Differentiating intramolecular spodium bonds from coordination bonds in two polynuclear zinc(ii) Schiff base complexes

Two new zinc(ii) complexes, [{N(CN)(2)}Zn(L-1)Zn{mu-1,5-N(CN)(2)}](2) (1) and [{mu-1,5-N(CN)(2)}{N(CN)(2)}Zn(L-2)Zn{mu-1,5-N(CN)(2)}](n) (2) {H2L1 = 2,2 '-[(2,2-dimethyl-1,3-propanediyl)bis(nitrilomethylidyne)]bis[6-methoxyphenol] and H2L2 = 2,2 '-[(2,2-dimethyl-1,3-propanediyl)bis(nitrilomethylidyne)]bis[6-ethoxyphenol]} have been synthesized and characterized. The structures of both complexes have been confirmed by X-ray crystallography. A subtle difference in the aromatic ring of the Schiff base ligand (6-ethoxy in H2L2 and 6-methoxy in H1L1) has a strong influence on the final solid state structure. In addition, the O-atom of the methoxy groups in 1 forms stronger intramolecular spodium bonds with Zn(ii) than the O-atom of the ethoxy group in 2. This has been analysed using density functional theory (DFT) calculations and a combination of the quantum theory of atoms in molecules (QTAIM) and noncovalent interaction (NCI) plot index computational tools.