Synthesis and characterization of saccharinato complexes of various groups 9-12 metals.

Abstract

The aim of the study was the synthesis and characterization of new mixed ligand saccharinato complexes of various groups 9, 10, 11 and 12 metals, i.e. M = Cd(II), Co(II), Zn(II), Hg(II), Cu(II), and Ni(II) using dimethyl sulfoxide (DMSO) and amine-based ligands such as ethylenediamine (en), N-methyldiethanolamine (MDEA) and 2-(methylamino)ethanol (MEA) from the precursor [M(C₇H₅SO₃N)₂(H2O)₄]·2H₂O. The new complexes were characterized by elemental analyses, solution Nuclear Magnetic Resonance (NMR), UV–Vis spectroscopy, IR ATR spectroscopy, thermal analysis and single crystal X-ray diffraction. All complexes are mononuclear except complex (9) which is a dinuclear Cu(II) complex. A number of the saccharinato complexes are diamagnetic, i.e. trans-[Cd(sac)₂(dmso)₂(H₂O)₂] (1), cis-[Zn(sac)₂(dmso)₂] (3), [Hg(sac)₂(dmso)(H₂O)] (4) and trans-[Cd(sac)₂(en)₂] (11) and were characterised by NMR. Some of the complexes are paramagnetic, including trans- [Co(sac)₂(dmso)₂(H₂O)₂] (2), [Cu(sac)₂(dmso)(H₂O)₂] (5), [Cu(sac)₂(N,O,O-mdea)₂] (7), [Co(sac)₂(N,O,O-mdea)₂] (8) and [Ni(sac)₂(en)₂] (10). All complexes containing the DMSO ligand were successfully analysed by single crystal X-ray diffraction, i.e. complexes (1) to (5). The complexes crystallized in the monoclinic P21/c space group together with complex (11). Complexes [Ni(N,O,O-mdea)]·2(sac) (6), [Cu₂(μ-O)₂(mea)₄]·2(sac) (9), and [Co₂(en)₄(CO₃)₂]·2(sac)3H₂O (12) were found to crystallize in the triclinic P-1 space group. In DMSO complexes, the metal ion is positioned at the centre of symmetry and complexes (1) and (2) are octahedrally coordinated by two monodentate DMSO ligands which are trans to each other and two aqua-ligands which are also trans to each other. The ligands in complex (3) are tetrahedrally coordinated to the Zn(II) ion in the cis position and in complex (4) a distorted trigonal bipyramidal complex was found whereby the DMSO groups are disordered over two places and the site occupancy factors were refined to 0.504(4) and 0.496(4), respectively. Complex (5) consisted of Cu(II) ions in a trigonal bipyramidal geometry. Complexes (6) and (12) have an octahedral coordination geometry with the metal ion positioned at the centre of symmetry. Complex (9) is a centrosymmetric binuclear complex containing two strongly distorted square-pyramidal coordinated copper(II) ions bound together by two alkoxo bridges. The bridging oxygen is a deprotonated oxygen of the ethanolic group of MDEA. The MDEA ligand also coordinates to the copper(II) ions through its nitrogen, while the other ethanolic group is not involved in the coordination. For complexes (6), (9) and (12) the saccharin acts as a weak counter ion and complex (12) has a lattice containing three water molecules of crystallization held together by a hydrogenbonded network. The saccharin ligands in the mononuclear complexes are coordinated via the N-atom. Thermal behaviour of the complexes was studied using DTA and TGA in nitrogen atmosphere. The complexes are stable below 200 °C and after that they start to show degradation and decomposition characteristics. The complexes lose ligands first and the saccharinate anion at higher temperatures for complexes (1) to (5) and (11). For complexes (6), (9) and (12) there is an interchangeable loss of amine ligands with saccharin anions. All the complexes show either endothermic or exothermic DTA peaks at various stages.