Transition metal electronic distortions

Because the electron-counting paradigm incorporates the 18-electron rule when appHed to transition-metal complexes, exceptions can be expected as found for classical coordination complexes. Relatively minor exceptions are found in (Tj -C H )2Fe2C2BgHg [54854-86-3] (52) and [Ni(B2QH22)2] A [11141-32-5] (53). The former Q,n electrons) is noticeably distorted from an idealized stmcture, and the latter is reminiscent of the and complexes discussed above. An extremely deficient electron count is obtained for complexes such as P7036-06-9] which have essentially undistorted... 

Slovokhotov, Yu.L. and Struchkov, Yu.T (1984) X-ray crystal structure of a distorted tetrahedral cluster in the salt [(Ph P)4Au4N] BF4 . Geometrical indication of stable electronic configurations in post-transition metal complexes and the magic number 18-e in centred gold clusters. Journal of Organometallic Chemistry, 177, 143-146. 

Stable Mn(HI) compounds, Mn(R2r fc)3, have been known for a long time (42, 46). The structure of Mn(Et2C tc)3 is elucidated (47). The inner geometry of the Mn(CS2)3 core does not conform to the usual D3 point symmetry of transition metal complexes of this type, but shows a strong distortion attributed to the Jahn-Teller effect. The electronic spectrum (48, 49) and the magnetic properties of this type of complexes are well studied (50). 

An interesting example of t 3 coordination of a boratabenzene to a transition metal has been observed for a Zr(IV)-boratanaphthalene complex (Scheme 20).35 Thus, treatment of the illustrated 1-boratanaphthalene with Cp+ZrCl3 furnishes an adduct in which the metal-carbon distance for the 3, 4, and 5 positions of the heterocycle (2.53-2.56 A) is significantly shorter than for the 2 and 6 positions (2.77-2.81 A). It is suggested that this distorted bonding mode is the consequence of the high electron demand of Zr(IV), which prefers coordination to the most electron-rich carbon atoms. ... 

Our focus is on the most comprehensively studied series, the monophosphides of the first-row transition metals, whose structures successively distort from NaCl-type (ScP) to TiAs-type (TiP), NiAs-type (VP), MnP-type (CrP, MnP, FeP, CoP), and NiP-type, forming stronger metal-metal and phosphorus-phosphorus bonding with greater electron count (Fig. 11) [63-65], The P atoms are six-coordinate, but... 

Kambara presented a ligand field theoretical model for SCO in transition metal compounds which is based on the Jahn-Teller coupling between the d-electrons and local distortion as the driving force for a spin transition [193]. The author applied this model also to interpret the effect of pressure on the ST behaviour in systems with gradual and abrupt transitions [194]. By considering the local molecular distortions dynamically this model turned out to be suited to account for cooperative interactions during the spin transition [195]. 

Wade expanded the 1971 hypothesis to incorporate metal hydrocarbon 7T complexes, electron-rich aromatic ring systems, and aspects of transition metal cluster compounds [a parallel that had previously been noted by Corbett 19) for cationic bismuth clusters]. Rudolph and Pretzer chose to emphasize the redox nature of the closo, nido, and arachno interconversions within a given size framework, and based the attendant opening of the deltahedron after reduction (diagonally downward from left to right in Fig. 1) on first- and second-order Jahn-Teller distortions 115, 123). Rudolph and Pretzer have also successfully utilized the author s approach to predict the most stable configuration of SB9H9 (1-25) 115) and other thiaboranes. 

The remaining sections of this chapter examine particular classes of cations that show electronically induced distortions. Section 8.2 explores the distortions caused by lone pairs and Section 8.3 explores the distortions found in transition metals. 

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