Polynuclear nickel (II) and copper (II) complexes of hexaazamacrocycles incorporating pairs of diethylenetriamine subunits separated by aromatic spacers

Abstract

A series of Ni(II) and Cu(II) complexes of the hexaaza macrocycles, 3,6,9,17,20,23-hexaazatricyclo[23.3.1.1 11,15]triaconta-1(29),11(30),12,14,25,27-hexaene (L 1) and 3,6,9,16,19,22-hexaazatricyclo[22.2.2.2 11,14]triaconta-1(26),11(29),12,14(30),24(28),25-hexaene (L 2), have been prepared and the crystal structures determined for [Ni 2L 1(O 2CCH 3) 2(H 2O) 2](ClO 4) 2 ( 1), [Ni 2L 2(DMF) 6](ClO 4) 4 · 2H 2O ( 2), {[Cu 2L 2Br(O 2CCH 3)](ClO 4) 2} n ( 3), [Cu 2L 2(μ-CO 3)(H 2O) 2] 2(ClO 4) 4 · 8H 2O ( 4), [Cu 2L 2(O 2CCH 3) 2](BF 4) 2 ( 5), and [Cu 2L 1(μ-imidazolate)Br] 2Br 4 · 6H 2O ( 6). In these complexes, two metal centers are bound per ligand; in 1 and 3– 6, the N 3 subunits of L 1 or L 2 coordinate meridionally to the metal centers, whilst in 2, each N 3 subunit in L 2 adopts a facial mode of coordination. The binuclear cations in 1 and 2 have chair-like conformations, with the distorted octahedral Ni(II) coordination spheres completed by terminal water and a bidentate acetate ligand in 1 and three DMF ligands in 2. The Cu(II) centers in 3– 6 generally reside in square planar environments, although a weakly binding ligand enters the coordination sphere in some cases, generating a distorted square pyramidal geometry. The binuclear [Cu 2L 2] 4+ units in 3, 4 and 5 adopt similar bowl-shaped conformations, stabilized by H-bonding interactions between pairs of amine groups from L 2 and a perchlorate or tetrafluoroborate anion. In 3, the binuclear units are linked through acetate groups, bridging in a syn- anti fashion, to produce a zig-zag polymeric chain structure, whilst 4 incorporates a tetrameric cation consisting of two binuclear units linked via a pair of carbonate bridges. Compound 6 features an imidazolate bridge between the two Cu(II) centers bound by L 1. Pairs of [Cu 2L 1(μ-imidazolate)] 3+ units are then weakly linked through a pair of bromide anions.