emission properties of 1 and 2, including the energy transfer from organic ligands and cyanide complexes towards lanthanide ions, are strongly modulated by the change of temperature in the broad 120–300 K range. As a result, colorimetric luminescent temperature sensing exploiting a wide emission colour range was achieved for both 1 and 2. Moreover, 2 reveals the temperature dependent ratio between the intensities of sharp emission lines of TbIII and DyIII which can be used as a thermometric parametric for ratiometric luminescent detection of temperature. The related thermometer perfomance was examined for various excitation wavelengths, and the best parameters of relative thermal sensitivity, Sr > 1% K−1, with the maximal value 2.2(3)% K−1, and temperature uncertainty, δT < 1 K, are detected for 270 nm excitation in the range 120–200 K.

Hexacyanidometallates of CoIII and FeIII were combined with photoluminescent EuIII(3-pyridone) complexes resulting in a series of crystalline materials built of trimetallic cyanido-bridged chains, [Eu(3-pyridone)2(H2O)4][Co1−xFex(CN)6]·H2O (x = 0, 0.03, 0.06, 0.09, 0.12, 0.15, 0.25, 0.5, 0.75, 1; compounds 1, 2, …, 9, 10). They are isostructural, revealing a Eu–Co/Fe zigzag coordination chain topology, with a statistical arrangement of Co and Fe sites occupying the same crystallographic position of the bridging [MIII(CN)6]3− moiety. Replacement of CoIII with slightly larger FeIII going from 1 to 10 leads to the gradual expansion of the unit cell caused mainly by the elongation of the lattice constant c related to the alignment of coordination chains. The unit cell parameters depend linearly on the Fe fraction, obeying Vegard's law; thus, 1–10 can be considered as molecular substitutional alloys based on the formation of a Co/Fe solid solution within the flexible coordination network. The variation of the Co/Fe ratio governs the optical properties, leading to tunable absorption and emission characteristics from red emissive, weakly coloured 1–2 to weaker emissive, red coloured 8–10. Fe-free compound 1 is colourless, while the addition of Fe in 2–10 induces an orange to red colour related to the absorption at ca. 420 nm of ligand-to-metal charge transfer (LMCT) origin. Upon UV light excitation, Fe-free compound 1 shows significant room temperature EuIII-centered red emission, enhanced by the energy transfer from [CoIII(CN)6]3− and 3-pyridone to EuIII centers. Red emission is detectable over the whole family of 1–10, also for the Co-free compound 10, indicating that the hexacyanidoferrate(III) ion can be applied as a molecular linker in the construction of lanthanide-based luminescent coordination frameworks. However, on increasing the Fe fraction, both the overall emission intensity and the emission quantum yield decrease exponentially accompanied by the gradual shortening of the emission lifetimes. This indicates that all the Eu–Co/Fe compounds absorb UV light similarly, but the Fe centers do not transfer the energy towards Eu(III) efficiently, which is related to the disturbing presence of LMCT and metal-centered ligand field excited states in the visible range.

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.

The macrocyclic ligand calix[4]arene (L1) and its sulphur-containing analogue thia[4]calixarene (L2) are promising precursors for functional molecular materials as they offer rational functionalization with various organic groups. Here, we present the first example of lanthanide-based coordination polymers built from the macrocyclic thiacalix[4]arene backbone bearing four carboxylic moieties, namely, ligand H4L3. The combination of H4L3 with the Tb3+ and Dy3+ cations led to the formation of 1D ladder-type coordination polymers with the formula [LnIIIHL3DMF3]·(DMF) (where DMF = dimethylformamide and Ln = Tb or Dy, denoted as HL3–Tb and HL3–Dy), which resulted from the coordination of the lanthanide cations with the partially deprotonated ligand HL33− that behaved as a T-shape connector. The coordination sphere around the metal was completed by the coordinated DMF solvent molecules. By combining both Tb3+ and Dy3+ cations, isostructural heterobimetallic solid solutions HL3–Tb1−xDyx were also prepared. HL3–Tb and HL3–Dy showed visible light photoluminescence originating from the f–f electronic transitions of pale green emissive Tb3+ and pale yellow emissive Dy3+ with efficient sensitization by the functionalized thia[4]calixarene ligand HL3. In the HL3–Tb1−xDyx solid solutions, the Tb/Dy ratio governed both the emission colour as well as the emission quantum yield, which reached even 28% at room temperature for HL3–Tb. Moreover, HL3–Dy exhibited a slow magnetic relaxation effect related to the magnetic anisotropy of the dodecahedral Dy3+ complexes, which were well isolated in the crystal lattice by expanded organic spacers.

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

We report an efficient pathway toward sensitization of red room temperature Eu

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, (H5O2)2(H)[YbIII(hmpa)4][CoIII(CN)6]2·0.2H2O (1, hmpa = hexamethylphosphoramide), composed of molecular {YbCo2}3- anions noncovalently bonded to acidic H5O2+ and H+ ions, is reported. The resulting YbIII complexes present a slow magnetic relaxation below 6 K and room temperature NIR 4f-centered photoluminescence sensitized by [Co(CN)6]3- ions. The microporous framework, built on these emissive magnetic molecules, exhibits a high proton conductivity of the H-hopping mechanism reaching σ of 1.7 × 10-4 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, Sr > 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 EuIII emission by the charge-transfer (CT) states related to d8-d10 heterometallophilic interactions achieved by the simultaneous application of tetracyanidometallates of PtII/PdII and dicyanidometallates of AuI/AgI in the construction of a trimetallic d-d-f assembly. The combination of Eu3+, [MII(CN)4]2- (M = Pt, Pd), and [MI(CN)2]- (M = Au, Ag) ions along with 4,4'-bipyridine N,N'-dioxide (4,4'-bpdo) results in four novel isostructural 2D {[EuIII(4,4'-bpdo)(H2O)2][MII(CN)4]}·[MI(CN)2]·H2O (MII/MI = 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 {EuIII[MII(CN)4]}n square grids coexisting with metal-organic {EuIII(4,4'-bpdo)}n chains, with the further attachment of [MI(CN)2]- ions through metallophilic {MII-MI} interactions. This results in dinuclear {MIIMI} units generating an orange emissive metal-to-metal-to-ligand charge-transfer (MMLCT) state, whose energy is tuned by the applied d8-d10 metal centers. Thanks to these CT states, 1-4 exhibit room temperature red EuIII photoluminescence enhanced by energy transfer from {MIIMI} 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 EuIII-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 EuIII 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 PtII/AuI cyanide metal complexes is proven to be the best candidate for the sensitization of room temperature EuIII luminescence.

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.

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

We present an advanced material exhibiting a spin crossover (SCO) effect generated by the combined application of two external stimuli, temperature and chemical treatment related to the crystallization solvent exchange. The reported material is based on a bimetallic {[FeII(4-Brphpy)4]3[ReV(CN)8]2}⋅7MeOH [1, 4-Brphpy = 4-(4-bromophenyl)pyridine] coordination network built of cyanido-bridged layers and interstitial methanol molecules. A weakly bonded solvent can be exchanged into the water, which results in a hydrated phase, {[FeII(4-Brphpy)4]3[ReV(CN)8]2}⋅5H2O (1-hyd). The difference in solvent content between 1 and 1-hyd is sufficient to induce a remarkable change in spin transition properties. Despite the {N6} coordination environment around Fe(II), 1 reveals a stable high-spin state in the whole 2–300 K temperature range, which was assigned to the stiffening of the framework due to a series of non-covalent interactions involving solvent and 4-Brphpy ligands. Upon the exchange of solvent to water, the framework of 1-hyd becomes more flexible producing a thermally induced SCO effect, which occurs in two distinguishable steps in the broad 70–250 K range. The 1 to 1-hyd transformation can be reversed by immersion in the original solvent, thus, the chemical ON–OFF switching of a thermal SCO effect was achieved. This work shows that solvent exchange processes within bimetallic layered FeII–[ReV(CN)8]3– networks give an efficient route for reversible chemical modulation of thermally induced SCO properties.

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 {Fe9[M(CN)8]6(Me3tacn)8}·14MeOH (Me3tacn = 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 Me3tacn ligand dramatically modifies the character of the spin transition phenomenon when confronted with the previously reported {Fe9[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.

An inorganic three-dimensional [NiII(H2O)2]2[WIV(CN)8]·4H2O (1) framework undergoes a single-crystal-to-single-crystal transformation upon thermal dehydration, producing a fully anhydrous phase NiII2[WIV(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 [NiII(H2O)2(NC)4]2– to the square-planar diamagnetic [NiII(NC)4]2– moieties.

Hexacyanidochromate(III) anion is here explored as the building block for the construction of bimetallic 3d-4f coordination polymers that combine spin ordering and luminescence. We report the two-dimensional cyanido-bridged {[NdIII(pmmo)2(H2O)3][CrIII(CN)6]} (1) layered framework obtained by the spontaneous crystallization from the aqueous solution of Nd3+, pyrimidine N-oxide (pmmo), and [CrIII(CN)6]3–. 1 crystallizes as light green plates in the orthorhombic Pbca space group and reveals a topology of a square grid built of nine-coordinated [NdIII(μ-NC)4(H2O)3(pmmo)2]− complexes of a nearly capped square antiprism geometry, and six-coordinated octahedral [CrIII(CN)6]3– moieties. Because of the presence of cyanide-mediated ferromagnetic coupling between paramagnetic NdIII (J = 9/2) and CrIII (S = 3/2) centers, 1 exhibits a long-range ferromagnetic ordering below Curie temperature of 2.8 K, with a tiny magnetization-field hysteresis loop detected at 1.8 K. Under the UV light irradiation, 1 shows the near-in...

The introduction of 4-bromopyridine (4-Brpy) to a self-assembled MII-[NbIV(CN)8] (M = 3d metal ion) coordination system results in the formation of three-dimensional cyanido-bridged networks, {[MII(4-Brpy)4]2[NbIV(CN)8]}·nH2O (M = Zn, n = 1, 1; M = Mn, n = 0.5, 2; M = Ni, n = 2, 3). All these compounds are coordination frameworks composed of octahedral [MII(4-Brpy)4(μ-NC)2] complexes bonded to square antiprismatic [NbIV(CN)8]4– ions bearing four bridging and four terminal cyanides. 1 and 2 crystallize in the chiral I4122 space group as the mixture of two enantiomorphic forms, named 1(+)/1(−) and 2(+)/2(−), respectively. The chirality is here induced by the spatial arrangement of nonchiral but sterically expanded 4-Brpy ligands positioned around MII centers in the distorted square geometry, which gives two distinguishable types of coordination helices, A and B, along a 4-fold screw axis. The (+) forms contain left handed helices A, and right handed helices B, while the opposite helicity is presented in the...

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-) .

Polynuclear coordination clusters (PCCs) provide considerable design capabilities towards various functions based on structural non-rigidity and spin state transitions, optical performance, catalytic properties and porosity. The elaboration of new synthetic pathways is fundamental towards advanced switchable and sensing materials, however, the recognition of the structure–property correlations and their optimization is also a key issue. In this context, the current review underlines the role of internal and external functionalization of recognized discrete cluster cores, as the basis for well-designed performance. In particular, we present here the essential update on the recent advances in the overall functionalization of polycyanido-bridged cores (chapter 2). Moreover, we discuss the polymetallic coordination cores constructed with other ligands (short oxido-, hydroxido-, chalcogenido- and other bridges as well as by long multitopic panelling ligands) by indicating the examples of solid-solutions and site selective occupation along the mixed-metal cluster cores (chapter 3), and external decoration of such clusters with ligands, complexes and polynuclear fragments (chapter 4). We also highlight the key properties, indicate the structure–property correlations, and show the power and limitations of the methods used in the presented studies. Finally, we provide the comparison between cyanido-bridged systems and other systems, and indicating possible future research pathways towards the development of PCCs based multicomponent functional systems.