A Comparison of the Self Assembled Frameworks of Three Cobalt(II) Coordination Compounds Bearing Dipicolinic Acid and Chelidamic Acid Ligands

A comparison of the self assembled lattice structures of unpublished coordination compound, [Co(dipic-OH)(OH2)(3)]center dot 1.5H(2)O (I) (where dipic-OH = 4-hydroxypyridine-2,6-dicarboxylate anion) and two novel cobalt(II)-containing coordination compounds, [Co(dipic)(pyz)(OH2)]center dot 0.25DMSO (II) (where dipic = dipicolinate anion and pyz = 2-(H-pyrazol-3-yl)-pyridine) and [Co(dipic-OH)(pyz)(OH2)]center dot H2O (III), have revealed remarkable distinctions in the hierarchy of their respective structures. The three dimensional (3-D) layered scaffold of compound I and the zigzag motifs of compounds II and III were found to have been created via unique hydrogen bonding patterns. Interestingly, compound III displayed a secondary 3-D channel framework, which was made possible by pi-pi stacking interactions. Spectroscopic studies yielded results that were consistent with the predicted behaviors of the various species of substituted ligands. X-ray crystallography revealed that compound I crystallized in the monoclinic space group C2/c with a = 14.734(3) a<<, b = 6.8664(14) a<<, c = 22.411(5) a<<, alpha = 90A degrees, beta = 90.097(7)A degrees, gamma = 90A degrees, V = 2267.4(8) a<<(3), Z = 8; compound II crystallized in the monoclinic space group P2(1)/n with a = 11.621(3) a<<, b = 12.391(3) a<<, c = 12.537(4) a<<, alpha = 90A degrees, beta = 102.148(11)A degrees, gamma = 90A degrees, V = 1764.8(8) a<<(3), Z = 4; and compound III crystallized in the orthorhombic space group Pccn with a = 21.899(2) a<<, b = 10.8845(11) a<<, c = 15.7093(13) a<<, alpha = 90A degrees, beta = 90A degrees, gamma = 90A degrees, V = 3744.4(6) a<<(3), Z = 8.