Structures of molecular addition compounds. I. Monomethyl amine—boron trifluoride, H3CH2N–BF3
Structures of molecular addition compounds. I. Monomethyl amine—boron trifluoride, H3CH2N–BF3
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分子加成化合物的结构。 一甲胺-三氟化硼，H3CH2N-BF3。
DOI：
10.1107/s0365110x50000276
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发表时间：
1950
期刊：
影响因子：
--
通讯作者：
J. Hoard
中科院分区：
文献类型：
--
作者：
S. Geller;J. Hoard
从H_3CH~N-BFA晶体中获得的X射线数据表明，它是一个单线结构单元，a=5.06，b--7-28，c--5.81 A，/？-101 31‘，含有两个化学计量比分子。所有的X射线数据都与空间群P_2z/m一致。原子(氢除外)的近似位置是通过各种Patterson合成确定的，参数通过各种傅立叶合成进行修正。H3CHgN-BF3的结构有几个重要而有趣的特征。BN键为1.58A，比根据Pauling共价半径预测的值长0.09A，并对B和N的电负性差异进行了修正。然而，这种化合物在常温下是稳定的。在H_3CH~N-BF_3(/_B-Nc=114)中，氮原子不形成四个等价的四面体。甲基和氟原子为交错构型。BF键值(1-37A)的FBF角(111)和FBN角(108)与四面体值(IO928‘)的偏差。从预测值1-39 A.(Schomaker&Stevenson，1941；Bauer&比奇，I941)和CN键(I.50 A.)从1.47A.开始不能说是非常重要的，因为误差的限度可能会使这些差异变得不真实。另一方面，从tIsCCN-BF3的X射线衍射研究结果(本系列的第二篇论文)和(H3C)~O-BF3的电子衍射研究结果中，有一些证据表明这些差异是可能的。前者的结果毫无疑问地表明，硼原子不需要形成四个等价的四面体键，而后者的结果表明，在H3CH2N-BF8中CN键是可能伸展的。计算了所有重要的原子间距，并讨论了分子在晶体中的堆积排列。近年来，随着许多新的硼化合物的发现，以及新旧化合物有趣而重要的性质的发现，使对它们的研究增加了。通常认为，在三卤化硼或三甲基硼等分子中，硼具有很强的
X-ray data obtained from crystals of H3 CH~ N-BFa lead to a monoelinie unit of structure with a= 5.06, b--7-28, c--5.81 A.,/?-101 31', containing two stoichiometric molecules. All of the X-ray data are consistent with the space group P2z/m. Approximate positions of the atoms (other than hydrogen) were determined by the use of various Patterson syntheses, and the parameters refined by means of various Fourier syntheses. There are several important and interesting features of the structure of H3CHgN-BF3. The BN bond is 1.58 A., 0.09 A. longer than the value predicted on the basis of Pauling's covalent radii with application of a correction for difference of electronegativity between boron and nitrogen. Yet the compound is stable at ordinary temperatures. The nitrogen atom does not form four equivalent tetra-hedral bonds in H3CH~ N-BF3 (/_B-NC= 114). The methyl group and fluorine atoms are in the staggered configuration. The deviations of the FBF angle (111) and the FBN angle (108) from the tetrahedral value (I09 28'), of the value for the BF bond (1-37 A.) from the predicted value, 1-39 A.(Schomaker & Stevenson, 1941; Bauer & Beach, I941), and of the CN bond (I. 50 A.) from 1.47 A. cannot be said to be very significant since the limits of error may be such as to make these differences unreal. On the other hand, there is some evidence from the results of the X-ray diffraction investigation of tIsCCN-BF3 (the second paper in this series) and of the electron diffraction investigation of (H3C)~ O-BF3 that indicates that these differences are possible. The results of the former study leave little doubt that the boron atom need not form four equivalent tetrahedral bonds, whereas the results of the latter give some indication that the stretching of the CN bond in H3CH2N-BF8 is probable. All of the important interatomic distances have been calculated and the packing arrangement of the molecules in the crystal is discussed.Introduction The discovery, in recent years, of many new boron com-pounds, and of interesting and important properties of both old and new compounds, has led to increased study of them. It is generally considered that in molecules such as the boron trihalides or trimethyl boron, boron has a strong