The structure of 9:10-anthrahydroquinone dibenzoate was determined by the application of twoand three-dimensional transforms together with Fourier projections. The atomic coordinates and asymmetric temperature factors were refined by the least-squares method. The crystals are triclinic with one molecule per unit cell: a=8.91, b=12.60, c=5.83/~; c~=105.2 °, fl=106.5 °, 7=58.2°.Space group PI. For the three axiM zones (334 reflexions) taken together the reliability factor (R) was 0.094. The standard deviations of the coordinates are approximately 0.014 /~. The benzene rings of the benzoate groups are inclined to the plane of the anthracene nucleus at an angle of 110"5 ° . One of the bonds in the benzene ring has a value of 1.3 /l and there is an intermolecular distance between a hydrogen atom of this ring in one molecule and the centre-symmetrical hydrogen atom in another molecule of approximately 1.8/~.
9: 10-Anthrahydroquinone dibenzoate has a centrosymmetric molecule, and crystallizes with one molecule per unit cell. As a result, its transform can be distinguished directly in its reciprocal lattice, without complication from fringe functions or complex phase considerations. From a study of this transform has been developed a simple graphical method of deriving accurately the orientation, within the crystal, of any aromatic molecule, and, with favourable centrosymmetric molecules, of estimating the signs of the principal structure factors.
The preparations of MexSi(GeH3)4-x (x = 3, 2, 1, 0) and MexGe(GeH3)4-x(x = 3, 2, 1), by reaction of dry GeH3Na with the corresponding chloride, have been refined. 1,2-Me2Ge3H6, 2,2-Me2Ge3H6 and 1,2,2-Me3Ge3H5 have been prepared by the successive reactions of I2 and MeMgI on MeGe3H7. Further unstable or minor products indicated in these reactions are (GeH3)4Si, 1,1,2,2-Me4Ge3H4 and 1,2,2,3-Me4Ge3H4 together with traces of other permethyltrigermanes . Vibrational, 1H n.m.r . and mass spectra of these species are reported together with 29Si and 73Ge n.m.r . observations on the MexSi(GeH3)4-x family.
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