Tetranuclear Nickel(II) Complexes Composed of Pairs of Dinuclear LNi 2 Fragments Linked by Acetylenedicarboxylate, Terephthalate, and Isophthalate Dianions: Synthesis, Structures and Magnetic Properties

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)