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

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posted on 2015-05-18, 00:00 authored by Moumita Pait, Antonio Bauzá, Antonio Frontera, Enrique Colacio, Debashis Ray
Carboxylato (R = tBu and Et) and carbonato bridges have been utilized for nickel­(II)-based aggregates [Ni4(μ-H2L)23-OH)21,3-O2CBut)2]­(NO3)2·H2O·2DMF (1·H2O·2DMF), Ni4(μ-hyHL)23-OMe)21,1-N3)21,3-O2CEt)2]·4H2O (2·4H2O), and Ni64-L)­(μ3-L)26-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/synsyn-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-synsyn-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 13 to explain the exchange interaction mechanisms and to support the magnitude and sign of the magnetic coupling constants between the NiII ions.