Pseudotrigonal bipyramid

Vibrational spectroscopy (37, 55, 300) provided the best evidence for ClFsO possessing a pseudotrigonal bipyramidal structure of symmetry Cf, in which 2 fluorines occupy the axial and 1 fluorine, 1 oxygen, and a sterically active free valence electron pair occupy the equatorial positions (see structure III). At Rocketdyne (55), a thorough spectroscopic study was carried out including the infrared spectra of gaseous, solid, and matrix-isolated ClFsO and the Raman spectra of the gas and the liquid. 

Nitrate complexes, including hydrated nitrates, have been well studied. This ion is almost always bidentate towards a lanthanide ion, and discrete complexes or complex anions are usually formed, in contrast to the sulfate complexes mentioned above. The complex anions [M(N03)5]2-, where M = Ce, Eu, Ho or Er, have had their structures reported and are pseudotrigonal bipyramidal. The M—O distances are Ce—O = 2.553-2.591 A and Er—0 = 2.392-2.493 A.385-8 The (Hpy)N03-Yb(N03)3 aqueous system has been studied, aftd (Hpy)2[Yb(N03)5] isolated from it and characterized by X-ray powder pattern.389... 

Fig. 1. Pseudotrigonal bipyramid structure and molecular orbital of the 3c - 4e bond...

In the case of the other hypervalent element compounds, these structural differences are strictly reflected in their terminology. For instance, sulfonium salts such as Me3S+Cl are clearly differentiated from sulfuranes such as Ph2SCl2. The latter is a hypervalent species of decet structure [10-S-4] and pseudotrigonal bipyramid with a linear Cl-S-Cl hypervalent bond however, the former is not a hypervalent compound and has pseudotetrahedral geometry with octet structure [8-S-3]. 

KSeOPs is formed exothermaUy by reaction of SeOp2 and Kp qqjg spectra confirm the expected geometry with two fluorine atoms at the apices of a pseudotrigonal bipyramid, in agreement with the prediction of the Valence Shell Electron Pair Repulsion (VSEPR) model. ... 

Sn0 H20 has an adamantane-like [Sn Og] structure, similar to that found in [Sn604(0Me)4] the latter compound was obtained by the controlled hydrolyses of Sn(OMe)2. The tin atoms in [Sn604(0Me)4] have a distorted pseudotrigonal bipyramidal geometry. ... 

Recent reports by two groups propose two new and entirely different models for similar catalytic dial-kylzinc additions. One of these assumes a pentavalent, pseudotrigonal bipyramidal zinc(II) catalyst (93) and the otherpurports transfer of the alkyl group from the carbonyl-bearing meud (94 Figure 55). 

Another interesting complex, Pb4Zr2(0-i-Pr),6 (Fig. 33) (148), contains a central (Pr-i-0)Pb(/i2-0-i-Pr)2Pb(0-t-Pr) unit bonded to two Pb(/r2-0-i-Pr)3Zr(0-/-Pr)3 units. The six metals are nearly planar, and each terminal iso-propoxo group of the (Pr-/-0)Pb( t2-0-i-Pr)2Pb(0-/-Pr) unit binds to a distinct PbZr(0-/-Pr)6 unit. The coordination number of Pb2 is 4, and the overall geometry of this lead atom is sawhorse or pseudotrigonal bipyramidal, with an (unseen) equatorial lead lone pair. 

The anionic lO-Bi-4 species, (2), has distorted pseudotrigonal bipyramidal geometry about the bismuth atom <92TL6653>. The corresponding iodinium triflate, where tetracoordinate, cationic iodine replaces the bismuth atom, assumes similar geometry <82JA902, 93JA2488>. 

A tetracoordinated organobismuth ate complex 44 (lO-Bi-4) has also been synthesized. Its structure characterized by X-ray crystallography shows that the bismuth atom has a distorted pseudotrigonal bipyramidal configuration, where the apical positions are occupied by two oxygen atoms [92TL6653], The equatorial plane is occupied by two carbon atoms and a lone pair of electrons. The apical Bi-O bond lengths (2.273 and 2.306 A) are remarkably shorter than the sum of the van der Waals radii (3.74 A) and approximate to that of the covalent radii (2.18 A). 

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