Carbonyl coordination modes

NMR measurements also provide information on the coordination of the ligands in the uranyl polymers. Solid-state I c-NMR confirms the coordination modes of the carboxylate ligands to the uranyl ion that is, both monodentate and bidentate carboxylate coordination modes are evident. The uranyl dicarboxyl ate polymers which possess two moles of coordinated DMSO exhibit two carbon-13 carbonyl resonances, one at about 175 ppm downfield from tetramethylsilane (TMS) and one at about 185 ppm. The polymers which possess only one mole of coordinated DMSO exhibit only the carbonyl peak near 185 ppm. Based on other known coordination compounds, the 175 ppm peak can be assigned to monodentate carboxylate and the 185 ppm peak to bidentate carboxylate. Thus, 7-coordination predominates in the polymers with either one or two moles of solvent coordinated to the uranyl ion, which is consistent with the infrared results reported elsewhere (5). 

Complex (860)2085 containing a (/i-aqua)bis(/i-carboxylato) core reacts with urea to provide the first example of urea coordination to a dinickel(II) site.2067 In the resulting (861), the urea molecule binds through its carbonyl-O to one of the Ni11 ions, which is the most commonly observed coordination mode. 

Low valent transition metal centers preferentially coordinate to the phosphorus in diazaphospholes. Accordingly, P-coordinated complexes of [l,2,3]diazapho-spholes with Cr, W, Fe, and Mn carbonyls were obtained as early as 1980 [1, 2,4], Later, Kraaijkamp et al. observed [108] both P- or -coordination modes in complexes of [l,2,3]diazaphospholes with MX2(PEt3) (M = Pt, Pd X = C1, Br). Methanolysis of these complexes led to the diazaphosphole ring opening and formation of five membered metallacyclic P,/V-chelates (103), incorporating P-bonded phosphonite and /V-coordinated hydrazone functionalities (Scheme 32) [109],... 

DF calculations were carried out on CO complexes of small neutral, cationic, and anionic gold clusters Au with n= 1-6. The -coordination mode (terminal C-coordination) was found to be the most favorable one irrespective of the charge of the cluster, and cluster planarity is more stable for the bare clusters and their carbonyls. As expected, adsorption energies are greatest for the cationic clusters, and decrease with size. Instead, the adsorption energies of... 

The third ligand was assumed to be coordinated to the metal center via the deprotonated 3-hydroxy and 4-carbonyl groups. This coordination mode allows delocalization of the electronic structure and intermolecu-lar electron transfer from the ligand to Cu(II). The Cu(I)-flavonoxy radical is in equilibrium with the precursor complex and formed at relatively low concentration levels. This species is attacked by dioxygen presumably at the C2 carbon atom of the flavonoxyl ligand. In principle, such an attack may also occur at the Cu(I) center, but because of the crowded coordination sphere of the metal ion it seems to be less favourable. The reaction is completed by the formation and fast rearrangement of a trioxametallocycle. 

In this second case, the results of the calculations were in good agreement with the experimental data . The organolithium compound with the RC=0 coordinated in the proposed /rs fashion may now explain the significant shift of the carbonyl stretching mode from 2047 cm in n-BuLi—CO to 1635 cm in w-Bu—C(0)Li (equation 1). 

As with carbonyl coordination, the degree of backbonding in the linear mode of coordination is influenced by the complex charge, metal oxidation state and nature of the ancillary ligands. An example of how both the oxidation state and the relative d orbital energies influence vN0 is shown dramatically in the pentacyanonitrosyl systems M(NO)(CN) " (z = 2, M = Fe,... 

Diaza-1,3-butadiene (a-Diimine) Ligands Their Coordination Modes and the Reactivity of Their Metal Complexes, 21, 152 Diene-Iron Carbonyl Complexes, 1, 1... 

Organometallic compounds have long been used as ligands their most frequent application is as metal carbonyls [74c,91,450,451]. These ligands, for instance 754, are interesting as ambidentate ligand systems, in which some coordination modes can be realized [91,450,451] ... 

Interaction of C02 with petroleum ether solutions of cis-Mo(N2)2 (PMe3)4 results in the formation of the pale yellow complex trans-Mo (C03) (PMe3)4 and of variable amounts of the carbonyl-carbonate derivatives Mo(C03) CO(PMe3)4 and Mo(C03) CO(PMe3)3 2. The yellow complex is a micro-crystalline, moderately air stable solid, which can be heated at 40-50°C for several hours without noticeable decomposition. Its infrared spectrum displays bands at 1670, 1155 and 1100 cnr1, which by comparison with the spectrum of a sample 50% enriched in C02 can be assigned to vibrations associated with the coordinated C02 molecules, but no conclusions as to the coordination mode of the C02 ligand can be inferred from this data. 

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