907: core electrons Is-4d of Hg are described by an "effective core potential" (ECP-60) with the inclusion of relativistic effects, 0. Andrae. U. Hlussermann. M . Dolg. H. Stoll, H. Preuss, Theoret. Chim Acta 1990. 77, 123; for H an SV (split valence) basis was utilized, for C, P a n SVP (SV plus polariration) basis. A. Schafer, H. Horn, R. Ahlrichs, J Chem Phys. 1992, 97,2571, for Hg a (7~.6p.5d)'I6~,3p,2d] basis, in MP2 calculations for P a TZVPP was utilized, A . Schafer. C. Huber, R. Ahlrichs, J. Chem. Phys. 1993, 100,589, and for Hg a (7~.7p.Sd.If)'[6~.4p,2d.lf] basis; the DFT calculations are based on the BP-86 Function. A. D. Becke, Phys. Rev. A 1988,38. 3098; J. P. Perdew, Phi;$. Rer B 1986. 33, 8822; ihid. 1986, 34, 7406 (E); The RI-DFT method was employed. K. Eichkorn. 0. Treutler, H. Ohm, M. Haser, R. Ahlrichs, Chem. Phj.\. Lprirrs 1995. 240, 283, all basis sets are available under ftp.chemie.unikarlsruhe de with login anonymous in directory publbasis For (HgPR), to (HgPRj, SCF-force constant calculations were performed: all isomers correspond to a local minimum of the potential surface, for the pentamer an imaginary frequency was calculated, symmetry degradation has an insignificant influence on the structure and energy.[8] The calculated energy difference between the all-cis and the all-trans isomer of (HgPR), of 6.4 kJ mol-I gave for four trans or cis positions results a diflerence of I 7 k l mol. ' Tor cis and rruns neighbors.[9] J. Li, P. Pyykko. C/ie.m. Phyr.