SOLID-STATE LITHIUM CYANOCOBALTATES WITH A HIGH-CAPACITY FOR REVERSIBLE DIOXYGEN BINDING - SYNTHESIS, REACTIVITY, AND STRUCTURES

Lithium pentacyanocobaltate coordination polymers with the formulas Li -3[Co(CN)(5)]. 4DMF (1, DMF = N,N-dimethylformamide) and Li-3[Co(CN)(5 )]. 2DMF (2) have been synthesized and structurally characterized. Bot h compounds react reversibly with O-2, forming 1:1 superoxo complexes. Compound 2 reacts more rapidly and has the highest reported capacity for a solid O-2 carrier (55 std cm(3)/g). In contrast to previously re ported dioxygen complexes of cyanocobaltates, the novel ability of 1 a nd 2 to react reversibly with O-2 is made possible by the interaction of Li cations with the nucleophilic N atoms of the cyanide ligands. Th is interaction effectively reduces the basicity of the cyanide ligands , decreasing the net electron density on Co(2+) and hence weakening th e charge-transfer interaction with O-2. The structure of 1 was determi ned from single-crystal X-ray diffraction measurements. It crystallize s in the triclinic space group P (1) over bar (no. 2) with a = 11.568( 7) Angstrom, b = 14.244(3) Angstrom, c = 8.118(3) Angstrom, alpha 97.4 4(2)degrees, beta = 103.00(4)degrees, gamma = 94.64(3)degrees, and Z = 2. Monocrystals of 2 suitable for X-ray structural analysis could not be grown, but the structure was solved ab initio from synchrotron pow der diffraction data by using a simulated-annealing technique. The mon oclinic cell. of 2 in space group P2(1)/n (no. 14) has cell parameters a 15.4455(8) Angstrom,b = 8.4216(4) Angstrom, c = 14.1505(8) Angstrom , beta = 97.780(3)degrees, and Z = 4.