Novel dichloro(bis{2-[1-(4-methylphenyl)-1H-1,2,3-triazol-4-yl-κN 3 ]pyridine-κN})metal(II) coordination compounds of seven transition metals (Mn, Fe, Co, Ni, Cu, Zn and Cd)

The synthesis, characterization, DFT and, in two cases, the structure of seven novel dichloro(bis{2-[1-(4-methylphenyl)-1H-1,2,3-triazol-4-yl-κN 3 ]pyridine-κN})metal(II) coordination compounds ([M(L 2 ) 2 Cl 2 ]), containing transition metals of groups 7–12, are described. Both experimentally measured magnetic moment and DFT calculations showed that d 5 Mn(II) (with µ eff = 5.62 B.M., S = 5/2), d 6 Fe(II) (with µ eff = 5.26 B.M., S = 2), d 7 Co(II) (with µ eff = 3.98 B.M., S = 3/2), d 8 Ni(II) (with µ eff = 3.00 B.M., S = 1) and d 9 Cu(II) (with µ eff = 1.70 B.M., S = ½) are all paramagnetic, while d 10 Zn(II) and Cd(II) are diamagnetic with S = 0. DFT calculations on the possible isomers of these coordination compounds, showed that the cis–cis–trans and the trans–trans–trans isomers, with the pyridyl groups trans to each other, are the lowest in energy. The trans–trans–trans isomers were experimentally characterized by X-ray crystallography for [Ni(L 2 ) 2 Cl 2 ] and [Zn(L 2 ) 2 Cl 2 ]·L 2 in this study. In the solid state the coordination compounds are connected by intermolecular hydrogen bonds, mainly involving the chloride atoms, to form 3D supramolecular structures. Computational chemistry calculations, using Natural Bonding Orbital calculations, identified these inter-molecular hydrogen bonds, C–H⋯Cl, by a donor–acceptor interaction from a filled lone pair NBO on Cl to an empty antibonding NBO on (C–H). The inter-molecular hydrogen bonds were also identified by QTAIM determined bonding paths between Cl and the respective hydrogen. The theoretically calculated computational chemistry results thus give an understanding on a molecular level why in the solid state where inter-molecular forces and packing play a role, the trans–trans–trans isomers are mostly obtained.