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We report the synthesis and structural characterisation of two titanium(IV) complexes. A new titanium(IV) complex bearing four picolinato ligands, denoted as Ti(pic)4, has been prepared under solvothermal conditions. This complex identified by single-crystal diffraction is a new example of an octacoordinated environment for titanium(IV) and is close to an ideal triangular dodecahedron. A second synthesis of a hexaprismatric carboxylato titanium complex formulated as [Ti6(μ3-O)6(O iPr)6(μ-O2CC5H3NCOO iPr)6] starting from a dissymmetric anhydride pyridine carboxylic precursor is described. The solid-state analysis shows the presence of a single compound among 13 possible species. Calculations gave evidence of a highly selective mechanism leading to the formation of the final product. [ABSTRACT FROM AUTHOR]

For polymorphic solid-state systems containing multiple distinct crystal structures of the same composition, identifying rational pathways to selectively target one particular structure is an important synthetic capability. Cation exchange reactions can transform a growing library of metal chalcogenide nanocrystals into different phases by replacing the cation sublattice, often while retaining morphology and crystal structure. However, only a few examples have been demonstrated where multiple distinct phases in a polymorphic system could be selectively accessed using nanocrystal cation exchange reactions. Here, we show that roxbyite (hexagonal) and digenite (cubic) Cu 2- x S nanoparticles transform upon cation exchange with Cd 2+ , Zn 2+ , and In 3+ to wurtzite (hexagonal) and zincblende (cubic) CdS, ZnS, and CuInS 2 , respectively. These products retain the anion and cation sublattice features programmed into the copper sulfide template, and each phase forms to the exclusion of other known crystal structures. These results significantly expand the scope of structure-selective cation exchange reactions in polymorphic systems.

Tetrapod-shaped ZnO nanocrystals exhibit exceptional optoelectronic properties, including intense ultraviolet photoluminescence emission, that make them attractive for applications that include lasers, sensors, and photocatalysts. However, synthetic methods that produce ZnO tetrapods typically include high-temperature vapor-deposition approaches that do not readily achieve characteristic dimensions of less than 100 nm or colloidal methods that require added metal dopants, which modify the inherent properties of ZnO. Here, we report a robust, modified solution-phase synthetic protocol for generating colloidal ZnO tetrapods that does not require the use of metal dopants. The ZnO tetrapod arm lengths can be tuned from 10 to 25 nm by adjusting the amount of Zn reagent used in the reaction. Subsequent seeded-growth produced even larger colloidal ZnO tetrapods with 62 nm arms. Photoluminescence (PL) measurements confirm that the tetrapods are of high crystalline quality, and the ultraviolet PL emission wavelengths that are observed fall between those of previously reported metal-doped colloidal ZnO tetrapods, which exhibit dopant-induced red- or blue-shifts. Furthermore, the reaction strategy can be modified to produce cobalt-substituted ZnO, offering a chemical pathway to tetrapod-shaped Zn1-xCoxO nanocrystals.