A New Family of Ni4 and Ni6 Aggregates from Self-Assembly of [Ni2] Building Units: Role of Carboxylate and Carbonate Bridges

Abstract

[eng] Carboxylato (R = tBu and Et) and carbonato bridges have been utilized for nickel(II)-based aggregates [Ni4(μ-H2L)2(μ3- OH)2(μ1,3-O2CBut)2](NO3)2·H2O·2DMF (1·H2O·2DMF), Ni4(μ-hyHL)2(μ3-OMe)2(μ1,1-N3)2(μ1,3-O2CEt)2]·4H2O (2·4H2O), and Ni6(μ4-L)(μ3-L)2(μ6-CO3)(H2O)8](ClO4)·9H2O (3·9H2O). Building blocks [Ni2(μ-H2L)]3+, [Ni2(μ-hyHL)]3+, and [Ni2(μ-L)]+ originating from [Ni2(μ-H2L)]3+ have been trapped in these complexes. The complexes have been characterized by X-ray crystallography, magnetic measurements, and density functional theory (DFT) analysis. In 1, the magnetic interactions are transmitted through the μ3-phenoxido/μ3-hydroxido/syn− syn-tBuCO2 −, μ3-phenoxido/μ3- hydroxido, and double μ3-phenoxido/ double μ3-hydroxido bridges with J = +11.4 cm−1, J1 = −2.1 cm−1, and J2 = −2.8 cm−1, respectively. In 2, the interactions are ferromagnetic, with J1 = +27.5 cm−1, J2 = +20.62 cm−1, and J3 = +1.52 cm−1 describing the magnetic couplings through the μ- phenoxidoo/μ3-methoxido, μ-azido/μ3-methoxido, and μ3-methoxido/μ3-methoxido exchange pathways, respectively. Complex 3 gives J1 = −3.30 cm−1, J2 = +1.7 cm−1, and J3 = −12.8 cm−1 for exchange pathways mediated by μ-phenoxido/μ-carbonato, μ- alkoxido/μ-alkooxido/μ-syn−syn-carbonato, and the μ-phenoxido/μ-carbonato, respectively. Interestingly, 1 and 3 below 20 K and 35 K, respectively, show an abrupt increase of the χMT product to reach a magnetic-field-dependent maximum, which is associated with a slightly frequency-dependent out-of-phase alternating-current peak. DFT calculations have also been performed on 1−3 to explain the exchange interaction mechanisms and to support the magnitude and sign of the magnetic coupling constants between the NiII ions.