Coordination geometry trigonal planar

For complexes with a ri2 coordination of the BELT ligand, a large number of structures are known with a large variety of coordination numbers and geometries trigonal-planar (TP), tetrahedral (TET), square-planar (SQP), trigonal-bipyramidal (TBP), square-pyramidal (SQPY) octahedral (OCT) and distorted octahedral (DOCT) (see Scheme 4). Nevertheless, some structures are more common than others. Only one example of both the SQPY [5] and DOCT [6] and two examples of OCT [7,8] have been reported. Linear structures M-q2 - BH4 (T2.1) and LM-(q2 - BH4 ) (T2.2) have only been computationally studied [9,10] and are not models of any experimental compound. Several computational studies have also been performed in order to study q2 complexes with higher coordination numbers [11-17]. 

In order to understand the biochemistry of mercury more completely, it is important to describe the chemistry of this element with sulfhydryl donors in the most common coordination environments. Ideally, one would examine mercuric complexes within a construct that was basically invariant, but which allowed for preparation of mercury compounds in the most common structures. The desired coordination modes include linear (or slightly bent) for 2-coordinate complexes, trigonal planar (or slightly T-shaped) for 3-coordinate compounds and tetrahedral for 4-coordinate complexes. Figure 1. Unfortunately, diere are no known native systems that allow for this diversity of metal coordination geometry. However, given advances in peptide synthesis and the prediction of... 

Reaction of 2 equiv of H0Si(0 Bu)3 with B(0 Bu)3 as a neat mixture at 80 °C results in the formation of Bu0B[0Si(0 Bu)3]2, which can be readily isolated in crystalline form (79%) [64], X-ray crystallography revealed that BuOB[OSi(O Bu)3]2 is monomeric in the soUd state, with a trigonal planar coordination geometry about boron (Fig. 5). Similarly, B[0Si(0 Bu)3]3 can be formed by reaction of B(0 Bu)3 with 3 equiv of H0Si(0 Bu)3 in toluene [64]. The related triphenylsiloxide compound B(OSiPh3)3 had been previously reported [109]. 

Cobalt(II) alkoxides are known and monomeric forms are part of a wider review.413 The interest in these compounds pertains to a potential role in catalysis. For example, a discrete cobalt(II) alkoxide is believed to form in situ from a chloro precursor during reaction and performs the catalytic role in the decomposition of dialkyl pyrocarbonates to dialkyl carbonates and carbon dioxide.414 A number of mononuclear alkoxide complexes of cobalt(II) have been characterized by crystal structures, as exemplified by [CoCl(OC(t-Bu)3)2 Li(THF)].415 The Co ion in this structure and close relatives has a rare distorted trigonal-planar coordination geometry due to the extreme steric crowding around the metal. 

In (362), the cation is distorted trigonal pyramidal with the axial positions occupied by one S atom and the central P atom of the P3 ligand. In the anion the nickel center is bonded to six S-donors of three xanthate ligands. Upon reaction with dppe an approximately square planar NiS2P2 complex results.938 A similar coordination geometry is found for the two complexes (361a,b) 939,940... 

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