Madeleine Helliwell’s research while affiliated with University of Manchester and other places

Dichalcogenoimidodiphoshinato lead complexes, [Pb((EPⁱPr2)2N)2] (E=S, Se) have been synthesized and characterized. The crystal structure of [Pb((SeSPⁱPr2)2N)2]), has been solved by single‐crystal X‐ray crystallography and reported. These complexes have been used as single‐source precursors to synthesise PbS and PbSe nanoparticles by hot‐injection method in an oleylamine/trioctylphosphine mixture. Powder X‐ray diffraction (p‐XRD) studies indicate that the nanoparticles produced are cubic. The optical band gaps estimated from the absorption spectrum fitting curve indicate significant tuning of the bulk band gap, blue shifting towards the visible region of the electromagnetic spectrum.

A Cu(II)-methylmalonate complex, (C3H7N6)4[Cu(II)(C4H4O4)2](H2O)4Cl2 (1) (where C3H7N6 = protonated melamine, C4H4O4 = methylmalonic acid), has been synthesized from aqueous media and its crystal structure was determined by single-crystal X-ray diffraction. The anionic Cu(II)-methylmalonate complex mediated formation of interesting supramolecular assemblies in the solid state by means of ionic interactions with protonated melamine. Moreover, other forces such as antielectrostatic H-bonding and π⁺–π⁺ interactions also play a crucial role in defining the final 3-D architecture of 1. An interesting stacking among protonated melamine molecules is studied by DFT calculations. Lattice water molecules and chlorides form various hydrogen bonds to take part in the self-assembly processes.

Lead sulfide and lead selenide thin films have been deposited from dichalcogenoimidophosphinate lead(II) complexes by AACVD. The synthesis of the precursors, [Pb((S)PPh2)2N)2] and [Pb((Se)PPh2)2N)2], are reported and the single crystal X-ray crystal structure of [Pb((S)PPh2)2N)2] determined. The films were characterised by p-XRD and SEM.

A calcium complex of N-phthaloylglycine (CaNPG) has been synthesized, and its crystal structure has been characterized by X-ray diffraction method. The FT-IR and fluorescence spectra for CaNPG have been recorded. N-phthaloylglycine ligand coordinates to Ca ion through the carboxylate O atoms as a bidentate ligand, and Ca ion does not play an important role in florescence spectrum. In order to support experimental findings and also investigate molecular surfaces, natural bond orbital (NBO) and nonlinear optical (NLO) optical properties of CaNPG complex, density functional theory calculations have been performed by hybrid B3LYP level. The very small energy gap between α-spin frontier molecular orbitals (FMOs) is demonstrated that CaNPG is a very reactive, chemically soft and optically active complex. The high stabilization energies of hyperconjugative interactions are also demonstrate that the charge mobility in CaNPG is very high. As consistent with above findings, first static hyperpolarizability of CaNPG has been found to be 10 times higher than pNA which is a NLO material.

[2.2]Paracyclophane-1,9-dienes substituted with n-octyl chains have been synthesised from the corresponding dithia[3.3]paracyclophanes using a benzyne induced Stevens rearrangement. The use of 2-(trimethylsilyl)phenyl trifluoromethanesulfonate and tetra-n-butylammonium fluoride as the in situ benzyne source gave significantly improved yields over traditional sources of benzyne and enabled the preparation of n-octyl substituted [2.2]paracyclophane-1,9-dienes on a multi-gram scale.

Six new tricationic Ir(III) complexes of cyclometalating ligands derived from 1-methyl-2-(2'-pyridyl)pyridinium or 1-methyl-4-(2'-pyridyl)pyridinium are described. These complexes of the form [Ir(III)(C^N)2(N^N)](3+) (C^N = cyclometalating ligand; N^N = α-diimine) have been isolated and characterised as their PF6(-) and Cl(-) salts. Four of the PF6(-) salts have been studied by X-ray crystallography, and structures have been obtained also for two complex salts containing MeCN and Cl(-) or two Cl(-) ligands instead of N^N. The influence of the position of the quaternised N atom in C^N and the substituents on N^N on the electronic/optical properties are compared with those of the analogous complexes where C^N derives from 1-methyl-3-(2'-pyridyl)pyridinium (B. J. Coe, et al., Dalton Trans., 2015, 44, 15420). Voltammetric studies reveal one irreversible oxidation and multiple reduction processes which are mostly reversible. The new complexes show intramolecular charge-transfer absorptions between 350 and 450 nm, and exhibit bright green luminescence, with λmax values in the range 508-530 nm in both aqueous and acetonitrile solutions. In order to gain insights into the factors that govern the emission properties, density functional theory (DFT) and time-dependent DFT calculations have been carried out. The results confirm that the emission arises largely from triplet excited states of the C^N ligand ((3)LC), with some triplet metal-to-ligand charge-transfer ((3)MLCT) contributions.

New blue or blue-green emitting iridium complexes have been synthesised with cyclometalating ligands derived from the 1-methyl-3-(2'-pyridyl)pyridinium cation. Efficient luminescence is observed in MeCN or aqueous solutions, with a large range of lifetimes in the μs region and relatively high quantum yields.

The chemical basis of the blue-black to pink-orange color change on cooking of lobster, due to thermal denaturation of an astaxanthin-protein complex, α-crustacyanin, in the lobster carapace, has so far been elusive. Here, we investigate the relaxation of the astaxanthin pigment from its bound enolate form to its neutral hydroxyketone form, as origin of the spectral shift, by analyzing the response of UV-vis spectra of a water-soluble 3-hydroxy-4-oxo-β-ionone model of astaxanthin to increases in pH, and by performing extensive quantum chemical calculations over a wide range of chemical conditions. The enolization of astaxanthin is consistent with the X-ray diffraction data of β-crustacyanin (PDB code: 1GKA) and whose crystals possess the distinct blue color. We find that enolate formation is possible within the protein environment and associated with a large bathochromic shift, thus offering a cogent explanation for the blue-black color and the response to thermal denaturation and revealing the chemistry of astaxanthin upon complex formation.

Cu(II) malonate complex with formula [Cu(C3H2O4)(C6H8N2)(H2O)](2)center dot 4H(2)O (1) [C6H8N2=2-picolylamine, C3H2O42-=malonate dianion] has been synthesized by mixing the reactants in their stoichiometric proportion and its crystal structure has been determined by single-crystal X-ray diffraction. In 1, monomeric neutral metal malonate units [Cu(C3H2O4)(C6H8N2)(H2O)] are interlinked with each other through hydrogen bonds, weak lone pair...pi and cuprophilic interactions to generate supramolecular dimers, which in turn further associated through hydrogen bonding to form infinite 1D chains. Water dimers, through series of hydrogen bonds and weak pi-stacking forces are found to be responsible for interconnection of 1D chains, which resulted in a 3D network. A density functional (DFT) study of the energetic features of several noncovalent interactions observed in the solid state have been analyzed and characterized using Bader's theory of "atoms-in-molecules". We also present here Hirshfeld surface analysis to investigate the close intermolecular contacts.

In the Purex process the selective uranium and plutonium extraction (and back extraction) from nitric acid into 30% tri butyl phosphate/ odourless kerosene is used to separate uranium and plutonium from each other and fission products in spent nuclear fuel recycle process. The presence of dibutyl phosphate (a tributyl phosphate degradation product) can inhibit the uranium (and plutonium) back extraction process by forming very stable solvent phase complexes with these actinides. However, the types of complexes that exist and prevent back extraction have not been fully characterised. A model compound approach has been adopted in which the co-ordination chemistry of UO22+ with a range of P=0 and P(0)OH ligands have been studied. These complexes have been characterised using spectroscopic techniques including IR, Raman, UV7 vis, 31NMR NMR, and by single crystal X-ray diffraction to assess their utility in identifying molecular species under extraction conditions. We report full structural characterisation of [UO2(NO3)2(MDPhP)2], [UO2(NO3)DppmO2] and [UO2(Dpp)2(MeOH)] where MDPhP = methyl diphenyl phosphine oxide, Dpp = diphenyl phosphate and DppmO2 = Bis(diphenyl phosphino) methane dioxide