Synthesis and structural characterizations of mononuclear zinc complexes with an unprecedented terminal bidentate coordination mode of the flexible 1,1,3,3-tetrakis(3,5-dimethyl-1-pyrazolyl)propane ligand

Four new complexes, [Zn(tdmpp)(2)H2O](ClO4)(2)center dot H2O (1), [Zn(NCS)Cl(tdmpp)] (2), [ZnI2(tdmpp)] (3) and [ZnCl2(tdmpp)] (4), were prepared and structurally characterized. The 1,1,3,3-tetrakis(3,5-dimethyl-1-pyrazoly)propane (tdmpp) ligand in the above compounds represents the first example of a flexible tetradentate nitrogen donor ligand in which the ligand is coordinated to the metal center as a terminal chelating ligand. The perchlorate ion in 1 acts as an uncoordinated anion, while in 2 the SCN and chlorine ligands and in 3 the iodine ligand participate in the coordination sphere of the metal center. The coordination ability of these anions and significant effects of non-covalent C-H center dot center dot center dot pi and C-H center dot center dot center dot X (X = O, Cl and I) interactions play a major role in the crystal packing of these compounds. In 1, the zinc atom adopts a distorted trigonal bipyramidal geometry and the [Zn(tdmpp)(2)H2O](2+) cations are linked by C-H center dot center dot center dot O hydrogen bonds to give a 1-D chain structure. In the structures of 2 and 3, the mononuclear neutral molecules form a 1-D chain structure along the b-axis through C-H center dot center dot center dot Cl and C-H center dot center dot center dot I hydrogen bonds, respectively. These chains are linked by intermolecular C-H center dot center dot center dot pi interactions to generate a three-dimensional network. Crystals of compound 4 were not suitable for X-ray diffraction studies and therefore its structure could only be investigated in the solid state by infrared spectroscopy and elemental analysis. (C) 2014 Elsevier Ltd. All rights reserved.