Structural and magnetic modulations of copper(II) azido complexes: unexpected in situ reactions of mono-N-donor pyridine-based co-ligands

Low-temperature hydrothermal reactions of copper salts with NaN3 and structurally related pyridine-based ligands, 1-(4-pyridyl)pyridinium, 3-chloromethylpyridine, 4-benzylpyridine, and quinoline (L4), respectively, led to the formation of four new magnetic complexes, [Cu3(L1)2(N3)6]n (1), [Cu3(L2)2(N3)6]n (2), [Cu(L3)2(N3)2] (3), and [Cu(L4)(N3)2]n (4). In these complexes, L1, L2, and L3 are pyridine, 3-azidomethylpyridine, and 4-benzoylpyridine, being generated in situ by the decomposition, azido substitution, and oxidation reaction of the 1-(4-pyridyl)pyridinium, 3-chloromethylpyridine, and 4-benzylpyridine, respectively. 1 and 2 have similar structures being composed of double end-on azido-bridging planar [Cu3(L)2(N3)6] trinuclear units, which are further linked into a two-dimensional layer by the end-to-end azido bridges of themselves, along with their weak end-on coordination. It is interesting that the only slight differences of geometrical parameters in 1 and 2 have led to distinct magnetic interactions between the trinuclear units, where the former is antiferromagnetic but the latter is ferromagnetic, whereas 3 has a mono-nuclear core structure, which is further extended to a one-dimensional (1D) chain by weakly coordinated end-on azido bridges. 4 consists of unique 1D chains with double end-on azido bridge bonding distorted five-coordinated Cu(II) centers, and exhibits ferromagnetic intrachain interactions. In the structures of these complexes there also exist weak inter-layer or inter-chain hydrogen bonds, which should also be responsible for some magnetic behavior at low temperature. In addition, primary structural and magnetic comparisons and discussions have also been performed by combining other reported azido-Cu(II) systems with related pyridyl-based co-ligands. These results show that the selection of synthesis conditions and slight decoration of co-ligands (or geometric differences of them) have important influences on the structures and magnetic properties of resulting metal azido complexes.