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)benzene (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 Ni 2+ ions affords a mixture of mononuclear and binuclear complexes, which are readily separated by cation exchange chromatography and crystallized as their perchlorate salts, [NiL 1 ](ClO 4 ) 2 ( 1 ) and [Ni 2 L 1 (H 2 O) 6 ](ClO 4 ) 4 · 4H 2 O ( 2 ). Similar treatment of L 2 and L 3 with excess Ni 2+ ions affords exclusively the binuclear complexes [Ni 2 L 2 (H 2 O) 6 ](ClO 4 ) 4 ( 3 ) and [Ni 2 L 3 (H 2 O) 6 ](ClO 4 ) 4 ·3H 2 O ( 4 ), respectively. Reaction of all three ligands with excess Cu 2+ ions also yields binuclear complexes, which may be isolated as neutral species, [Cu 2 LBr 4 ]· x DMF ( 5, L = L 1, x = 1; 6, L = L 2, x = 0; 7, L = L 3, x = 0), or as perchlorate salts, [Cu 2 L(H 2 O) 4 ](ClO 4 ) 4 · x H 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 Cu 2+ ions in a 1:1 mole ratio and isolated as its perchlorate salt, [CuL 1 ](ClO 4 ) 2 ·2H 2 O ( 11 ). The X-ray structures of complexes 1 ·H 2 O, 4, 5, and 11 have been determined. Compound 1 ·H 2 O crystallizes in the monoclinic space group P 2 1 / c (No. 14) with a = 9.212(3) Å, b = 17.805(8) Å, c = 16.501(6) Å, β = 103.36(3)°, V = 2633(1) Å 3, and Z = 4; 4, in the monoclinic space group P 2 1 / c (No. 14) with a = 9.108(4) Å, b = 25.857(5) Å, c = 17.524(2) Å, β = 92.73(2)°, V = 4122(2) Å 3, and Z = 4; 5, in the trigonal space group P 3 1 21 (No. 152) with a = 10.889(5) Å, c = 22.220(9) Å, V = 2281(1) Å 3, and Z = 3; and 11, in the monoclinic space group P 2 1 / c (No. 14) with a = 9.45(1) Å, b = 19.51(2) Å, c = 15.10(1) Å, β = 96.93(8)°, V = 2763(4) Å 3, and Z = 4. The nickel(II) and copper(II) centers in the mononuclear complexes, 1 ·H 2 O 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.