Square pyramidal structure

The most important members of this class are the osmium nitrido, and the osmyl complexes. The reddish-purple K2[OsNCl5] mentioned above is the result of reducing the osmiamate. The anion has a distorted octahedral structure with a formal triple bond Os=N (161pm) and a pronounced /ram-influence (pp. 1163-4), i.e. the Os-Cl distance trans to Os-N is much longer than the Os-Cl distances cis to Os-N (261 and 236 pm respectively). The anion [OsNCls] also shows a rram-effect in that the Cl opposite the N is more labile than the others, leading, for instance, to the formation of [Os NCl4] , which has a square-pyramidal structure with the N occupying the apical position. 

These compounds are generally believed to have square pyramidal structures (X-ray, PPr3) [157d] and have typical spectroscopic properties of transition-metal hydrides (IrHCl2(PBu2Me)2 i/(Ir—H) 1998 cm-1). 

On this basis, the bent nitrogens with square pyramidal structures like Ir(NO)Cl2(PPh3)2 are assigned to the M111 (d6) oxidation state in keeping with other examples of this stereochemistry, such as RhCH3I2(PPh3)2. 

M(NO)Cl2(PPh3)2. Both these compounds have a square pyramidal structure with bent apical M-N-0 linkage and similar bond angles. There is, however, a difference of 70cm-1 in t/(N-0). 

M(NO)(OCOCF3)2(PPh3)2. Both these complexes have 5-coordinate geometries with monodentate carboxylates. The rhodium compound has a square pyramidal structure with bent Rh-N-O (122°) but the iridium compound has a tbp structure with straight equatorial Ir-N—O (178°). The position of i/(N—O) reflects this difference (1800 cm-1 (Ir) and 1665 cm-1 (Rh)). 

Many of the nitrosyls studied are 5-coordinate, and analysis of crystallographic results indicates that, in general, in the trigonal bipyramid structures NO is found in the equatorial position in a linear geometry whereas in a square pyramidal structure, there is a bent M—N—O linkage in an apical position. A further point of interest is that in compounds like Ir(NO)Cl2(PPh3)2, the nitrosyl group bends in the more hindered (P—Ir—P) plane. 

The anionic pentafluorophenyls have square pyramidal structures but are evidently non-rigid in solution (19F NMR shows all ligands equivalent). The neutral adducts are also square pyramidal (apical C6F5, trans-L) [192],... 

A number of tertiary phosphine complexes with bulky ligands (Figure 3.80) have modified square pyramidal structures, examples being M(I)3Br2, Pt(II)3Br2 and Pd(III)3Br2 (all X-ray) [136]. 

Compounds of the type [PeX(R2dtc)2] have been obtained by treating [Fe(R2dtc)3] complexes with concentrated hydrohalic acids. [FeCl(Et2dtc)3] has been studied by Hoskins and White (264) it has a square pyramidal structure, with the chlorine atom at the apex, and with the Fe atom situated 62 pm above the basal plane of the four sulfur atoms. A similar structure is found (265) for the monoiodo derivative [FeI(Et2dtc)2]. The chloro complex has been synthesized (266) by the following reaction. 

Kawashima reported the structure of 1-phenyl-l//-phosphirene 102 which has a distorted square-pyramidal structure (Scheme 35) [82, 83], The observed elongation of the C=C bond has been interpreted in terms of the tt-o interaction in similar ways by Regitz [39] for cyclic phosphirene and by Clark [14] for phosphirenium ions 17. 

The solid state structure of complex 7b is shown in Figure 25.1. Similar to parent chelating ether complex [9b], the solid-state structure of 7b shows a distorted square-pyramidal structure with the benzylidene moiety at the apical position. The N-aryl ring is located above the benzylidene moiety resulting in the relatively close contact of the benzylidene proton with the 7r-aromatic system of the mesityl group. 

The complexes of Tc(V) and Re(V) containing an M=0 core in the coordination sphere exhibit a square pyramidal structure, while those containing an 0=M=0 core are octahedral. 

Some recent interest in the technetium chemistry has been focused on complexes possessing a Tc=N3+ core. Tetrachloronitridotechnetate(VI) complexes can easily be synthesized by the reaction of pertechnetate with sodium azide in concentrated hydrochloric acid [34], Although its square-pyramidal structure resembles that of tetrachlorooxotechnetate(V) complexes, stable character of the nitrido complexes in aqueous solution shows a remarkable contrast to the oxo complexes. However, when a strong acid and a coordinating ligand are absent, the interconversion of di(p-oxo)nitridotechnetium(VI) complexes to the monomeric form occurs in the following complicated manner [35]... 

These spectroscopic data support a square-pyramidal structure in solution with the phosphines mutually trans disposed, the chloride and the carbonyl group occupying the basal sites, and the hydride ligand located at the apex. This structure fully agrees with that found in the solid state, by X-ray diffraction analysis for the related compound OsHCl(CO)(PCy3)218, and for ab initio DFT (Becke 3LYP) methods for the model complex OsHC1(CO)(PH3)2.19... 

Compound 18 adopts the now-familiar square-pyramidal structure. Reaction between it and PyO causes its decomposition to MTO and a disulfide... 

C5Me5)Ir Co2(CO)4(/i-CO)B3Fl7 274. Pyrolysis of 274 results in H2 loss and the formation of (ij5-G5Me5)Ir Go2(GO)5B3H5 275 which has a BH-capped square pyramidal structure.154... 

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