Structural Variability of Cobalt(II) Coordination Polymers:  Three Polymorphs of Co3(TMA)2 [TMA = Trimesate, C6H3(COO)33-]

The aqueous reaction of cobalt(II) sulfate with trimesic acid (H3TMA = 1,3,5-benzenetricarboxylic acid) in the presence of a base yields complexes with the general formula of Co3(TMA)2. The identity of the base determines the specific structural characteristics of the complexes formed. When sodium hydroxide is used, a novel cobalt(II) coordination polymer, {[NaCo3(TMA)2(μ3-OH)](μ2-H2O)4(H2O)7·1.5H2O}n (1), is produced. Compound 1 contains NaCo3(OH) clusters connected via TMA ligands into 1D chains, and 1 crystallizes in the orthorhombic space group Pbca with a = 18.907(2) Å, b = 14.565(3) Å, c = 21.414(4) Å, and Z = 8. When triethylamine is used, the previously reported 1D zigzag chain coordination polymer, [Co3(TMA)2(H2O)12]n (2), is produced. When tetraethylammonium hydroxide is used, a trinuclear cobalt(II) complex, [Co3(TMA)2(H2O)14]·4H2O (3), is produced that has a structure identical to a segment of the zigzag chain of 2. Compound 3 crystallizes in the triclinic space group P1̄ with a = 6.6542(5) Å, b = 10.7114(7) Å, c = 12.3567(7) Å, α = 99.008(4)°, β = 102.553(6)°, γ = 107.344(7)°, and Z = 1.