Syntheses, structures and magnetic behaviors of 1D and 3D µ1,5-dicyanamide bridged copper(II) coordination polymers containing a symmetrical 1,2-diamine as a chelator

Abstract

Two neutral copper(II) coordination polymers, [Cu(en)(µ1,5-dca)(dca)]n (1) and [Cu3(en)2(µ1,5-dca)6]n (2) [en = 1,2-ethanediamine, dca = dicyanamide], with µ1,5-dicyanamide bridges have been isolated. X-ray structural analysis reveals that each Cu(II) center in the asymmetric unit of 1 adopts a distorted square pyramidal geometry with a CuN5 chromophore ligated through two N atoms of the symmetrical 1,2-ethanediamine (en) ligand, one nitrile N atom of a terminal dca ligand and two nitrile N atoms of the μ1,5 bridging dca ligand. 1 is an example of coordination polymer containing both μ1,5-dca and terminal dca. Adjacent copper atoms are connected by dca ligands in the μ1,5-bridging mode affording a 1D chain structure. In the crystalline state, these 1D chains are further associated through weak intermolecular NH⋯N hydrogen bonds to form a 2D sheet structure, viewed along the crystallographic b axis. The asymmetric unit of 2 contains two types of copper(II) centers (Cu1 and Cu2). Cu1 adopts a distorted square pyramidal geometry with a CuN5 chromophore coordinated through two N atoms of the bidentate ligand (en) and three nitrile N atoms of three different μ1,5 bridged dca ligands, whereas Cu2 is connected to six nitrile atoms of six different μ1,5 bridged dca ligands, resulting in a distorted octahedral geometry with a CuN6 chromophore. Adjacent copper atoms are connected by μ1,5-bridging dca ligands to form a 3D network coordination polymer structure, which contains multiple NH∙∙∙N hydrogen bonds in the crystalline state. A variable-temperature magnetic susceptibility study shows very weak antiferromagnetic interactions among the neighboring metal centers through the μ1,5-dca bridges with J = −0.12 cm−1 for complex 1 and J = −0.19 cm−1 for complex 2.