Assemblies, Crystal Structures, And Properties Of Octacyanometallate-based Complexes

This paper reviews the development in the field of octacyanometallate-based complexes, then two different systems Ni/M (M = W and Mo) and Ln/W have been carried out.For Ni/W system, four single crystals, [Ni(L¹)3]2[Mo(CN)8]·2H₂O (1), (H₂L²)0.5[NiL²][W(CN)8]·2DMF·H₂O (2), [Ni(L³)]3[W(CN)8]2·4H₂O (3) and [Ni(L4)]2[Mo(CN)8]·8H₂O (4) (L^1L4 are organic ligands), containing different types of ligands have been obtained. In 1, discrete [Ni(L¹)3]2+ and [Mo(CN)8]4- ions form a three-dimensional supramolecular framework through hydrogen bonds, while [Ni(L²)]2+ and [W(CN)8]3- in 2 are linked in alternating fashion to form a one-dimensional linear structure. Similar to 2, [Ni(L²)]2+ and [W(CN)8]3- ions in 3 are linked in alternating fashion to form two-dimensional corrugated layers. Furthermore, 3 indicates the presence of a ferromagnetic coupling between Ni(II) and W(V) ions. 4 presents a distorted three-dimensional diamond network, where Mo and Ni atoms act as linkers and connectors, respectively. The magnetic characterization indicates weak antiferromagnetic interactions between Ni(II) centers in 4. In addition, the macrocyclic ligands have some impacts on the structures of Ni/W system.For Ln/W system, a series of [Ln(H₂O)n][W(CN)8] complexes have been synthesized, among which seven single crystals have been obtained. SC-XRD analysis reveals the topology of [Ln(H₂O)n][W(CN)8] has a neutral corrugated layer consisting of 12-member Ln2W2(CN)4 puckered squares. It should be pointed out that the geometries of the center Ln(III) atoms transform from the nine-coordinated monocapped square antiprism for LaW, NdW, EuW, and GdW, to the eight-coordinated square antiprism for HoW, ErW, and TmW with increasing atomic number of the Ln(III) atoms, while the formulae of Ln/W complexes change from Ln(H₂O)5[W(CN)8] (Ln = La, Nd Eu, Gd) to Ln(H₂O)4[W(CN)8] (Ln = Ho, Er, Tm). RT-PXRD results indicate with increasing atomic number of the Ln(III) atoms, phase transition occurs from phase A of [Ln(H₂O)5][W(CN)8] (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb) to phase B of [Ln(H₂O)4][W(CN)8] (Ln = Ho, Er, Tm). TGA and VT-PXRD results show that the structures change reversibly into [Ln(H₂O)4][W(CN)8] (Ln = Sm, Eu, Gd, Tb) with the loss of the first coordinated water molecule firstly, and then that a collapse of framework structure with the loss of the rest four coordinated water molecule on heating for [Ln(H₂O)5][W(CN)8] (Ln = Sm, Eu, Gd, Tb). But for [Ln(H₂O)4][W(CN)8] (Ln = Ho, Er, Tm) and [Ln(H₂O)5][W(CN)8] (Ln = La, Ce, Pr, Nd), the structures collapse directly during coordinated water molecules losing gradually while heating. The magnetic characterization indicates weak antiferromagnetic interactions in [Eu(H₂O)5][W(CN)8] and [Er(H₂O)4][W(CN)8].