From 1-D Coordination Polymers to 3-D Hydrogen-Bonding Networks: Crystal Engineering and Magnetism of CuII−dca−Cyanopyridine Supramolecular Systems (dca = Dicyanamide, N(CN)2-)

Abstract

Three-dimensional (3-D) metallo-supramolecular architectures 1−3 based on CuII−dca−cypy systems [dca = dicyanamide, N(CN)2-, and cypy = n-cyanopyridine (n = 4, 3, 2)], which are extended by combining metal-coordination and second-sphere hydrogen-bonded interactions, were rationally designed and structurally characterized by single-crystal X-ray diffraction. Reaction of CuII with dca and 4- or 3-cypy afforded two similar neutral one-dimensional (1-D) coordination polymers, [Cu(dca)2(4-cypy)2]n (1) and [Cu(dca)2(3-cypy)2]n (2), in which the octahedral CuII centers are linked through double μ1,5-dca bridges and the cypy moieties act as monodentate terminal ligands via their pyridyl nitrogen donors. The coordination chains of 1 and 2 are further cross-linked by C−H···N interactions between the free nitrile N atoms of cypy and H atoms of the pyridyl ring, creating two interpenetrating 3-D networks (for 2, further weaker hydrogen-bonding interactions between the amide N atoms of dca and the H atoms in 3-cypy combined the two networks into a single net). When substituting the 4- or 3-cypy with 2-cypy, a single μ1,5-dca bridged 1-D chain [Cu(dca)2(pyom)]n (3) was isolated in which the square-pyramidal CuII center is chelated to the ligand O-methyl picolinimidate (pyom), generated from 2-cypy via addition of methanol across the C⋮N group. These 1-D chains are further cross-linked by weak Cu−Ndca interactions to form corrugated 2-D (6,3) sheets, which are highly interdigitated and further expanded to result in a 3-D network through interlayer C(N)−H···N interactions. Variable-temperature magnetic susceptibility measurements reveal the existence of very weak antiferromagnetic or nil interactions between the CuII centers in complexes 1−3, and the magneto-structural correlations of such μ1,5-dca−CuII 1-D systems are also discussed.