Trigonal bipyramid coordination structures

A template synthesis employing Ni(OAc)2, 2,5-dihydroxy-2,5-dimethyl-1,4-dithiane, and 3,3 -iminobis(propylamine) gave the water-soluble five-coordinate complex [Ni(495)], the crystal structure of which shows trigonal bipyramidal coordination of Ni11 with the central amine and terminal thiolates in plane and the two imino nitrogens in axial positions. Solvatochromism of the complex is interpreted in terms of S" H bonding, which may be of relevance to the catalytic cycle in hydrogenases.1341... 

The crystal structure of o-(Me2NCH2)C6H4GeMePhCl was determined by a single crystal X-ray diffration study. In this species germanium exists in a distorted trigonal bipyramidal coordination with a Ge—N bond distance of 2.479(11) A or 2.508 A (11), respectively (two slightly different conformations) (Figure 29). 

To investigate whether a relationship exists between the solution structures of the hydridorhodium diphosphite species [RhH(CO)2(diphosphite)] [48] and catalytic performance, van Leeuwen and co-workers extensively studied the rhodium-diphosphite complexes formed under hydroformylation conditions by high-pressure NMR (HPNMR) techniques. It is well known that these complexes have a trigonal bipyramidal (TBP) structure. Two isomeric structures of these complexes, one containing the diphosphite coordinated in a bis-equatorial (ee) fashion and one containing the diphosphite in an equatorial-axial (ea) fashion, are possible (Fig. 4). 

This results in a highly distorted trigonal bipyramidal coordination geometry at zinc (Figure 60). The solid state structure of the dibenzo-18-crown-6 analog of 120 has also been estabhshed by an X-ray crystal structure determination. Its structural features are closely related to those of 120. 

Tetraphenylbismuthonium diphenylbis(trifluoroacetato)bismuthate (equation 51)182 contains a distorted tetrahedral cation and an anion (69), the structure of which has been interpreted in terms of a stereochemically active lone pair. This appears to be the only four-coordinate trigonal bipyramidal bismuth structure established to date in antimony chemistry these types... 

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