4-Cyanopyridine complexes [MX2(4-CNpy)(x)](n) (with X = Cl, Br and x=1, 2): crystal structures, thermal properties and a comparison with [MX2(3-CNpy)(x)](n) complexes

摘要

Eleven new complexes [MX2(4-CNpy)(x)]((n)) with M = Mn, Fe, Co, Ni, Cu, and Zn, X = Cl and Br, 4-CNpy = 4-cyanopyridine, and x = 1 and 2 have been prepared and their structures were characterized by X-ray powder diffraction (XRPD). The reaction of the transition metal halides MX2 (M = Mn, Fe, Co, Ni, Cu and X = Cl, Br) with 4-CNpy leads to the formation of coordination compounds with the composition [MX2(4-CNpy)(2)](n) first. In all these compounds, the metal atoms are octahedrally coordinated by four halogen atoms and two 4-CNpy ligands. The halogen atoms bridge the metal atoms, leading to infinite [MX2](n) chains. The 4-CNpy molecules coordinate through their pyridine N atoms (N-py) and form lateral "wings" on the [MX2](n) chains. The manganese compound [MnBr2(4-CNpy)(2)](n) shows polymorphism with a fully reversible phase transition. The thermal behaviour of compounds [MX2(4-CNpy)(2)]((n)) was investigated by a combined differential thermal and thermogravimetric analysis (DTA-TG). DTA results show that thermal annealing of [MX2(4-CNpy)(2)](n) at around 240-260 degrees C leads to compounds of composition [MX2(4-CNpy)(1)](n) (M = Mn, Fe, Co and X = Cl, Br). In these compounds, 4-CNpy acts as a bidentate ligand: the N-py and N-CN atoms both coordinate to the metal atoms, building (nearly) linear M-py-C?N-M bridges between the [MX2](n) chains. This results in two-dimensional (2D) networks, which form the layer structures of the [MX2(4-CNpy)(1)](n) compounds. In all bromo compounds [MBr2(4-CNpy)(1)](n), the 4-CNpy bridges exhibit a head-to-tail-disorder with an inverted orientation of the 4-CNpy molecules between the metal atoms. Further heating of [MX2(4-CNpy)(1)](n) leads to [MnBr2(4-CNpy)(1/2)](n), [FeCl2(4-CNpy)(1/3)](n), [CoCl2(4-CNpy)(1/3)](n) and [CoBr2(4-CNpy)(1/3)](n) but their structures could not be determined yet. Additionally, the zinc compound [ZnBr2(4-CNpy)(2)] was prepared. In its both polymorphs, the Zn atoms are tetrahedrally coordinated by two bromine atoms and two 4-CNpy ligands (via the N-py atoms) to form discrete complexes. Upon heating to 240 degrees C, the Zn compound decomposes to ZnBr2 without forming intermediate phases. In all compounds [MX2(4-CNpy)(x)]((n)), the coordination behavior of the 4-CNpy ligand was investigated by infrared (IR) spectroscopy. A comparison with the structures of the corresponding 3-CNpy compounds is given. This article aims at emphasizing the versatile ability of cyanopyridine to act as a mono- or bidentate ligand to build structures with isolated complexes, chains, double chains and planar or wavy 2D networks.