(μ-Hydroxo)bis(μ-acetato)dimetal complexes: structural and magnetochemical characterization of the Cr(III)Ni(II) and the Cr(III)Cr(III) species

The perchlorate salts of the cations [LCr(μ-OH)(μ-OOC·CH3)2NiL] 2+ (1) and [LCr(μ-OH)(μ-OOC·CH3)2CrL] 3+ (2), where L represents the macrocyclic tridentate amine 1,4,7-trimethyl-1,4,7-triazacyclononane have been characterized by X-ray crystallography. The core-structures consist of bioctahedra in which the metal ions (Cr III, Ni II in 1 and Cr III, Cr III in 2) are bridged by one hydroxo and two acetate groups. A moderate antiferromagnetic coupling (J=−18.5 cm−1; H=−2J S1·S2) has been evaluated for the Cr IIINi II pair 1 from the variable-temperature (2–290 K) SQUID measurements, thus revealing a spin doublet ground state. The doublet ground state has also been confirmed by EPR measurements (2–50 K). In 2 the Cr(III) centers are also antiferromagnetically coupled.