부산대학교 도서관

The crystal structure and hydrogen positions of serandite, NaMn{sub 2}[Si{sub 3}O{sub 8}(OH)], have been refined from single-crystal X-ray and time-of-flight neutron diffraction data at ambient conditions. The proton occupies an asymmetric, double-well position between O3 and O4, confirming one of the shortest asymmetric hydrogen bonds known in minerals with d(O3{hor_ellipsis}O4) = 2.464(1) {angstrom} (X-ray) and 2.467(1) {angstrom} (neutron). The proton position closest to O3 has about 84% occupancy and an O-H distance of 1.078(3) {angstrom}, and the position closest to O4 has an occupancy of 16% and an O-H distance of 1.07(1) {angstrom}. The d(H{hor_ellipsis}O) of these hydrogen bonds is 1.413(3) {angstrom} and 1.41(1) {angstrom}, respectively. Hydrogen bond angles are 164{degree} for H1 and 168{degree} for H2. The Si{sup IV}-OH bond length [1.628(1) {angstrom}] is intermediate in length among the three other Si-O bonds in the dominantly (84%) hydrated Si1 tetrahedron. These new structure data for a very strong hydrogen bond may be useful for extending spectroscopy-structure correlation diagrams into the region of very low energy O-H stretching.