Synthesis and Characterization of Zinc(II) Complexes with Diamines and Thiolates

Abstract

Recent studies on the biochemical role of zinc(II) complexes of thiolates and amino acids encouraged our attention in the spectral and structural chemistry of zinc. Thus, the better insight of the role of zinc demands further systematic structural studies on the model compounds. The present dissertation describes the synthesis, spectral and structural characterization of zinc(II) complexes containing thiolate, diamine and 1,10-phenanthroline ligands. The first series consists of five new zinc(II) thiolate complexes; [Zn4(Cym)4Cl4] (1) with space group P-21/n, [Zn(Cym-Cym)Cl2]n (2) with space group P21/c, [Zn(Cys)Cl]·H2O (3), [Zn(Msa)2] (4) and [Zn(Mnt)2(H2O)] (5), where Cym-H = cysteamine, Cym-Cym = cystamine, Cys-H = cysteine, Msa-H = 2-mercaptosuccinic acid and Mnt-H = 2-mercaptonicotinic acid. The second series comprises eight zinc(II) diamine complexes; [Zn(Dach)2][ZnCl4] (6) with space group Pna21, [Zn(Dach)(NCS)2] (7) with space group Pbca, [Zn(Dap)(NCS)2][Zn(Dap)(NCS)2]n (8) with space group Pbca, [Zn(TMEDA)(NCS)2] (9), (TMEDA-H2)2+[ZnCl4]2- (10) with space group P-1, [Zn(Mnt-Mnt)(en)].H2O (11) with space group P-1, [Zn(Dap)(Mnt)Cl] (12) and [Zn(en)(NCS)2]. (13), where Dach = cis-1,2-diaminocyclohexane, TMEDA = N,N,N ˊ ,Nˊ -tetramethylethylenediamine, en = 1,2-diaminoethane, Dap = 1,3diaminopropane, Mnt-H = 2-mercaptonicotinic acid. In the third series two new zinc(II) complexes of 1,10-phenanthroline (phen); [Zn(Phen)(Mnt)Cl] (14) and {[Zn(phen)2(H2O){Ag(CN)2}][Ag(CN)2]•MeOH}n (15) with space group P -1 are presented. The complexes were characterized by CHNS analysis, FTIR and NMR (1H, 13C) spectroscopy. The FTIR and NMR spectroscopic data indicated the coordination of the ligands to the metal centre and were discussed in terms of the nature of bonding. The crystal structures of eight complexes; (1), (2), (6), (7), (8), (10), (11) and (15) were determined by X-ray crystallography. The structure of [Zn4(Cym)4Cl4] (1) shows that the complex exists in the form of a tetranuclear molecule in which zinc atoms are bridged by S atoms of Cym forming an eight-membered ring. The complex consists of two crystallographically independent Zn(II) ions. Zn1 and symmetry related ion are coordinated by two sulfur atoms and two nitrogen atoms of Cym, while Zn2 and symmetry related ion exhibit a ZnS2Cl2 setup. In both coordination environments, zinc atom adopts a distorted tetrahedral geometry. The complex (2), [Zn(Cym-Cym)Cl2]n exists in the form of a polymer consisting of Zn(Cym-Cym)Cl2 v

monomeric units in which each zinc atom acquires a tetrahedral environment and it is coordinated by two chloride ions and two nitrogen atoms of bridging Cym-Cym ligands. The sulfur atoms of cystamine retained the disulfide linkage instead of coordinating to metal center. The structure of complex (6) is composed of [Zn(Dach)2]2+ cations and [ZnCl4]2- anions. The Zn atoms in both ionic species adopt a distorted tetrahedral geometry. In [Zn(Dach)(NCS)2] (7), the Zn(II) atom is bonded to one 1,2-diaminocyclohexane molecule and to two terminal thiocyanate ions via the nitrogen atoms adopting a slightly distorted tetrahedral geometry. The crystal structure of complex [Zn(Dap)(NCS)2][Zn(Dap)(NCS)2]n (8) consists of two types of molecules, a discrete monomer and a polymeric one. The asymmetric unit of (TMEDA-H2)2+[ZnCl4]2- (10) consists of one tetrachloridozincate(II) anion and two halves of tetramethylethylenediaminium cations. Each of the two diaminium ions is located on an inversion center and one of them is disordered over two sites in a 0.780 (17):0.220 (17) ratio. The cations and anions are connected via N---H...Cl hydrogen bonds into chains extending along the [011] direction. In the crystal structure of complex [Zn(Mnt-Mnt)(en)]·H2O (11), the asymmetric unit consists of a zinc(II) ion bound to two Mnt ligands (in the form of a disulfide) and an ethylenediamine molecule, and a water of crystallization. The asymmetric units are joined together to form a one-dimensional polymeric chain. Each zinc atom is five coordinated with three carboxylic oxygen atoms of Mnt and two N atoms of bidentate en ligand. The crystal structure of a heterobimetallic coordination polymer {[Zn(phen)2(H2O){Ag(CN)2}] [Ag(CN)2]•MeOH}n (15) consists of dinuclear [Zn(Phen)2(H2O){Ag(CN)2}]+ cations, [Ag(CN)2]- anions and a methanol molecule. The non-coordinated [Ag(CN)2]- anions are linked to [Zn(Phen)2(H2O){Ag(CN)2}]+ cations through Ag---Ag (argentophilic) interactions resulting into the formation of chains. H-bonds and π-π interactions further connect these chains to constitute a 3D network. The complexes (1), (2), (6), (7), (8), (9) and (13) were also investigated by DFT modeling and frequency calculations. The complexes (1) and (2) were investigated in the solid state by infrared spectroscopic measurements, DFT modeling and frequency calculations using periodic DFT methodology. The vibrational modes sensitive to the N and S ligand coordination to Zn(II) and to the coordination polyhedron were determined. The C-S stretching vibrations appeared in the most characteristic modes are able to distinguish different binding behaviour of the CS donor group in the two Zn(II) ions. The structures of [Zn(Dach)2][ZnCl4] (6),