Nd5O4Cl[AsO3]2 and Gd5O4Br3[SeO3]2: Two lanthanoid oxide halides with complex “lone-pairȁ
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- 作者：Dong-Hee Kang ; Joseph Wontcheu ; Thomas Schleid
- 关键词：Lanthanides ; Oxide halides ; Oxoarsenates(III) ; Oxoselenates(IV) ; Crystal structures
- 刊名：Solid State Sciences
- 出版年：2009
- 出版时间：February 2009
- 年：2009
- 卷：11
- 期：2
- 页码：299-304
- 全文大小：538 K
文摘
Both compounds, neodymium oxide chloride oxoarsenate(III) Nd5O4Cl[AsO3]2 and gadolinium oxide bromide oxoselenate(IV) Gd5O4Br3[SeO3]2, were prepared by solid-state reactions from mixtures of the corresponding binary oxides and halides, and their crystal structures have been determined by X-ray diffraction of single crystals. They crystallize monoclinically (a = 1241.62(9) pm, b = 565.78(4) pm, c = 902.03(7) pm, β = 116.454(3)° for Nd5O4Cl[AsO3]2 and a = 1243.70(9) pm, b = 549.91(4) pm, c = 1005.28(8) pm, β = 91.869(3)° for Gd5O4Br3[SeO3]2) in space group C2/m with two formula units per unit cell. The non-isotypic crystal structures contain three crystallographically different M3+ cations (M = Nd and Gd). The coordination sphere of (M1)3+ consists of eight oxygen atoms (CN = 8) exclusively, whereas (M2)3+ carries six oxygen atoms and one X− anion (X = Cl and Br, CN = 7) in each case. For (M3)3+, however, CN = 8 is realized by six oxygen atoms and two Cl− anions in Nd5O4Cl[AsO3]2, but five oxygen atoms and three Br− anions in Gd5O4Br3[SeO3]2. The isolated pyramidal [AsO3]3−/[SeO3]2− anions (d(As3+–O2−) = 175–179; d(Se4+–O2−) = 165–174 pm) originate from three oxygen atoms (O2 and two O3), which surround the As3+/Se4+ cations together with the stereochemically active non-bonding electron pair (lone pair) Ψ1-tetrahedrally ((O–As–O) = 95–102; (O–Se–O) = 95–96°). Both crystal structures are built up of corrugated two-dimensional lanthanoid–oxygen layers consisting of edge- and corner-shared [OM4]10+ tetrahedra (d(O2−–Nd3+) = 228–242; d(O2−–Gd3+) = 226–235 pm). The single Cl− anion in the neodymium and the two crystallographically independent Br− anions in the gadolinium compound reside in between these sheets, where the lone-pair electrons at the As3+/Se4+ cations point into the center of channels, which are formed by lanthanoid–oxygen layers and halide chains.