Lanthanide elements carbonyls

In iV-confused porphyrins, this agostic coordination mode has been observed frequently. To date, monomeric complexes of this macrocycle with divalent manganese (35, 26), divalent iron (36, 29), lanthanides (57), rhodium carbonyl (55), and group 12 elements (34), have been structurally characterized that exhibit this peculiar type of metal binding. A generic structure for several of... 

Elements of this group do not form stable carbonyls. M(CO) compounds, where M = Pr, Nd, Gd, Ho, Eu, Er, Yb, and U, may be prepared by condensation of metal atoms with carbon monoxide at low temperatures.Some low-valent lanthanide... 

The most electropositive elements, including lanthanides. Favoured where organic anion is stable. Multicentre bonds involving carbon. Carbon atom associated with two or more metal atoms in multicentre m.o.s. Electropositive elements where cation would be strongly polarizing (Chapter 3). Carboranes. Some transition metal clusters, especially carbonyls (Chapter 11). 

M—C bond distances are always significantly shorter to terminal than to bridging carbonyl ligands. There is a general parallel between M—CO(terminal) and the atomic radius of the metal. The radii of the corresponding elements at the beginning of the Second and Third Transition Series are almost equal, on account of the contraction which occurs across the lanthanides. Consequently the Mo— CO and W—CO bonds in the hexacarbonyls Mo(CO) and W(CO) are both 2.06 A in length. 

Although stable, homoleptic, mononuclear and polynuclear complexes of carbon monoxide are known for almost every transition element, a number of experiments indicate that actinide carbonyls (e.g. U(CO) ) are not stable at ambient temperature. However, uranium carbonyls can be prepared in cryogenic matrices [6,7]. Co-condensation of uranium vapor with CO in a 4K argon matrix yields species identifiable by infrared spectroscopy (in particular, Voo) uranium carbonyls, U(CO) . Derived force constants suggest bonding patterns rather similar to those observed for zero-valent early transition-element and lanthanide carbonyls. However, decomposition of these actinide carbonyls occurs at temperatures above about 30 K. 

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