Coordination modes of a series of xylylene-bridged bis(1,4,7-triazacyclonon-1-yl) ligands: Synthesis, structure, and properties of nickel(II) and copper(II) complexes

Three bis(1,4,7-triazacyclonon-1-yl) ligands, 1,2-bis(1,4,7-triazacyclonon-1-ylmethyl) (L-1), 1,3-bis(1,4,7- triazacyclonon-1-ylmethyl)benzene (L-2), and 1,4-bis(1,4,7-triazacyclonon-1-ylmethyl)benzene (L-3), have been synthesized and their nickel(II) and copper(II) coordination chemistry investigated. Reaction of L-1 with excess Ni2+ ions affords a mixture of mononuclear and binuclear complexes, which are readily separated by cation exchange chromatography and crystallized as their perchlorate salts, [NiL1](ClO4)(2) (1) and [Ni2L1(H2O)(6)](ClO4)(4) . 4H(2)O (2). Similar treatment of L-2 and L-3 With excess Ni2+ ions affords exclusively the binuclear complexes [Ni2L2(H2O)(6)](ClO4)(4) (3) and [Ni3L3(H2O)(6)](ClO4)(4) . 3H(2)O (4), respectively. Reaction of all three ligands with excess Cu2+ ions also yields binuclear complexes, which may be isolated as neutral species, [Cu2LBr4]. xDMF (5, L = L-1, x = 1; 6, L = L-2, x = 0; 7, L = L-3, x = 0), Or as perchlorate salts, [Cu3L(H2O)(4)](ClO4)(4) . xH(2)O (8, L = L-1, x = 5; 9, L = L-2, x = 4; 10, L = L-3, x = 5). The mononuclear copper(II) complex of L-1 is prepared by reaction of L-1 with Cu2+ ions in a 1:1 mole ratio and isolated as its perchlorate salt, [CuL1](ClO4)(2) . 2H(2)O (11). The X-ray structures of complexes 1.H2O, 4, 5, and 11 have been determined. Compound 1.H2O crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 9.212(3) Angstrom, b = 17.805(8) Angstrom, 16.501(6) Angstrom, beta = 103.36(3)degrees, V = 2633(1) Angstrom(3), and Z = 4; 4, in the monoclinic space group P2(1)/c (No. 14) with a = 9.108(4) Angstrom, b = 25.857(5) Angstrom, c = 17.524(2) Angstrom, beta = 92.73(2)degrees, V = 4122(2) Angstrom(3), and Z = 4; 5, in the trigonal space group P3(1)21 (No. 152) with a = 10.889(5) Angstrom, c = 22.220(9) Angstrom, V = 2281(1) Angstrom(3), and Z = 3; and 11, in the monoclinic space group P2(1)/c (No. 14) with a = 9.45(1) Angstrom, b = 19.51(2) Angstrom, c = 15.10(1) Angstrom, beta = 96.93(8)degrees, V = 2763(4) Angstrom(3), and Z = 4. The nickel(II) and copper(ll) centers in the mononuclear complexes, 1.H2O and 11, lie in distorted octahedral environments, sandwiched by the two facially coordinating triamine rings of L-1 In complex 4, the two triamine rings of L-3 coordinate to separate nickel(II) centers, with the distorted octahedral coordination sphere about each of the metal centers being completed by water molecules. Similarly, in complex 5, the two triamine rings of L-1 bind separate copper(II) centers, with the distorted square pyramidal coordination sphere about each of the metal centers being completed by bromide anions.