Abstract
Two series of isostructural double An(IV) and guanidinium carbonates were obtained as single crystals of the formula [C(NH2)3]6[An(CO3)5] · nH2O (An = Th, U, Np, and Pu; n = 3 (I) and 4 (II)) and examined by X-ray diffraction. For the Pu(IV) complexes, a = 10.490(2) A, b = 33.798(5) A, c = 10.519(2) A, β = 119.414(7)°, space group P21/c, Z = 4, R = 0.0369 (I) and a = 16.0895(18) A, b = 13.1458(14) A, c = 16.6951(18) A, β = 108.116(6)°, space group C2/c, Z = 4, R = 0.0171 (II). Both series of complexes contain the anions [An(CO3)5]6−, in which the An atom is coordinated to five chelating bidenate carbonate ions. The coordination polyhedra of the An atoms are distorted bicapped square antiprisms. Within both the series, the An-O bond lengths decrease monotonically only for the sequence Th-U-Np. The average Np-O and Pu-O bond lengths in both tri- and tetrahydrates are virtually equal. The IR and electronic absorption spectra of the complexes obtained were studied. The absorption bands due to the f-f transitions experience bathochromic shifts in the spectra of the U4+ and Pu4+ carbonate complexes and hypsochromic shifts in the spectra of the Np4+ complexes.
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