Apatite, the most common phosphate mineral, is generally described by the formula Ca5(PO4)3(OH,F,Cl) or, more completely with regard to its usual description in P 63/ m symmetry, by the unit cell content [Ca4][Ca6][(PO4)6][OH,F,Cl]2. An earlier volume of the Reviews series (Kohn et al. 2002) has dealt with the mineralogy and crystallography of apatite sensu stricto (Hughes and Rakovan 2002) and the diverse compounds that adopt apatite or apatite-like structures (Pan and Fleet 2002; Huminicki and Hawthorne 2002). In addition, apatite compilations have appeared at regular intervals (Wychoff 1965; McConnell 1973; Nriagu and Moore 1984; Brown and Constantz 1994; Elliott 1994) as the breadth of apatite chemistry has expanded and the level of understanding of its importance with respect to the mineral, materials, environmental, and biological sciences increased. It is not therefore, the purpose of this chapter to restate these excellent reviews, but rather, to focus on microporosity in apatites, a feature which allows ion conduction and exchange, and that is proving to be an important consideration for fashioning synthetic analogues of these minerals in technologically advantageous ways.

The notion of apatite as an industrially significant microporous mineral is not new. In 1944, V. M. Goldschmidt who had studied apatite deposits in Scandinavia and at that time had found refuge from war-ravaged Europe at the Macaulay Institute of Soil Research, Aberdeen (Kauffman 1997; McIntyre 2004) persuaded C. A. Beevers to undertake a new refinement of fluorapatite. The results collected in the seminal paper of Beevers and McIntyre (1946), lead not only to the most accurate crystallographic data available at that time, but also provided the first overview of [Ca4][Ca6][(PO4)6][F] …

Apatite - An Adaptive Framework Structure

Monovalent RAl (R=HC[C(Me)N(2,6-iPr2C6H3)]2) reacts with E2Et4 (E=Sb, Bi) with insertion into the weak E-E bond and subsequent formation of RAl(EEt2)2 (E=Sb 1; Bi 2). The analogous reactions of RGa with E2Et4 yield a temperature-dependent equilibrium between RGa(EEt2)2 (E=Sb 3; Bi 4) and the starting reagents. RIn does not interact with Sb2Et4 under various reaction conditions, but formation of RIn(BiEt2)2 (5) was observed in the reaction with Bi2Et4 at low temperature.

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Temperature-Dependent Electron Shuffle in Molecular Group 13/15 Intermetallic Complexes

Adsorption of CO on PtBi2 and PtBi surfaces

The new phase Ba2Bi3 crystallizes in the W2CoB2 structure type. Its structure contains rigorously planar anionic layers of (4.6.4.6)(4.62)2 nets with three- and four-bonded Bi, that are separated by Ba atoms. An unexpected site preference is observed in the coloring variant Ba2BiSb2 with Sb occupying only the three-bonded sites. The nonclassical bonding in the anionic network can be rationalized from a reformulation of the Zintl concept as (Ba2+)2[Bi3]3-(e-). Bonding distances suggest that the extra electron fills Bi−Bi antibonding states. The densities of states obtained from TB-LMTO-ASA calculations show metallic character for both compounds.

Nonclassical bonding in the novel structure of Ba2Bi3 and unexpected site preference in the coloring variant Ba2BiSb2.

Investigations in the ternary RE−Mn−Bi systems where RE is an early rare earth element have revealed the existence of the polybismuthides RE3MnBi5 (RE = La−Nd), previously known only for the Ce member, and the new compound Sm2Mn3Bi6. Their structures were determined from single-crystal X-ray diffraction data. The RE3MnBi5 compounds adopt the hexagonal inverse Hf5Cu3Sn-type structure (Pearson symbol hP18, space group P63/mcm, a = 9.7139(11)−9.5438(16) A, c = 6.4883(7)−6.4089(11) A for RE = La−Nd), containing chains of face-sharing Mn-centered octahedra. Sm2Mn3Bi6 adopts a new monoclinic structure type (Pearson symbol mP22, space group P21/m, a = 10.3917(8) A, b = 4.4557(3) A, c = 13.2793(10) A, β = 108.0100(10)°) in which the Mn centers are coordinated by Bi atoms in diverse geometries (distorted octahedral, trigonal bipyramidal, and distorted tetrahedral (seesaw)) and participate in extensive metal−metal bonding in the form of chains of Mn3 clusters. Homoatomic bonding interactions involving nominally ani...

Ternary Rare-Earth Manganese Bismuthides: Structures and Physical Properties of RE3MnBi5 (RE = La−Nd) and Sm2Mn3Bi6

The ternary rare-earth gallium bismuthide LaGaBi(2) has been prepared through reaction of the elements. Its structure (Pearson symbol hP24, hexagonal, space group P6/mmm, Z = 6, a = 13.5483(4) A, c = 4.3937(1) A) contains columns of La(6) trigonal prisms centered by Bi atoms. These columns are surrounded by a framework consisting of three-atom-wide Bi ribbons and Ga(6) rings. Additional Bi atoms are sandwiched between pairs of Ga(6) rings. LaGaBi(2) is structurally closely related to La(13)Ga(8)Sb(21). A retrotheoretical analysis of the structure through extended Huckel band structure calculations suggests an interesting electronic situation in which strong multiple bonding in the Ga-Ga network coexists with weak hypervalent bonding in the Bi-Bi network and confirms the metallic behavior seen in electrical resistivity measurements.

Lanthanum gallium bismuthide, LaGaBi2.

Samarium orthosilicate oxy­apatite, Sm5(SiO4)3O, contains SiO44− tetrahedra [Si—O 1.611 (7)–1.629 (5) A] and O2− anions, separated by samarium cations in CN7 [Sm—O 2.2428 (4)–2.641 (7) A] and CN9 sites [Sm—O 2.428 (5)–2.846 (5) A]. The full occupancy of the samarium sites implies a mixed valency of four Sm3+ and one Sm2+ per formula unit.

Mark G. Morgan

Papers

Lanthanum gallium bismuthide, LaGaBi2.

Samarium orthosilicate oxyapatite, Sm5(SiO4)3O

Platinum silicon antimonide (PtSiSb)

Lanthanum gallium manganese antimonide La 12 Ga 3.5 Mn 0.5 Sb 23.5

Lanthanum Gallium Tin Antimonides LaGaxSnySb2