Trigonal bipyramid coordination

Results from an array of methods, including X-ray absorption, EXAFS, esr and magnetic circular dichroism, suggest that in all ureases the active sites are a pair of Ni" atoms. In at least one urease,these are 350 pm apart and are bridged by a carboxylate group. One nickel is attached to 2 N atoms with a fourth site probably used for binding to urea. The second nickel has a trigonal bipyramidal coordination sphere. 

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... 

Figure 80 Trigonal bipyramidal coordination capsule with a chemical formula of C H igNdosPdig, a molecular mass of 7,103 Da, and a dimension of 3 x 2.5 x 2.5 nm.

N40 donor set ligands with pyridyl and phenolic arms form mononuclear complexes with approximately trigonal-bipyramidal coordination geometries.888... 

Similarly, Sn—Sn in (ClSnMe2)2, is short at 277.0 pm and there is relatively weak intermolecular Sn... Cl interaction, giving a double chain and trigonal bipyramidal coordination. Similar geometry is found with MeN(CH2CH2CH2)2 which bonds through two C and N in the Sn—Sn linked dimer. 

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). 

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