William N. Lipscomb

On the crystal structures, residual entropy and dielectric anomaly of methanol

The orthorhombic form of methanol has the space group D~-Cmcm. There are four molecules in a unit cell of dimensions a = 6-43, b= 7.24 and c=4.67 A. Infinite zigzag chains of hydrogen bonds exist parallel to the (100) face. The C-O distance is 1.42 A, and the O . O hydrogen-bond distance is 2.66 A, indicating strong hydrogen bonds. Surrounding a particular methyl, there are two methyls at 3.88 A, four methyls at 4.01 A, two oxygens at 3.86/~ and four oxygens at 4-09 A. The diffraction effects obtained from single crystals cooled through the ~ point indicate that the transition is a simple displacive transformation involving a puckering of the infinite hydrogenbonded chains, preserving the infinite chains of hydrogen bonds. The essential aspects of this transformation may be described by a monoclinic unit, containing two molecules, with a=4-53, b=4-69, c=4.91 /~ and fl=90 ° in the space group C~h-P2~/m, although the presence of some weak reflections suggests a superlattice. It is concluded that the residual entropy is zero, and that the dielectric anomaly is associated with the puckering of the chains discussed above.

The Valence Structure of the Boron Hydrides

A set of extended valence postulates is presented including the concept of the localized three‐center bond. These postulates are applied systematically to the boron hydrides and account for their unusual geometry, their unexpected dipole moments, and the fact that they are not ``electron‐deficient.

The crystal and molecular structure of 1,4-dithiadiene

A non-planar six-membered ring with the boat configuration has been established for the molecular structure of 1,4-dithiadiene, C4H4S ~. Molecular parameters, which suggest a model of Cgv symmetry, are C-S---1.78±0.05 A, C----C = 1-29±0.05 A, C--C--S_--__ 124 ° and C-S-C~_--100% The crystals are orthorhombic, the space group is ~2 C2v-Cmc2~, and the unit cell dimensions are a ---11-28, b---6.41 and c---7.36 A.

Least Squares Refinements of B10H14, B4H10, and B5H11

New interatomic distances in B10H14, B4H10, and B5H11 indicate that the B–B distances which are more strongly bound in the simplified valence theory are slightly shorter than other B–B distances. The position of the unique hydrogen atom in B5H11 is now somewhat more satisfactory in relation to the plane of symmetry of the isolated molecule. The improvement of agreement of observed and calculated x‐ray intensities suggests that least squares refinements as usually applied are not carried through enough iterations.

Crystal and Molecular Structure of Diboron Tetrachloride, B2Cl4

X‐ray diffraction study of a single crystal of B2F4 indicates a planar, centrosymmetric molecule with B–B=1.67±0.045 A, B–F=1.32±0.035 A and angle F–B–F=120°. There are two molecules in a monoclinic unit cell of symmetry P21/n and parameters of a=5.49, b=6.53, c=4.83, and β=102.5°.

STRUCTURES OF THE BORON HYDRIDES

Evidence for the structures of B2H6, B4H10, B5H9, B5H11, and B10H14 is reviewed. Correlations of the boron arrangements with known structures have been pointed out, and a systematic discussion of the boron‐hydrogen distances is given.

Semitopological Approach to Boron‐Hydride Structures

A semitopological approach to the structures of boron hydrides is discussed in detail, as an extension of the equations of orbital and electron balance derived by Eberhardt, Crawford, and Lipscomb. This consistent set of principles gives the presently known boron hydrides whose frameworks are icosahedral fragments, and predicts (1) the hydrogen arrangement in B6H10, (2) that a stable B8 hydride will probably be either B8H12 or B8H14, (3) B9H13 should not exist, and (4) that no B7 hydride should exist.

The Crystal and Molecular Structure of Tetraborane

The molecular structure of tetraborane B4H10 has been determined from 616 observed reflections from single crystals. The ordered phase is monoclinic P21/n, with four molecules in a unit cell with parameters, a=8.68, b=10.14, c=5.78A, and β=105.9°. Complete three‐dimensional Fourier syntheses, including one from which the boron atoms had been subtracted, were employed to locate unambiguously the positions of all atoms.Molecular dimensions indicate that the isolated molecule has symmetry C2v. The boron atoms form two triangles BIBIBII with a common edge BI–BI the angle between the planes of the triangles being 118.1°. Each of the two BI borons has one attached hydrogen atom, and each BII has two attached hydrogen atoms. The remaining four hydrogen atoms form bridges between the four BI–BII pairs. Molecular parameters are four BI–BII=1.845±0.002A, BI–BI=1.750A, BII–BII=2.786A, six B–H=1.11±0.04A, four BI–H (bridge)=1.21±0.03A, and four BII–H (bridge)=1.37±0.10A. Mean values and their average deviations have ...

Crystal and Molecular Structure of B9H15

With only the information that B and H alone are present, and that the melting point is —20°, the molecular structure of B9H15, a new boron hydride, has been determined from single crystals by x‐ray diffraction methods. There are four molecules in the unit cell, space group P21/n, with a=11.80 A, b=6.94 A, c=11.25 A, and β=109° 9′. The boron skeleton, solved by three‐dimensional Patterson and trial and error methods, and refined by least squares methods, is a fragment of the icosahedron formed by removing three connected borons not forming an equilateral triangle. Hydrogen atoms, located from three‐dimensional difference maps, agree with those expected from previously known boron hydrides. The over‐all agreement factor is R=Σ∥F0| — |Fc∥/Σ|F0|=0.155.Computations on the UNIVAC Scientific 1103 Computer are described briefly, with emphasis on the use of fractional shifts of parameters in the least squares method. A least squares normalized weighted sum of squares of residuals is proposed as a better criterion...

MOLECULAR STRUCTURE OF B10H12(CH3CN)2

An x‐ray diffraction study of single crystals of B10H12 (CH3CN)2 has yielded the positions of all atoms, including hydrogen atoms. The structure is regarded as a substitution derivative of the B10H14—2 structure having C2v symmetry, two bridge hydrogens and two BH2 groups. A B–N single bond replaces a B–H of each BH2 group and the acetonitrile residue is linear with normal bond distances, except for C–CH3=1.45 A in agreement with C–CH3=1.46 in acetonitrile itself.The unit cell is monoclinic, of symmetry I2/c, and has parameters a=7.81, b=11.31, c=14.18, and β=96°52′. Final values of R=0.15 and r=0.12 were obtained, as described in the text.