The adoption of the sp1 23 hybridization for the nitrogen orbitals may appear at first quite unsuitable, as the bond orbitals have been estimated to contain much more p-character.22 However, during the course of the calculations it was noticed that repulsion integrals evaluated in different ways, thus having different values, still lead to the same relative energies for different systems. This is not surprising since in this problem the relevent repulsion integrals enter into the molecular integrals J, K, and / in such a manner that they largely cancel out in the expression for total electronic energy. Since a change in the degree of hybridization merely leads to a change in the values of all the repulsion (22) (a) L. Pauling, "The Nature of the Chemical Bond," 3rd Ed., Cornell University Press, Ithaca, N. Y., 1960; (b) A. B. F. Duncan.

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Some mixed bis(morpholine-4-dithiocarbamato-S,S′)antimony(III) complexes [(OC 4 H 8 NCS 2 ) 2 SbL] with oxygen or sulfur donor ligands [L = -OOCCH 3 (1), -OOCC 6 H 5 (2), -SOCCH 3 (3), -SCH 2 COOH (4), -OOCC 6 H 4 (OH) (5), -SCH 2 CH 2 CH 3 (6), -OC 6 H 5 (7), ½ -SCH 2 CH 2 S-(8)] have been synthesized by reacting the chloro-bis(morpholine-4-dithiocarbamato-S,S′)antimony(III) with corresponding oxygen or sulfur donor ligands in 1:1 or 2:1 stoichiometries. These have been characterized by melting point, molecular weight determination (cryoscopically), antimony (iodometrically) and sulfur (gravimetrically) estimation, elemental analyses (C, H and N), UV-visible, FT-IR, far IR, multinuclear NMR ( 1 H and 13 C)], TG/DTA analysis, ESI-mass and powder X-ray diffraction studies. The splitting of the strong band observed at 1046-1066 cm À1 due to υ(C-S) indicated anisobidentate mode of binding of the dithiocarbamate group, which was further supported by a 13 C NMR signal appearing at around δ 200 due to NCS 2 moiety. The base peak observed at m/z 444.9 supports the strong chelating nature of the morpholine-4-dithiocarbamate compared to the other hetero ligands used. TGA revealed that, complexes 21 and 4 were decomposed in three steps; also 6 was decomposed in two steps, followed by the formation of Sb 2 S 3 . The results obtained by antimicrobial screening tests indicate that complex 3 showed a maximum zone of inhibition (20 mm) against Trichoderma ressie at a concentration of 200 μg ml À1 . Complexes 2, 3 and 8 are most active (zone of inhibition (ZI) 17-20 mm) against both of the fungal species Aspergillus niger and Trichoderma ressie as well as complex 4 (ZI 17 mm) and 6 (ZI 18 mm) against Trichoderma ressie.