DINUCLEAR COPPER(II) COMPLEXES OF THE TETRADENTATE THIADIAZOLE LIGANDS BPMTD (2,5-BIS((2-PYRIDYLMETHYL)THIO)THIADIAZOLE) AND BPTD (2,5-BIS(2-PYRIDYLTHIO)THIADIAZOLE) - X-RAY STRUCTURES OF [CU-2(BPTD)(MU(2)-BR)(2)BR-2] AND [CU(BPMTD)CL-2](N) AND SPECTROSCOPIC, ELECTROCHEMICAL, AND MAGNETIC STUDIES

Dinuclear copper(II) complexes of two new, tetradentate (N-4), dinucle ating ligands 2,5-bis((2-pyridylmethyl)thio) thiadiazole (BPMTD) and 2 ,5-bis(2-pyridylthio) thiadiazole (BPTD) are described. The complexes [Cut(BPMTD) (mu 2-Cl)(2)Cl-2].2CH(3)OH.0.5CH(3)CN (1), [Cu-2(BPTD)(mu( 2)-X(2))(2)X(2)] (X = Cl(2), X = Br(3)), [Cu-2(BPTD)(mu(2)-OH)(NO3)(3) ] (4), and [Cu(BPMTD)Cl-2](n) (5) were isolated and the X-ray crystal structures of 3 and 5 determined. 3 crystallized in the monoclinic sys tem, space group C2/c, with a = 11.750(2) Angstrom, b = 14.235(3) Angs trom, c = 12.243(3) Angstrom, beta = 107.53(2)degrees, and Z = 4 (R = 0.031 and R(w) = 0.027). 5 crystallized in the orthorhombic system, sp ace group Pbca, with a = 15.088(4) Angstrom, b = 13.642(8) Angstrom, c = 8.986(4) Angstrom, and Z = 4 (R = 0.058 and R(w) = 0.054). In 3 two slightly distorted square-pyramidal copper(II) centers are bridged si multaneously by the diazole (N-2) and by two halogens in an axial equa torial arrangement. A preliminary structure for 1 indicates a similarl y bridged species, but Cu-Cu separations differ markedly (3.224(4) Ang strom (1); 3.556(2) Angstrom (3)), due to the different chelate ring s izes. Low room-temperature magnetic moments and variable-temperature m agnetic studies (4-300 K) indicate the presence of weak antiferromagne tic exchange in 1-3 and strong antiferromagnetic exchange in 4. For th e first time, the thiadiazole N-2 group is examined as a superexchange bridge between copper(II) centers and is found to propagate spin coup ling less effectively than pyridazine or phthalazine (thiadiazole < ph thalazine < pyridazine). Cyclic voltammograms for 1-3 in DMF are typic al for one-step, two-electron, quasi-reversible redox processes associ ated with the Cu-2(II)/Cu-2(I) redox couple. A most unusual 1-dimensio nal, zigzag, polymeric dinuclear structure exists in 5, with no involv ement of the thiadiazole nitrogens in bonding to copper, but with the peripheral pyridine rings linking the six-coordinate copper(II) center s, which involve an equatorial CuN2Cl2 donor set and long axial intera ctions with exocyclic sulfur atoms.