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Issue 42, 2010
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A unique single carboxylate-bridged spin-frustrated chiral Mn(II) metallatriangle

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The reaction between Hmbpymca ligand (prepared in situ from the hydrolysis of 5-methyl-4-cyano-bispyrimidine with NaOH and further neutralization with 2 M HCl) and Mn(ClO4)2·4H2O in 1 : 1 molar ratio afforded the triangulo-trimanganese(II) complex [Mn3(bpymca)3(H2O)6]Cl3·6H2O 1. The chloride anions in this complex come from the HCl used in the neutralization process. The molecular structure of 1 consists of cationic molecular triangles [Mn3(μ-mbpymca)3(H2O)6]3+ with C3 symmetry, chloride anions and crystallization water molecules, all of them involved in an extensive network of hydrogen bonds, leading to a chiral network. Within the [Mn3(μ-mbpymca)3(H2O)6]3+ cations, seven-coordinated Mn(II) ions are bridged by both oxygen atoms of the carboxylate groups and exhibit a MnO5N2 compressed pentagonal bipyramidal coordination environment. The temperature dependence of the magnetic susceptibility shows the presence of weak antiferromagnetic interactions between MnII ions mediated by the carboxylate group of the mbpymca ligand and the existence of a 3D antiferromagnetic ordering below 4 K, which has its origin in the AF inter-trimer exchange interactions mediated by the strong hydrogen bonds present in the crystal of 1. The experimental magnetic susceptibility data above 7 K could be satisfactorily fitted to the theoretical analytical expression derived from the spin Hamiltonian H = −J(S1S2 + S1S3 + S2S3) with J = −0.782(3) cm−1 and g = 2.092(3). The model predicts a degenerate ground state with an S = 1/2, which is typical of triangular trimetallic spin frustrated systems containing metal with non-integer spins. DFT calculations were performed on the molecular structure as found in the solid state to support the experimental J value and the MnOcarbMn as the primarily exchange pathway.

Graphical abstract: A unique single carboxylate-bridged spin-frustrated chiral Mn(ii) metallatriangle

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The article was received on 06 Jun 2010, accepted on 26 Jul 2010 and first published on 04 Oct 2010

Article type: Paper
DOI: 10.1039/C0DT00613K
Citation: Dalton Trans., 2010,39, 10286-10292
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    A unique single carboxylate-bridged spin-frustrated chiral Mn(II) metallatriangle

    J. E. Perea-Buceta, A. J. Mota, J. Costes, R. Sillanpää, J. Krzystek and E. Colacio, Dalton Trans., 2010, 39, 10286
    DOI: 10.1039/C0DT00613K

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