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)(BF(4))(2)·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(II)(2)(L(Tz2))(H(2)O)(4)(4) (2), Cu(II)(2)(L(Tz4))(BF(4))(2)(2) (4); two nickel(II) complexes, Ni(II)(2)(L(Tz1))(H(2)O)(3)(CH(3)CN)(4)·0.5(CH(3)CN) (5) and Ni(II)(2)(L(Tz4))(H(2)O)(4)(4)·H(2)O (8); and seven cobalt(II) complexes, Co(II)(2)(L(Tz1))(μ-BF(4))(3)·H(2)O (9), Co(II)(2)(L(Tz2))(μ-BF(4))(3)·2H(2)O (10), Co(II)(2)(L(Tz3))(H(2)O)(2)(4) (11), Co(II)(2)(L(Tz4))(μ-BF(4))(3)·3H(2)O (12), [Co(II)(2)(L(Tz1))(SCN)(4)]·3H(2)O (13), [Co(II)(2)(L(Tz2))(SCN)(4)]·2H(2)O (14), and [Co(II)(2)(L(Tz3))(SCN)(4)]·H(2)O (15). The tetranuclear complexes are Cu(II)(4)(L(Tz1))(2)(H(2)O)(2)(BF(4))(2)(6) (1), Cu(II)(4)(L(Tz3))(2)(H(2)O)(2)(μ-F)(2)(6)·0.5H(2)O (3), and Ni(II)(4)(L(Tz3))(2)(H(2)O)(4)(μ-F(2))(6)·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 [HS-HS] state between 300 and 1.8 K.