Structures square antiprismatic

The influence of electron-count on cluster geometry has been very elegantly shown by a crystallographic study of the deep-red compound [K(ctypt)]g [Ge9]- [Ge9] .2.5en, prepared by the reaction of KGe with cryptand in ethylenediamine. [Ge9] has the C4, unicapped square-antiprismatic structure (10.10c) whereas [Ge9]- , with 2 less electrons, adopts a distorted Dit, structure which clearly derives from the tricapped trigonal prism (p. 153).The field is one of... 

Figure 13.27 The structures of cationic clusters of Bim"+. The dimensions cited for Bi9 + were obtained from an X-ray study on [(Bi9 +)(Bi )(HfCl6 )3] the corresponding average distances for Bi9 + in BiCli 1 7 i.e. [(Bi9 +)2(BiCl5 )4(Bi2Cl8 )] are 310, 320 and 380pm respectively. The square antiprismatic structure of Big " was established by an X-ray study of Bi8[AlCl4]2. ...

Again, these forms are energetically very similar distortions from the idealized structures make it difficult to specify one or other, and the particular structure actually found must result from the interplay of many factors. [TaFg] , [ReFg] and [Zr(acac)4] are square antiprismatic, whereas [ZrFg] " and [Mo(CN)g] are dodecahedral. The nitrates [Co(N03)4] and Ti(N03)4 may both be regarded as dodecahedral, the former with some distortion. Each nitrate ion is bidentate but the 2... 

Also of interest are the octacyano complexes, (M(CN)g] (M = Mo, W), whieh are commonly prepared by oxidation of the M" analogues (using MnO,) or Ce" ) and whose structures apparently vary, aceording to the environment and counter cation, between the energetically similar square-antiprismatic and dodecahedral forms. 

The simplest of the ir-bondcd Re-C compounds is the green, paramagnetic, crystalline, therm ly unstable ReMen, w ich, after WMe, was only the second hexamethyl transition metal compound to be synthe zed 11976). It reacts with LiMe to give the unstable, pyrophoric, Lii[ReMe(,, which has a square-antiprismatic structure, and incorporation of oxygen into the coordination sphere greatly H reases the stability, wit e,ss Re CMe, which is thermally stable up to 200 C, and Re "0[Pg.1068]

Key Colour % indicates preparation but no report of colour) mp/°C (na indicates value not reported) coordination 9 ttp = tricapped trigonal prismatic 8 d = dodecahedral 8 sa = square antiprismatic 8 btp = bicapped trigonal prismatic 8,7 = mixed 8- and 7-coordination (SrBr2 structure) 7 cc = capped octahedral 7 pbp = pentagonal bipyramidal 6 o = octahedral 6 och = octahedral chain, 6 ol = octahedral layered. 

The 8-coordinate species [Mo(Et2dtc)4] can be obtained by reaction of Mo(CO)e with tetraethylthiuram disulfide (1 2) in acetone under N2. The X-ray structure revealed square-antiprismatic coordination, with a crystallographic, twofold axis coinciding with the molecular pseudo 4 axis (158). The magnetism and spectra of [M(dtc)4]"" (M = Mo or W n = 0 or 1) have been interpreted in terms of dodecahedral symmetry (159). 

The more molecular character of 9 in comparison to 8-gallium is responsible for a decrease of the bond lengths by about 25 pm. These results prove that 9, considering its synthesis as well as the electronic structure, has to be classified in between polyhedral gallium clusters such as the square antiprismatic cluster GajjiCnHcih2- 72 and metalloid clusters. 

T. Baker, DuPont Central Research In reference to your so-called iso-closo iridaborane complex, H(PPh3)2IrB9H9, we have recently published two papers (1,2) dealing with isoelec-tronic, isostructural ten-vertex ruthenacarborane complexes and have demonstrated that these structures are related to the common closo bicapped square antiprismatic structure by the removal of two electrons (i.e. 2N skeletal electrons for an N vertex polyhedron). Such complexes have been referred to as hyper-closo to imply that the electronic unsaturation is not primarily metal-based (as in, for example, nido-(PPh3)2RhC2B8-Hx 2 (3) or closo-(PPh3)ClRh(1,7-C,BQH,) (4), but is delocal-... 

Both calcium oxalate monohydrate and dihydrate - whewellite and weddelite - contain eight-coordinated Ca2+ in distorted square-antiprismatic geometry, but there is one coordinated water in the former, two in the latter. Whewellite has a layer structure through the sharing of three edges of each coordination square-antiprism with three adjacent polyhedra weddelite has a chain structure (128). The trihydrate also contains eight-coordinated Ca2+ (129). 

The geometry at cerium is distorted square antiprismatic with a mean stagger of -28°, a value noticeably less than that (42°) observed in the porphyrin complex. The Ce-N distances are in the range 2.411(9)-2.430(9) A, distances that are markedly shorter than those in the porphyrin structure that range between 2.467(3) and 2.483(3) A (Fig. 8). 

The dianionic Ga8 cluster [Ga8(flu)8]2 453 (flu = fluorenyl) has been synthesized by salt metathesis reaction between a metastable Ga Br solution and fluorenyllithium.344 The eight Ga atoms form a square antiprismatic core. This is rather unexpected because 453, which is a z/oro-cluster according to the Wade-Mingos rules, was expected to adopt the dodecahedral structure as was observed for the corresponding boron clusters. However, computational calculations demonstrated that in the case of eight Ga atoms, the formation of a square antiprismatic structure is energetically favored (Figure 33). 

Complexes of the lanthanides with only one ligand of this type have been reported so far. Paetzold and Bochmann (276) have reported the complexes of lanthanide perchlorates with DMSeO which have the composition Ln(DMSe0)8(C104)3. A distorted square antiprismatic structure with a point group symmetry )4 has been proposed for these complexes. 

Figure 1. The structure of c o%o-[(PMe2Ph)2(l-NiBgFlyCl2-2,4)] showing the bi-capped-square antiprismatic arrangement of the NiB cluster, which is analo-...

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