Synthesis, crystal structures and photochromic properties of two coordination polymers based on a rigid tetracarboxylic acid ligand

Manganese(II) and nickel(II) coordination polymers, [Mn(L)(H2O)2] n (1) and [Ni(L)·14H2O] n (2), have been synthesized from a rigid viologen-based tetracarboxylic acid ligand, 1,1′-bis(3,5-dicarboxyphenyl)-4,4′-bipyridinium dichloride (H4L·2Cl) and the Mn(II)/Ni(II) chlorides. The compounds have been characterized by infrared spectra, elemental analyses, single-crystal and powder X-ray diffraction analyses and thermogravimetric analyses. Compound 1 has a 2D coordination network with uncoordinated carboxyl groups, which further stack into a 3D supramolecular structure by hydrogen-bonding interactions. Compound 2 shows a 3D supramolecular framework with 1D channels along the crystallographic b-axis, formed from zigzag chains through hydrogen-bonding interactions. Both compounds display prominent photochromic and photomagnetic behavior upon light irradiation, suggesting that they may be potential photomagnetic materials.