Hexagonal-prismatic metal-organic cages and metal-organic polymers based on 1,1'-(5-methyl-1,3-phenylene)bis(1H-imidazole) ligand: Synthesis, structural characterization and magnetic property

A serial of hexagonal-prismatic metal organic cages (MOCs), [Co-6(OH)(2)(HCOO)(6)(pbim)(6)(H2O)(6)]<middle dot>SO4<middle dot>2HCOO<middle dot>8H(2)O (1<middle dot>2HCOO<middle dot>8H(2)O), [Ni-6(OH)(2)(HCOO)(6)(pbim)(6)(H2O)(6)]<middle dot>SO4<middle dot>2HCOO<middle dot>8H(2)O (2<middle dot>HCOO<middle dot>8H(2)O), {[Co-6(mu(3)-OH)(2)(mu-HCOO)(6)(pbim)(6)(H2O)(6)]<middle dot>ClO4}(3+)<middle dot>3HCOO<middle dot>solvent (3<middle dot>3HCOO<middle dot>solvent) and {[Ni-6(mu(3)-OH)(2)(mu-HCOO)(6)(pbim)(6)(H2O)(6)]<middle dot>ClO4}(3+)<middle dot>3HCOO<middle dot>solvent (4<middle dot>3HCOO<middle dot>solvent), was constructed from shuttlecock-like C-3-symmetric [M-3(mu(3)-OH) (mu-HCOO)(3)(H2O)(3)] (M = Co2+ or Ni2+) clusters generated in situ and a clip-like ligand 1,1'-(5-methyl-1,3-phenylene)bis(1H-imidazole) [pbim]. Interestingly, one SO42- or ClO4- anion was encapsulated in each cage of MOCs 1-4 through cooperative O-H & ctdot;O and C-H & ctdot;O hydrogen-bonding interactions. It was also found that those SO42--/ClO4--encapsulated MOCs, especially SO42--encapsulated MOC of Ni2+, displayed quite stability in methanol. Notably, when the crystal parent solution of MOC 1 was disturbed or MOC 1 was immersed in its parent solution for a long time, it resulted in the formation of a 2D coordination polymer [Co(pbim)(2)(H2O)(2)]<middle dot>2HCOO (5) with helical architecture. Unexpectedly, a novel 2D coordination polymer [Ni-4(pbim)(2)(CH3O)(4)(C6H5COO)(4)]<middle dot>2H(2)O (6<middle dot>2H(2)O) based on in-situ produced cubane-like [Ni-4(mu(3)-CH3O)(4)(mu-COO)(2)] cluster was solvothermally synthesized through the reaction of benzoic acid with relatively stable MOC 2 in DMF. Magnetic studies show that there are antiferromagnetic coupling exchanged by mixed hydroxyl/carboxylate bridges in shuttlecock-like [M-3(mu(3)-OH) (mu-HCOO)(3)(H2O)(3)] clusters of 1 and 2 or in cubane-like [Ni-4(mu(3)-CH3O)(4)(mu-COO)(2)] cluster of 6. The best fits for their magnetic behaviours gave the following coupling constants: J = -2.05 cm(-1) for 1, J = -1.74 cm(-1) for 2, and J(1) = -2.85 cm(-1) and J(2) = -4.01 cm(-1) for 6.