The self-assembly of [Nb(IV)(CN)(8)](4-) with different 3d metal centers in an aqueous solution and an excess of pyrazole resulted in the formation of four 3D isostructural compounds {[M(II)(pyrazole)(4)](2)[Nb(IV)(CN)(8)].4H(2)O}(n), where M(II) = Mn, Fe, Co, and Ni for 1-4, respectively. All four assemblies crystallize in the same I4(1)/a space group and show identical cyanido-bridged structures decorated with pyrazole molecules coordinated to M(II) centers. All four compounds show also long-range magnetic ordering below 24, 8, 6, and 13 K, respectively. A thorough analysis of the structural and magnetic data utilizing the molecular field model has allowed for an estimation of the values of coupling constants J(M-Nb) attributed to the one type of M(II)-NC-Nb(IV) linkage existing in 1-4. The J(M-Nb) values increase monotonically from -6.8 for 1 through -3.1 for 2 and +3.5 for 3, to +8.1 cm(-1) for 4 and are strongly correlated with the number of unpaired electrons on the M(II) metal center. Average orbital contributions to the total exchange coupling constants J(M-Nb) have also been identified and calculated: antiferromagnetic J(AF) = -21.6 cm(-1) originating from the d(xy), d(xz), and d(yz) orbitals of M(II) and ferromagnetic J(F) = +15.4 cm(-1) originating from d(z(2)) and d(x(2)-y(2)) orbitals of M(II). Antiferromagnetic interaction is successively weakened in the 1-4 row with each additional electron on the t(2g) level, which results in a change of the sign of J(M-Nb) and the nature of long-range magnetic ordering from ferrimagnetic in 1 and 2 to ferromagnetic in 3 and 4.

The design and construction of switchable materials attracts tremendous interest owing to the potential in information storing and processing or molecular sensing. [1][2][3][4] The archetypal examples involve a diversity of Fe II -, [5,6] Fe III - [7] or Co IIbased [8][9][10] spin-crossover (SCO) compounds, Co III/II -catecholate/semiquinone systems, [1,11] as well as d-d bimetallic and sd-d trimetallic cyanide-bridged systems revealing chargetransfer-induced spin transitions (CTIST). [12][13][14][15][16][17][18] Some of these compounds, for example Prussian blue analogues, are particularly promising from the point of view of photoswitching between nonmagnetic and magnetized (that is, T B , T C ) states, owing to magnetic coupling through molecular bridges in discrete species [14,15] and extended networks. [17,18] Such bistability also emerged in the magnetochemistry of octacyanidometalates, exploiting metal-to-metal electron transfer in HS Co II L[W V (CN) 8 ] 3À (L = pyrimidine, 4-methylpyridine) [19,20] or canonical SCO in Fe II L[Nb IV (CN) 8 ] 4À extended networks [21] (L = 4-pyridinealdoxime). A magnetic hysteresis loop with a coercivity of 1-3 T were observed in an optically excited low-temperature metastable phase.

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.

IV (CN) 8 ]} n chiral R and centric β crystallizing in space groups P4 1 and P1, respectively. Both polymorphs exhibit extremely similar structures and are soft ferrimagnets with critical temperatures of 43 and 42 K, respectively. The presence of coordinated urea in the noncentrosymmetric R produces NLO functionality, second harmonic generation (SHG), whereas centric β is just another molecular magnet. As a result of interaction of both functionalities below magnetic ordering temperature, the magnetization-induced SHG (MSHG) is observed for polymorph R. The observed MSHG/SHG signal ratio was the largest among moleculebased noncentrosymmetric magnets. The presence of urea molecules in both polymorphs gives also rise to their interesting topotactic reactivity. Both polymorphs can be easily transformed into a new entity {[Mn II (H 2 O)] 2 [Nb IV (CN) 8 ] 3 2.5MeOH} n 2b with significant shift of critical temperature T c to 70 K. Subsequent hydration of 2b leads to {[Mn II (H 2 O) 2 ] 2 [Nb IV (CN) 8 ] 3 4H 2 O} n 3 with T c of 47 K.

The first single chain magnet (SCM) based on the orbitally degenerate [Os(CN)6]3− anion was prepared. The high energy barriers are a result of interplay of Mn3+ single-ion magnetic anisotropy and highly anisotropic three axes exchange interactions between the paramagnetic centres.

We report a new bimetallic cyanido-bridged trinuclear complex [Cu(enpnen)][Mo(CN)]·6.75HO (1) (enpnen = N,N'-bis(2-aminoethyl)-1,3-propanediamine) that shows reversible photomagnetic effect. The photo-induced increase of magnetization is characterized by the irradiation temperature-dependent shapes of the χ T( T) plots and different magnetization values at low temperature in high magnetic field, suggesting multiple photoexcited states. The photomagnetic effect in 1 is explained through two possible processes simultaneously: the light-induced metal-to-metal charge transfer (MMCT) in the Cu-NC-Mo pair and the light-induced excited spin-state trapping (LIESST) effect in Mo center. A numerical model assuming the simultaneous existence of three possible states after irradiation: the MMCT Cu-NC-Mo-CN-Cu state, the LIESST Cu-NC-Mo-CN-Cu state, and the ground-state Cu-NC-Mo-CN-Cu was applied to the data and resulted in Cu-Mo exchange coupling constants J = 11 cm and J = 109 cm for the MMCT and LIESST mechanisms induced states, respectively. Fractions of respective states after irradiations at different temperatures were also calculated, shedding light on the influence of irradiation temperature on the photomagnetic mechanism. The proposed model can provide the interpretative framework for testing and refinement of the mechanism of photomagnetic effect in other coordination networks with cyanido-bridged Cu-[Mo(CN)] linkages.

Reaction between [Ni(cyclam)](2+) and [W(CN)(8)](4-) leads to the formation of a 3D diamond-like network [Ni(cyclam)](2)[W(CN)(8)]·3.5H(2)O (1). The structure is characterised by a network of intersecting channels of 3-4 Å in diameter, filled with crystallisation water, most of which is released upon drying in air, causing the crystals to collapse. Analogous compound [Ni(cyclam)](2)[Nb(CN)(8)]·3.5H(2)O (2), based on paramagnetic Nb(IV), could only be obtained as a powder, due to the decomposition of the [Nb(CN)(8)](4-) complex under slow diffusion conditions. It shows long-range magnetic ordering with T(C) = 11.8 K and magnetic hysteresis at 2 K. These properties are lost upon drying in air. After rehydration differently shaped hysteresis appears, which together with AC susceptibility measurements suggests the formation of a multiphase system. Subsequent dehydration-rehydration experiments show partial reversibility.

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