The Solvent Effect on the Isotropic Hyperfine Interaction in Some Aliphatic Polyamine Copper(I1) Complexes V. G. K. M. Pisipati,"'? N. V. S. RaoS zyxwvu and V. Muralikrishnat V. S. Murthy and T. Kesavan zyxwvut Faculty of Physical Sciences, Nagarjuna University, Nagarjuna Nagar 522 5 10, India Department of Physics, I.I.T., Madras 600 036, India ESR and optical absorption studies are described for a number of copper(1I) chelates with aliphatic polyamines, exhibiting both square pyramidal and square bipyramidal coordination around the copper ion. The complexes studied were bis(N,N'-dimethylethylenediamine)copper(II) sulphate tetrahydrate, bis(N,N'-diethylethylenediamine)copper(II) nitrate, diaquosulphato(N,N,W,N'-tetramethylethylenedi- amine)copper(II) hydrate, dinitrato(N,N,N',N'-tetramethylethylenediamine)copper(II), dichloro(NJV,N',N'- tetramethy1ethylenediamine)copper (n) and dithiocyanato(N,NJV',iV-tetramethylethylenediamine)copper(II). The ESR measurements were carried out in methanol, dimethyl sulphoxide, dimethylformamide and pyridine, at room and liquid nitrogen temperatures. The molecular orbital coefficients were estimated assuming an zyxwvutsrq axial symmetry. The parameter x, proportional to the hyperfine constants shows a variation with the solvent for all these complexes. The x values in solution are lower than the corresponding average x values reported in the solid state for each complex. The solvent effect and the influence of zyx 4s character in the ground state are discussed. The x values, either calculated or reported, for a number of copper complexes for [40], [30, N], [ZO, 2N], [0,3N] and [4N] environments around copper(Il) are presented. INTRODUCTION The structure and bonding characteristics of copper(I1) chelates with different environments around the paramagnetic ion have been ~ t u d i e d ' ~ in order to deduce the nature of the molecular orbital (m.0.) coefficients. It was found that these parameters exhibit similar qualitative characteristics for substances with a similar type of environment around copper(II), irres- pective of the chemical structure of the ligand. Such studies carried out on copper(I1) complexes where the chemical environment around copper(I1) consisted of two oxygen and two nitrogen atoms resulting from tetradentate Schiff bases,'a6 or four nitrogens contri- buted from aliphatic polyamines,',* inferred qualita- tively similar m.0. coefficients. Ternary complexes of copper with 8-hydroxyquinoline and salicylic acid or substituted salicylic acids, involving three oxygens and one nitrogen atom in the copper(I1) coordination, exhibited similar characteristic m.0. coefficients inde- pendent of the chemical structure of the ligand? Further, Kwik et zyxwvutsrq u1.l' also reported that the m.0. coefficients of the copper complexes formed with 2,2'- bipyridyl or l,l0-phenanthroline and different amino acids (glycine, alanine, valine, tyrosing, serine, aspartic and glutamic acids), possessing a coordination of three nitrogens and one oxygen atom around copper(II), * Author to whom correspondence should be addressed. t Department of Physics. f Department of Chemistry. show similar qualitative characteristics, irrespective of the substitution on the ligand. The Abragam, Horowitz and Price' ' parameter, where zyxw x =the effective field per unpaired electron, z S, = the total spin of the ion, S(ri) = the delta function term and sZi =the spin of the ith electron, is found to be remarkably constant for a particular type of envi- ronment. Since unpaired electrons in d orbitals cannot contribute to x, it was proposed that the finite value of x results from a polarization of the inner filled s orbitals by the unpaired d electrons. This parameter z x, which is related to the hyperfine contact term, K, is negative and is considered to be nearly constant for a large number of compounds of the first row transition elements. McGarVey'* carried out extensive calcula- tions, mainly on single crystal data, and concluded that it can vary as much as 30%, depending on the ligand, the host lattice and the geometry of the chelate. Allen and S~ullane~.~ studied the nature of x for a number of tetradentate copper(I1) complexes with a cis [20,2N] environment, and concluded that x is constant with an average value of -3.918. In the case of aliphatic polyamine complexes of copper(I1) with [4N] coordination, an average value of -3.700 was rep~rted.'.~ We have calculated the values of x for [30, NI9 and [3N, 01 environments around copper(I1) from the availabie literature data (ESR and optical 0 Wiley Heyden Ltd, 1984 CCC-0030-4921/84/0022-0629$03.50 ORGANIC MAGNETIC RESONANCE, VOL. 22, NO. 10, 1984 629