Construction of porous Mn(II)-based metal–organic frameworks by flexible hexacarboxylic acid and rigid coligands
Solvothermal reactions of hexa[4-(carboxyphenyl)oxamethyl]-3-oxapentane (H6L) with rigid coligands, 2,2′-bipyridine (bipy), 1,4-bis-(1-imidazolyl)benzene (dib), and 4,4′-bis(1-imidazolyl)biphenyl (bibp) in the presence of manganese salts produce four porous Mn(II) metal–organic frameworks (Mn–MOFs), namely, Mn3(L)(bipy)2 (1), Mn3(L)(dib) (2), Mn3(L)(dib)(H2O)2 (3), and Mn6(L)2(bibp)1.5(H2O)54. Single crystal X-ray diffraction analyses reveal that 1–4 consist of trinuclear MnII subunits, which are further connected into four interesting nets, 4,4-connected pts net for 1, 4,6-connected fsc net for 2, and two novel nets for 3 and 4, by the synergistic effect of carboxylate groups and functionally complementary N-donor ligands. They exhibit high potential solvent accessible volumes of 35.0%, 33.5%, 45.1%, and 56.5% for 1–4, respectively. Magnetic studies indicate the presence of weak antiferromagnetic interactions between MnII centers in these compounds.