Molecular geometry coordination compounds

Coordination complexes are a remarkably diverse group of molecules that form from virtually all transition metals In a variety of oxidation states. These compounds involve an extensive array of ligands, and they adopt several molecular geometries. 

Although the results obtained by comparison of bond lengths and coordination numbers are illustrative they should be used with care. Since this approach does not take into account the nature of the ligands it is only a very rough one. It is nevertheless remarkable, that solid and molecular tin(II) compounds (which differ also chemically) possess similar geometries and distances around the tin atom. 

It is especially important to investigate the molecular structure of coordination compounds in the vapor phase because the relatively weak coordination interactions may be considerably influenced by intermolecular interactions in solutions and especially in crystals. It has been shown that the geometrical variations can be correlated with other properties of the molecular complexes ). In particular the structural changes in the F3B N(CH3)3 and CI3B N(CH3)3 molecules ) relative to the respective monomeric species unambiguously indicated boron trichloride to be a stronger acceptor than boron trifluoride. Data on the geometry and force field have also been correlated ). 

Hargittai, M., Hargittai, I. The molecular geometries of coordination compounds in the vapor phase. Budapest Akad6miai Kiado Amsterdam Elsevier 1977... 

M. Hargittai and 1. Hargittai, Molecular Geometries of Coordination Compounds in the Vapor Phase , Elsevier,... 

Inorganic templating and self-assembly provide coordination compounds whose geometries make possible the synthesis of complex structures, namely of cyclic multiporphyrin arrays [9.13a, 9.179], of inorganic rotaxanes [9.97a, 9.180], of multi-catenates and catenands (see 181) [8.281, 8.282] and even of molecular knots (see 182) [8.282, 9.77, 9.181] (in 181 and 182 a) with, b) without Cu(l) template). 

It is not possible to draw general conclusions from these observations, but it should be clear that biological activity of fourth main group (organo)metal compounds may depend as well on some factors which are as yet unknown and which are possibly related with the occurrence of certain types of coordination structures with very specific molecular geometries. Here, in my opinion, a field for further explorative research lies wide open. 

The molecular geometry of Sr(OC6H2-f-Bu3)2(THF)3 can best be described as distorted trigonal bipyramidal. The large aryl oxide groups occupy two of the equatorial sites, which allows the f-Bu groups to better extend into space without causing serious repulsive contacts. The metal center in this compound has an unusually low coordination number of five.132... 

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