HYROGEN BOND IN CRYSTAL STRUCTURE OF SALTS OF SYMMETRIC POLYMETHYLFERRICINIUM CATİONS (SYM.[(CH3)mC5H5–m]2Fe+X – , m=3,4,5 or МеnFc+X – , n = 6, 8, 10; X– = PF6 – , BF4 – , Br3 – )

The article explains reasons of elongation (0.019 Å) of the bond between iron–cyclopentadienyl ring in the 1,2,4,1,2,4-hexamethylferricinium (sym. Ме6Fc+ ) cation formed due to the one-electron oxidation of iron atom of sym.1,2,4,1,2,4-hexamethylferrocene (sym. Ме6Fc) molecule which is 2-2.5 times smaller (0.04–0.05 Å) than that observed in pairs of ferrocene/ferricinium (Fc/Fc+ ), sym. octamethylferrocene/sym.octamethylferricinium (Ме8Fc/Me8Fc+ ) and decamethylferrocene/decamethylferricinium (Ме10Fc/Ме10Fc+ ). For this purpose, X-ray structural parameters characterizing the interaction between cation and anion in the sym.Ме6Fc+PF6 – complex was compared with appropriate parameters in Ме8Fc+BF4 – , Ме10Fc+Br3 and Ме10Fc+PF6 – complexes; and it was mooted that there is an F …H type hydrogen bond in this complex taking into account the length of the non-valent F…H contact (bond) in the sym. Ме6Fc+PF6 – complex. The lengths of Р–F bonds and F–P–F angles of the PF6 – anion in the listed 4 sandwich complexes were compared with appropriate parameters in the РF6 – anion of the LiРF6 crystal. It has been unequivocally proved that F…H hydrogen bonds exist in the sym.Ме6Fc+PF6 – complex.