Berry pseudo-rotation

Even more complex experiments have been performed on matrix isolated Fe(C0)4, generated by UV photolysis of Fe(C0)5. Isotopic labelling coupled with CW-CO laser pumping (65) of the CO stretching vibrations ( 1900 cnrl) showed that the rearrangement mode of Fe(C0)4 follows an inverse Berry pseudo-rotation as shown in Figure 8. 

Bernoulli principle, 11 656-657 Berry pseudo-rotation, 16 62 Bertrandite, 3 638, 640-641 Bertrand lens, 16 470-471 Beryl, 3 638, 640 color, 7 329... 

The potential energy surface displayed in Figures 5a and 5b shows that there is no potential energy barrier between the square pyramid at A = >B = 101.3° and the two trigonal bipyramids situated at the two minima. Movement along the reaction coordinate connecting the two trigonal bipyramids is usually described as the Berry pseudo-rotation.13... 

Two papers looking at the photochemistry of iron carbonyls touching upon aspects of their photochemistry that are central to the work below are discussed now. The paper of Hubbard and Lichtenberger [36] from 1981 examined the photoelectron spectrum of Fe(CO)5 in the gas phase. This paper is of relevance as they claimed to have evidence of Jahn-Teller distortions in the Fe(CO)5 cation. Here for the first time it is explicitly mentioned that highly symmetrical transition metal complexes in general have good potential for observable Jahn-Teller activity with regards to their photochemistry after ionization and/or dissociation. They found that ionization into the E state showed Jahn-Teller activity and discussed this in terms of non-Berry pseudo-rotation. 

Fig. 11 Representation of lowest adiabatic potential of singlet (S = 0) and triplet (S = 1) Fe(CO)4 around T Jahn-Teller conical intersection at tetrahedral (7 ) geometry. There are three equivalent two-dimensional troughs in the space spanned by each pair-wise selection of equal L-M-L angles (boxed vs unboxed). The topological connectivity where the troughs intersect is indicated. There are two non-equivalent epikemel distortion directions E[ 2(Td,h) leading to 6 equivalent C2v minima ( ), and 12 equivalent Cs(x) saddle-points respectively. The non-Berry pseudo-rotation barrier is very small ( 5kcal mol ). CASSCF optimised geometrical parameters for singlet and triplet states are shown at the top left...

Fig. 12 Octahedral representation of Fe(CO)4 T (8) t Jahn-Teller surface (originally devised by Poliakoff and Ceulemans in [66]). The non-Berry pseudo-rotation paths shown in Fig. 11 are the paths between opposite vertexes on the octahedron, which are C2v minima ( ) reached by following the forward and reverse directions of epikernel E. The Cj saddle-points (x) lie at the centre of each edge...

The stability of pentacoordinate phosphorus compounds has been discussed in terms of apicophilicity of the ligands. The isomerization of these compounds arises from intramolecular ligand permutation via Berry pseudo-rotation or turnstile rotation. It is of interest to know whether the concepts developed in the field of phosphorus chemistry are applicable or not to related organosilicon compounds. It is the aim of this Section to critically review recent studies of the dynamic stereochemistry of pentacoordinate organosilanes. 

Fig. 6-29 Berry pseudo rotation in a pentavalent phosphorus compound.

Fig. 2.13 Berry pseudo-rotation interconverts one trigonal bip5Tamidal structure into another via a square-based pyramidal intermediate. The numbering scheme illustrates that axial and equatorial sites in the trigonal bipyramid are interchanged.

A discussion that goes beyond Berry pseudo-rotation and considers the lever mechanism in SF4 (based on a trigonal bipyramidal structure with an equatorial site occupied by a lone pair of electrons) and related species is M. Mauksch and P. von R. Schleyer (2001) Inorganic Chemistry, vol. 40, p. 1756. 

Outline the mechanism of Berry pseudo-rotation, giving two examples of molecules that undergo this process. 

Figure 6. The restricted Berry pseudo-rotation mechanism proposed for the intramolecular metal core rearrangements observed in solution for the clusters [M2Ru4H2(CO)i2L2] (M = Cu, Ag or Au L = a variety of monodentate phosphine ligands or L2 = a variety of bidentate diphosphine ligands). The mechanism exchanges the two coinage metals in sites M(l) and M(2) of the trigonal bipyramidal M2RU3 unit in the metal skeletons of the clusters via a square-based pyramidal intermediate (reprinted by permission of the Royal Society of Chemistry from ref. 36).

Although the octahedron is stereochemically rigid, loss of a hgand gives a 5-coordinate species which can undergo Berry pseudo-rotation (see Figure 3.13). Although, earlier... 

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