The Crystal and Molecular Structure of B5H11

Abstract

The molecular structure of B5H11 has been determined from 299 x-ray diffraction maxima which have been analyzed by three-dimensional Fourier and least-squares methods. There are four molecules in a monoclinic unit cell, in the space group P21/n, having parameters a=6.76, b=8.51, c=10.14A, and β=94.3°. Although no molecular symmetry is demanded by the space group, the molecular dimensions indicate C8 symmetry for the isolated molecule. The boron skeleton is a fragment of the icosahedronlike arrangement in B10H14, and can also be derived from the tetragonal pyramid in B5H9 by opening up one of the basal B–B bonds. The apex boron BI is ``singly'' bonded to two hydrogens, one of which HVII, is very weakly bonded to the two outer borons BIII. Each BIII is ``singly'' bonded to two hydrogen atoms. Each of the remaining two borons BII is ``singly bonded'' to one hydrogen atom, and there are three bridge hydrogens, one bridging the BII–BII bond and two bridging the BII–BIII bonds. Molecular parameters are two BI–BIII=1.865, two BII–BIII=1.75, two BI–BII=1.72, one BII–BII=1.77A, seven B–H=1.07, six B–H (bridge) =1.24A, one BI–HVII=1.00 and two BIII–HVII=1.67A. The BIII–BI–BIII angle is 107°. Bond angles to hydrogen strongly resemble those in the other known boron hydrides.

FALDI‐based decomposition of an atomic interaction line leads to 3D representation of the multicenter nature of interactions

“…To compare with 1 , we decided to investigate the interactions of two systems that, relative to each other, should display quite opposing degrees of multicenter bonding nature. The interaction between a boron (B1) and hydrogen (H7) atom in diborane, 2 in Figure , is well‐known as consisting of a large degree of multicenter character . However, the interaction between carbon atoms C9 and C12 in n ‐butane, 3 in Figure , which is representative of a classic single covalent CC bond, provides an example of a bicentric interaction.…”

“…Despite such conceptual difficulties, a large number of interactions have been formally classified (by a multitude of methods) as multicenter bonds. For instance, the remarkable differences observed between the structures of B 2 H 6 and C 2 H 6 led to the discovery of a large number of diborane structures with multicenter bonds . Moreover, multiple ligands which can bridge metal–metal bonds—such as chlorine atoms or carbonyl ligands—have been discovered and are well‐known examples of formal M⋅⋅⋅X⋅⋅⋅M multicenter bonds .…”

Further refinements of some rigid boron compounds

“…=(0, 1.70, 2.12) (~, r/, 0=(0, 2.12, 2.81) A, error 0.52. Lavine & Lipscomb (1954) solved this structure, and refinement to R=0.106 was done by Moore, Dickerson & Lipscomb (1957). The present refinement reduced R to 0.093, a significant improvement on the 2~o level, and the new coordinates are given in Table 2.…”

An account of some computing experiences

“…~ Fo, and w = 1 when 4 Fmin. >__ Fo (Lavine & Lipscomb, 1954) were used in most of our studies except as described below.…”

“…Unfortunately, the Fourier method of computing standard deviations (Hughes & Lipscomb, 1946;Cruickshank, 1949) is not usually modified to include weights related in at least a general way to standard deviations of the observations. We have found that a leastsquares refinement of AgN03 cyclooctatetraene with weights, as described by Lavine & Lipscomb (1954), gave standard deviations less by a factor of two than the standard deviations obtained from a similar refinement of the same compound but with the use of unit weights at every stage of the calculation, including the probable error computation. If the errors are truly random, it is a well-known result of the least-squares procedure that the 'best' system of weighting gives the lowest standard deviations.…”