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The structure of cuprous iodide-methyl isocyanide, CuI,CH,-NC, has been determined by X-ray methods. The crystals are monoclinic, spacegroup CZlc, with a = 13-88, b = 13.20, c = 5.765 A, @ = 105'. The atomic positions have been determined from b-and c-axis electron-density projections and from the components C, and S, of the generalised Fourier projection calculated with the data F(hk l). There are doubl6 chains of copper and iodine atoms running parallel to the c-axis. Cu( 1) , a t the centre of the chain, is bonded tetrahedrally to four iodine atoms at 2.64 and 2.67 A. Cu(2), on alternate sides of the chain, is bonded tetrahedrally to two iodine atoms [shared with Cu( l)] a t 2.73 %i and to two CH,*NC groups which are at the sides of the chain. There are also short Cu Cu distances, indicating bonds, 2-89 and 3.42 A. CUPROUS IODIDE-METHYL ISOCYANIDE, a stable crystalline complex, was first prepared by Hartley from cuprous cyanide and methyl iodide. Decomposition yielded methyl isocyanide, but never methyl iodide; later, the compound was prepared from methyl isocyanide and cuprous iodide and is further described by Irving and Jonason.2 Attempts at molecular-weight determination in acetonitrile solution suggested that the complex is not monomeric; a similarity to Wells's tetrameric CuI,As(C,H,), seemed possible and the structure determination was undertaken. Crysta Data.-CuI,CH,*NC, M = 231.6, monoclinic, a = 13.88, b = 13-20, t = 5765 A, p = 105', U = 1020 A3, D, = 2.94 (by flotation), 2 = 8, D, = 3.02, F(000) = 832.Single-crystal oscillation and Weissenberg photographs.Space-group C2/c (No. 15), Cu-K, radiation, p = 575 cm.-l. EXPERIMENTALThe crystals are colourless needles, elongated along c. Oscillation and Weissenberg photographs were taken about the c and b axes. The intensities of the hkO and h02 reflections, and later hk 1 reflections were measured visually, and Lorentz and polarisation corrections applied. Approximate scale and temperature factors were determined from a *' Wilson plot "; more accurate values were later derived by comparison of lFcl with IFo], and from difference syntheses.The crystal used to record the hkO data was nearly square in cross section, of thickness 0.06 mm., and the needle axis was parallel to the oscillation axis. The linear absorption coefficient is 575 cm-l. Absorption corrections A(hk0) were estimated by a method based on that of Albrecht 4 for all inner, and a selection of outer reciprocal lattice points. Apart from 6 inner reflections, the correction is equivalent to an additional temperature factor, AB-

The structure of the plant estrogen, mirestrol, in the form of its monobromo-derivative, has been investigated by two-and three-dimensional methods of X-ray analysis. These lead to the structure (VI), which corresponds to the chemical formula C,,H,,O, and incorporates a partly reduced isoflaven nucleus. The bromine atom was first placed by the calculation of a Patterson projection along [OlO] in the monoclinic crystal structure, and the positions of the carbon and oxygen atoms were then found by three successive calculations of the three-dimensional electron-density distribution. The distinction between carbon and oxygen atoms in the molecule was made from a projection of the difference between the electron density derived with the observed F values and with a set calculated by assuming that all the atoms present (other than bromine) were carbon.The structure found for mircestrol appears to have interesting biogenetic relations and to account both for the chemical properties of the compound and, in general terms, for its biological activity.THE study of the structure of the plant Estrogen, mircestrol, described in this paper, has been carried out in close collaboration with Drs. D. G. Bounds and G. S. Pope, who prepared the active compound from the plant Pueraria mirijca found in Thailand. The use of X-ray methods to investigate its structure was initially suggested on account of the very small amount of material they could obtain. The structure now found by the X-ray analysis of monobromomirestrol appears to account very well for the chemical and spectroscopic properties of mirestrol which they describe in the following paper.l Mircestrol itself was first examined crystallographically by Dr. M. S. Webster in two differently hydrated crystalline modifications. The molecular weight determined from the measured density and unit-cell dimensions agreed with the formula C,,H,,O, but the accuracy was not sufficient to rule out the alternative analytically permissible formula C,H,O,.lThe complexity of the molecule was clearly too great to permit a detailed X-ray analysis of its structure without the introduction of a heavy atom into the molecule. A bromine derivative was sought, since the average scattering factor for X-rays of the mircestrol molecule as a whole, measured as dzj2, is approximately equivalent to that of a bromine atom; the monobromo-derivative, when prepared, appeared to be a suitable simple substitution product.(1) (11) (111)The molecular structure for monobromomircestrol (111) has been deduced by two-and three-dimensional methods of X-ray analysis. Initially the positions of the bromine atoms in the crystal were determined from Patterson projections. Two following electrondensity projections served to place the nine additional atoms of the structural unit (I), and the remaining carbon and oxygen atoms were located in stages ( 11) and ( 111), through 1 Rounds and Pope, following paper.