Hexagonal bipyramid

The known uranium(VI) carbonate soHds have empirical formulas, 1102(003), M2U02(C03)2, and M4U02(C03)3. The soHd of composition 1102(003) is a well-known mineral, mtherfordine, and its stmcture has been determined from crystals of both the natural mineral and synthetic samples. Rutherfordine is a layered soHd in which the local coordination environment of the uranyl ion consists of a hexagonal bipyramidal arrangement of oxygen atoms with the uranyl units perpendicular to the orthorhombic plane. Each uranium atom forms six equatorial bonds with the oxygen atoms of four carbonate ligands, two in a bidentate manner and two in a monodentate manner. 

The majority of U(V1) coordination chemistry has been explored with the trans-ddo s.o uranyl cation, UO " 2- The simplest complexes are ammonia adducts, of importance because of the ease of their synthesis and their versatihty as starting materials for other complexes. In addition to ammonia, many of the ligand types mentioned ia the iatroduction have been complexed with U(V1) and usually have coordination numbers of either 6 or 8. As a result of these coordination environments a majority of the complexes have an octahedral or hexagonal bipyramidal coordination environment. Examples iuclude U02X2L (X = hahde, OR, NO3, RCO2, L = NH3, primary, secondary, and tertiary amines, py n = 2-4), U02(N03)2L (L = en, diamiaobenzene n = 1, 2). The use of thiocyanates has lead to the isolation of typically 6 or 8 coordinate neutral and anionic species, ie, [U02(NCS)J j)/H20 (x = 2-5). 

Chlorophyll b [519-62-0] M 907.52, sinters at 86-92 , sinters at 170 , dec at 160-170 , m 183-185 , 190-195 , [alj, -267 (Me2CO + McOH), [a] j-133 (McOH + Pyridine 95 5). See purification of chlorophyll a, and is separated from "a" by chromatography on sucrose [UV, IR Stoll and Weidemann Helv Chim Acta 42 679, 681 7959]. It forms red-black hexagonal bipyramids or four sided plates from dilute EtOH and has been recrystd from CHCl3-MeOH. It is soluble in MeOH, EtOH, EtOAc and insoluble in pet ether. [J Am Chem Soc 88 5037 1966.]... 

Figure 31.7 (a) The octahedral anion in Cs2[U02CU]. (b) Pentagonal bipyramidal coordination of U in dinuclear [U02(02CMe)2L]2 (L = OPPhs, OAsPhs). (c) Hexagonal bipyramidal coordination of U in uranyl nitrate, U02(N03)2-6H20. 

An older study277 established 8-coordination as a hexagonal bipyramid in [Ph2 Pb(OOCMe)3 ]". 

For example, both Hiickel aromatics B and C conform to the Wade-Mingos electron counting rules [2] (see Chapter 1.1.2) and to the structural systematics developed for boranes and heteroboranes [1] the hexagonal bipyramid with the apices removed is in agreement with an arachno electron count of 18 SE for (CH)g [2],... 

Among the known structures, the hexagonal bipyramidal (Has) geometry seems to be less common than others and it has only been definitely established for a few uranyl complexes (94—97). Probably an axial colHnear grouping, as in 0—U—0, is necessary for obtaining a geometry for the complexes. None of the octa-coordinated lanthanide complexes has a Hea geometry. 

Goethite Adcular Stars (twins), hexagons, bipyramids, cubes, thin rods... 

Chiu prepared monodisperse crystalline particles of metal sulfides, such as lead sulfide (PbS cubes 100 A) (I), cupric sulfide (CuS hexagonal bipyramids 200 A) (2), and zinc sulfide (ZnS multifaceted spheres 0.1-0.4 p,m) (3) by introducing hydrogen sulfide gas into dilute acidic solutions of the ethylenediamine tetraacetic acid (EDTA) complexes of the corresponding metal ions (10 4-10-1 mol dm-3) for several minutes at room temperature. 

In contrast to the hexagonal prismatic morphology of low-temperature quartz, it has been assumed that the characteristic morphology of high-temperature quartz is hexagonal bipyramidal where no 1010 faces appear on the crystal... 

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