1210 the same structure is found for ga2se3 and

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Unformatted text preview: ds are summarized in Table 7.9. The following points are noteworthy. The hexagonal a- and B-forms of Ga2S3 are isostructural with the A1 analogues and an additional form, y-GazSs, adopts the related defect sphalerite structure derived from cubic ZnS (zinc blende, p. 1210). The same structure is found for Ga2Se3 and GazTe3 but for the larger In"' atom octahedral coordination also becomes possible. The corresponding Tl"' sesquichalcogenides Tl2X3 are either Table 7.9 Stoichiometries and structures of the crystalline chalcogenides of Group 13 elements Ga2S Gas (yellow) layer structure with Ga-Ga bonds Gas5 a-Ga2S3(yellow) ordered defect wurtzite (hexagonal ZnS) P-Ga2S3 defect wurtzite y-GazS3 defect sphalerite (cubic ZnS) GazSe GaSe (like Gas) GaTe (like Gas) (Ga3Te2) Ga2Se3defect sphalerite Ga2Te3 defect sphalerite Ga2Te5 chains of linked {GaTe4} plus single Te atoms InS (red) like Gas In& see text a-InzS3 (yellow) cubic y'-A1203 p-In2S3 (red) defect spinel, Y-Alz03 In6S7 see text T12S (black) distorted Cd12 layer lattice (Tl' in threefold coordination) TL& chains of linked {Tl'''S4} tetrahedra (Tl1)3[T1"'S3] TIS (black) like TlSe, T1'[Tl"'S2] [No T12S3known] TIS2 T1' polysulfide TlzS5 (red and black forms) T1' polysulfide T12S9 T1' polysulfide ImSe3 contains [(In''')3]" groups: In'TInPlSe? InSe diGo&ed NaCl, somewhat like Gas In~Se7 like In& a-InzSe3 defect wurtzite, but of In octahedral P-InzSe3 ordered defect wurtzite (hexagonal ZnS) T15Se3 complex Cr~B3-type structure TlSe (black) chains of edgeshared (Tl"'Se4} tetrahedra T1' [Tl"'Se2 ] T12Se3 In4Te3 like In4Se3 InTe like TlSe (cubes and tetrahedra) In3Te4 a-In2Te3 defect sphalerite (cubic ZnS) P-InzTe3 T15Te3 Cr5B3 layer structure, CN of T1 varies up to 9 and Te up to 10 TlTe variant of W5Si3 (complex) (T12Te3) 254 Aluminium, Gallium, Indium and Thallium non-existent or of dubious authenticity, perhaps because of the ready reduction to T1' (see Tl13, p. 239). Gas (yellow, mp 970") has a hexagonal layer structure with Ga-Ga bonds (248 pm); each Ga is coordinated by 3 and lGa, and the sequence of s layers along the c-axis is.. SGaGaS,SGaGaS.. -; the compound can therefore be considered as an example of Ga". The structures of GaSe, GaTe, red Ins and InSe are similar. By contrast, InTe, TIS (black) and TlSe (black, metallic) have a structure which can be formalized as M'[M"'X2]; each Tl"' is tetrahedrally coordinated by 4 Se at 268pm and the tetrahedra are linked into infinite chains by edge sharing along the c-axis (see structure), whereas each T1' lies between these chains and is surrounded by a distorted cube of 8 S e at 342pm. This explains the marked anisotropy of properties, especially the metallic conductivity in the (001) plane and the semiconductivity along the caxis. Similar edge-linked {GeSe4} tetrahedra are found in CsloGasSel4 which was obtained as transparent pale-yellow crystals by heating an equimolar mixture of GaSe and C s in a carefully controlled temperature programme; the compound features the unprecedented finite complex anion [Se2Ga(p-Se2Ga)$3e2]'0- which is 1...
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