Harminder Singh et al ELECTRON SPIN RESONANCE, NUCLEAR QUADRUPOLE RESONANCE, REFLECTANCE AND MAGNETIC PARAMETERS OF COBALT (II) AND NICKEL (II) COMPLEXES USING DENSITY FUNCTIONAL THEORY Int J Cur Res Rev, Nov 2012 / Vol 04 (22) Page 12 IJCRR Vol 04 issue 22 Section: General Sciences Category: Research Received on: 14/09/12 Revised on: 26/09/12 Accepted on: 09/10/12 ELECTRON SPIN RESONANCE, NUCLEAR QUADRUPOLE RESONANCE, REFLECTANCE AND MAGNETIC PARAMETERS OF COBALT (II) AND NICKEL (II) COMPLEXES USING DENSITY FUNCTIONAL THEORY Harminder Singh 1 , A.K. Bhardwaj 2 , M.L. Sehgal 2 , Susheel K. Mittal 3 1 Lovely Professional University, Phagwara, India 2 Department of Chemistry, D.A.V. College, Jalandhar, India 3 School of Chemistry and Biochemistry, Thapar University, Patiala, India E-mail of Corresponding Author: smittal@thapar.edu ABSTRACT Density Functional Theory was used to calculate and correlate 14 ESR, NQR, Reflectance and Magnetic parameters of 20 Co +2 and Ni +2 complexes such as [CoX 4 ] 2- (X = F, Cl , Br ,I), [Co(OH 2 ) 4 ] 2+ , [Co(NCO) 4 ] 2- , [CoX 6 ] 4- (X = F, Cl), [NiX 4 ] 2- (X = Cl ,Br, I, NCO), [NiX 6 ] 4- (X=F, Cl ,Br, I) [Ni(H 2 O) 6 ] 2+ , [Ni(NH 3 ) 6 ] 2+ , [Ni(CH 3 NH 2 ) 6 ] 2+ , [Ni(NH 3 ) 4 (NCS) 2 ]. All computations were carried out in the gas phase using ADF2010.02 by applying Single Point, LDA, Default , Spin Orbit, Unrestricted, None, Collinear commands using DZ or TPZ basis sets. The complexes were optimized to obtain two ESR (g 11 , g 22 , g 33 , g iso , a 11 , a 22 , a 33 , A ten ) and three NQR parameters [, q 11 , q 22 , q 33 , NQCC]. Two Reflectance parameters [ complex, % covalent character] were calculated from g iso . In addition, five magnetic [ soc ,  t ,  net, t 2g electron delocalization and its constant k] and two more ESR [H^, ΔE hf ] parameters were calculated by combining the ESR and Reflectance data. We verified the Laplace equation using the NQR data. The delocalization parameter (k) and the reflectance parameter called Nephelauxetic ratio ( 35 ) were found to have almost the same values as both determine the covalence in complexes. The calculated values of parameters were found in agreement with their reported values. Keywords: DFT, ESR, NQR, Reflectance, Magnetism, Nephelauxetic ratio, delocalization parameter INTRODUCTION Effective Spin Hamiltonian (H^) is a mathematical expression that determines energy of an ESR transitions when an ESR active metal ion is surrounded by ligands in a definite geometry. It depends upon a number of ESR parameters [anisotropic and isotropic splitting factors (g 11 ,g 22 , g 33 , g iso ), hyperfine coupling constants( a 11 ,a 22 ,a 33 ,A ten )], NQR parameters [electric field gradient or efg (q 11, q 22 ,q 33 ), Nuclear Quadrupole Coupling Constant(Q)] * , total electronic spin (S), Bohr Magneton of both the electron ( e ) and the nucleus ( n ), nuclear spin quantum number (I), g n (nuclear magnetic ratio) * Q or e Q is the nuclear quadrupole moment. q Or e q is the electric field gradient and product of these quantities (e Q× e q= e 2 Qq) is nuclear quadrupole coupling constant (Q). and nature of surrounding nuclei having quadrupole moments(I1). No doubt, ESR studies on some biologically important (1-2) Co +2 and catalytically (3) suitable Ni +2 complexes has already been reported, yet a correlation of their ESR, NQR, Reflectance and Magnetic parameters with the help of a software is rarely found in the literature. With certain commands, the software gave five ESR and NQR parameters. They were together used to calculate two more ESR parameters [effective spin Hamiltonian (H^) and hyperfine coupling energy (E hf )]. The g iso parameter was further correlated to two Reflectance parameters [spin orbit coupling constant ( complex ), %