A unique 2D framework containing rhombic tetrameric cobalt(II) of mixed Td and Oh geometries linked by two different rigid ligands: Synthesis, crystal structure and magnetic properties

A new 2D coordination polymer with the formula [Co4(μ3-OH)2(H2nip-2H)2(H2nip-H)2(bpe)2]n (1) (H2nip = 5-nitro-isophthalic acid, bpe = trans-1,2-bis(4-pyridyl)ethylene), has been hydrothermally synthesized and structurally characterized. The structure of 1 is built around uncommon, rhombic {Co4} clusters with double Td and double Oh Co(II) geometries, which are extended into 2D network by the rigid deprotonated H2nip and bpe bridges. Magnetic property study indicates there is weak antiferromagnetic coupling interaction between Co(II) ions, which mainly arises from the antiferromagnetic coupling interaction in the tetramer, based on the nature of the μ3-hydroxyl group and syn–syn carboxylate-bridged modes.