Showing papers by "Alexander J. Blake published in 2015"
TL;DR: Molecular uranium(IV)–arsenic complexes featuring formal single, double and triple U–As bonding interactions are reported, informing the understanding of the bonding of actinides with soft donor ligands and may be of use in future ligand design in this area.
Abstract: To further our fundamental understanding of the nature and extent of covalency in uranium-ligand bonding, and the benefits that this may have for the design of new ligands for nuclear waste separation, there is burgeoning interest in the nature of uranium complexes with soft- and multiple-bond-donor ligands. Despite this, there have so far been no examples of structurally authenticated molecular uranium-arsenic bonds under ambient conditions. Here, we report molecular uranium(IV)-arsenic complexes featuring formal single, double and triple U-As bonding interactions. Compound formulations are supported by a range of characterization techniques, and theoretical calculations suggest the presence of polarized covalent one-, two- and threefold bonding interactions between uranium and arsenic in parent arsenide [U-AsH2], terminal arsinidene [U=AsH] and arsenido [U≡AsK2] complexes, respectively. These studies inform our understanding of the bonding of actinides with soft donor ligands and may be of use in future ligand design in this area.
95 citations
TL;DR: Six compounds based on dipicolinic acid esters have been synthesized and Hirshfeld surfaces used to investigate the structure-directing effects of functional groups in controlling their solid-state behavior, demonstrating control of the solid- state structure of these dipiclinic acid derivatives through the choice offunctional groups.
Abstract: Six compounds based on dipicolinic acid esters have been synthesized and Hirshfeld surfaces used to investigate the structure-directing effects of functional groups in controlling their solid-state behavior. Compounds 1–4 are 4-bromo dipicolinic acid esters substituted with methyl, ethyl, propyl, and benzyl groups, respectively. The main structure-directing motif within 1–3 is a pairwise O···H interaction involving two carbonyl oxygen atoms and two aromatic H atoms. The introduction of bulky benzyl groups in 4 forces a significant change in the position of this interaction. Compounds 2 and 4 were used in Suzuki coupling reactions to prepare extended analogues 5 and 6, respectively, and their solid-state behavior was also studied using Hirshfeld surfaces. Extension of these dipicolinic acid esters results in the complete loss of the pairwise O···H interaction in 5, where the dominant structure-directing motifs are π-based interactions. However, the pairwise O···H interaction reappears for the more flexible 6, demonstrating control of the solid-state structure of these dipicolinic acid derivatives through the choice of functional groups.
65 citations
TL;DR: Surprisingly, the characterization data are overall consistent with charge transfer from uranium to the cyclo-P5 unit to give a cyclo -P5 charge state that approximates to a dianionic formulation.
Abstract: Reaction of [U(TrenTIPS)] [1, TrenTIPS=N(CH2CH2NSiiPr3)3] with 0.25 equivalents of P4 reproducibly affords the unprecedented actinide inverted sandwich cyclo-P5 complex [{U(TrenTIPS)}2(μ-η5:η5-cyclo-P5)] (2). All prior examples of cyclo-P5 are stabilized by d-block metals, so 2 shows that cyclo-P5 does not require d-block ions to be prepared. Although cyclo-P5 is isolobal to cyclopentadienyl, which usually bonds to metals via σ- and π-interactions with minimal δ-bonding, theoretical calculations suggest the principal bonding in the U(P5)U unit is polarized δ-bonding. Surprisingly, the characterization data are overall consistent with charge transfer from uranium to the cyclo-P5 unit to give a cyclo-P5 charge state that approximates to a dianionic formulation. This is ascribed to the larger size and superior acceptor character of cyclo-P5 compared to cyclopentadienyl, the strongly reducing nature of uranium(III), and the availability of uranium δ-symmetry 5f orbitals.
43 citations
TL;DR: This experimentally confirms the theoretically predicted excellent π-acceptor character of HAsAsH, and is tantamount to full reduction to the diarsane-1,2-diide form.
Abstract: The HAsAsH molecule has hitherto only been proposed tentatively as a short-lived species generated in electrochemical or microwave-plasma experiments. After two centuries of inconclusive or disproven claims of HAsAsH formation in the condensed phase, we report the isolation and structural authentication of HAsAsH in the diuranium(IV) complex [{U(TrenTIPS)}2(μ-η2:η2-As2H2)] (3, TrenTIPS=N(CH2CH2NSiPri3)3; Pri=CH(CH3)2). Complex 3 was prepared by deprotonation and oxidative homocoupling of an arsenide precursor. Characterization and computational data are consistent with back-bonding-type interactions from uranium to the HAsAsH π*-orbital. This experimentally confirms the theoretically predicted excellent π-acceptor character of HAsAsH, and is tantamount to full reduction to the diarsane-1,2-diide form.
40 citations
TL;DR: In this article, a range of thorium(IV)-halide, −amide, and −alkyl complexes supported by a sterically demanding triamidoamine ligand were reported.
22 citations
TL;DR: In this article, an unusual Hauser base cubane, a homoleptic and a base-stabilized magnesium complex featuring the same guanidinate ligands are reported.
Abstract: The synthesis of the guanidine MesN{C(NCy2)}N(H)Mes (LH; Mes = 2,4,6-Me3C6H2, Cy = cyclohexyl), and its use as a proligand for the synthesis of alkaline earth metal complexes are reported. Described herein are (i) an unusual Hauser base cubane, (ii) a homoleptic and a base-stabilized magnesium complex featuring the same guanidinate ligands, and (iii) the comparison of a series of alkaline earth (Mg, Ca, Sr, Ba) bis(guanidinate) complexes, which allows the opportunity to compare the changing trends in bonding as the Group is descended. The reaction between LH and MeMgI(OEt2)2 yields the Hauser base as a mixture of the tetramer [Mg4L4(μ3-I)4] (1a) and dimer [Mg2L2(μ-I)2(OEt2)2] (1b), and the reaction with two equivalents of MgnBu2 leads to the formation of four-coordinate [MgL2] (2), which features a square-planar geometry for the magnesium cation, or five-coordinate [MgL2(THF)] (3), depending on the solvent used. 1a is the first crystallographically-characterized cubane structure to consist of four LAeX (L = ligand, X = halide) units. The complexes [AeL2(THF)2] (Ae = Ca, 4; Ae = Sr, 5) and [BaL2] (6) were synthesized via redox transmetallation/ligand exchange reactions. Complex 6 is the first example of a homoleptic, monomeric barium complex of the NCN ligand family, with the structure stabilized by a number of barium-arene interactions in the solid state.
22 citations
TL;DR: The complexes reported herein have been characterised by X-ray diffraction, NMR, IR, UV/Vis, and Mössbauer spectroscopies, cyclic voltammetry, density functional theory calculations, and elemental analyses, which have enabled to elucidate the electronic structure of the complexes.
Abstract: Treatment of anhydrous FeX2 (X = Cl, Br, I) with one equivalent of bis(diphenylphosphino)ethane (dppe) in refluxing THF afforded analytically pure white (X = Cl), light green (X = Br), and yellow (X = I) [FeX2(dppe)]n (X = Cl, I; Br, II; I, III). Complexes I–III are excellent synthons from which to prepare a range of cyclopentadienyl derivatives. Specifically, treatment of I–III with alkali metal salts of C5H5 (Cp, series 1), C5Me5 (Cp*, series 2), C5H4SiMe3 (Cp′, series 3), C5H3(SiMe3)2 (Cp′′, series 4), and C5H3(But)2 (Cptt, series 5) afforded [Fe(Cp†)(Cl)(dppe)] 1Cl–5Cl, [Fe(Cp†)(Br)(dppe)] 1Br–5Br, and [Fe(Cp†)(I)(dppe)] 1I–5I (Cp† = Cp, Cp*, Cp′, Cp′′, or Cptt). Dissolution of 1I–5I in acetonitrile, or treatment of 1Cl–5Cl with Me3SiI in acetonitrile (no halide exchange reactions were observed in other solvents) afforded the separated ion pair complexes [Fe(Cp†)(NCMe)(dppe)][I] 1SIP–5SIP. Attempts to reduce 1Cl–5Cl, 1Br–5Br, and 1I–5I with a variety of reductants (Li-Cs, KC8, Na/Hg) were unsuccessful. Treatment of 1Cl–5Cl with LiAlH4 gave the hydride derivatives [Fe(Cp†)(H)(dppe)] 1H–5H. This report provides a systematic account of reliable methods of preparing these complexes which may find utility in molecular wire and metal–metal bond chemistries. The complexes reported herein have been characterised by X-ray diffraction, NMR, IR, UV/Vis, and Mossbauer spectroscopies, cyclic voltammetry, density functional theory calculations, and elemental analyses, which have enabled us to elucidate the electronic structure of the complexes and probe the variation of iron redox properties as a function of varying the cyclopentadienyl or halide ligand.
13 citations
TL;DR: The conclusion was made that β-1 was an example of a “disappearing polymorph”, which could initially be crystallized with ease and was used to seed the growth of the disappearing polymorph α-1.
Abstract: Recrystallization of [PdCl2([9]aneS2O)] ([9]aneS2O = 1-oxa-4,7-dithiacyclononane), 1, and [PtCl2([9]aneS2O)], 2, by diffusion of Et2O vapor into solutions of the complexes in MeNO2 yielded three phases of 1 and two phases of 2. The known phase of 1, herein designated α-1, was obtained under ambient conditions. A second phase, designated β-1, was initially also obtained by this method; however, following the advent of a third phase, γ-1, all subsequent efforts over a period of a year to crystallize β-1 yielded either γ-1, obtained by carrying out the recrystallization at elevated temperature, or α-1, commonly found throughout the study. This persistent absence of a phase which could initially be crystallized with ease led us to the conclusion that β-1 was an example of a “disappearing polymorph”. The first phase obtained of 2, designated α-2, was obtained by recrystallization under ambient conditions and is isomorphous and isostructural with α-1. The second phase β-2 was obtained by slight elevation of the...
13 citations
TL;DR: Space-filling diagrams and percent buried volume calculations indicated that aryl-substituted carbazolyl ligands offer a steric cleft better suited to stabilization of low-coordinate magnesium complexes.
Abstract: 1,3,6,8-Tetra-tert-butylcarbazol-9-yl and 1,8-diaryl-3,6-di(tert-butyl)carbazol-9-yl ligands have been utilized in the synthesis of potassium and magnesium complexes. The potassium complexes (1,3,6,8-tBu4carb)K(THF)4 (1; carb=C12H4N), [(1,8-Xyl2-3,6-tBu2carb)K(THF)]2 (2; Xyl=3,5-Me2C6H3) and (1,8-Mes2-3,6-tBu2carb)K(THF)2 (3; Mes=2,4,6-Me3C6H2) were reacted with MgI2 to give the Hauser bases 1,3,6,8-tBu4carbMgI(THF)2 (4) and 1,8-Ar2-3,6-tBu2carbMgI(THF) (Ar=Xyl 5, Ar=Mes 6). Structural investigations of the potassium and magnesium derivatives highlight significant differences in the coordination motifs, which depend on the nature of the 1- and 8-substituents: 1,8-di(tert-butyl)-substituted ligands gave π-type compounds (1 and 4), in which the carbazolyl ligand acts as a multi-hapto donor, with the metal cations positioned below the coordination plane in a half-sandwich conformation, whereas the use of 1,8-diaryl substituted ligands gave σ-type complexes (2 and 6). Space-filling diagrams and percent buried volume calculations indicated that aryl-substituted carbazolyl ligands offer a steric cleft better suited to stabilization of low-coordinate magnesium complexes.
12 citations
TL;DR: The structures of the four molecules have been fully characterized by single crystal and powder X-ray diffraction and overall, the geometrically shorter molecules 1 and 3 display close-packed structures, whereas the more extended 2 and 4 assemble into more open supramolecular systems.
Abstract: The crystallization of two dihydropyridyl molecules, 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl)benzene ([C40H24N10]·2DMF, 1·2DMF; DMF = dimethylformamide) and 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl)phenylbenzene ([C46H28N10]·2DMF, 3·2DMF), and their respective oxidized pyridyl analogues, 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)pyridyl)benzene ([C40H20N10], 2) and 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)pyridyl)phenylbenzene ([C46H24N10]·DMF, 4·DMF), has been achieved under solvothermal conditions. The dihydropyridyl molecules are converted to their pyridyl products via in situ oxidative dehydrogenation in solution. The structures of the four molecules have been fully characterized by single crystal and powder X-ray diffraction. The oxidized pyridyl products, 2 and 4, are more elongated due to aromatization of the dihydropyridyl rings at each end of their parent molecules 1 and 3, respectively. The solid-state supramolecular structures of the pyridyl molecules are distinct from the dihydro...
11 citations
TL;DR: A number of thermally stable, conjugated, blue-emitting vinylene bis(vinyl quinolinyl)benzene derivatives were prepared and three of them were characterised by single crystal X-ray crystallography as mentioned in this paper.
Abstract: A number of thermally stable, conjugated, blue-emitting vinylene bis(vinyl quinolinyl)benzene derivatives were prepared and three of them were characterised by single crystal X-ray crystallography. They exhibit blue to bluish-green emission (fluorescence and electroluminescence) depending on the substituents. Their effectiveness as electron transporters in red and green organic light emitting diodes (OLEDs) has been explored. The phenyl and naphthyl substituted compounds were found to be superior to Alq3 in OLEDs as electron transporters. The electron mobility of the parent molecule, phenyl, thienyl and naphthyl substituted compounds were determined to be 8.0 × 10−7, 3.3 × 10−6, 5.5 × 10−6 and 8.0 × 10−6 cm2 V−1 s−1 respectively. Lifetime measurements were carried out for the red and green fluorescent devices and compared with Alq3 as an electron transporter. Some vinylene bis(vinyl quinolinyl)benzene derivatives show significantly longer lifetimes than analogous devices made with Alq3 as the electron transport layer. Purple to dark blue emitting devices were achieved from two of the derivatives.
TL;DR: In this article, the same authors proposed a one-pot approach to the cyclisation of chiral N-heterocyclic carbene (NHC) ligand precursors (effectively three steps from commercial N-Boc-α-amino alcohols).
TL;DR: Chiral 2D and 3D metal-organic coordination polymers were synthesized by heating a solution of copper(ii) salts, 4,4´-bipyridine (bpy), and α-hydroxycarboxylic acids, viz., S-3,3-dimethyllactic (H2dml) or S- 3-phenyllactic(H2phl) acid, in a water-N,N´-dimethylformamide mixture as discussed by the authors.
Abstract: Chiral 2D and 3D metal-organic coordination polymers [Cu2(bpy)2(Hdml)2(HCOO)]-(HCOO)·2H2O (1) and [Cu(bpy)(Hphl)(HCOO)]·H2O (2) were synthesized by heating a solution of copper(ii) salts, 4,4´-bipyridine (bpy), and α-hydroxycarboxylic acids, viz., S-3,3-dimethyllactic (H2dml) or S-3-phenyllactic (H2phl) acid, in a water—N,N´-dimethylformamide mixture. The structures of compounds 1 and 2 were determined by single-crystal X-ray diffraction. Compound 2 was characterized by X-ray powder diffraction, IR spectroscopy, thermogravimetric analysis, and elemental analysis.
TL;DR: Large-scale central facilities such as Diamond Light Source fulfil an increasingly pivotal role in many large-scale scientific research programmes and continuing access to beamtime has now become a major priority for those who direct such programmes.
Abstract: Large-scale central facilities such as Diamond Light Source fulfil an increasingly pivotal role in many large-scale scientific research programmes. We illustrate these developments by reference to energy-centred projects at the University of Nottingham, the progress of which depends crucially on access to these facilities. Continuing access to beamtime has now become a major priority for those who direct such programmes.
TL;DR: In this article, a review of recent advances in high pressure studies of coordination complexes, many of which have been conducted at synchrotrons or other central facilities, is presented.
Abstract: The application of pressures of up to about 10 GPa may induce significant geometric, configurational, conformational and packing changes in molecular solids. This review highlights and describes recent advances in high pressure studies of coordination complexes, many of which have been conducted at synchrotrons or other central facilities. The main focus is on the wide range of geometric changes which occur with pressure. In some cases these changes have associated physical effects, and the review describes materials exhibiting negative linear compressibility, spin cross-over phenomena, magnetism and molecular conduction, as well as detailing the exciting possibilities for future developments in this area of research.
TL;DR: In this paper, the same authors proposed a one-pot approach to the cyclisation of chiral N-heterocyclic carbene (NHC) ligand precursors (effectively three steps from commercial N-Boc-α-amino alcohols).
Abstract: The amidoamines (S)-Ar1CONHCHRCH2NHAr2 [Ar1 = o-C6H4SO3H, R = Bn, iBu, iPr; Ar2 = 2,6-iPr2C6H4, 2,6-Et2C6H4, 2,4,6-Me3C6H2] cyclise to (S) 1-aryl-substituted 4,5-dihydro-1H-imidazolinium species with HC(OEt)3 in moderate-to-excellent yields on heating to 150–175 °C (nine examples, four isolated yields of 48 to >97 %). They are attained as their o-C6H4(SO3–)(CO2Et) salts. The latter are readily deprotonated to afford analytically pure (S) 1-aryl-substituted 4,5-dihydro-1H-imidazoles (imidazolines). The purification of the intermediate sulfonate salts is not always necessary, and analytically pure imidazolines are isolated by simple kugelrohr distillation (nine examples, 45–95 %) after basification. Imidazoline alkylation provides a library of (S)-N-alkylimidazolinium salts (23 examples, 74–97 %). As the initially required amidoamines are available in simple one-pot reactions, the overall approach constitutes a rather efficient approach to this useful family of chiral N-heterocyclic carbene (NHC) ligand precursors (effectively three steps from commercial N-Boc-α-amino alcohols; BOC = tert-butyloxycarbonyl).