MAGNETIC INTERACTION IN THE KETO AND ENOL FORMS OF BINUCLEAR COPPER(II) COMPLEXES WITH A ROBSON-TYPE LIGAND - X-RAY CRYSTAL-STRUCTURE OF [CU-2(HL)(MU-N-3)(H2O)(C2H5OH)(CLO4)]

Three dicopper(II) complexes, [Cu-2(H(2)L)(mu-N-3)] (ClO4)(2) . 1/2C(2 )H(5)OH (1), [Cu-2(HL)(mu-N-3) (H2O) (C2H5OH) (ClO4)] (2) and [Cu-2(L) (mu-N-3)]. DMF (3) have been synthesized and characterized, where H,L is the pentadentate binucleating ligand 2,6-diformyl-4-methylphenol d i(benzoylhydrazone). Because of the existence of a hydrazide structure in the lateral chain, the ligand H(3)L can lose one, two or three hyd rogen atoms to form the keto form (1), mixed keto-enol form (2) or eno l form (3) of the binuclear copper(II) complexes, respectively. The cr ystal structure of 2 has been determined. Crystal data for 2: monoclin ic, space group P2(1)/c, a = 10.967(4), b = 7.684(2), c = 35.724(7) An gstrom,beta = 90.08 degrees,2=4. The analysis of variable-temperature magnetic susceptibility data indicates that there is an antiferromagne tic interaction between the copper(II) ions in these complexes with th e exchange parameters (2J) of -86.8 cm(-1) for 1, -132.4 cm(-1) for 2 and -176.7 cm(-1) for 3. The effect of a tautomeric isomeride on the m agnetic interaction was discussed in relation to molecular mechanics a nd CNDO/2 methods.