A series of novel complexes of La(III) with substituted pyrazolines and mixed ligand complexes with these pyrazolines and thio-ligands have been synthesized and characterized by elemental analysis, molecular weight measurement, Fourier transform infra-red, 1 H and 13 C NMR spectroscopy. The particle/crystallite sizes were confirmed by powder X-ray diffraction, scanning electron microscopy and transmission electron microscopic techniques. Optical characterizations have been performed by electronic absorption and fluorescence emission spectroscopies in order to investigate their luminescence behaviour, which reveals fairly good quantum yield and fluorescence life time for some of the complexes. Thermal analyses such as thermogravimetric and differential thermal analysis indicate that these complexes are thermally stable at high temperature. Investigations pertaining to solid-state optical absorption spectra and photoelectron yield spectroscopy reveal that upon thermal annealing beyond 300°C, these compounds form dark-brown to black semiconducting materials with an optical band gap between 1.9 and 2.3 eV. Abbreviations: La-PyH : La-HPY = [La(C 15 H 12 N 2 OH) 2 (H 2 O)Cl]; La-PyH-dtc = [La(C 15 H 12 N 2 OH)(C 5 H 10 NS 2)(2H 2 O)Cl]; La-OCPy-xan: [La(C 15 H 12 N 2 OOCH 3)(C 2 H 5 OCS 2)(2H 2 O)Cl] ARTICLE HISTORY

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Praseodymium forms complexes easily with nitrogen and oxygen donor pyrazolines and also forms mixed ligand complexes with these pyrazolines and sulfur donor thio ligands such as dithiocarbamates and xanthates.

Mixed-Iigand complexes of antimony(III) of the types SbCl(C,5H, 2 N 2 OX)(C2oH, 3 ClNO 2 ) and Sb(C,5H, 2 N 2 OX) 2 (C 2 oH 13 ClNO 2 ) [where C, 5 H I2 N 2 O.X = 3(2'-hydroxyphenyl)-5-(4-X-phenyl)pyrazoline {where X = H, -CH 3 , -OCH 3 & -CI} and C 20 H| 3 C1NO 2 = 2-(N-salicylidine)-5-chlorobenzophenone] have been synthesized by the reaction of dichloroantimony(III) pyrazolines and chloroantimony(III) dipyrazolines with sodium salt of 2-(N-saIicylidine)-5-chIorobenzophenone in 1:1 molar ratio in anhydrous benzene at elevated temperature. These newly synthesized derivatives have been characterized by elemental analysis (C, H, N, Cl, and Sb), molecular weight measurement, UV-Visible spectroscopy and spectral studies [near and far IR , multinuclear NMR (Ή & I3 C) and FAB mass]. The bonding mode of pyrazolines and coordinationno. of antimony(III) in these derivatives are discussed. Antibacterial and antifungal potential of dichloroantimony(III) pyrazolines, chloroantimony(III) dipyrazolines and these newly synthesized derivatives are also discussed.

= deprotonated 3(2′hydroxyphenyl)-5-(4′-substituted phenyl) pyrazolines (X = H, CH 3 , OCH 3 , Cl), have been synthesized. These newly synthesized derivatives have been physicochemically characterized by elemental analysis (C, H, N, Cl and Fe), magnetic moment data, thermogravimetric analysis, molar conductance, cyclic voltammetry, spectral analysis (UV-visible, IR, far IR and fast atom bombardment mass spectrometry). Scanning electron microscopy, transmission electron microscopy and X-ray powder diffraction studies have been carried out for powdered samples, which show nanometric particles of these derivatives. Antibacterial and antifungal potential of free pyrazoline and some iron(III) complexes have been evaluated.