Square-planar geometry

Penta-atomic polyhalide anions [XY4] favour the square-planar geometry (D4h) as expected for species with 12 valence-shell electrons on the central atom. Examples are the Rb+ and Cs+ salts of [C1F4], and KBrp4 (in which Br-F is 189 pm and adjacent angles F-Br-F are 90 ( 2°). The symmetry of the anion is slightly... 

Since X-ray determinations of structure were too time-consuming to be widely used in the l9-2()s and 1940s and. in addition, square-planar geometry was a comparative rarity, any paramagnetic compound, which on the basis of stoichiometry appeared to be 4-coordinate, was presumed to be tetrahedral. 

Their existence led Werner to infer a square-planar geometry for Pt. ... 

The absolute configuration of products obtained in the highly stereoselective cycloaddition reactions with inverse electron-demand catalyzed by the t-Bu-BOX-Cu(II) complex can also be accounted for by a square-planar geometry at the cop-per(II) center. A square-planar intermediate is supported by the X-ray structure of the hydrolyzed enone bound to the chiral BOX-copper(II) catalyst, shown as 29b in Scheme 4.24. 

Its structure shows the trans-influence of hydride and pronounced distortion from square planar geometry (H—Rh-P 70.7°) owing to steric crowding. (RhH(PPh3)3 is rather less distorted (H-Rh-P 75.8°) [118a], This 16-electron complex shows no tendency to add an extra molecule of phosphine, unlike the less hindered RhH(PEt3)3. It is, however, an active... 

The cation has significant tetrahedral distortion from square planar geometry (P—Ir—P 150°) to minimize non-bonding interactions. It undergoes various oxidative addition reactions... 

The similar species Ir(PMe3)4 likewise shows tetrahedral distortion from square planar geometry (P-Ir—P 152.6-158.9°). It undergoes some remarkable oxidative addition reactions with species like H2O and H2S (Figure 2.72). 

Similarly, all three isomers have been isolated for PtBr(N02)NH3(py) and PtCl(N02)(NH3)(MeNH2) while Chernyaev used the synthesis of all three isomers of [Pt(NH3)py(NH20H)(N02)]+Cl- as evidence for a square planar geometry [146],... 

Consider the possibility that the reaction proceeds in stages (a) addition of C1 to a vacant axial position, (b) loss of any equatorial Cl", (c) collapse of this structure to the stable square-planar geometry. This sequence is shown ... 

The Pd lT) and Pt ll) complexes yilB dtc) HI, 46) are diamagnetic and have a square planar geometry 112,113) like the nickel analogues. In CH2CI2 they can be oxidised irreversibly on a rotating platinum electrode, the Pd compound at a higher potential than the Pt compound (1.21 and 0.92 V vs s.c.e., respectively) 150). 

The structure of [Ir(cod)(dppf)]PF6 shows approximately square-planar geometry at Ir, and the cp rings of the dppf ligand are close to parallel and staggered.592 The systems [Ir(cod)(LL)]C104, where LL = dppf, l-diphenylphosphino-2-(7V,7V-dimethylamino)methyl ferrocene and 1,6-diferrocene-2,5-diazahexane, catalytically trimerize PC=CH to 1,3,5-triphenylbenzene.593 The electrochemistry of [Ir(dppf)2]BPh4 shows two one-electron reductions at —1.560 V and -1.755 V vs. ferrocenium/ ferrocene.753... 

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