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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, [{LnIII(apdo)(H2O)4}{CoIII(CN)6}]·2H2O (Ln = Nd, 1; Tb, 2; Dy, 3; Er, 4; Tm, 5; Yb, 6). They are hybrid organic–inorganic layered frameworks composed of cyanido-bridged {Ln2(μ-NC)4Co2} squares linked by Ln–apdo–Ln bridges into a coordination network of a mixed 4- and 8-metal ring topology. Lanthanide(III) complexes, [LnIII(μ-apdo)2(H2O)4(μ-NC)2]+, of a distorted dodecahedral geometry are isolated by diamagnetic [CoIII(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 NdIII-containing 1, DyIII-containing 3, and YbIII-containing 6. The related alternate-current magnetic data were precisely analyzed, indicating the multiple magnetic relaxation pathways, including a direct process, str...

Three-dimensional bimetallic cyanido-bridged frameworks, [LnIII (2,2'-bipyridine N,N'-dioxide)2 (H2 O)][CuI 2 (CN)5 ]⋅5 H2 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.

In this chapter, the optical and magnetic properties of multifunctional cyanido-bridged metal assemblies are introduced. Cyanido-bridged metal assemblies draw much attention due to their magnetic properties and functionalities. As for magnetic properties, they have an advantage to show long-range magnetic ordering due to strong magnetic couplings between magnetic metal ions via cyanide. In addition, the cyanido-bridged metal assemblies can acquire structural diversity and various electronic states by combination of metal ions and ligand, resulted in their functionalities. For examples, introduction of transition metal ions showing charge transfer and spin crossover could allow switching of spin states by external stimuli, and metal assemblies containing lanthanide ions are expected to show luminescence and slow magnetic relaxation. Herein, some cyanido-bridged metal assemblies with unique characters of photoinduced magnetization, luminescence, and slow magnetic relaxation are presented.

Heterotrimetallic twenty-metal-centred {[MIIxCuII13–x(Me3tacn)12(H2O)][WIV(CN)8]2[WV(CN)8]5}·[WV(CN)8]·n(solvent) (M = Co, x = 1, 1; M = Ni, x = 1.5, 2; M = Mn, x = 1.5, 3; M = Fe, x = 1.5, 4; solvent = MeOH, H2O) and fifteen-metal-centred {CoII[CuII(Me3tacn)]8[WV(CN)8]6}·18MeOH (5) metal–cyanide clusters have been synthesized and characterized. They were obtained by the combination of Cu(II) complexes of 1,4,7-trimethyl-1,4,7-triazacyclonane (Me3tacn) with octacyanidotungstate(V) ions with the addition of other transition metal ions. Using nitrates of Co(II), Ni(II) and Mn(II), or a perchlorate of Fe(II), twenty-metal-centred 1–4 were generated while the application of Co(II) perchlorate gave fifteen-metal centred 5. 1–4 exhibit an open-winged cage topology with octahedral sites partially occupied by non-copper 3d metal centers while five-coordinated sites are occupied only by Cu(II). In 5, Co(II) occupies the centre of a six-capped body-centred cube topology while Cu(II) remains at the external sites. The added transition metal ions enhance the stability of W(V), partially hampering the reduction to W(IV) in 1–4 when compared with the bimetallic {Cu13W7} analogue. It also enables a straightforward synthesis of 5 involving only W(V) without the electrochemical stabilization of this oxidation state. As a result, 1–5 exhibit enhanced magnetic properties when compared with their Cu–W analogues. The addition of Co, Ni, Mn and Fe into the {Cu13W7} clusters produces also the (+3) charge of trimetallic molecules, and breaks the molecular and crystal symmetry, which is reflected by the crystallization of a chiral cluster core with [WV(CN)8]3– counterions in the chiral P21212 space group. Our work shows efficient control over the nuclearity, charge, chirality and magnetism of metal–cyanide clusters achieved by anion-assisted incorporation of various 3d metal ions into the CuII(Me3tacn)[W(CN)8]n− system.

The switching of single-molecule magnet behaviour and photoluminescence by the level of humidity is presented. A functional material, {[Dy(H2O)3(2-pyrrolidone)4][Co(CN)6]}·nH2O (1), based on {DyIIICoIII} molecules was prepared. 1 exhibits two crystalline phases switchable by the humidity level at room temperature: the low humidity phase, 1LH, stable below 42% relative humidity (RH), and the high humidity phase, 1HH, stable above 47% RH; the 42–47% range of RH gives a unique bistable system. Both 1LH and 1HH are yellow emissive single-molecule magnets due to the intrinsic optical and magnetic properties of DyIII complexes. The reversible single-crystal-to-single-crystal transformation from 1HH to 1LH leads to a significant slowdown of magnetic relaxation as depicted by a three-fold increase of the efficient anisotropic thermal energy barrier. The transformation from 1HH to 1LH also results in the modification of the emission characteristics, including a noticeable shift in the emission colour from almost white to yellow. Therefore, 1 is a magneto-luminescent molecular switch driven by the humidity level, also showing phase bistability for application in memory devices.

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

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.

Cyanido-bridged {CoII9[WV(CN)8]6} Single-Molecule Magnets grow spontaneously from the methanolic solution of Co2+ and [WV(CN)8]3− ions. Here, these molecules were combined with the 2,2′-bipyridine N-oxide (2,2′-bpmo) ligand resulting in three novel crystalline phases: {CoII[CoII(2,2′-bpmo)(MeOH)]6[CoII(2,2′-bpmo)(MeCN)]2[WV(CN)8]6}·8H2O·2MeCN·2MeOH (1) and {CoII[CoII(2,2′-bpmo)(MeOH)]8[WV(CN)8]6}·H2O·8.5MeCN·11.5MeOH (2) which grow from the MeOH–MeCN solution, and {CoII[CoII(2,2′-bpmo)(EtOH)]8[WV(CN)8]6}·3H2O·5.5MeCN·5EtOH (3) which crystallizes from the EtOH–MeCN mixture. They are constructed by {CoII9WV6} clusters of a six-capped body-centered cube topology, coordinating 2,2′-bpmo ligands at the external CoII sites. 1–3 exhibit different composition and geometrical arrangement in their outer fac-[CoII(μ-NC)3(2,2′-bpmo)(solvent)]− moieties, and different solvent organization in the intercluster space. This results in a well pronounced geometrical isomerism of cluster cores being further related to the diverse non-covalent interaction schemes governing the supramolecular arrangement of the molecules. 1, 2, and 3 reveal ferromagnetic coupling within Co–NC–W linkages leading to a high-spin ground state of 15/2, and slow magnetic relaxation at low temperatures. The single-molecule magnet characteristics are only slightly modulated by the solvent-dependent variation of the structural features.

A gel crystallization technique was successfully applied in the pioneering preparation of a single-crystalline form of the three-dimensional copper(II) octacyanidomolybdate(IV) network, which is a photomagnetic material. This assembly crystallizes with the formula {[CuII(H2O)]2[MoIV(CN)8]}·2H2O in the tetragonal crystal system and reveals a three-dimensional cyanido-bridged framework constructed of five-coordinate square-pyramidal [CuII(H2O)(NC)4]2– complexes and [MoIV(CN)8]4– ions of square-antiprismatic geometry. First-principles calculations by the GGA + U method indicate that the visible-light absorption band, crucial for the observation of a photomagnetic effect, is interpreted in terms of MoIV to CuII charge transfer, which is enabled owing to the accompanying pz spx transition of the nitrogen atoms of the bridging cyanido ligands. The optical transitions in the visible range are anisotropic, and the most efficient light absorption along the [111] direction corresponds to the alignment of the cyanide bridges.

A building block approach has led to the construction of two unique bifunctional magneto-luminescent molecular materials, {[DyIII(4-pyridone)4(H2O)2][MIII(CN)6]}·nH2O (M = Co, n = 2, 1; M = Rh, n = 4, 2), incorporating the cyanido-bridged dinuclear {DyIIICoIII} (1) or {DyIIIRhIII} (2) molecules, that crystallize within the supramolecular network in the attractive non-centrosymmetric Cmc21 space group. Both compounds reveal dual physical properties of colour-tunable photoluminescence and slow relaxation of magnetization. While 1 exhibits multi-coloured photoluminescence ranging from yellow to blue, tuned by the excitation wavelength, 2 additionally reveals nearly white light emission under 336 nm excitation at room temperature. 1 and 2 show 4f-metal-centered strong magnetic anisotropy presenting Single-Molecule Magnet (SMM) behaviour with the large anisotropic energy barriers of 187(6) K for 1, and 214(4) K for 2. We have shown and discussed that the replacement of [CoIII(CN)6]3− by the heavier [RhIII(CN)6]3− analogue in {[DyIII(4-pyridone)4(H2O)2][MIII(CN)6]}·2H2O crystalline materials is an efficient route towards white light emissive solid state matrices composed of Single-Molecule Magnets with enhanced magnetic anisotropy. Such extraordinary photoluminescent molecule-based magnets can become good prerequisites for future application in bifunctional optical and magnetic devices.

Three-dimensional cyanido-bridged bimetallic assemblies [MnII(4-Xpy)4]2[NbIV(CN)8]·nH2O (4-Xpy: 4-halopyridine; X = I and n = 0, (1); X = Cl and n = 0.5, (2)) are synthesized. 1 and 2 have chiral and achiral structures, respectively. The chiral structure of 1 is composed of achiral building blocks, which lead to an enantiopure compound through a spontaneous resolution process. In the crystal structure of 1, the halogen bonds between 4-Ipy and cyanide distort the structure, lowering the crystal symmetry. Both 1 and 2 show ferrimagnetism with Curie temperatures (TC) of 22 K and 28 K, respectively. Due to the chiral and polar structure in the I41 space group, 1 exhibits SHG phenomena, while such nonlinear optical phenomena are quenched in 2 due to its centrosymmetry.

The complexes of paramagnetic lanthanide(3+) ions (Gd3+,Tb3+) with 3-pyridone molecules combined in an aqueous solution with paramagnetic hexacyanidochromate(III) metalloligands led to the formation of two novel crystalline {[LnIII(3-pyridone)2(H2O)4][CrIII(CN)6]}·H2O (Ln = Gd, 1; Ln = Tb, 2) materials. They are composed of bimetallic Ln–Cr cyanido-bridged zig-zag chains which are further tightly connected by the rich system of hydrogen bonds involving terminal cyanides, water molecules and 3-pyridone ligands. Both 1 and 2 have a very weak yellowish colour as their strong absorption, related to the d–d transitions of the cyanide Cr(III) complex and 3-pyridone ligands, is moved to the UV range. 1 and 2 exhibit Ln–Cr antiferromagnetic exchange mediated within the coordination chains by molecular cyanide bridges. The magnetic susceptibility for the GdIII–CrIII 7/2–3/2 spin alternating chains of 1 was successfully analysed using quantum Monte Carlo simulations, giving a magnetic coupling constant, J, of −0.82 K. The additional interchain magnetic interactions ensured by the hydrogen bonding network result in the low temperature phase transition to the magnetically ordered state. Magnetic heat capacity measurements showed that 1, which has isotropic Gd(III) spin centers, becomes a molecule-based magnet below 1.06 K, while 2, bearing the highly anisotropic Tb(III), shows a higher critical temperature of 1.61 K. Thus, we show and discuss the crucial role of the non-covalent interactions in the induction of magnetic ordering for low dimensional cyanido-bridged coordination systems, and the positive impact of magnetic anisotropy on the strengthening of magnetic interactions.

Ytterbium (3+) ions combined with 3-pyridone and hexacyanido-cobaltate(iii) anions in a concentrated aqueous solution produce cyanido-bridged {[Yb

Cyanide-bridged {Mn

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

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

Cyanido-bridged high-spin $\{Co^{II}[Co^{II}(MeOH)_{3}]_{8}[W^{V}(CN)_{8}]_{6}\} (Co_{9}W_{6})$ clusters revealing single-molecule magnet behavior were combined with 4,{4}'-bipyridine-N,N′-dioxide (4,{4}'-bpdo) linkers, giving unique H-bonded supramolecular $\{Co^{II}_{9}(MeOH)_{24}[W^{V}(CN)_{8}]_{6}\}\cdot 4,{4}'-bpdo \cdot MeOH \cdot 2H_{2}O$ (1) chains and one-dimensional coordination $\{Co^{II}[Co^{II}(4,{4}'-bpdo)_{1.5}(MeOH)]_{8}[W^{V}(CN)_{8}]_{6}\} \cdot 2H_{2}O$ (2) nanowires. The hydrogen-bonded chains of 1 are embedded within the three-dimensional supramolecular network stabilized by the series of noncovalent interactions between $Co_{9}W_{6}$ clusters, 4,{4}'-bpdo, and solvent molecules. The coordination nanowires 2, revealing an average core diameter of about 11 \AA , are arranged parallel with the significant separation in the crystal structure, leading to a microporous supramolecular network with broad channels (12 × 12 \AA) filled by methanol and water. Both 1 and 2 are stable only in a mother solution or an organic protectant, whereas they undergo the fast exchange of methanol ligands to water molecules during drying in the air. Synthesized materials preserve the magnetic characteristics of $Co_{9}W_{6}$ clusters with an effective ferromagnetic coupling, giving a ground-state spin of 15/2. For 2, the additional antiferromagnetic intercluster interactions are observed. Below 3 K, the frequency-dependent $\chi _{M}$ (T) signals of 1 and 2 indicate the onset of slow magnetic relaxation. For 1, the relaxation time follows the Arrhenius law with an energy gap of $\Delta / k_{B}= 10.3(5) K$ and $\tau _{0}= 4(1) \times 10^{-9} s$, which is consistent with 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

Ytterbium (3+) ions combined with 3-pyridone and hexacyanido-cobaltate(III) anions in a concentrated aqueous solution produce cyanido-bridged {[YbIII(3-pyridone)2(H2O)2][CoIII(CN)6]} (1) chains. The resulting YbIII complexes of an elongated octahedral geometry reveal two coexisting functionalities: a field-induced slow magnetic relaxation with an energy barrier of ΔE/kB = 45(1) K at Hdc = 1 kOe, and an YbIII-centered near-infrared fluorescence in the 950–1100 nm range sensitized by 3-pyridone and [CoIII(CN)6]3−.

Cyanide-bridged {MnII9[WV(CN)8]6} clusters with the ground state spin SSG = 39/2 were connected by a 4,4′-dipyridyl disulfide (4,4′-dpds) linker into 2-D double-connected coordination layers of the I0O2 type, {MnII9(4,4′-dpds)4(MeOH)16[WV(CN)8]6}·12MeOH (1). The intercluster contacts are controlled by the bridging MnII–(4,4′-dpds)–MnII coordination modes and direct hydrogen bonds W–CN···HOMeOH–Mn in three crystallographic directions, with the vertex-to-vertex contact unprecedented in {Mn9W6}-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 WV–CN–MnII 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 Jap = −8.0 cm–1, Jeq = −19.2 cm–1 (related to apical and equatorial CN...

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 {[MnII(R-mpm)2]2[NbIV(CN)8]}·4H2O (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 μ0ΔH = 5.0 T attaining the value of ∼5 J mol–1 K–1. The obtained maximal value of −ΔSm is comparable to previously reported results for polycrystalline octacyanidoniobate-based bimetallic coordination polymers. A substantial anisotropy of magnetocaloric effect between the easy plane and ...

An octacyanidometalate-based nanochannel magnet, Co7[W(CN)8]4Cl2·29H2O, is reported. Single-crystal synchrotron X-ray diffraction measurements reveal that this compound has a three-dimensional cyanido-bridged network based on {Co5W4}n columns situated along the c-axis. The channels resemble a lotus root and have a remarkably large diameter of 1.4 nm, which corresponds to a 44% vacancy. Although the channel size is very large, the compound exhibits ferromagnetic ordering with a Curie temperature of 29 K and coercive field of 5500 Oe. Such a ferromagnetic lotus root can adsorb large molecules and may realize host–guest chemistry in ferromagnets.

The rare heteroligand pentacyanidonitrosylmolybdate(I) anion was employed in the construction of d–f bimetallic cyanido-bridged {[LnIII(dmf)6][MoI(CN)5(NO)]} (Ln = Gd, 1; Eu, 2) chains crystallizing in the non-centrosymmetric Pna21 space group. 1 exhibits Gd–Mo antiferromagnetic coupling giving rise to the ferrimagnetic spin chain behaviour with the onset of magnetic ordering below 2 K, and shows high second harmonic generation (SHG) activity with SH susceptibility of 1.2 × 10−10 esu, opening a novel family of non-centrosymmetric molecule-based magnets.

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 {[EuIIIxTbIII1–x(3-OHpy)2(H2O)4][CoIII(CN)6]}·H2O (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 e...

An inorganic three-dimensional [Ni

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.

Using a polyamine cation tetrenH55+ (tetren = tetraethylenepentaamine), we tailored the dynamic layered material (tetrenH5)1.6{CoII(H2O)2[MIV(CN)8]}4·xH2O (1, M = W, x = 12; 2, M = Mo, x = 11.2). 1 and 2 consist of strongly corrugated two-dimensional (2D) cyano-bridged monolayers {CoII(H2O)2[MIV(CN)8]}n2n– of square grid topology stacked in an alternate manner with cationic layers of tetrenH55+ and H2O molecules. The observed single-crystal-to-single-crystal (SCSC) transformation is due to the reversible dehydration of 1 and 2 to the respective monocrystalline materials (tetrenH5)1.6{CoII[MIV(CN)8]}4 (1deh and 2deh). Structural modifications consist of the change of coordination number (C.N.) of Co(II) from 6 to 4 and a degree of corrugation of the coordination skeleton resulting in changes of orthorhombic cell dimensions. The exposition of 1deh to vapors of H2O, MeOH, HCONH2, and MeCN gives 1reh, 1deh·5.6MeOH, 1deh·4HCONH2, and 1deh·2.4MeCN phases, respectively. 1reh reveals structural, physical, and phy...

Molecular magnetism is a new and extremely fascinating field on the borders of chemistry, physics and materials science. The design and synthesis of molecule-based magnets requires the chemist to exert considerable control over the molecules to arrange them appropriately. It also demands the development of new theories to explain the complex magneto-structural behaviour of these intriguing solids. Molecular magnetism is still at a very early stage of development. The main challenge is to increase the strength of the magnetic interactions between spin carriers so the resulting materials can be usable at room temperature. However, molecular magnets exhibit true potential to become multifunctional materials. They show some considerable advantages over conventional magnets: optical transparency, chemical sensitivity and low weight to name just a few. The following article is not a complete review of the field. Its aim is rather to show how beautiful and versatile magnetic molecular solids can be, and to encourage the in-depth study of the subject.

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.

Temperature-variable single-crystal synchrotron X-ray diffraction and 133Cs NMR studies were performed for a cyanido-bridged layered metamagnet, Cs4CoII[WV(CN)8]Cl3 (1), to elucidate the origin of its unusually high thermal durability up to ca. 523 K (250 °C). 1 reveals a layered structure composed of negatively charged two-dimensional cyanido-bridged Co–W layers ({CoII[WV(CN)8]Cl3}4−) and cesium ions between and within the layers, where there is a lack of both non-coordinated and coordinated solvent molecules that is an important and characteristic feature of the crystal structure. The cesium ions are surrounded by chlorides and cyanides of the coordination layers, and some Cs+⋯Cl−, Cs+⋯N, and Cs+⋯C distances are shorter than the estimated sums of an ionic radius of Cs+ and ionic or van der Waals radii of Cl−/CN−. These short distances suggest strong interactions between Cs+ and Cl−/CN−, which stabilize the crystal structure by connecting the layers. The temperature-dependent single-crystal structural analyses show that there is no significant structural change upon heating up to 473 K, and indicate that the short distances between Cs+ and Cl−/CN− still remain. Thus, the high thermal durability of 1 is due to not only the absence of solvent molecules but also the existence of strong Cs+⋯Cl− and Cs+⋯−NC interactions. The 133Cs NMR spectrum shows four peaks assignable to the four independent Cs+ ions in the crystal structure. The observed peaks were located in high ppm owing to the hyperfine interactions between the nuclear spin of Cs and electron spins from the magnetic centers CoII and WV. As temperature increased, the peaks moved to low ppm, and the shifts of the peaks are expressed by the Curie–Weiss law indicating no large structural changes around Cs+ ions, that is, the Cs+ ions are fixed at the same positions. This proves the presence of strong interactions involving Cs+ and terminal ligands of cyanido-bridged layers of 1 being responsible for its high thermal stability.

Octacyanidometallates make an important branch of cyanide-based molecular magnets that not only follow the trends in modern magnetochemistry and materials science but also have stimulated these fields from the very beginning and still blaze a trail by introducing new concepts such as heterotrimetallic systems, new functionalities and cross-effects like photo-switching of magneto-optical properties and setting new records in magnetic ordering temperatures or magnetic exchange interactions. The following paper focuses on a special class of molecular magnets which, to the best of our knowledge, have not been reviewed so far: octacyanide-based magnetic clusters. A complete list of all known molecules incorporating octacyanides with an extensive discussion of their structures, topologies and magnetic properties, with special attention paid to multifunctional systems, is provided. Several milestone-clusters are discussed thoroughly to emphasize their particular importance in the development of crystal engineering and molecular magnetism.

The self-assembly of iron(II) ions with rare octacyanidorhenate(V) metalloligands in a methanolic solution results in the formation of a nanometric pentadecanuclear $\{ Fe^{II}_{9}[Re^{V}(CN)_{8}]_{6}(MeOH)_{24}\}⋅10 MeOH$ (1) molecule with a six-capped body-centered cubic topology. The cluster demonstrates a thermally-induced spin-crossover phase transition at $T_{1/2}=195 K$ which occurs selectively for a single $Fe^{II}$ ion embedded in the center of a cluster core.

Octacyanidometallates make an important branch of cyanide-based molecular magnets that not only follow the trends in modern magnetochemistry and materials science but also have stimulated these fields from the very beginning and still blaze a trail by introducing new concepts such as heterotrimetallic systems, new functionalities and cross-effects like photo-switching of magneto-optical properties and setting new records in magnetic ordering temperatures or magnetic exchange interactions. The following paper focuses on a special class of molecular magnets which, to the best of our knowledge, have not been reviewed so far: octacyanide-based magnetic clusters. A complete list of all known molecules incorporating octacyanides with an extensive discussion of their structures, topologies and magnetic properties, with special attention paid to multifunctional systems, is provided. Several milestone-clusters are discussed thoroughly to emphasize their particular importance in the development of crystal engineering and molecular magnetism.

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.

Complexes of lanthanides(III) (Ce-Yb) with 2,2'-bis(2-oxazoline) (Box) combined with octacyanidomolybdate(V) gave a series of magneto-luminescent coordination polymers, {[Ln(III)(Box)n(DMF)m][Mo(V)(CN)8]}·x(solvent) (1-12). They are built of cyanido-bridged layers of a mixed 4- and 8-metal rings topology and show unique sliding of layers dependent on a 4f metal ion. For light lanthanides, dominant phase A, {[Ln(III)(Box)2(DMF)2][Mo(V)(CN)8]}·1.5MeCN (Ln = Ce, 1; Pr, 2; Nd, 3), consists of ideally aligned, not shifted layers, giving large channels (13.7 × 14.0 Å). Intermediate lanthanides reveal phase B, {[Ln(III)(Box)2(DMF)2] [Mo(V)(CN)8]}·H2O (Ln = Sm, 4; Eu, 5; Gd, 6; Tb, 7; Dy, 8), of smaller pores (8.4 × 10.6 Å) due to layer-H2O hydrogen bonding, which induces sliding of CN(-)-bridged layers. Heavy lanthanides show phase C, {[Ln(III)(Box)(DMF)3][Mo(V)(CN)8]}·MeCN (Ln = Ho, 9; Er, 10; Tm, 11; Yb, 12), with large channels (13.7 × 13.7 Å) of a similar size to light lanthanides. This effect comes from the changes in Ln(III) coordination sphere affecting solvent-layer interactions. Compounds 1-12 reveal diverse emission depending on the interaction between Ln(III) and Box luminophors. For 2-5, 9, and 12, the ligand-to-metal energy-transfer-induced visible f-centered emission ranging from green for Ho(III)-based 9, orange from Sm(III)-based 4, to red for Pr(III)- and Eu(III)-containing 2 and 5, respectively. Near-infrared emission was found for 2-4, 9, and 12. Red phosphorescence of Box was detected for Gd(III)-based 6, whereas the selective excitation of ligand or Ln(III) excited states resulting in the switchable red to green emission was found for Tb(III)-based 7. The materials revealed Ln(III)-Mo(V) magnetic coupling leading to ferromagnetism below 2.0 and 2.2 K for 4 and 7, respectively. The onset of magnetic ordering at low temperatures was found for 6 and 8. Compounds 1-12 form a unique family of cyanido-bridged materials of a bifunctional magneto-luminescence character combined with dynamic structural features.

The synthesized chiral (R)- and (S)-2-(1-hydroxyethyl)pyridine ligands (R/S-mpm) were introduced to self-assembled CoII-[WV(CN)8] and NiII-[WV(CN)8] magnetic systems giving a remarkable series of four enantiopure cyanido-bridged clusters, {MII[MII(R/S-mpm)(MeOH)]8[WV(CN)8]6}·14MeOH (M = Co, 1-R and 1-S; M = Ni, 2-R and 2-S). They consist of 15 metal centers, 9 CoII or NiII ions, and 6 [WV(CN)8]3– ions, embedded in a 6-capped body-centered cube topology. Bidentate enantiopure mpm ligands coordinated to eight external CoII or NiII sites induce their chiral character, which results in the strong natural optical activity in the broad UV–vis range of 200–700 nm. All (1-R/S) and (2-R/S) clusters reveal cyanido-mediated ferromagnetic exchange interaction giving high-spin ground states of 15/2 (1-R/S) and 12 (2-R/S). For (2-R/S) forms of {Ni9W6}, the exchange constant J = +16.1 cm–1 was obtained using exact diagonalization of the exchange Hamiltonian. Because of the significant magnetic anisotropy, (1-R/S) forms of {Co9W6} cluster reveal the low temperature onset of the slow magnetic relaxation characteristic of single-molecule magnets (SMMs). Thus, they can be considered as a rare example of chiral SMM molecules.

A bimetallic pentadecanuclear cyanido-bridged $\left \{Fe_{9}[W(CN)_{8}]_{6}(MeOH)_{24}\right \} \cdot xMeOH$ cluster of an $Fe^{II/III}–W^{IV/V}$ mixed valence nature, reveals a reversible single-crystal-to-single-crystal transformation, concomitant with metal-to-metal charge transfer between Fe and W ions. The dominance of $^{HS}Fe^{II}-NC-W^{V}$ units at a high temperature, and $^{HS}Fe^{III}-NC-W^{IV}$ units at a low temperature, leads to an unprecedented reversed thermal hysteresis loop in magnetic measurements.

Two chiral luminescent derivatives of pyridine bis(oxazoline) (Pybox), (SS/RR)-iPr-Pybox (2,6-bis[4-isopropyl-2-oxazolin-2-yl]pyridine) and (SRSR/RSRS)-Ind-Pybox (2,6-bis[8H-indeno[1,2-d]oxazolin-2-yl]pyridine), have been combined with lanthanide ions (Gd(3+), Nd(3+)) and octacyanotungstate(V) metalloligand to afford a remarkable series of eight bimetallic CN(-)-bridged coordination chains: {[Ln(III)(SS/RR-iPr-Pybox)(dmf)4]3[W(V)(CN)8]3}n ⋅dmf⋅4 H2O (Ln = Gd, 1-SS and 1-RR; Ln = Nd, 2-SS and 2-RR) and {[Ln(III)(SRSR/RSRS-Ind-Pybox)(dmf)4][W(V)(CN)8]}n⋅5 MeCN⋅4 MeOH (Ln = Gd, 3-SRSR and 3-RSRS; Ln = Nd, 4-SRSR and 4-RSRS). These materials display enantiopure structural helicity, which results in strong optical activity in the range 200-450 nm, as confirmed by natural circular dichroism (NCD) spectra and the corresponding UV/Vis absorption spectra. Under irradiation with UV light, the Gd(III)-W(V) chains show dominant ligand-based red phosphorescence, with λmax ≈660 nm for 1-(SS/RR) and 680 nm for 3-(SRSR/RSRS). The Nd(III)-W(V) chains, 2-(SS/RR) and 4-(SRSR/RSRS), exhibit near-infrared luminescence with sharp lines at 986, 1066, and 1340 nm derived from intra-f (4)F3/2 → (4)I9/2,11/2,13/2 transitions of the Nd(III) centers. This emission is realized through efficient ligand-to-metal energy transfer from the Pybox derivative to the lanthanide ion. Due to the presence of paramagnetic lanthanide(III) and [W(V)(CN)8](3-) moieties connected by cyanide bridges, 1-(SS/RR) and 3-(SRSR/RSRS) are ferrimagnetic spin chains originating from antiferromagnetic coupling between Gd(III) (SGd = 7/2) and W(V) (SW = 1/2) centers with J1-(SS) = -0.96(1) cm(-1), J1-(RR) =-0.95(1) cm(-1), J3-(SRSR) = -0.91(1) cm(-1), and J3-(RSRS) =-0.94(1) cm(-1). 2-(SS/RR) and 4-(SRSR/RSRS) display ferromagnetic coupling within their Nd(III)-NC-W(V) linkages.

Two-dimensional cesium bimetal cyano-bridged assemblies CsI4CoII[MoV(CN)8]Cl3 (CsCoMo) and CsI4CoII[WV(CN)8]Cl3 (CsCoW) were synthesized. The negatively charged and solvent-free {CoII[MV(CN)8]Cl3}4– (M = Mo, W) coordination layers are separated by Cs+ ions. Themogravimetric measurements show that these compounds reveal high thermal durability up to 523 K (250 °C), which is due to the absence of solvent molecules in their crystal structures. The magnetic measurements show that CsCoMo and CsCoW are metamagnets showing the field-induced transition from an antiferromagnetic phase with Neel temperature of 25 K to a ferromagnetic phase, which is observed at high critical magnetic field of 24 kOe at 1.8 K. These originate from antiferromagnetic interactions between ferromagnetically coupled cyano-bridged CoII–MV layers, and the contribution from single-ion anisotropy of CoII.

Unique two dimensional enantiopure cyanido-bridged {[Mn(II)(R-mpm)2]2[Nb(IV)(CN)8]}·4H2O and {[Mn(II)(S-mpm)2]2[Nb(IV)(CN)8]}·4H2O (-S) (mpm = α-methyl-2-pyridine-methanol) ferrimagnets with TC = 23.5 K were synthesized and characterized. They reveal natural optical activity (NOA) due to the chiral crystal structure, and magnetic optical activity (MOA) in the presence of an external magnetic field, with the strong enhancement in the magnetically ordered phase below TC.

Unique one-dimensional cyanido-bridged {[EuIII(RR-Pri-Pybox)(dmf)4]3[WV(CN)8]3}n·dmf·8H2O (1-RR) and {[EuIII(SS-Pri-Pybox)(dmf)4]3[WV(CN)8]3}n·dmf·8H2O (1-SS) (Pri-Pybox = 2,2′-(2,6-pyridinediyl)bis(4-isopropyl-2-oxazoline)) chains were synthesized and characterized. They combine chiral helicity with paramagnetism and thermally switchable luminescence, and have a great potential in the aspect of magneto-optical phenomena.

The novel layered {CoII3(2,2′-bpdo)4(H2O)4[WV(CN)8]2}·8H2O (1) network (2,2′-bpdo = 2,2′-bipyridine-1,1′-dioxide) is built of 2-D corrugated cyanide-bridged brick-wall skeletons parallel to the bc crystallographic plane. The coordination of chelating 2,2′-bpdo to Co(II) gives 7-membered coordination rings. Magnetic and heat capacity measurements performed on monocrystalline samples reveal ferromagnetic ordering below TC of 6 K. Magnetic anisotropy of the ordered phase is represented by the easy axis oriented in the ac crystallographic plane. Bulk magnetic anisotropy is confronted with a local anisotropy of Co complexes: a strong axial anisotropy of trans,cis,cis-[CoII(μ-NC)2(H2O)2(2,2′-bpdo)] moieties represented by gx(2) = 2.06, gy(2) = 2.95 and gz(2) = 7.30, and a planar anisotropy of trans,cis,cis-[CoII(μ-NC)2(2,2′-bpdo)2] represented by gx(3) = 5.40, gy(3) = 4.82 and gz(3) = 2.28, determined by CASSCF/RASSI/SINGLE_ANISO ab initio calculations. The experimental data are explained by the molecular field simulation of the magnetic structure using the above theoretical data.