Abstract
The tetranuclear nickel(II) complexes [(LNi^II^~2~)~2~(acetylenedicarboxylate)][BPh~4~]~2~ (2[BPh~4~]~2~), [(LNi^II^~2~)~2~(terephthalate)][BPh~4~]~2~ (3[BPh~4~]~2~), and [(LNi^II^~2~)~2~(isophthalate)][BPh~4~]~2~(4[BPh~4~]~2~), where L^2–^ represents a macrocyclic hexaaza‐dithiophenolate ligand, have been synthesized and characterised by UV/Vis spectroscopy, IR spectroscopy, X‐ray crystallography, and magnetic susceptibility measurements. Each dicarboxylate dianion acts as a quadridentate bridging ligand linking two bioctahedral LNi~2~ units via μ~1,3~‐bridging carboxylate functions to generate discrete [(LNi^II^~2~)~2~(dicarboxylate)]^2+^ dications with a central LNi~2~(O~2~C–R–CO~2~)Ni~2~L core. The structures differ mainly in the distance between the center of the Ni···Ni axes of the isostructural LNi~2~ units (8.841(1) Å in 2[BPh~4~]~2~, 10.712(1) in 3[BPh~4~]~2~, and 9.561(1) in 4[BPh~4~]~2~) and the tilting angle between the two Ni~2~O~2~ planes (86.3° in 2[BPh~4~]~2~, 58.2° in 3[BPh~4~]~2~, 20.9° in 4[BPh~4~]~2~). Magnetic susceptibility measurements on the complexes over the range 2.0–295 K reveal the presence of weak ferromagnetic exchange interactions between the Ni^II^ ions within the dinuclear subunits with values for the magnetic exchange constant J~1~ of 23.1(5), 18.1(5), and 14.2(5) cm^–1^ for 2[BPh~4~]~2~, 3[BPh~4~]~2~, and 4[BPh~4~]~2~, respectively (H = –2__J__S~1~S~2~). The magnitude of the exchange interaction J~2~ across the dicarboxylate bridges is in all cases less than 0.1 cm^–1^, suggesting that no significant interdimer exchange coupling occurs in 2[BPh~4~]~2~–4[BPh~4~]~2~. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)