Coordination compounds built up from MIICl2 and 3-cyanopyridine: double chains, single chains and isolated complexes

Abstract

The coordination polymers [M^IICl₂(3-CNpy)₂]_n, with 3-CNpy = 3-cyanopyridine and M^II = Mn, Fe, Co, Ni, Cu, Zn (1a–6a), were synthesised and the related structures determined by X-ray powder diffraction (XRPD). In 1a–5a the metal atoms are octahedrally coordinated by four chlorine atoms and two 3-CNpy ligands. The Cl atoms are bridging two M atoms, leading to infinite [M^IICl₂]_n chains. The 3-CNpy molecules coordinate through their pyridine N atoms (N_py) and form lateral “wings” on the chains. Upon heating to 230–290 °C, compounds 1a–5a release half of the organic ligands and transform into [M^IICl₂(3-CNpy)₁]_n (1b–5b). The crystal structures of 1b and 3b–5b were also determined from X-ray powder data. Compounds 1b and 3b–5b are built up by double chains of [M₂^IICl₄]_n units. Each metal atom is coordinated by two μ₂- and three μ₃-bridging chlorine atoms and one 3-CNpy ligand. In none of the investigated compounds does the 3-CNpy molecule act as a bridging ligand, which is in contrast to [M^IIBr₂(3-CNpy)₁]_n. The compound [Zn^IICl₂(3-CNpy)₂] shows two polymorphic forms (α-6a and β-6a). In both polymorphs, the Zn atoms are tetrahedrally coordinated by two chlorine atoms and two 3-CNpy ligands to form discrete complexes. Upon heating to 290 °C, α-6a and β-6a decompose into ZnCl₂ and 3-CNpy without forming intermediate phases. In all compounds, the coordination mode of the 3-CNpy ligand was investigated by IR spectroscopy.