Reversible Guest-Induced Magnetic and Structural Single-Crystal-to-Single-Crystal Transformation in Microporous Coordination Network {[Ni(cyclam)]₃[W(CN)₈]₂}<i>_n</i>

Planar honeycomb-like coordination network {[Ni(cyclam)]3[W(CN)8]2}n (cyclam = 1,4,8,11-tetraazacyclotetradecane) was obtained in the self-assembly reaction of [Ni(cyclam)]2+ and [W(CN)]83-. Its structure is characterized by void channels along the a axis. The compound shows reversible water adsorption in the temperature range of 25−40 °C with the formation of {[Ni(cyclam)]3[W(CN)8]2}n·16nH2O, accompanied by single-crystal-to-single-crystal transformation. The structural transformation significantly changes the character of intraplane magnetic exchange interactions

Reversible Guest-Induced Magnetic and Structural Single-Crystal-to-Single-Crystal Transformation in Microporous Coordination Network {[Ni(cyclam)]₃[W(CN)₈]₂}<i>_n</i>

Planar honeycomb-like coordination network {[Ni(cyclam)]3[W(CN)8]2}n (cyclam = 1,4,8,11-tetraazacyclotetradecane) was obtained in the self-assembly reaction of [Ni(cyclam)]2+ and [W(CN)]83-. Its structure is characterized by void channels along the a axis. The compound shows reversible water adsorption in the temperature range of 25−40 °C with the formation of {[Ni(cyclam)]3[W(CN)8]2}n·16nH2O, accompanied by single-crystal-to-single-crystal transformation. The structural transformation significantly changes the character of intraplane magnetic exchange interactions

Dehydration of Octacyanido-Bridged Ni^II-W^IV Framework toward Negative Thermal Expansion and Magneto-Colorimetric Switching

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

Dehydration of Octacyanido-Bridged Ni^II-W^IV Framework toward Negative Thermal Expansion and Magneto-Colorimetric Switching

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

Dehydration of Octacyanido-Bridged Ni^II-W^IV Framework toward Negative Thermal Expansion and Magneto-Colorimetric Switching

An inorganic three-dimensional [Ni^II­(H₂O)₂]₂­[W^IV­(CN)₈]·​4H₂O (<b>1</b>) framework undergoes a single-crystal-to-single-crystal transformation upon thermal dehydration, producing a fully anhydrous phase Ni^II₂­[W^IV­(CN)₈] (<b>1d</b>). The dehydration process induces changes in optical, magnetic, and thermal expansion properties. While <b>1</b> reveals typical positive thermal expansion of the crystal lattice, greenish-yellow color, and paramagnetic behavior, <b>1d</b> 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 [Ni^II­(H₂O)₂­(NC)₄]^2– to the square-planar diamagnetic [Ni^II­(NC)₄]^2– moieties

Proton-Conducting Humidity-Sensitive Ni^II–Nb^IV Magnetic Coordination Network

The 2D coordination network (NH4)2[NiII(cyclam)]3[NbIV(CN)8]2·21H2O (1·21H2O) was obtained on a cation-assisted synthetic pathway. The reaction between [Ni­(cyclam)]2+ and [Nb­(CN)8]4– in the presence of excess of NH4Cl resulted in the formation of negatively charged coordination layers with the simultaneous incorporation of the NH4+ cations into the microporous channels of the structure. 1·21H2O network can be partly dehydrated in a single-crystal-to-single-crystal structural transformation to give (NH4)2[NiII(cyclam)]3[NbIV(CN)8]2·14H2O (1·14H2O). The dehydration-induced structural changes, in particular the deformation of CN–-bridges and the disruption of interlayer interactions, give rise to the solvatomagnetic effect. Fully hydrated 1·21H2O phase is a ferrimagnet with a critical temperature of magnetic ordering of 7.6 K and a narrow magnetization hysteresis loop, while 1·14H2O hydrate is an antiferromagnet with Tc = 7.2 K and metamagnetic transition at 6.3 kOe. Thanks to the presence of the NH4+ ions in the structure, the proton conductivity of ∼4 × 10–5 S cm–1 (295 K, 100% relative humidity, RH) is observed with the activation energy of 0.80 eV

The Rule Rather than the Exception: Structural Flexibility of [Ni(cyclam)]²⁺-Based Cyano-Bridged Magnetic Networks

Changes in structure and magnetic properties accompanying guest removal, inclusion, or exchange in two CN-bridged 2D networks of honeycomb topology: {[Ni­(cyclam)]₃[Fe­(CN)₆]₂}_<i>n</i> (<b>1</b>) and {[Ni­(cyclam)]₃[Cr­(CN)₆]₂}_<i>n</i> (<b>2</b>) (cyclam = 1,4,8,11-tetraazacyclotetradecane) were studied by PXRD and magnetic measurements. For each compound four pseudopolymorphic forms differing in structure and magnetic characteristics were identified: fully hydrated form stable in water, partly hydrated form stable in the air at ambient conditions, anhydrous form, and MeOH-modified form. All forms can be reversibly transformed into one another by several interconversion pathways, which fully correspond between Fe and Cr compounds. All forms of <b>1</b> and <b>2</b> are metamagnetic-like with varied <i>T</i>_c and critical field <i>H</i>_cr. For several forms, differently shaped magnetic hysteresis loops can be observed. For the partly hydrated and MeOH modified forms structure models are proposed on the basis of PXRD data. Correlations between structural features and magnetic properties are discussed

Cyanido-Bridged Clusters with Remote N‑Oxide Groups for Branched Multimetallic Systems

The combination of [W^V(CN)₈]^3– anions with 3d metal cations M^II in MeOH leads to the formation of pentadecanuclear spherical cyanido-bridged clusters {M­[M­(solv)₃]₈[M′(CN)₈]₆}, <b>M</b>_<b>9</b><b>M′</b>_<b>6</b>. 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 (<i>S</i>_GS = ¹⁵/₂, <i>g</i>_eff = 3.4) clusters or chains of clusters {Co₉W₆(<i>N</i>,<i>O</i>-L)_<i>x</i>} (<i>N</i>,<i>O</i>-L – pyrazine mono-N-oxide, <i>pzmo</i>; 4,4-bipyridine mono-N-oxide – 4,4′-<i>bpmo</i>) 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 <i>N</i>,<i>O</i>-donor linkers L. The systematic occurrence of such motifs in the series <b>1</b>–<b>3</b> is a result of preference for the Co–N_L coordination over the Co–O_L coordination, controlled also by strongly competing supramolecular interactions including simple hydrogen bonding {_LNO···H-donor} as well as cooperative π-costacked hydrogen bonding in double cyclic synthons {Co–O–H_MeOH···O–N_bpmoN−}₂. The observed coordination backbones are discussed in terms of the potential to bind the specific external molecular units and create the new type of branched molecular organization. The magnetic properties are confronted with structural differences along <b>1</b>–<b>3</b>, considering coordination polyhedra, Co–N bond lengths, Co–N–C angles, and hydrogen bonds. The diversity of slow magnetic relaxation images for the known Co₉W₆ based phases are discussed in terms of local deformation of Co coordination polyhedra and global deformation of cyanide bridged backbones

Implementation of Chirality into High-Spin Ferromagnetic Co^II₉W^V₆ and Ni^II₉W^V₆ Cyanido-Bridged Clusters

The synthesized chiral (<i>R</i>)- and (<i>S</i>)-2-(1-hydroxyethyl)­pyridine ligands (<i>R</i>/<i>S</i>-mpm) were introduced to self-assembled Co^II-[W^V(CN)₈] and Ni^II-[W^V(CN)₈] magnetic systems giving a remarkable series of four enantiopure cyanido-bridged clusters, {M^II[M^II(<i>R</i>/<i>S</i>-mpm)­(MeOH)]₈­[W^V(CN)₈]₆}­·14MeOH (M = Co, <b>1</b>-<i>R</i> and <b>1</b>-<i>S</i>; M = Ni, <b>2</b>-<i>R</i> and <b>2</b>-<i>S</i>). They consist of 15 metal centers, 9 Co^II or Ni^II ions, and 6 [W^V(CN)₈]^3– ions, embedded in a 6-capped body-centered cube topology. Bidentate enantiopure mpm ligands coordinated to eight external Co^II or Ni^II sites induce their chiral character, which results in the strong natural optical activity in the broad UV–vis range of 200–700 nm. All (<b>1</b>-<i>R</i>/<i>S</i>) and (<b>2</b>-<i>R</i>/<i>S</i>) clusters reveal cyanido-mediated ferromagnetic exchange interaction giving high-spin ground states of 15/2 (<b>1</b>-<i>R</i>/<i>S</i>) and 12 (<b>2</b>-<i>R</i>/<i>S</i>). For (<b>2</b>-<i>R</i>/<i>S</i>) forms of {Ni₉W₆}, the exchange constant <i>J</i> = +16.1 cm^–1 was obtained using exact diagonalization of the exchange Hamiltonian. Because of the significant magnetic anisotropy, (<b>1</b>-<i>R</i>/<i>S</i>) 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