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

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

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

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

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

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

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

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

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

Four new three-dimensional (3-D) coordination frameworks based on the heptacyanomolybdate(iii) anion were prepared and characterised by magnetic measurements: {[Mn II (imH) 2 ] 2 [Mn II (H 2 O)(imH) 3 ][Mn II (imH) 4 ] [Mo III (CN) 7 ] 2 ·6H 2 O} n (1) (imH = imidazole), {[Mn II (H 2 O) 2 (imH)] 3 [Mn II (H 2 O)(imH) 2 ][Mo III (CN) 7 ] 2 ·5H 2 O} n (2), {[Mn II (Htrz)(H 2 O) 2 ][Mn II (Htrz) 0.7 (H 2 O) 2.3 ][Mo III (CN) 7 ]·5.6H 2 O} n (3) (Htrz = 1,2,4-triazole) and {[Mn II (H 2 O) 2 ] 3 [Mn II (H 2 O) 4 ][Mo III (CN) 7 ] 2 ·6H 2 O·2urea} n (4). All four compounds exhibit long-range ferrimagnetic ordering and exhibit an opening of their magnetic hysteresis loops at 1.8 K; 1 and 2 exhibit the highest coercive fields among all known [Mo III (CN) 7 ]-based assemblies, 5000 and 4500 Oe respectively. The coercivity of 1-4 is correlated with the geometry of the heptacyanomolybdate(iii) anion and the cyanide bridging pattern. A paramagnetic analogue of compound 1, {[Mn II (imH) 2 ] 2 [Mn II (H 2 O)(imH) 3 ][Mn II (imH) 4 ][Re III (CN) 7 ] 2 ·6H 2 O} n (1Re), where the heptacyanomolybdate(iii) anion is substituted by the diamagnetic heptacyanorhenate(iii) anion is also reported which constitutes the first example of a coordination framework based on [Re III (CN) 7 ] 4- .

Carefully selected molecular bridging ligands formate, cyanide and azide, that are known to transmit strong magnetic interactions, have been successfully inserted into the {[MnII(H2O)2]2[NbIV(CN)8]·4H2O}n (Mn2Nb) ferrimagnetic parent framework, resulting in the additional molecular bridging of the two MnII centres in three new coordination polymers: {(NH4)[(H2O)MnII-(μ-HCOO)-MnII(H2O)][NbIV(CN)8]·3H2O}nMn2NbHCOO, {(NH4)[(NH3)MnII-(μ-CN)-MnII(H2O)][NbIV(CN)8]·2H2O}nMn2NbCN and {(NH4)[(H2O)MnII-(μ-N3)-MnII(H2O)][NbIV(CN)8]·3H2O}nMn2NbN3. The extra bridging ligands cross-linking the two MnII centers strongly influence the long-range ferrimagnetic order of the NbIV-CN-MnII parent framework by introducing competing antiferromagnetic interactions. The values of the JMnMn constants were obtained by fitting the magnetic properties of the MoIV congeners {(NH4)[(H2O)MnII-(μ-HCOO)-MnII(H2O)][MoIV(CN)8]·3H2O}nMn2MoHCOO, {(NH4)[(NH3)MnII-(μ-CN)-MnII(H2O)][MoIV(CN)8]·2H2O}nMn2MoCN and {(NH4)[(H2O)MnII-(μ-N3)-MnII(H2O)][MoIV(CN)8]·3H2O}nMn2MoN3, where the paramagnetic NbIV was substituted by the diamagnetic MoIV, thus disabling the long-range magnetic ordering of the CN-framework. Our strategy demonstrates how chemists can control the magnetic behavior of molecular magnets by subtle and rational structural modification based on chemical knowledge.

A series of diluted molecular magnets {[MnII(H2O)2]2[MIV(CN)8]·4H2O}n (M = Nb/Mo) exhibiting a ferrimagnetic phase have been synthesized and investigated to demonstrate the first example of site percolation in magnetic coordination polymers. It is the first case of a magnetic percolation study with selective site substitution, where magnetic ions of only one type are replaced by their diamagnetic analogues leaving the other magnetic sublattice untouched. By modifying the molecular field model the NbIV concentration dependence of the magnetic ordering temperature was reproduced and the percolation threshold was determined.

A detailed study of the magnetocaloric effect in two isostructural bimetallic compounds {[M II (H 2 O) 2 ] 2 [Nb IV (CN) 8 ]·4H 2 O} n (M = Mn, Fe) is presented. The substances show sharp phase transitions to the long-range magnetically ordered state with ferromagnetic coupling between M and Nb sublattices in the case of the Fe-based sample (FeNb, T c = 43 K) and antiferromagnetic coupling for the Mn-based sample (MnNb, T c = 50 K). The magnetic entropy change was found to reach 5.07 J mol -1 K -1 (9.09 J kg -1 K -1 ) for MnNb and 4.82 J mol -1 K -1 (8.65 J kg -1 K -1 ) for FeNb under the applied magnetic field change of 5 T. Isothermal entropy changes corresponding to different field changes are demonstrated to collapse on a single master curve, which confirms the magnetic transitions in FeNb and MnNb to be of the second order. The results obtained for FeNb and MnNb are discussed in the context of MCE tunability by un/blocking of magnetic connectivity through dis/reconnection of spatially extended ligands., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Two magnetic coordination polymers with mixed cyanide-azide bridging based on octacyanoniobate(iv) and octacyanomolybdate(iv) are reported: {(NH 4 )[(H 2 O)Mn II -(μ-N 3 )-Mn II (H 2 O)][M IV (CN) 8 ]·3H 2 O} n Mn 2 MN 3 (M = Nb or Mo). Cyanide ligands form the 3-D framework of Mn 2 MN 3 , while azide ligands connect two Mn II centres together. Both CN - and N 3 - are known in magnetochemistry for their marked magnetic coupling abilities which in the case of Mn2NbN3 lead to competitive antiferromagnetic interactions within the Nb IV -CN-Mn II and Mn II -N 3 -Mn II structural motifs. This competition results in a peculiar magnetic behaviour consistent with a non-collinear magnetic structure.

The molecular structures and magnetic properties of homoleptic iron(ii) compounds [Fe(bpp-COOMe) 2 ](ClO 4 ) 2 (1) and [Fe(bpp-triolH 3 ) 2 ](ClO 4 ) 2 (2) have been investigated to ascertain their spin crossover (SCO) behaviour. In these hexacoordinated complexes, the bpp (2,6-bis(pyrazol-1-yl)pyridine) ligands adopt a mer-mer coordination mode and carry COOMe or C(O)NHC(CH 2 OH) 3 para substituents, respectively, on the central pyridyl ring. In spite of the almost equal donor power of the ligands to the iron(ii) centre, the two compounds feature different spin state configurations at room temperature. Compound 1 displays a highly-distorted octahedral environment around the iron(ii) centre, which adopts a high spin (HS) state at all temperatures, even under an external applied pressure up to 1.0 GPa. By contrast, 2 is characterized by a more regular octahedral coordination around the metal ion and exhibits a low spin (LS) configuration at or below room temperature. However, it shows a thermally-induced SCO behaviour at T > 400 K, along with Light-Induced Excited Spin State Trapping (LIESST) at low temperature, with T LIESST = 38 K. Since DFT (U)M06/6-311+G(d) geometry optimizations in vacuo indicate that both complexes should adopt a HS state and a highly-distorted coordination geometry, the stabilization of a LS configuration in 2 is ultimately ascribed to the effect of intermolecular hydrogen bonds, which align the [Fe(bpp-triolH 3 ) 2 ] 2+ cations in 1D chains and impart profound differences in the geometric arrangement of the ligands.

Hexacyanidometalates (M = Fe III , Co III ) and multisite anion receptor HAT(CN) 6 (1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile) recognize each other in acetonitrile solution and self-assemble into the novel molecular networks (PPh 4 ) 3 [M(CN) 6 ][HAT(CN) 6 ] (M = Fe, 1; Co, 2) and (AsPh 4 ) 3 [M(CN) 6 ][HAT(CN) 6 ]·2MeCN·H 2 O (M = Fe, 3; Co, 4). 1-4 contain the stacked columns {[M(CN) 6 ] 3- ;[HAT(CN) 6 ]} ∞ separated by the organic cations. All of the M-C[triple bond, length as m-dash]N vectors point collectively towards the centroids of pyrazine rings on neighboring HAT(CN) 6 molecules, with N cyanide centroid pyrazine distances that are under 3 Å. The directional character and structural parameters of the new supramolecular synthons correspond to collective triple anion-π interactions between the CN - ligands of the metal complexes and the π-deficient areas of HAT(CN) 6 . Physicochemical characterisation (IR spectroscopy, UV-Vis spectroscopy, cyclic voltammetry) and dispersion-corrected DFT studies reveal the dominating charge-transfer (CT) and polarisation characters of the interactions. The electronic density flow occurs from the CN - ligands of [M(CN) 6 ] 3- to the HAT(CN) 6 orbital systems and further, toward the peripheral -CN groups of HAT(CN) 6 . Solid-state DFT calculations determined the total interaction energy of HAT(CN) 6 to be ca. -125 kcal mol -1 , which gives ca. -15 kcal mol -1 per one CN - HAT(CN) 6 contact after subtraction of the interaction with organic cations. The UV-Vis electronic absorption measurements prove that the intermolecular interactions persist in solution and suggest a 1 : 1 composition of the anion-π {[M(CN) 6 ] 3- ;[HAT(CN) 6 ]} chromophore, with the formation constant K add = (5.8 ± 6) × 10 2 dm 3 mol -1 and the molar absorption coefficient ε add = 180 ± 9 cm -1 dm 3 mol -1 at 600 nm, as estimated from concentration-dependent studies.

The self-assembly of copper(ii) complexes with two Schiff base ligands: L1 O = N 3 and L2 = N 4 and octacyanidomolybdate(iv) ions yields two discrete molecules of odd nuclearity, namely pentametallic [Cu(L1 O )(py)] 4 [Mo IV (CN) 8 ]·14H 2 O (1), Cu 4 Mo and trimetallic [Cu(L2)] 2 [Mo IV (CN) 8 ]·9H 2 O (2), Cu 2 Mo. Both molecular systems have been characterised structurally and magnetically, revealing a photomagnetic effect. In the case of (1) a metal-to-metal charge transfer (MMCT) mechanism is proposed. The analysis of magnetic interactions in the photogenerated state of (1) assumes the formation of the metastable cluster CuCu I Mo V where metal centres in Mo V -CN-Cu II linkages are ferromagnetically coupled with J 2 = 104(3) cm -1 . In (2) the increase in the magnetisation is due to the singlet-triplet transition on the Mo IV centre leading to the formation of the metastable CuMo. The presence of the paramagnetic Mo (S = 1) centre linking the Cu II (S = 1/2) centres allows for effective ferromagnetic interaction of 3 paramagnetic centres with coupling constant J 2 = 20.2(7) cm -1 .

A series of isostructural C3-symmetrical triple stranded dinuclear lanthanide [Ln2L3](NO3)3 molecules have been synthesized using subcomponent self-assembly of Ln(NO3)3 with 2-(methylhydrazino)benzimidazole and 4-tert-butyl-2,6-diformylphenol, where Ln = Tb (1), Dy (2), Ho (3), Er (4), Tm (5), and Yb (6). The temperature dependent and field dependent magnetic properties of 1-6 were modeled using the van Vleck approximation including the crystal field term HCF, the super-exchange term HSE and the Zeeman term HZE. Ferromagnetic interactions were found in 1, 2, 4 and 6, while antiferromagnetic interactions were found in 3 and 5. The erbium analogue reveals field induced SMM behaviour.

A series of isostructural octanuclear lanthanide complexes of general formula [Ln8(sao)4(μ3-OH)4(NO3)12(DMF)12] (Ln = Nd (), Sm (), Eu (), Gd (), Tb (), Dy (), Ho (), Er (); DMF = dimethylformamide) have been prepared via reactions of salicylaldoxime (saoH2), tetramethylammonium hydroxide (Me4NOH) with the appropriate lanthanide nitrate salt (Ln(NO3)3·6H2O). The metallic skeletons of the complexes describe [Ln4] tetrahedra encapsulated inside a [Ln4] square with the inner core stabilised through μ3-OH(-) ions and the periphery by μ4-sao(2-) ligands. The magnetic properties of compounds were investigated by dc and ac magnetometry. Temperature dependent ac magnetic susceptibility data reveal that the dysprosium analogue () displays an out-of-phase signal in the absence of an applied magnetic field indicative of slow relaxation of the magnetization typical of a Single-Molecule Magnet (SMM). Micro-SQUID measurements reveal temperature and sweep rate dependent hysteresis below 1.0 K.

The first example of the [Nb(CN)(8)]-based pillared-layered-type framework system {[Mn(II)(2)(bpdo)(H(2)O)(4)][Nb(IV)(CN)(8)]·6H(2)O}(n) (bpdo = 4,4'-bipyridyl-N,N'-dioxide) has been obtained and characterized structurally and magnetically. The presented results provide the first evidence for substantial magnetic anisotropy of [Nb(IV)(CN)(8)].

We report on the synthesis, molecular structure and magnetic properties of two novel coordination polymers: [{Cu(II)(4)(pic)(2)(H(2)O)(2)(MeOH)}{W(V)(CN)(8)}(2)]·MeOH·4H(2)O (1) and [{Mn(II)(3)(HCOO)(2)(H(2)O)(4)}{Mn(II)(H(2)O)(3)(HCONH(2))}(2){Nb(IV)(CN)(8)}(2)]·4HCONH(2)·2H(2)O (2). The single-crystal X-ray diffraction analysis of 1 shows that its molecular structure can be interpreted as a cyanido bridged (3,4,7)-connected 2D bilayer built of two different subnets sharing the tungsten centers. The magnetic measurements suggest that the system reveals long-range ferromagnetic ordering between Cu(II) and W(V) centers below 13.4 K. The molecular structure of (2) reveals a 2D topology of layers built of cyanido and formato bridging ligands. The system reveals ferrimagnetic behavior with a critical temperature at 17.8 K.

We have synthesized the octacyanoniobate-based cyano-bridged 3D ferromagnet {[Fe(II)(H(2)O)(2)](2)[Nb(IV)(CN)(8)].4H(2)O}(n) and characterized structurally, spectroscopically (XANES/EXAFS, IR, UV-Vis, Resonance Raman, (57)Fe Mössbauer spectroscopy) and magnetically. crystallizes in the tetragonal system, space group I4/m, a = 11.989(5) A, c = 13.237(5) A, V = 1902.6(13) A(3). 3D coordination architecture comprises two types of Nb(IV)-C-N-Fe(II)(HS) (HS = high spin) linkages with Fe-N-C angles of 154.5 degrees and 167.5 degrees . The XANES/EXAFS spectra at Fe:K and Nb:K lines confirm the presence of Nb(IV)-C-N-Fe(II) linkages. Magnetic measurements reveal ferromagnetic ordering below T(c) = 43 K with some non-collinearity of Nb(IV) (S = 1/2) and Fe(II) (S = 2) magnetic moments. The molecular field model simulation reproduces well the M(T) curve and T(c) value with one average exchange coupling constant J(FeNb) = + 8.1 cm(-1).