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

A series of Ni(II) and Cu(II) complexes of the hexaaza macrocycles, 3,6,9,17,20,23-hexaazatricyclo[23.3.1.111,15]triaconta-1(29),11(30),12,14,25,27-hexaene (L1) and 3,6,9,16,19,22-hexaazatricyclo[22.2.2.211,14]triaconta-1(26),11(29),12,14(30),24(28),25-hexaene (L2), have been prepared and the crystal structures determined for [Ni2L1(O2CCH3)2(H2O)2](ClO4)2 (1), [Ni2L2(DMF)6](ClO4)4 · 2H2O (2), {[Cu2L2Br(O2CCH3)](ClO4)2}n (3), [Cu2L2(μ-CO3)(H2O)2]2(ClO4)4 · 8H2O (4), [Cu2L2(O2CCH3)2](BF4)2 (5), and [Cu2L1(μ-imidazolate)Br]2Br4 · 6H2O (6). In these complexes, two metal centers are bound per ligand; in 1 and 3–6, the N3 subunits of L1 or L2 coordinate meridionally to the metal centers, whilst in 2, each N3 subunit in L2 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 [Cu2L2]4+ units in 3, 4 and 5 adopt similar bowl-shaped conformations, stabilized by H-bonding interactions between pairs of amine groups from L2 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 L1. Pairs of [Cu2L1(μ-imidazolate)]3+ units are then weakly linked through a pair of bromide anions.

Graphical abstractMacrocyclic ligands incorporating two diethylenetriamine chelating subunits, separated by m-xylyl and p-xylyl spacers, form binuclear Ni(II) and Cu(II) complexes, which in some cases assemble into species with higher nuclearity.Figure optionsDownload full-size imageDownload as PowerPoint slide