LCP theory

In chemistry, ligand close packing theory (LCP theory), sometimes called the ligand close packing model describes how ligand – ligand repulsions affect the geometry around a central atom "Teaching the VSEPR model and electron densities" R. J. Gillespie and C. F. Matta, Chem. Educ. Res. Pract. Eur.: 2001, 2, 73-90] . It has been developed by R.J Gillespie and others from 1997 onwards Reinterpretation of the Lengths of Bonds to Fluorine in Terms of an Almost Ionic Model E A. Robinson , S A. Johnson, Ting-Hua Tang, and R J. Gillespie Inorg. Chem., 36 (14), 3022 -3030, 1997. ic961315b S0020-1669(96)01315-8] and is said to sit alongside VSEPR which was originally developed by R.J Gillespie and R Nyholm"Inorganic stereochemistry" Gillespie, R.J. & Nyholm, R.S. (1957). Quarterly Reviews of the Chemical Society, 11, 339-380 DOI: 10.1039/QR9571100339 ] . The inter-ligand distances in a wide range of molecules have been determined. The example below shows a series of related molecules"Bonding and Geometry of OCF₃⁻, ONF₃, and Related Molecules in Terms of the Ligand Close Packing Model" Gillespie RJ, Robinson EA, Heard GL. Inorg Chem. 1998 Dec 28;37(26):6884-6889 DOI: 10.1021/ic981037b] :

LCP and VSEPR

LCP and VSEPR make very similar predictions as to geometry but LCP theory has the advantage that predictions are more quantitative particularly for the second period elements, Be, B, C, N, O, F. Ligand -ligand repulsions are important when
*the central atom is small e.g. period 2, (Be, B, C, N, O)
*the ligands are only weakly electronegative compared to the central atom
*the ligands are large compared to the central atom
* there are 5 or more ligands around the central atom

References