Characterization of 3-D metal-organic frameworks formed through hydrogen bonding interactions of 2-D networks with rectangular voids by Co^II- and Ni^II-pyridine-2,6-dicarboxylate and 4,4'-bipyridine or 1,2-di(pyridyl)ethylene

Abstract

Pyridine-2,6-dicarboxylic acid (pdcH) and 4,4'-bipyridyl (4,4'-bpy) reacts under hydrothermal condition with Co(II)- or Ni(II)-nitrate to form very similar 2-D metal-organic framework (MOF) structures with the empirical formula [M(pdc)(4,4'-bpy)]·1/2MeOH (M = Co(II), 1 and Ni(II), 2). Compound 1 crystallizes in the monoclinic space group P2/n with a = 11.419(3) Å, b = 10.290(2) Å, c = 15.695(5) Å, β = 96.052(5)°, V = 1833.9(13) Å3, Z = 4, R1 = 0.046, WR2 = 0.125, and S = 1.059. Compound 2 also crystallizes in the monoclinic space group P2/n with a = 11.249(5) Å, b = 10.277(2) Å, c = 15.607(5) Å, β = 97.916(5)°, V = 1787.1(13) Å, Z = 4, R1 = 0.058, WR2 = 0.155, and S = 0.99. Rectangular voids of approximate dimension 8.9 × 5.5 Å formed in these two structures remain empty. Each 2-D sheet thus formed is stacked on top of each other with an intricate array of hydrogen bonding, showing a perpendicular distance of ~8.1 and 7.8 Å in 1 and 2, respectively. When 1,2-di(4-pyridyl)ethylene is used in place of 4,4'-bipyridyl to construct the MOFs, only Ni(II)-nitrate affords crystals whose structure differs greatly from that of 1 or 2. Here, 1,2-di(4-pyridyl)ethylene is not bonded to the metal but exists in the lattice in diprotonated form, and a hydrogen-bonded 3-D structure of discrete (dpeH)[Ni(pdc)]·5HO (3) units is formed. Compound 3 crystallizes in the monoclinic space group P2/n with a = 8.915(2) Å, b = 19.844(6) Å, c = 15.799(5) Å, β = 96.083(5)°, V = 2779.2(19) Å, Z = 4, R1 = 0.0391, WR2 = 0.0998, and S = 1.096. Interestingly, in 3, an acyclic trimeric water cluster is hydrogen bonded to the spacer and a free carboxylate O atom.