title: Influence of the Ion Coordination Number on Cation Exchange Reactions with Copper Telluride Nanocrystals.
abstract: Cu2-xTe nanocubes were used as starting seeds to access metal telluride nanocrystals by cation exchanges at room temperature. The coordination number of the entering cations was found to play an important role in dictating the reaction pathways. The exchanges with tetrahedrally coordinated cations (i.e., with coordination number 4), such as Cd(2+) or Hg(2+), yielded monocrystalline CdTe or HgTe nanocrystals with Cu2-xTe/CdTe or Cu2-xTe/HgTe Janus-like heterostructures as intermediates. The formation of Janus-like architectures was attributed to the high diffusion rate of the relatively small tetrahedrally coordinated cations, which could rapidly diffuse in the Cu2-xTe NCs and nucleate the CdTe (or HgTe) phase in a preferred region of the host structure. Also, with both Cd(2+) and Hg(2+) ions the exchange led to wurtzite CdTe and HgTe phases rather than the more stable zinc-blende ones, indicating that the anion framework of the starting Cu2-xTe particles could be more easily deformed to match the anion framework of the metastable wurtzite structures. As hexagonal HgTe had never been reported to date, this represents another case of metastable new phases that can only be accessed by cation exchange. On the other hand, the exchanges involving octahedrally coordinated ions (i.e., with coordination number 6), such as Pb(2+) or Sn(2+), yielded rock-salt polycrystalline PbTe or SnTe nanocrystals with Cu2-xTe@PbTe or Cu2-xTe@SnTe core@shell architectures at the early stages of the exchange process. In this case, the octahedrally coordinated ions are probably too large to diffuse easily through the Cu2-xTe structure: their limited diffusion rate restricts their initial reaction to the surface of the nanocrystals, where cation exchange is initiated unselectively, leading to core@shell architectures. Interestingly, these heterostructures were found to be metastable as they evolved to stable Janus-like architectures if annealed at 200 °C under vacuum.
authors.affiliation: Department of Nanochemistry, Istituto Italiano di Tecnologia (IIT) , via Morego, 30, 16163 Genova, Italy.|Dipartimento di Chimica e Chimica Industriale, Università degli Studi di Genova , via Dodecaneso, 31, 16146 Genova, Italy.
authors.forename: Renyong
authors.initials: R
authors.lastname: Tu
authors.affiliation: Department of Nanochemistry, Istituto Italiano di Tecnologia (IIT) , via Morego, 30, 16163 Genova, Italy.|State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology (WUT) , No. 122, Luoshi Road, Wuhan 430070, PR China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Xie
authors.affiliation: Department of Nanochemistry, Istituto Italiano di Tecnologia (IIT) , via Morego, 30, 16163 Genova, Italy.|IMEM-CNR , Parco Area delle Scienze, 37/A, 43124 Parma, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Bertoni
authors.affiliation: Drug Discovery and Development, Istituto Italiano di Tecnologia (IIT) , via Morego, 30, 16163 Genova, Italy.
authors.forename: Aidin
authors.initials: A
authors.lastname: Lak
authors.affiliation: CompuNet, Istituto Italiano di Tecnologia (IIT) , via Morego, 30, 16163 Genova, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Gaspari
authors.affiliation: ISMAC - Istituto per lo Studio delle Macromolecole del CNR , via Bassini, 15, 20133 Milano, Italy.
authors.forename: Arnaldo
authors.initials: A
authors.lastname: Rapallo
authors.affiliation: CompuNet, Istituto Italiano di Tecnologia (IIT) , via Morego, 30, 16163 Genova, Italy.|Department of Pharmacy and Biotechnology, University of Bologna , via Belmeloro, 6, 40126 Bologna, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Cavalli
authors.affiliation: Department of Nanochemistry, Istituto Italiano di Tecnologia (IIT) , via Morego, 30, 16163 Genova, Italy.
authors.forename: Luca De
authors.initials: LD
authors.lastname: Trizio
authors.affiliation: Department of Nanochemistry, Istituto Italiano di Tecnologia (IIT) , via Morego, 30, 16163 Genova, Italy.
authors.forename: Liberato
authors.initials: L
authors.lastname: Manna