Stable GaX2, InX2 and TlX2 radicals.

The chemistry of the Group 13 metals is dominated by the +1 and +3 oxidation states, and simple monomeric M(II) species are typically short-lived, highly reactive species. Here we report the first thermally robust monomeric MX2 radicals of gallium, indium and thallium. By making use of sterically demanding boryl substituents, compounds of the type M(II)(boryl)2 (M = Ga, In, Tl) can be synthesized. These decompose above 130 °C and are amenable to structural characterization in the solid state by X-ray crystallography. Electron paramagnetic resonance and computational studies reveal a dominant metal-centred character for all three radicals (>70% spin density at the metal). M(II) species have been invoked as key short-lived intermediates in well-known electron-transfer processes; consistently, the chemical behaviour of these novel isolated species reveals facile one-electron shuttling processes at the metal centre.

A stable two-coordinate acyclic silylene.

Simple two-coordinate acyclic silylenes, SiR(2), have hitherto been identified only as transient intermediates or thermally labile species. By making use of the strong σ-donor properties and high steric loading of the B(NDippCH)(2) substituent (Dipp = 2,6-(i)Pr(2)C(6)H(3)), an isolable monomeric species, Si{B(NDippCH)(2)}{N(SiMe(3))Dipp}, can be synthesized which is stable in the solid state up to 130 °C. This silylene species undergoes facile oxidative addition reactions with dihydrogen (at sub-ambient temperatures) and with alkyl C-H bonds, consistent with a low singlet-triplet gap (103.9 kJ mol(-1)), thus demonstrating fundamental modes of reactivity more characteristic of transition metal systems.

Is gluconate a good model for isosaccharinate in uranyl(VI) chemistry? A DFT study.

The geometries, relative energies and spectroscopic properties of a range of α-isosaccharinate complexes of uranyl(VI) are studied computationally using ground state and time-dependent density functional theory. The effect of pH is accommodated by varying the number of water and hydroxide ligands accompanying isosaccharinate in the equatorial plane of the uranyl unit. For 1 : 1 complexes, the calculated uranyl ν(asym) stretching frequency decreases as pH increases, in agreement with previous experimental data. Three different isosaccharinate chelating modes are studied. Their relative energies are found to be pH dependent, although the energetic differences between them are not sufficient to exclude the possibility of multiple speciation. At higher pH, the uranyl-ligand interactions are dominated more by the equatorial OH(-) than by the organic ligands. Calculated electronic excitation energies support experiment in finding the lowest energy transitions to be ligand → metal charge transfer. (13)C NMR chemical shifts are calculated for the coordinated isosaccharinate in the high pH mimics, and show good agreement with experimental data, supporting the experimental conclusion that the five-membered chelate ring is favoured at high pH. The effect of increasing the isosaccharinate concentration is modelled by calculating 1 : 2 and 1 : 3 uranyl : α-isosaccharinate complexes. Comparison of the results of the present study with those from our closely related investigation of uranyl(VI)-D-gluconate complexes (Dalton Transactions 40 (2011) 11248) reveals strong similarities in structure, bonding, coordination geometry and electronic excitations, but also differences in ΔG for key ligand replacement reactions, suggesting that caution should be exercised when using gluconate as a thermodynamic model for isosaccharinate in uranyl(vi) chemistry.

Computational investigation of the speciation of uranyl gluconate complexes in aqueous solution.

The geometries, relative energies and spectroscopic properties of a range of D-gluconate complexes of uranyl(VI) are studied computationally using density functional theory. The effect of pH is accommodated by varying the number of water and hydroxide ligands accompanying gluconate in the equatorial plane of the uranyl unit. For 1 : 1 complexes, the calculated uranyl ν(asym) stretching frequency decreases as pH increases, in agreement with previous experimental data. Three different gluconate chelating modes are studied. Their relative energies are found to be pH dependent, although the energetic differences between them are not sufficient to exclude the possibility of multiple speciation. (13)C NMR chemical shifts are calculated for the coordinated gluconate in the high pH mimics, and show good agreement with experimental data, supporting the experimental conclusion that the six-membered chelate ring is favoured at high pH. Attempts to improve the description of the aqueous environment via the addition of second solvation shell water molecules resulted in significantly worse agreement with experiment for ν(asym). The effect of increasing the gluconate concentration is modelled by calculating 1 : 2 and 1 : 3 uranyl : D-gluconate complexes.

Group 3 and lanthanide boryl compounds: syntheses, structures, and bonding analyses of Sc-B, Y-B, and Lu-B σ-coordinated NHC analogues.

Reaction of [Ln(CH(2)SiMe(3))(2)(THF)(n)][BPh(4)] (Ln = Sc, Y, Lu ; n = 3, 4) with Li{B(NArCH)(2)}(THF)(2) (Ar = 2,6-C(6)H(3)(i)Pr(2)) formed the first group 3 and lanthanide boryl compounds, Sc{B(NArCH)(2)}(CH(2)SiMe(3))(2)(THF) and Ln{B(NArCH)(2)}(CH(2)SiMe(3))(2)(THF)(2) (Ln = Y, Lu), which contain two-center, two-electron Ln-B σ bonds. All of these systems were crystallographically characterized. Density functional theory analysis of the Ln-B bonding found it to be predominantly ionic, with covalent character in the σ-bonding Ln-B HOMO.