Di- and Tetra-Nuclear Copper(II), Nickel(II), and Cobalt(II) Complexes of Four Bis-Tetradentate Triazole-Based Ligands: Synthesis, Structure, and Magnetic Properties

Four bis-tetradentate N-4-substituted-3,5-{bis-[bis-N-(2-pyridinemethyl)]aminomethyl}-4H-1,2,4-triazole ligands, L-Tz1-L-Tz4 differing only in the triazole N-4 substituent R (where R is amino, pyrrolyl, phenyl, or 4-tertbutylphenyl, respectively) have been synthesized, characterized, and reacted with M-II(BF4)(2)center dot 6H(2)O (M-II = Cu, Ni or Co) and Co(SCN)(2). Experiments using all 16 possible combinations of metal salt and L-TzR were carried out: 14 pure complexes were obtained, 11 of which are dinuclear, while the other three are tetranuclear. The dinuclear complexes include two copper(II) complexes, [Cu-2(II)(L-Tz2)(H2O)(4)](BF4)(4) (2), [Cu-2(II)(L-Tz4)(BF4)(2)](BF4)(2) (4); two nickel(II) complexes, [Ni-2(II)(L-Tz1)(H2O)(3)(CH3CN)](BF4)(4)center dot 0.5(CH3CN) (5) and [Ni-2(II)(L-Tz4)(H2O)(4)](BF4)(4)center dot H2O (8); and seven cobalt(II) complexes, [Co-2(II)(L-Tz1)(mu-BF4)](BF4)(3)center dot H2O (9), [Co-2(II)(L-Tz2)(mu-BF4)](BF4)(3)center dot 2H(2)O (10), [Co-2(II)(L-Tz3)(H2O)(2)](BF4)(4) (11), [Co-2(II)(L-Tz4)(mu-BF4)](BF4)(3)center dot 3H(2)O (12), [Co-2(II)(L-Tz1)(SCN)(4)]center dot 3H(2)O (13), [Co-2(II)(L-Tz2)(SCN)(4)]center dot 2H(2)O (14), and [Co-2(II)(L-Tz3)(SCN)(4)]center dot H2O (15). The tetranuclear complexes are [Cu-4(II)(L-Tz1)(2)(H2O)(2)(BF4)(2)](BF4)(6) (1), [Cu-4(II)(L-Tz3)(2)(H2O)(2)(mu-F)(2)](BF4)(6)center dot 0.5H(2)O (3), and [Ni-4(II)(L-Tz3)(2)(H2O)(4)(mu-F-2)](BF4)(6)center dot 6.5H(2)O (7). Single crystal X-ray structure determinations revealed different solvent content from that found by microanalysis of the bulk sample after drying under a vacuum and confirmed that 5', 8', 9', 11', 12', and 15' are dinuclear while 1' and 7' are tetranuclear. As expected, magnetic measurements showed that weak antiferromagnetic intracomplex interactions are present in 1, 2, 4, 7, and 8, stabilizing a singlet spin ground state. All seven of the dinuclear cobalt(II) complexes, 9-15, have similar magnetic behavior and remain in the [HSHS] state between 300 and 1.8 K.