Nickel(II), copper(II), palladium(II) and platinum(II) complexes of bidentate SN ligands derived from S-alkyldithiocarbazates and the X-ray crystal structures of the [Ni(tasbz) 2 ] and [Cu(tasbz) 2 ] á CHCl 3 complexes* Mohammad Akbar Ali** and Aminul H. Mirza Department of Chemistry, University of Brunei Darussalam, Jalan Tungku Link, Gadong BE 1410, Brunei Darussalam Ray J. Butcher Department of Chemistry, Howard University, Washington, DC 20059, USA Mizanur Rahman Department of Chemistry, University of Chittagong, Chittagong, Bangladesh Received 26 July 1999; accepted 19 November 1999 Abstract New complexes of general empirical formula, [M(NS) 2 ] á nCHCl 3 (M = Ni II , Cu II , Pd II or Pt II ; NS = anionic form of the thiophene-2-aldehyde Schi bases of S-methyl- and S-benzyldithiocarbazate; n = 0, 1) have been synthesized and characterized by physico-chemical techniques. Magnetic and spectroscopic evidence support a square-planar structure for these complexes. The crystal structures of the [Ni(tasbz) 2 ] and [Cu(tasbz) 2 ] á CHCl 3 complexes (tasbz = anionic form of the thiophene-2-aldehyde Schi base of S-benzyldithiocarbazate) have been determined by X-ray diraction. Both complexes have a trans-planar structure in which the two Schi base ligands are coordinated to the metal(II) ion as uninegatively charged bidentate ligands via the thiolate sulfur and the azomethine nitrogen atoms. Introduction Sulfur±nitrogen chelating agents derived from S-alkyl esters of dithiocarbazic acid and their transition metal complexes have been the subject of many studies [1±13] mainly because of their interesting physico-chemical properties [10, 11] and potentially bene®cial biological activities [2±5]. E.g., the nickel(II) complex of the 2-acetylpyridine Schi base derived from S-methyldi- thiocarbazate, [Ni(NNS)Cl], displays marked activity in the P388 lymphocytic Leukaemia test system [14]. Some Schi bases derived from S-alkyldithiocarbazates and their copper(II) complexes also exhibit a range of antifungal and antibacterial activities [2±5]. Although a large number of reports on the preparation and spectral characterization of transition metal±dithiocarbazate complexes are available, structural investigations by X- ray crystallography on such compounds are few. As part of our ongoing work on the coordination chemistry of such complexes, we describe here the preparation and characterization of nickel(II), copper(II), palladium(II) and platinum(II) complexes of the thiophene-2-aldehyde Schi bases of S-methyl- and S-benzyldithiocarbazates, together with the X-ray crystal structure determination of the bis-ligand nickel(II) and copper(II) complexes of the thiophene-2-aldehyde Schi base of S-benzyl- dithiocarbazate. Experimental Methods 1 H-n.m.r. spectra were recorded in DMSO-d 6 on either a Nicolet NI-300 or a Varian XL-100 spectrometer using TMS as internal reference. All other physical measure- ments and analytical procedures were similar to those described previously [5]. Preparation of the Schi bases The Schi bases were prepared by re¯uxing together equimolar solutions of the appropriate S-alkyldithio- carbazate and thiophene-2-carboxaldehyde in EtOH for ca. 1 h. On cooling the reaction mixture, the Schi bases crystallized from the reaction mixture. Recrystallization from EtOH aorded beautiful pale yellow crystals of the ligands. Htasbz (the thiophene-2-aldehyde Schi base of S-benzyldithiocarbazate): m.p. 185 °C (Found: C, 53.6; H, 4.3; N, 9.4; C 13 H 12 N 2 S 3 calcd.: C, 53.4; H, 4.1; N, 9.6%) Htasme (the thiophene-2-aldehyde Schi base of S-methyldithiocarbazate): m.p. 176 °C; (Found: C, 38.7; * tasbz = S-benzyl-b-N-(2-thienyl)methylenedithiocarbazate anion ** Author for correspondence Transition Metal Chemistry 25: 430±436, 2000. 430 Ó 2000 Kluwer Academic Publishers. Printed in the Netherlands.