Coordination geometry distortion

Sargeson and co-workers have structurally characterized encapsulated zinc in hexaaza cryptands.742 743 Related cryptands (l-methyl-8-amino-3,13-dithia-6,10,16,19-tetraazabicyclo[6.6.6]-icosane and l-methyl-8-amino-3-thia-6,10,13,16,19-pentaazabicyclo[6.6.6]icosane) incorporating thioether donors also formed complexes with zinc which were structurally characterized. In both cases the zinc ion was encapsulated in the macrobicyclic cavity and the octahedral coordination geometry distorted to the mixed nitrogen and thioether donor atoms.744... 

Biihl M, Hopp G, von Philipsborn W, Beck S, Prosenc M-H, Rief U and Brintzinger H-H (1996) Zirconium-91 chemical shifts and line widths as indicators of coordination geometry distortions in zirconocene complexes. Organometallics 15 778-785. 

Copper(I) tends towards a tetrahedral coordination geometry in complexes. With 2,2 -bipyr-idine as a chelate ligand a distorted tetrahedral coordination with almost orthogonal ligands results. 2,2 -Bipyridine oligomers with flexible 6,6 -links therefore form double helices with two 2,2 -bipyridine units per copper(I) ion (J. M. Lehn, 1987,1988). J. M. Lehn (1990 U. Koert, 1990) has also prepared such helicates with nucleosides, e.g., thymidine, covalently attached to suitable spacers to obtain water-soluble double helix complexes, so-called inverted DNA , with internal positive charges and external nucleic bases. Cooperative effects lead preferentially to two identical strands in these helicates when copper(I) ions are added to a mixture of two different homooligomers. 

Other paramagnetic bis(amidinate) iron(II) complexes of the type [But(NR)2]2Fe (R = Cy, Pr ) have been prepared analogously from the lithium amidinate salts and FeCl2- The coordination geometry around Fe is distorted tetrahedral (Scheme 137). 

The lithium derivatives Li[Me3SiNC(Ph)N(CH2) NMe2] ( = 2, 3) crystallize as dimers with each of the Li atoms bonding to two N atoms of an amidinate fragment in one ligand and to two N atoms of the other ligand in the dimer. The coordination geometry around the Li atoms is distorted tetrahedral (Scheme 176). ... 

If the BF2 groups in Ni(dmg-BF2)2 are substituted by BPh2 units (122), the complex also adopts the saddle-shaped conformation of type D (Fig. 32), in which the two dimethylglyoxime fragments are bent down from the N4 plane with a dihedral angle of about 27° between the two least-squares planes of the dioxime units. The coordination geometry around the nickel ion is distorted square-pyramidal, but there are no intermolecular Ni Ni interactions [167]. 

Fig. 37. [M(dioxime)3(BR)2] complexes 135-138 contain encapsulated metal ions and are clathrochelates. The coordination geometry of the metal ion is described by the distortion angle 4>...

The V(IIIj containing complexes V(R2magnetic moments of these air-sensitive compounds are characteristic of two unpaired electrons as is expected for a configuration, the coordination geometry is assumed to be a distorted octahedron (Dj). 

The stannaketenimine (entry 3, Table V) shown below was found to have a bent structure with an angle at the dicoordinate carbon atom of I540 S7 The coordination geometry of the tin atom is distorted owing to the short contact with one of the fluorine atoms of the trifluoromethyl substituents. The bond between the tin atom and the doubly bonded carbon... 

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. 

X-ray structural studies of the diamagnetic anion (406) confirm that the Ir(-I) center is in a distorted coordination geometry intermediate between square planar and tetrahedral, with the P donor atoms in a cis position. The metal-ligand bond distances do not show significant changes among (404), (405), and (406). The Ir1/0 and Ir0/(-1) redox couples are measured at easily accessible potentials and are solvent dependent. 

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