Imidazole has received considerable attention as a good ligand for a variety of metals. In addition to their ability to serve as models of active sites in metalloenzymes, transition metal complexes of imidazole (Him) could lead to potential applications such as electrochromic displays, photovoltaic cells and biomaterials [1][2].Ni(Him) 6 SO 4 .2H 2 O undergoes a reversible order-disorder phase transition at 223 K, monitored by differential scanning calorimetry and single-crystal X-ray diffraction. In both phases the [Ni(Him)] 2+ cation displays 3 symmetry as in other similar complex. SO 4 2-anions and one water are disordered, displaying 3.2 site symmetry in the P P 31c space group. It was of interest that the nature of this transition is due to the water reorientational motion, without space group change. We have estimated H from the configurational entropy. The results are similar to those obtained in thermal analysis in which H=3.529 KJ/mol. The water role is confirmed by analysis of powder samples in which the phase transition is precluded by water loss. 5,5'-diethylbarbituratic acid (barbH), also known as barbital is a barbiturate derivative used as a sedative and hypnotic drug, especially in the form of sodium barbital. Two new bis(5,5'-diethylbarbiturato) (barb) complexes of copper(II) and cadmium(II) with ethylenediamine (en) structurally characterized. cis-[Cu(barb) 2 (en)] 1 crystallizes in the monoclinic space group of C2/c and its asymmetric unit contains a half of the molecule, which has two-fold crystallographic symmetry. 1 consists of neutral monomeric units, in which, the copper(II) ion exhibits a highly distorted octahedral geometry by two barb anions and a neutral chelating en ligand. The individual molecules of 1 are held together by N-H···O hydrogen bonds, forming a threedimensional network.{[Cd(barb) 2 (µ-en)]·2H 2 O} n 2 is a one-dimensional coordination polymer and also crystallizes in the monoclinic crystal system (P2 1 /c). In 2, {[Cd(barb) 2 (en)] building blocks are connected in a zigzag arrangement by bridging NH 2 groups of en into a chain running parallel to the c axis, and the individual chains are further stacked by O-H···O and N-H···O hydrogen bonds to form a three-dimensional supramolecular framework. The barb ligands in both complexes act as bidentate ligands via the negatively charged imino N atom and one of the carbonyl O atoms adjacent to the imino N atom.
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