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The extent and nature of covalency in actinide complexes is an important and complex question. There are two main mechanisms of covalency, namely overlap of orbitals or degeneracy of the energies of the ligand and actinide metal, and computational approaches can play a significant part in rationalising the relative importance of each. In this work, we use a suite of computational approaches including Natural Bond Orbitals (NBO), Quantum Theory of Atoms in Molecules (QTAIM) and Interacting Quantum Atoms (IQA) to probe these effects in [E[double bond, length as m-dash]U[double bond, length as m-dash]E]

Oxidation of Cs4[U(NCS)8] in different solvents results in two mixed-valent uranium compounds. Spectroscopic, magnetic and computational data support a unique [UIVUVUIV][UVI] oxidation state assignment in [U(DMF)8(μ-O)U(NCS)5(μ-O)U(DMF)7(NCS)][UO2(NCS)5].

2,6-Bis(2-quinolyl)-4(1H)-pyridone 1, a novel quinoline analogue of the well-known ligand 2-terpyridone, shows unusual fluorescence with a large Stokes shift and low energy emission. Pyridine-pyridone tautomerism is investigated by NMR and theoretical methods and indicates that the low energy emission is from the pyridine form. 1 reacts with Ag(I) salts to give a double helical Ag2N6 core showing a BLUE shift in fluorescence with respect to the free ligand, which has been characterised experimentally and theoretically as involving an unusual mixed MLCT/ILCT excited state and emission from a singlet state.

Oxidation of [Pt(II)Cl(terpy)]+ (terpy = 2,2’:6’,2”-terpyridine) has been attempted with several oxidizing agents and in different experimental conditions in order to obtain a Pt(IV) complex suitable for the conjugation to nanovectors to be used in drug delivery targeting for anticancer therapy. The best compromise in terms of yield and purity of the final complex was obtained by microwave-assisted reaction at 70 °C in 50% aqueous H2O2 for 2 h. Under these conditions the quantitative formation of [Pt(IV)Cl(OH)2(terpy)]+ was observed. Subsequent synthetic steps were i) functionalization of [Pt(IV)Cl(OH)2(terpy)]+ in the axial position with succinic anhydride to obtain [Pt(IV)Cl(OH)(succinato)(terpy)]+, and ii) reaction of the latter with nonporous silica nanoparticles (SNPs) with an external shell containing primary amino groups to obtain a nanovector able to transport the Pt(IV) antitumor prodrug in form of conjugate Pt-SNP. Finally, the antiproliferative activity and cell accumulation of [Pt(II)Cl(terpy)]+, [Pt(IV)Cl(OH)2(terpy)]+, and Pt-SNP conjugate were measured on three cancer cell lines. Despite highly effective accumulation of Pt-SNP into cells, a modest increase in activity was observed with respect to the molecular species. Further experiments showed that the Pt-SNP conjugate can release [Pt(II)Cl(terpy)]+ upon reduction, but this metabolite may undergo hydrolysis, and the resulting aquo complex could coordinate once again the free amino groups of the SNPs. In the resulting tetraamine form, the Pt(II) complex conjugated to the SNPs cannot completely exert its antiproliferative activity.

Ten cationic heteroleptic iridium(III) complexes, [Ir(emptz)2(N^N)](PF6) were prepared from a cyclometalated iridium bridged-chloride dimer involving two ethyl-4-methylphenylthiazole-5-carboxylate (emptz) ligands. One X-ray crystallographic study was undertaken where the ancillary N^N ligand was 4,7-diphenyl-1,10-phenanthroline and revealed the anticipated structure, showing a distorted octahedral coordination geometry at Ir(III). The complexes were visibly luminescent with modestly structured emission at 540-590 nm and lifetimes (60-340 ns) consistent with phosphorescence. TD-DFT calculations suggest that strong MLCT character contributes to the visible absorption characteristics, whilst the moderately structured emission profiles indicate a (3)MLCT/(3)IL admixture of states to the phosphorescence.

The anticancer activity of cisplatin is triggered by its formation of intrastrand adducts involving adjacent G residues of DNA. To obtain information on the different conformers that can be formed{,} carrier ligands such as 2{,}2[prime or minute]-bipiperidine{,} which provide large steric bulk near the platinum coordination plane and decrease the dynamic motion about the Pt-N7 bonds{,} were introduced ({"}retro-modelling{"} approach). In the present study we investigate the effect of cis-1{,}4-diaminocyclohexane (cis-1{,}4-DACH) on the formation{,} stability{,} and stereochemistry of (cis-1{,}4-DACH)Pt(ss-oligo) adducts (ss-oligo = d(GpG) with 3[prime or minute]- and/or 5[prime or minute]-substituents). Interesting features of this ligand{,} absent in previous retro-modelling studies{,} include the large bite angle (expected to impede the ease of interconversion between possible conformers){,} the presence of two protons on each nitrogen (a characteristic associated with antitumor activity){,} and the absence of chiral centres. The use of cis-1{,}4-DACH has made it possible to detect different conformers in a system containing a primary diamine carrier ligand associated with anticancer activity and to confirm the previous hypothesis that the coexistence of different conformers established in studies of retro models having relatively bulky ligands is not an artefact resulting from carrier-ligand bulk. Moreover{,} the data for the (cis-1{,}4-DACH)Pt(d(GpG)) and (cis-1{,}4-DACH)Pt(d(GGTTT)) adducts indicate that at a temperature close to the physiological one (40 [degree]C) HH1 and [capital Delta]HT1 conformers are present in comparable amounts. In contrast{,} at low temperature (close to 0 [degree]C) the equilibrium shifts dramatically toward the more stable HH1 conformer (for the (cis-1{,}4-DACH)Pt(d(TGGT)) adduct the HH1 conformer is always dominant{,} even at high temperature). Notably{,} (cis-1{,}4-DACH)PtCl2 (Kiteplatin) has been recently reinvestigated and found to be particularly active against colorectal cancer (including oxaliplatin-resistant phenotypes).

A chiral, tridentate, pyridyl-functionalised NHC pro-ligand, S-L(Me)-H[PF₆], has been prepared diastereoselectively via a five step synthesis starting from 1R,3S-diamino-1,2,2-trimethylcyclopentane. The S prefix refers to the stereochemistry of a methyl substituted stereogenic carbon in one of the pyridyl arms which is generated by a stereoselective BH4(-) reduction of an imine precursor. The ligand has been coordinated to Rh(I) and Ir(I) to give trigonal bipyramidal complexes of the type [M(κ(3)-N,C,N'-S-L(Me))(1,5-COD)]PF6 (M = Rh, Ir) as single diastereomers. A combination of spectroscopic and X-ray techniques confirm the stereoselective formation of the thermodynamically preferred endo,endo isomer. Similar reactions with R,S-L(Me)-H[PF₆] gave a mixture of endo,endo-[M(κ(3)-N,C,N'-S-L(Me))(1,5-COD)](+) and exo,exo-[M(κ(3)-N,C,N'-R-L(Me))(1,5-COD)](+). The absolute configuration at the metal is, therefore, solely dictated by the stereochemistry of the single methylpyridyl carbon. The observation of stereoselection extends to the square planar Ni(II) complex [Ni(δ-κ(3)-N,C,N'-S-L(Me))Cl](+) which is isolated as one (δ) of the two possible conformational isomers. DFT studies have been employed to explain the observed stereoselectivity with the configurations observed in the solid state being confirmed as those of lowest energy.

The solid-state structure of the known complex [Et4N][U(NCS)5(bipy)2] has been re-determined and a detailed spectroscopic and magnetic study has been performed in order to confirm the oxidation states of both metal and bipy ligand. Electronic absorption and infrared spectroscopy suggest that the uranium is in its +4 oxidation state and this has been corroborated by emission spectroscopy and variable temperature magnetic measurements, as well as theoretical calculations. Therefore the bipy ligands are neutral, innocent ligands and not, as would be inferred from just a solid state structure, radical anions., We thank TCD and MINECO (MAT2012-38318-C03), and EC for a Marie Curie-IEF (PIEF-GA-2011-299356 to GL) for funding this work.