Lanthanide(III)/actinide(III) differentiation in mixed cyclopentadienyl/dithiolene compounds from X-ray diffraction and density functional theory analysis

摘要

Treatment Of [U(CP*)(2)Cl-2] with Na(2)dddt in thf afforded the "ate" complex [U(CP*)(2)Cl-(dddt)Na(thf)(2)] (1), and the salt-free compound [U(CP*)(2)(dddt)] (2) could be extracted from 1 with toluene (Cp* = eta-C5Me5; dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate). Reduction of 2 with Na(Hg) or addition of Na(2)dddt to [U(CP*)(2)Cl2Na(thf)(x)] in the presence of 18-crown-6 gave the first uranium(III) dithiolene compound, [Na(18-crown-6)(thf)(2)] [U(CP*)(2)(dddt)] (4). The dimeric lanthanide complexes [{Ln(Cp*)(2)(dddt)K(thf)(2)}(2)] (Ln = Ce (5), Nd (6)) were prepared by reaction of [Ln(Cp*)(2)Cl2K] with K(2)dddt, and in the presence of 15-crown-5, they were transformed into the cation-anion pairs [K(15-crown-5)2][Ln(Cp*)2(dddt)] (Ln = Ce (7), Nd (8)). The crystal structures of 2, 4(.)thf, 5-7, 7(.)0.5(pentane), and 8(.)0.5(pentane) were determined by X-ray diffraction analysis. Comparison of the structural parameters of the anions [M(CP*)(2)(dddt)](-) (M = U, Ce, Nd) revealed that the U-S and U-C(Cp*) distances are shorter than those expected from a purely ionic bonding model; the relatively small folding of the dddt ligand suggests that the interaction between the C = C double bond and the metal center is weak, in agreement with the NMR observations in solution. The structural data obtained from molecular geometry optimizations on the complexes [M(CP*)(2)(dddt)](-,0) (M = Ce, U) using relativistic density functional theory (DFT) calculations reproduce experimental trends. A detailed orbital analysis shows that the contraction of the metal-sulfur bond lengths when passing from [Ce(Cp*)(2)(dddt)] - to [U(CP*)(2)(dddt)](-) is partly related to the uranium 5f orbital-ligand mixing, which is greater than the cerium 4f orbital-ligand mixing. The comparison of the two [U(CP*)(2)(dddt)](-,0) species reveals a higher ligand-to-metal donation in the case of the U(IV) complex.