The structure and properties of tetrakis(tironato)cerate(IV), Na 12[Ce(C 6H 2O 2(SO 3) 2) 4]·9H 2O·6C 3H 7NO

Abstract

The title complex, prepared in 1 M NaOH, was crystallized from hot N, N-dimethylformamide/ ethanol solutions to give Na 12[Ce(C 6H 2O 2(SO 3) 2) 4]· 9H 2O·6DMF. The purple—brown crystals were examined by X-ray diffraction while inside quartz capillaries filled with DMF, (λ max 425 nm, ϵ 3664; λ sh 520 nm, ϵ 2240) and belong to space group Pbca, Z=8 with a=21.846(4), b=17.348(2), c=43.103- (6) Å, V=16.335(7) Å 3, D c=1.693 gcm t−3, D o=1.725 g cm t−3. Diffractometer data were collected using Mo Kα radiation to 2θ=43 o. For 7331 independent data with F o 2>3σ( F o 2) full matrix least squares refinement converged to unweighted and weighted R factors of 0.072 and 0.110, respectively, with a mixture of anisotropic and isotropic thermal parameters. The disordered DMF atom parameters were not refined. The structure consists of discrete monomeric Ce(C 6H 2S 2O 8) 4 12− units with 12 Na + counter cations and 10 H 2O molecules (two with half occupancy), and 6 DMF molecules of solvation filling up spaces between cations and anions. Cerium(IV) is in a general position with a coordination polyhedron close to the trigonal-faced dodecahedron, D 2d, with the angles between the two BAAB trapezoids of 2.3 o and 3.7 o. The average CeO(A) distance, 2.363(9) Å is longer than the average CeO(B) distance, 2.326(15)Å, with the reverse being true for one of the four tironato ligands. The average ring OCeO angle is 67.9(1) o. The cerium (IV) complex is found by cyclic voltammetry to undergo a quasi-reversible one-electron reduction (in strongly basic solution with excess tiron) with Ef=−497 mV vs. SCE, hence the ratio of the formation constants for tetrakis(tironato)cerate(IV) to that for tetrakis(tironato)cerate(III), K IV/ K III, is 10 33. Characterization of other tiron salts is reported.