title: The influence of halides in polyoxotitanate cages; dipole moment, splitting and expansion of d-orbitals and electron-electron repulsion.
abstract: Metal-doped polyoxotitanate (M-POT) cages have been shown to be efficient single-source precursors to metal-doped titania [TiO2(M)] (state-of-the-art photocatalytic materials) as well as molecular models for the behaviour of dopant metal ions in bulk titania. Here we report the influence halide ions have on the optical and electronic properties of a series of halide-only, and cobalt halide-'doped' POT cages. In this combined experimental and computational study we show that halide ions can have several effects on the band gaps of halide-containing POT cages, influencing the dipole moment (hole-electron separation) and the structure of the valance band edge. Overall, the band gap behaviour stems from the effects of increasing orbital energy moving from F to I down Group 17, as well as crystal-field splitting of the d-orbitals, the potential effects of the Nephelauxetic influence of the halides and electron-electron repulsion.
authors.affiliation: Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK. dsw1000@cam.ac.uk.
authors.forename: Schirin
authors.identifier: http://orcid.org/0000-0003-2624-7872
authors.initials: S
authors.lastname: Hanf
authors.affiliation: Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK. dsw1000@cam.ac.uk and School of Chemistry, University of Manchester, Oxford Road, Manchester, M13 9PL, UK. peter.matthews-2@manchester.ac.uk.
authors.forename: Peter D
authors.identifier: http://orcid.org/0000-0002-1362-8003
authors.initials: PD
authors.lastname: Matthews
authors.affiliation: Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK. dsw1000@cam.ac.uk and Institute of Materials Research and Engineering, Agency for Science, Technology and Research, 2 Fusionopolis Way, #08-03, Innovis, Singapore 138634, Singapore.
authors.forename: Ning
authors.initials: N
authors.lastname: Li
authors.affiliation: Institute of Materials Research and Engineering, Agency for Science, Technology and Research, 2 Fusionopolis Way, #08-03, Innovis, Singapore 138634, Singapore.
authors.forename: He-Kuan
authors.initials: HK
authors.lastname: Luo
authors.affiliation: Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK. dsw1000@cam.ac.uk.
authors.forename: Dominic S
authors.initials: DS
authors.lastname: Wright