Neutron powder diffraction studies of sulfuric acid hydrates.I.The structure of sulfuric acid hemitriskaidekahydrate D_2SO_4 centre dot 61/2D_2O

摘要

We report the first neutron diffraction data from D_2SO_4 centre dot 61/2D_2O.The crystal is monoclinic,space group Cm,with four formula units per unit cell.At 4.2 K the unit cell dimensions are a = 6.253 26(4) A,b=26.813 62(10) A,c=5.908 45(2) A,and beta= 112.1939(3) deg [V=917.286(6) A~3 and rho(deuterated) = 1664.14(2) kg m~(-3)].The deuteron positions refined from the neutron data are in agreement with those established by single crystal x-ray analysis [D.Mootz and A.Merschenz-Quack,Z.Naturforsch.B 42,1231 (1987)],but not with those found from the ab initio simulation of Hirsch and Ojamae [Acta Crystallogr,Sect.B:Struct.Sci.60,179 (2004)].The crystal consists of SO_4~(2-),D_3O~+ ions,and D_2O molecules hydrogen bonded to form a layered structure in which sheets of "icelike" D_3O~+ and D_2O are separated by layers of opposing SO_4~(2-) tetrahedra.