Structure and thermal vibrations of adenosine from neutron diffraction data at 123 K.

The crystal structure of adenosine, C10H13N5O4, Mr = 267.24, has been refined by full-matrix least-squares methods using single-crystal neutron diffraction data (sin theta/lambda less than 0.79 A-1) measured at 123 K. Crystal data at 123 K: monoclinic, P2l, Z = 2, a = 4.7885 (8), b = 10.240 (2), c = 11.772 (2) A, beta = 99.59 (2) degrees, V = 569.2 A3, lambda = 1.0402 (1) A, Dn = 1.559 Mg m-3, mu = 191.1 m-1, F(000) = 175.72 fm, R(F2) = 0.044, wR(F2) = 0.055, S = 1.13 for 2450 reflections with F2 greater than 0.0. Bond lengths and angles have e.s.d.'s less than 0.002 A and 0.1 degrees for non-H atoms and less than 0.004 A and 0.3 degrees for H atoms. Values are in general agreement with those previously obtained from room-temperature X-ray data and with those obtained for 9-methyladenine by neutron diffraction at 126 K. Small displacements of amino H atoms from the least-squares plane through the non-H atoms of the adenine part appear to be the result of hydrogen bonding. There is an intermolecular interaction C2--H2...O2' with an H...O distance of 2.20 A. In its thermal vibrations, the adenosine molecule behaves as two rigid segments with a torsional libration about the glycosidic bond of 14.4 deg2 at 123 K. The force constant for this libration, as determined from the diffraction data, is 73 (10) J mol-1 deg-2.