Intramolecular Long‐Range Exchange Coupling in Dinuclear Copper(II) Complexes with Cu…︁Cu Separations Greater than 10Å

Abstract

AbstractMagnetic long‐range exchange coupling between two unpaired electrons of two copper(II) ions in a square‐pyramidal ligand environment (d)1, which are rigidly separated by > 10 Å by an organic spacer ligand (e.g., a μ‐dicarboxylato ligand) has been systematically studied. The following complexes have been synthesized: [{LCu(OH2)}2(μ‐terephthalato)](ClO4)2 (I), [LCuII(OH2)(benzoato)](CIO4) (2), [{LCuII(NCS)}2(μ‐terephthalato)]‐2 CH3OH (3), [{LCuII(NCS)}2 (μ‐4,4′‐oxybisbenzoato)] · 3 CH3OH (4), [{LCuII(OH2)}2 (μ‐tetrafluoroterephthalato)](CIO4)2 (5), [{LCuII(OH2)}2{LCuII}2 (μ‐tetrafluorobenzoato)3](CIO4)2 · 6 H2O (6), [{LCuII(OH2)}2 (μ‐biphenyl‐4,4′‐dicarboxylato)](CIO4)2 (7), [LCuII(μ‐biphenyl‐4,4′‐dicarboxylato)]n (HZO)2n (8), [{LCuII(NCS)}2 (μ‐biphenyl‐4.4′‐dicarboxylato)] (9), [{LCu(OH2)}2, (μ‐trans,trans‐2,4‐hexadien1,6‐dicarboxylato)] (CIO4)2 (10) (L = 1,4,7‐trimethyl‐1,4,7‐triazacyclononane). Complexes 1, 2, 3, 4, and 6 have been characterized by X‐ray crystallography; the structure of 1 has been described previously.[15] Temperature‐dependent magnetic susceptibility data for all complexes 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 antiferromagnetic or, in the case of 6, ferromagnetic coupling has been observed (|J|⩽2cm−1; H= −2JS1 S2 S1 = S2 = 1/2). In contrast, in complexes 5 (2J=−80cm−1), 7(2J=−62cm−1), and 10 (2J = −100 cm−1) relatively strong intramolecular antiferromagnetic exchange coupling has been detected. The intramolecular Cu…︁Cu separation is 11.3Å in 5, 15.6 Å in 7, and approximately 12.0Å in 10. These data demonstrate that intramolecular antiferromagnetic exchange coupling of considerable magnitude is possible over distances > 15 Å, provided that the effective magnetic orbitals are favorably aligned.