STRUCTURAL STUDY OF HYPERVALENT COMPOUNDS BY ^<121>Sb AND ^<127>I MossBAUER SPECTROSCOPY

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Nature of the hypervalent bonds of X-Sb-X,O-Sb-X,O-Sb-O,N-Sb-X,C-Sb-X (X=halogens) and Cl-I-Cl, Cl-I-O,O-I-O in trigonal bipyramidal 10-Sb (V) -5, pseudo-trigonal bipyramidal 10-Sb (III) -4 with a lone pair, octahedral 12-Sb (V) -6 and pseudo-trigonal bipyramidal 10-I (III) -3 with two lone pairs was studied by ^<121>Sb and ^<127>I Mossbauer spectroscopy, and single crystal X-ray structural analysis.^<121>Sb and ^<127>I Mossbauer spectroscopy gave separately the information on the distribution of s- and p- electron density around Mossbauer atoms, thus the essential feature of the hypervalent bonds (3-center 4-electron bonds) as following was elucidated.(1) Both 5s and 5p_Z orbitals of antimony atoms being involved in the Sb-X bonding, it has both s and p character. On the other hand Sb-O bonding has mainly p character.(2) 5s orbitals of iodine do not contribute to l-O and l-Cl bond formation, only 5p_Z orbitals do.(3) The nature of the O-Sb-l bonding is very similar between trigonal bipyramidal 10-Sb (V) -5 and octahedral 12-Sb (V) -6.(4) The amount of negative charge on iodine depends on the strength of the Sb-l bondand the electronegativity of atom E in E-Sb-I (E=O,I,N,C) 3-c 4-e bond.