DMF/H2O Volume Ratio Controls the Syntheses and Transformations of a Series of Cobalt Complexes Constructed Using a Rigid Angular Multitopic Ligand.

Through middle-temperature solvothermal reactions of CoCl2·6H2O with the rigid-angled ligand 3-(2′-pyridyl)-5-(4″'-pyridyl)-1,2,4-triazole (Hdpt24), we obtained the three cobalt complexes {[Co(dpt24)2)]3·4DMF·1.5H2O}n (1), {[Co(dpt24)2)]2·H2O}n (2), and Co(dpt24)2(Hdpt24)·H2O] (4) at N,N-dimethylformamide (DMF)/H2O volume ratios of 9:1, 1:1, and 0:1, respectively. Interestingly, 1 underwent transformations into 2, {[Co(dpt24)2]·0.5DMF}n (3), and 4 when treated with DMF/H2O at volume ratios of 1:1, 1:9, and 0:1, respectively. Moreover, 3 and 4 converted back to 1 in 9:1 DMF/H2O and to 2 in 1:1 DMF/H2O; 3 transformed into 4 in H2O and vice versa in 1:9 DMF/H2O. Structurally, 1 is a three-dimensional (3D) 2-fold interpenetrating distorted NbO-type complex, 2 possesses a two-dimensional layer metal-organic framework, 3 is a 3D 2-fold interpenetrating typical NbO-type complex, and 4 is a wheel-shaped mononuclear neutral complex. This approach, using a mixed solvent's component ratio to direct the syntheses and conversions of four cobalt complexes, provides unprecedented control for crystal engineering. [ABSTRACT FROM AUTHOR]