Carbonyls face bridging

The face-bridging carbonyls in Fe4(CO)4Cp4 are strongly basic and, with Lewis acids, form a number of (9-bonded adducts of the type Fe4(C0)4 Je(C0A)xCp4... 

Whereas edge- and face-bridging hydrogen atoms are associated mainly with metal-metal orbitals already present in the tetrahedral skeleton (see last section) and therefore have limited steric requirements, terminal hydrides occupy a full coordination position. It is not surprising then that the only examples of tetrahedral species with terminal hydrides contain 11 and 10 carbonyls, [Ir4(CO)nH] and [Ir4(CO)ioH2]2 . (The assignment for [Ir4(CO)nH] is based on the structure determination of the analogous [Ir4(CO)nBr] and on the similarity of the ir spectra of the two species (11).)... 

Four of the eight triangular faces in octahedral Rh6(CO)16 (Rhftfri3-CO)4(CO),. J (Fig. 15.10) contain carbonyl groups bridging three metal atoms. The corresponding cobalt compound is thought to have a similar structure.17... 

Fig. 15.10 The Rh (CO)1

Pd7(CO)7(PMe3)7] has been isolated from the reaction of (23) with CO.115 This cluster has a monocapped octahedral structure with one phosphine attached to each Pd atom. Four of the carbonyl ligands bridge the octahedral faces, while the other carbonyls edge bridge (Pd—Pd 2.79(2) A). 

Q Terminal carbonyl groups Edge bridging carbonyl groups Face bridging carbonyl groups... 

Form A, as confirmed by an X-ray diffraction study (3), has structure XI (see Fig. 4) with six terminal and eight face-bridging CO groups (vco = 1640-1680 cm-1), whereas form B should have some edge-bridging carbonyl groups (rco = 1710-1760 cm-1) (37). On oxidation both... 

The zeolite interaction with this compound was evidenced by the low frequency shift experienced by the CO vibration of the face bridged carbonyls. Competition between residual or added water was witnessed suggesting that the solvating properties of the zeolite and water were similar and rather weak. Therefore the stabilization of these zerovalent carbonyls within the zeolite porous structure should be attributed to a cage rather than to a chemical effect. 

Two isomeric forms of hexadecacarbonylhexairidium(O), Ir6(CO)i6, are known a red isomer, isostmctural with Rli6(CO)i6, and a black isomer that has four edge-bridging carbonyl groups rather than face-bridging. The structure of the black isomer is described as Ir6(CO)i2(/u.2-CO)4. 

In this more carbonylated species the hexametal assembly assumes an octahedral architecture, with four carbonyl groups p3-face bridging and twelve terminal. This geometry is quite reminiscent of that exhibited by the red isomer of the isoelectronic homonuclear Ir6(CO)16 [164]. Although the expected spreading of the metal-metal distances, their averaged value still remains 2.77 A. 

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