Construction of Metal–Organic Frameworks Based on Two Neutral Tetradentate Ligands

The solvothermal reaction of two new neutral tetradentate
ligands
with different bivalent metal salts gave seven metal–organic
frameworks (MOFs): [Co2(L1) (trans-chdc)2]·5H2O (1), [Zn2(L1)­(trans-chdc)­(NO2)2]·DMF (2), [Cd2(L1)­(trans-chdc)2]·4H2O (3), [Zn2(L1)­(1,4-bdc)2]·(H2O)3 (4), [Cd2(L1)­(1,4-bdc)2]·DMF·(solvent)x (5), [Co­(L2) (trans-chdc)­(H2O)]·1.5H2O (6),
[Co­(L2) (1,4-bdc) (H2O)] · 2H2O (7), (L1 = 1,1′-oxybis­[3,5-diimidazole]-benzene, L2
= 1,1′-oxybis­[3,5-dipyridine]-benzene, trans-chdc = trans-1,4-cyclohexanedicarboxylic acid,
1,4-bdc = 1,4-benzenedicarboxylate). These MOFs were prepared to examine
the effects of the core metal ion or organic ligand on the topology
and interpenetration form. The results show that the imidazole ligand
can rotate easily to coordinate to metal ions, while pyridine ligand
exhibits the weaker coordinative abilities, which may influence the
self-assembly. Compounds 1, 3, and 5 are three-dimensional (3D) frameworks with 2-fold interpenetrated
forms, whereas complex 4 shows a 3-fold interpenetrated
structure. Interestingly, compound 2 exhibits a 4-fold
interpenetration. Compound 6 features a two-dimensional
polymeric layer structure which exhibits a rare 2-fold interpenetrating
3D hms array if H-bonds are taken into account. For compound 7, the dinuclear cobalt secondary building unit (SBU) assembles
with mixed ligands L2 and 1,4-bdc to construct a 3D α-Po structure.