Preparation, characterization and antifungal properties of nickel(II) complexes of tridentate ONS ligands derived from N-methyl-S-methyldithiocarbazate and the X-ray crystal structure of the [Ni(ONMeS)CN] ® H 2 O complex* Mohammad Akbar Ali** and Aminul Huq Mirza Department of Chemistry, Universiti Brunei Darussalam, Jalan Tungku Link, BE 1410, Negara Brunei Darussalam Mohamed Nazimuddin and Prakash Kanti Dhar Department of Chemistry, University of Chittagong, Chittagong, Bangladesh Ray J. Butcher Department of Chemistry, Howard University, Washington, DC 20059, USA Received 07 December 2000; accepted 29 January 2001 Abstract Nickel(II) complexes of general empirical formula, NiLX ® nH 2 O (L ¼ deprotonated form of the Schiff base formed by condensation of N-methyl-S-methyldithiocarbazate with 2-hydroxybenzaldehyde or 5-bromo-2-hydroxyben- zaldehyde; X ¼ Cl ) , Br ) , NCS ) , AcO ) or CN ) ; n ¼ 0, 1) have been prepared and characterized by a variety of physico-chemical techniques. Magnetic and spectroscopic data support a square-planar structure for these complexes. The crystal structure of the [Ni(ONMeS)CN] ® H 2 O complex (ONMeS ¼ anionic form of the 2- hydroxybenzaldehyde Schiff base of N-methyl-S-methyldithiocarbazate) has been determined by X-ray diffraction. The complex has a distorted square-planar structure in which the Schiff base is coordinated to the nickel(II) ion as a uninegatively charged anion coordinating via the phenolic oxygen atom, the azomethine nitrogen atom and the thione sulfur atom. The fourth coordination position is occupied by a cayano ligand. The antifungal properties of the Schiff bases and their nickel(II) complexes were studied against three plant pathogenic fungi. The ligands display moderate fungitoxicities against these organisms but their nickel(II) complexes are less active than the free ligands. Introduction Metal complexes of Schiff bases derived from S-alkyl esters of dithiocarbazic acid have been the subject of a large number of studies [1–15] due probably to their interesting properties [12–14] and potentially beneficial biological activities [5–7, 16, 17]. However, most of the studies reported so far involve complexes of tridentate chelating agents containing the NNS set of donor atoms; complexes of ONS ligands have not received much attention. Ligands with ONS donor atoms yield copper(II) complexes with interesting magnetic proper- ties [18–23]. Recently, an antimony(V) complex of the salicyladehyde Schiff base of S-benzyldithiocarbazate (an ONS ligand), has been shown to display marked activity against leukemia [24]. Nickel(II) complexes of some bivalent ONS thiosemicarbzone ligands have also been found to catalyze important reactions related to CO-dehydrogenase [25] and silane alcoholysis [26]. In view of the interesting physicochemical properties and potentially beneficial biological activities of metal com- plexes of ONS donor ligands and as part of our on- going study of metal complexes of Schiff bases derived from S-alkyl esters of dithiocarbazic acid, we report here the preparation and characterization of some nickel(II) complexes of two tridentate ONS ligands derived from N-methyl-S-methyldithiocarbazate, together with the X-ray crystal structure of the [Ni(ONMeS)CN] ® H 2 O complex. The chloro- and the thiocyanato complexes of nickel(II) of HL 1 (HL 1 is the 2-hydroxybenzaldehyde Schiff base of N-methyl-S-methyldithiocarbazate) were previously reported [19], but full characterization data for these complexes were not published. Experimental Methods All physical measurements and analytical procedures were similar to those described previously [5]. Preparation of the Schiff bases The Schiff bases were prepared by refluxing together equimolar amounts of the appropriate aldehyde and N- methyl-S-alkyldithiocarbazate in EtOH for ca. 2 h. The * CCDC Deposition Number 151839 ONMeS ¼ anion of N-meth- yl-S-methyl-b-N-(2-hydroxyphenyl)methylenedithiocarbazate ** Author for correspondence Transition Metal Chemistry 27: 27–33, 2002. 27 Ó 2002 Kluwer Academic Publishers. Printed in the Netherlands.