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Electronic Properties of the Axial Co−C and Co−S Bonds in B 12 Systems − A Density Functional Study
Author(s) -
Randaccio Lucio,
Geremia Silvano,
Stener Mauro,
Toffoli Daniele,
Zangrando Ennio
Publication year - 2002
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(20021)2002:1<93::aid-ejic93>3.0.co;2-y
Subject(s) - chemistry , corrin , density functional theory , crystallography , trans effect , hydrogen bond , molecule , crystal structure , bond length , crystal (programming language) , electronic structure , computational chemistry , cobalt , inorganic chemistry , organic chemistry , computer science , programming language
The numerous accurate structural data of cobalamins now available allows us to optimize the geometry of these systems, based on a simplified model by using density functional theory (DFT) calculations. This approach, which reproduces the trend of the experimental distances derived from EXAFS and X‐ray crystal structures in the corrin macrocycle, permit us to interpret the electronic properties in the NB3−Co−X axial system. In particular, the results are analyzed for cobalamins containing a sulfur ligand which exhibits a “regular” trans influence, i.e., when the Co−S bond shortens, the trans Co−NB3 bond lengthens. This feature appears in contrast with an anomalous effect (“inverse” trans influence) postulated a few years ago by analyzing the structural data of several alkylcobaloximes, LCo(DH) 2 R, a simple B 12 model, and attributed principally to the electronic properties of the alkyl group R. The present study on the NB3−Co−S fragment does not indicate that the “inverse” trans influence is a general rule in cobalamins. The accurate crystal structures of the [(SO 3 )Cbl](NH 4 ) and [(thiourea)Cbl](PF 6 ) cobalamins based on synchrotron diffraction data at 100 K are also reported for comparison with the theoretical study. The former crystal structure, including one co‐crystallized glycerol molecule, presents “for the first time” an ordered hydrogen‐bonding pattern for the solvent molecules.