INTRAMOLECULAR LONG-RANGE EXCHANGE COUPLING IN DINUCLEAR COPPER(II) COMPLEXES WITH CU...CU SEPARATIONS GREATER-THAN 10-ANGSTROM

Magnetic long-range exchange coupling between two unpaired electrons o f two copper(II) ions in a square-pyramidal ligand environment (d(x2-y 2))(1), which are rigidly separated by > 10 Angstrom by an organic spa cer ligand (e.g., a mu-dicarboxylato ligand) has been systematically s tudied. The following complexes have been synthesized: [{LCu(OH2)}(2)( mu-terephthalato)](ClO4)(2) (1), [LCu(II)(OH2)(benzoato)]-(ClO4) (2), [{LCu(II)(NCS)}(2)(mu-terephthalato)]. 2CH(3)OH (3), [{LCu(II)(NCS)}(2 )-(mu-4,4'-oxybisbenzoato)]. 3CH(3)OH (4), I)(OH2)}(2)(mu-tetrafluorot erephthalato)](ClO4)(2) (5), {LCu(II)}(2)-(mu-tetrafluorobenzoato)(3)] (ClO4)(2) . 6H(2)O (6), OH2)}(2)(mu-biphenyl-4,4'-dicarboxylato)](ClO4 )(2) (7), u(II)(mu-biphenyl-4,4'-dicarboxylato)](n)(H2O)(2n) (8), {LCu (II)(NCS)}(2)(mu-biphenyl-4,4'-dicarboxylato)] (9), ns,trans-2,4-hexad ien-1,6-dicarboxylato)](ClO4)(2) (10) (L = 1,4,7-trimethyl-1,4,7-triaz acyclononane). Complexes 1, 2, 3, 4, and 6 have been characterized by X-ray crystallography; the structure of 1 has been described previousl y.([15]) Temperature-dependent magnetic susceptibility data for all co mplexes have been measured over the range 2.0-298 K. In complexes 2, 3 , 4, 6, 8, and 9 only very weak, if any. intermolecular antiferromagne tic or, in the case of 6, ferromagnetic coupling has been observed (\J \ less than or equal to cm(-1); H = - 2JS(1) . S-2, S-1 = S-2 = 1/2). In contrast, in complexes 5 (2 J = - 80 cm(-1)), 7 (2J = - 62 cm(-1)), and 10 (2J = - 100 cm(-1)) relatively strong intramolecular antiferro magnetic exchange coupling has been detected. The intramolecular Cu... Cu separation is 11.3 Angstrom in 5, 15.6 Angstrom in 7, and approxima tely 12.0 Angstrom in 10. These data demonstrate that intramolecular a ntiferromagnetic exchange coupling of considerable magnitude is possib le over distances >15 Angstrom, provided that the effective magnetic o rbitals are favorably aligned.