One- and two-dimensional metal–dicyanamido complexes with a flexible bridging co-ligand: structural and magnetic properties

Abstract

Five coordination-polymers of formula [M(dca)₂(bpp)]_∞ [bpp is the flexible 1,3-bis(4′-pyridyl)propane ligand, dca = dicyanamido anion, M = Mn (1), Co (2), Zn (3), and Cd (4a and 4b)] have been synthesized and structurally characterized. Compounds 1, 2, 3 and 4a are isomorphous and consist of uniform chains in which adjacent metal ions are triply linked by two 1,5-dca and one bpp bridges and each metal ion is octahedrally coordinated with a trans geometry. The M(dca)₂ chain motif adopts a sinusoidal topology with the M(dca)₂M rings in a boat conformation, to adapt to the arc-shaped bpp ligand, which here acts as an intrachain bridge and takes an unusual GG conformation. Compound 4b is thermodynamically more stable than 4a. The structure of 4b consists of extended 2D coordination layers in which neighboring metal ions are linked by a bpp or two 1,5-dca bridges and the metal ion is in a cis-octahedral environment. The M(dca)₂ chain motif adopts a zigzag topology with the M(dca)₂M rings in the usual flat conformation, and the bpp ligand takes a TT conformation and acts as an “arch bridge” between adjacent chains to yield a corrugated (4,4) layer. Each layer is interpenetrated with two adjacent layers, generating an interesting 3D polycatenane. The temperature dependence of the magnetic susceptibility has been investigated for the Mn(II) and Co(II) species. 1 behaves as a 1D Heisenberg Mn(II) chain with a rather weak intrachain antiferromagnetic interaction, and 2 exhibits the complicated behavior characteristic of polynuclear Co(II) species with an octahedral coordination geometry.