U(III)-CN versus U(IV)-NC coordination in tris(silylamide) complexes.

Treatment of the metallacycle [UN*2(N,C)] [N* = N(SiMe3)2; N,C = CH2SiMe2N(SiMe3)] with [HNEt3][BPh4], [HNEt3]Cl, and [pyH][OTf] (OTf = OSO2CF3) gave the cationic compound [UN*3][BPh4] (1) and the neutral complexes [UN*3X] [X = Cl (3), OTf (4)], respectively. The dinuclear complex [{UN*(μ-N,C)(μ-OTf)}2] (5) and its tetrahydrofuran (THF) adduct [{UN*(N,C)(THF)(μ-OTf)}2] (6) were obtained by thermal decomposition of 4. The successive addition of NEt4CN or KCN to 1 led to the formation of the cyanido-bridged dinuclear compound [(UN*3)2(μ-CN)][BPh4] (7) and the mononuclear mono- and bis(cyanide) complexes [UN*3(CN)] (2) and [M][UN*3(CN)2] [M = NEt4 (8), K(THF)4 (9)], while crystals of [K(18-crown-6)][UN*3(CN)2] (10) were obtained by the oxidation of [K(18-crown-6)][UN*3(CN)] with pyridine N-oxide.

U-CN versus Ce-NC coordination in trivalent complexes derived from M[N(SiMe3)2]3 (M = Ce, U).

Reactions of [MN*3] (M = Ce, U; N* = N(SiMe3)2) and NR4CN (R = Me, Et, or (n)Bu) or KCN in the presence of 18-crown-6 afforded the series of cyanido-bridged dinuclear compounds [NEt4][(MN*3)2(μ-CN)] (M = Ce, 2a, and U, 2b), [K(18-crown-6)(THF)2][(CeN*3)2(μ-CN)] (2'a), and [K(18-crown-6)][(UN*3)2(μ-CN)] (2'b), and the mononuclear mono-, bis-, and tris(cyanide) complexes [NEt4][MN*3(CN)] (M = Ce, 1a(Et), and U, 1b(Et)), [NMe4][MN*3(CN)] (M = Ce, 1a(Me), and U, 1b(Me)), [K(18-crown-6)][MN*3(CN)] (M = Ce, 1'a, and U, 1'b), [N(n)Bu4]2[MN*3(CN)2] (M = Ce, 3a, and U, 3b), [K(18-crown-6)]2[MN*3(CN)2] (M = Ce, 3'a, and U, 3'b), and [N(n)Bu4]2[MN*2(CN)3] (M = Ce, 4a, and U, 4b). The mono- and bis(cyanide) complexes were found to be in equilibrium. The formation constant of 3'b (K3'b) from 1'b at 10 °C in THF is equal to 5(1) × 10(-3), and -ΔH3'b = 104(2) kJ mol(-1) and -ΔS3'b = 330(5) J mol(-1) K(-1).

Selectivity of azine ligands toward lanthanide(III)/actinide(III) differentiation: a relativistic DFT based rationalization.

Polyazines emerge as highly selective ligands toward actinide versus lanthanide separation. Electronic structures of several mono- and polyazine f-complexes of general formula MX3L (M(+3) = Ce, Nd, Eu, U, Am, and Cm; X = RCp(-) or NO3(-); L = N-donor ligand) related to Ln(III)/An(III) differentiation have been investigated using scalar relativistic ZORA/DFT calculations. In all cases, DFT calculations predict shorter An-N bonds than Ln-N ones whatever the azine used, in good agreement with available experimental data.