Gavin Whittaker

A phenol–imidazole pro-ligand that can exist as a phenoxyl radical, alone and when complexed to copper(II) and zinc(II)

A new N,O-bidentate, phenol–imidazole pro-ligand 2′-(4′,6′-di-tert-butylhydroxyphenyl)-4,5-diphenyl imidazole (LH) has been designed, synthesised, and characterised. LH possesses no readily oxidisable position (other than the phenol) and involves o- and p-substituents on the phenol ring that prevent radical coupling reactions. LH undergoes a reversible one-electron oxidation to generate the corresponding [LH]˙+ radical cation that possesses phenoxyl radical character. The unusual reversibility of the [LH]/[LH]˙+ redox couple is attributed, at least in part, to a stabilisation of [LH]˙+ by intramolecular O–H⋯N hydrogen bonding. The compounds [CuL2] (1) and [ZnL2] (2) have been synthesised and characterised structurally, spectroscopically, and electrochemically. The crystal structures of 1·4DMF, 1·3MeOH, and 2·2.5MeCN·0.3CH2Cl2 have been determined and each shown to possess an N2O2-coordination sphere, the geometry of which varies with the nature of the metal and the nature of the co-crystallised solvent. 1 and 2 each undergo two, reversible, ligand-based, one-electron oxidations, to form, firstly, [M(L)(L˙)]+ and secondly [M(L˙)2]2+. The [M(L)(L˙)]+ (M = Cu, Zn) cations have been generated by both electrochemical and chemical oxidation and their [ML2][BF4] salts isolated as air-stable, dark green, crystalline solids. The UV/vis, EPR, and magnetic characteristics of these compounds are consistent with each cation involving an MII (M = Cu or Zn) centre bound to a phenoxide (L−) and a phenoxyl radical (L˙). The structural information obtained by a determination of the crystal structures of [CuL2][BF4]·2CH2Cl2 and [ZnL2][BF4]·2CH2Cl2·0.75pentane fully supports this interpretation. For each of these salts, there is a clear indication that the coordinated phenoxyl radical is involved in intramolecular π–π stacking interactions that parallel those in galactose oxidase.

Preparation and mechanism of formation of acicular goethite–magnetite particles by decomposition of ferric and ferrous salts in aqueous solution using microwave radiation

Abstract Acicular geothite–magnetite particles were prepared directly by microwave-driven hydrolysis of an aqueous solution of ferric and ferrous salts in the ratio Fe 3+ :Fe 2+ = 1:2, which is appropriate to magnetite. The experimental conditions that influence the shape and size of the particles were determined, and the mechanism of the formation of acicular particles is discussed.

A phenoxyl radical complex ofcopper(II)

A new N,O-bidentate pro-ligand (HL), [ML2] (M = Cu, Zn) and [CuL2][BF4] have been synthesised; [CuL2].4DMF and [CuL2][BF4].2CH2Cl2 have been crystallographically and spectroscopically characterised; these data indicate that [CuL2]+ cations are constituted as [Cu2+(L.)(L-)]+ and involve the phenoxyl radical L..

[Ni(L)(MeCN)][BF4]2 {L = 2,5,8-trithia[9],(2,9)-1,10-phenanthrolinophane} as a building block for the synthesis of binuclear nickel(II) complexes: X-ray crystal structure and magnetochemistry of a singly F-bridged nickel(II) dimer

The substitution reactions of the coordinated acetonitrile molecule in [Ni(L)(MeCN)][BF4]2 (1) {L = 2,5,8-trithia[9],(2,9)-1,10-phenanthrolinophane} with three potentially bidentate ligands L′ (L′ = N3−, 4,4′-bipyridine and F−) have been studied both in solution and in the solid state with the aim of verifying the potential of 1 as a starting material for the synthesis of [{Ni(L)}2L′]n+ (n = 3, 4) NiII-binuclear compounds. While the mononuclear [Ni(L)(N3)]BF4 complex was isolated in the solid state from the reaction of 1 with N3−, the binuclear [{Ni(L)}2F][BF4]3·MeCN·H2O and [{Ni(L)}2(4,4′-bipy)][BF4]4 compounds have been obtained from the reactions of 1 with F− and 4,4′-bipy, respectively. The first two complexes have been characterised by X-ray diffraction studies. In [Ni(L)(N3)]+, a distorted octahedral geometry is achieved at the NiII, with five sites occupied by the macrocyclic ligand L and the sixth by a monodentate azide group. In [{Ni(L)}2F]3+, two [Ni(L)]2+ units are bridged by a fluoride ligand to give only the second example of a singly F-bridged NiII dimer. The magnetisation of [{Ni(L)}2F][BF4]3·MeCN·H2O and of [{Ni(L)}2(4,4′-bipy)][BF4]4 has been recorded over the temperature range 1.8–300 K and indicates a significant antiferromagnetic exchange in the former.

In situ neutron diffraction studies of single crystals and powders during microwave irradiationElectronic supplementary information (ESI) available: Crystallographic data (powder and single crystal data) in cif format (CCDC reference numbers 185472???185475). See http://www.rsc.org/suppdata/fd/b2/b203379h/

Microwave dielectric heating has become an important method in chemical synthesis and materials processing over the past 15 years, and in the case of the reactions in solutions, there is a well-developed understanding of heating mechanisms and their influence on reaction rate. In the solid-state however, there is much less clarity, despite the advantages to be gained from better insight into the way in which such electromagnetic radiation may couple directly to charge carriers, accelerating reactions in good conductors. The related issue of the influence of microwave irradiation on biological systems, in particular, proteins, and the way in which this may pose hazards to health is similarly poorly understood despite the obvious relevance this may have to the current debate on the influence of electromagnetic radiation, in particular, microwave transmission, on human health. One reason for the paucity of fundamental insight in both fields is because most work has been performed with microwave equipment whose design is derived from that of a domestic oven, and which is not ideal for in situ studies of microwave driven processes. We have been developing new methods of irradiating a variety of solid samples while measuring structural parameters through a range of diffraction techniques, and describe apparatus that will enable X-ray or neutron scattering measurements to be performed on powders or single crystals under microwave irradiation with controlled power level. We also describe preliminary studies of a single crystal of the molecular solid aspirin, and a powder of the microwave-susceptible ionic material BaTiO3, during microwave irradiation.

Synthesis and characterisation of pendant-arm alcohol derivatives of [9]aneN2S and complexation with CuII ([9]aneN2S = 1-thia-4,7-diazacyclononane)†

An improved detosylation of 4,7-bis(tolyl-p-sulfonyl)-1-thia-4,7-diazacyclononane to give the free amine [9]aneN2S has been accomplished using Li/NH3 or HBr/acetic acid. Reaction of [9]aneN2S with ethylene oxide, 1,1-dimethylethylene oxide and methylenecyclohexane oxide in alcoholic solution affords the potentially pentadentate ligands 4,7-bis(hydroxyethyl)-1-thia-4,7-diazacyclononane (H2L1), 4,7-bis(2-hydroxy-2-methylpropyl)-1-thia-4,7-diazacyclononane (H2L2) and 4,7-bis(2-cyclohexyl-2-hydroxymethyl)-1-thia-4,7-diazacyclononane (H2L3) respectively. The copper(II) complexes of these ligands have been prepared and reveal that increasing the steric bulk on the pendant arm has a marked effect upon the resultant co-ordination chemistry. Thus, the complex of H2L1 shows a dimeric structure [Cu2(HL1)2][PF6]2 1 in which one of the hydroxy groups has been deprotonated. With H2L2 two complexes can be isolated: the dimer [Cu2(HL2)2][PF6]2 2 and the monomer [Cu(HL2)][PF6] 3. In contrast, with H2L3 only the monomer [Cu(HL3)][PF6] 4 could be isolated. Single crystal structures of 1 and 3 have been determined. Magnetochemistry of 1 indicates that the two copper(II) centres are essentially non-coupled.