A complete review of all known octacyanide-based clusters with an extensive discussion of their structures, magnetic properties and multifunctionality.

tribute of molecule-based compounds called photomagnets and is inaccessible for conventional magnetic solids. The design and synthesis of such compounds, however, is a formidable challenge and only a few examples are known, all with rather low magnetic ordering temperatures well below the boiling point of liquid nitrogen. Herein, a cyanide-bridged coordination polymer {[Mn II (imidazole)]2[W IV (CN)8]}n exhibiting the highest light-induced magnetic ordering temperature ever observed and a magnetic hysteresis loop up to 90 K is reported. The photomagnetic effect results from the blue light excitation (450 nm) of the constituent octacyanotungstate(IV) moiety which then couples magnetically with manganese(II) resulting in light-induced ferrimagnetic ordering. The reported coordination framework shows also outstanding water sorption properties that are strongly correlated with the photomagnetic functionality. The photo-switching observed in the anhydrous state is completely quenched by the reversible capture of water with the fully hydrated phase becoming practically non-photomagnetic.

An alternating bimetallic {(H3O)[Ni(III)(cyclam)][Fe(II)(CN)6]·5H2O}n chain undergoes reversible dehydration at 40 °C accompanied by electron transfer which leads to Ni(II)-Fe(III) in about 50% of metal centres. The hydrated dark blue form is a paramagnet while the dehydrated yellowish-green form shows ferromagnetic coupling between neighbouring Ni(II) and Fe(III).

A new form of 2D honeycomb-like network is characterised by flat layers and undergoes single-crystal-to-single-crystal transformation to corrugated hexadecahydrate.

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 } n (1) and {[Ni(cyclam)] 3 [Cr(CN) 6 ] 2 } n(2) (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 1 and 2 are metamagnetic-like with varied T c and critical field H 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.

An inorganic three-dimensional [Ni(HO)][W(CN)]·4HO (1) framework undergoes a single-crystal-to-single-crystal transformation upon thermal dehydration, producing a fully anhydrous phase Ni[W(CN)] (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 [Ni(HO)(NC)] to the square-planar diamagnetic [Ni(NC)] moieties.

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.

Hexacyanidometallates of transition metal ions govern the topology and the photoluminescence of bimetallic d–f hybrid coordination networks incorporating uranyl cations.