Influence of Noncovalent Interactions on the Magnetic Behavior of Three Isostructural Layered Manganese(II) Dicarboxylate-Based Coordination Polymers

Three new isostructural manganese coordination polymers, [Mn(H2O)(bpdc)] (1), [Mn(DMF)( bpdc)] (2), and [Mn-(DMSO)(bpdc)] (3) (bpdc = benzophenone-4,4'-dicarboxylate), have been successfully crystallized employing solvent variation. A single crystal X-ray diffraction study revealed that the three solids built of manganese polyhedron (square pyramidal in 1 and octahedral in 2 and 3) extended into two-dimensional sheets through manganese carboxylate coordination interaction. The packing of the layers, however, was greatly influenced through hydrogen bonding exerted by the coordinated solvent molecules (H2O, DMF, and DMSO) occupying the apical position of the manganese polyhedron. Low-temperature antiferromagnetic interactions arising due to coupling between the adjacent Mn2+ ions showed a strong correlation with the variation in the packing of the layers. First-principles calculations of the electronic structures of the solids in terms of singlet (S = 0 with Noodleman's Broken Symmetry) and triplet (S = 1) states showed the superexchange interaction energies to be -0.24, -0.12, and -0.18 eV, respectively, for 1, 2, and 3; the magnetic exchange coupling variation is in correspondence with the decrease in H-bonding interaction holding the layers: H2O < DMSO < DMF. The paper also postulates a mechanistic pathway for the observed crystal packing in terms of supramolecular condensation of 1:1 manganese dicarboxylate complexes through a combination of coordination and H-bonding interactions.