Chemical bonding in the crystal structure of 1-hydrosilatrane

Abstract

A study has been made of the crystal and molecular structure of 1 hydrosilatrane HSi(OCH 2 CH 2 ) 3 N. The quantum chemical calculations of its crystal structure have been carried out. According to an estimate of the energy, the coordination bond N→Si is by 5 kcal mol -1 stronger than that in the crystal of 1 methylsilatrane. The charge values calcu lated within the framework of the topological analysis of the electron density demonstrate that the electron density of the coordination bond N→Si is primarily transferred to the region of the equatorial bonds Si-O and, to a lesser extent, to the bond Si-H. On going from the isolated molecule of 1 hydrosilatrane to its crystal, the interatomic distance N-Si decreases, mainly owing to the weak intermolecular interaction C-H…O.Key words: silatranes, 1 hydrosilatrane, X ray diffraction study, quantum chemical calcu lations, N→Si bond energy, density functional theory, basis sets of plane waves.As surprising as it may seem, the molecular and crystal structure of the parent compound of a broad family of silatranes, viz., 1 hydrosilatrane or silatrane, HSi(OCH 2 CH 2 ) 3 N (1), 1-4 has not been studied. This stems from the fact that so far the preparation of single crystals of 1 pos sessing high diffraction quality has failed. At the same time, the molecular structure of this compound, the most straightforward and convenient method of synthesis of which was suggested by one of us as early as 40 years ago, 5 attracted great interest of researchers. It was established by IR spectroscopy that the frequency and integral inten sity of the Si-H bond vibrations in molecule 1 (and, consequently, the distribution of electron density in the axial fragment N→SiH) depends on the polarity (dielec tric constant ε) of the solvent and temperature. 6 The electron diffraction and quantum chemistry meth ods allowed the study of the structure of molecule 1 in the gas phase. 7 It was found that a longer bond N→Si in an individual molecule of 1 (2.406 Å) (as compared to that in the structure we determined in the crystal) has an inter mediate value between the corresponding lengths of bonds N→Si in the molecules of 1 methylsilatrane (2) 8 and 1 fluorosilatrane (3) 9 (2.453 and 2.324 Å, respectively). Therefore, on the basis of the length of the bond N→Si molecule 1 is closer to 2 rather than to 3. This indicates the proximity of the values of the interaction energies of * Dedicated to academician A. I. Konovalov on his 75th birthday. the nitrogen and silicon atoms in the former two mol ecules. The bond length N→Si in molecule 1 calculated with the B3LYP/6 311G(d) and MP2 basis set amounts to 2.335 Å (see Ref. 10) and 2.351 Å (see Ref. 7), respec tively. As to the lengths of the bonds N-C, O-C, Si-O, and C-C, they are approximately the same as in mol ecules 2 and 3. In molecule 1 the silicon atom is shifted from the equatorial plane of three oxygen atoms surround ing it in the direction opposite to the nitrogen atom, the angle N-Si-O is smaller than 90°, while the angle Si-N-C is larger than 90°. ...

Correlation among the Gas-Phase, Solution, and Solid-Phase Geometrical and NMR Parameters of Dative Bonds in the Pentacoordinate Silicon Compounds. 1-Substituted Silatranes

“… a All calculations were performed with the 6-311G(d,p) basis set. b Reference . c Reference d Reference . …”

“…According to the data of IR and NMR spectroscopy and ED, X-ray, , and quantum chemistry methods, the coordination Si←N contact in silatranes turned out to be very sensitive not only to the internal factors, that is, to the X nature, but also to the external onesthe aggregate state of compounds and solvent polarity . For example, the transition of FSi(OCH 2 CH 2 ) 3 N from the solid phase (X-ray) to the gas phase (ED) results in the increase of the Si···N distance by 0.28 Å. , It seemed tempting, using only the δ N values measured in solution and assuming the validity of eq in any medium, to perform the estimations of the experimentally unavailable solution values of d SiN and, consequently, the reactivity of silatranes with this equation.…”

Crystal Structure of New 1-Phenyl-Substituted Tribenzsilatranes

“…As a result, silatranes 1 have a characteristic feature: hypersensitivity to internal (nitrogen environment) and external (phase state, solvent, temperature) factors [1,2,[6][7][8][9][10]. For instance, the Si• • • N contact length in X-Si(OCH 2 CH 2 ) 3 N (X = H, Me, F) in the gas phase, according to electron diffraction data and the results of quantum chemical calculations, exceeds the corresponding value in the crystalline phase (from XRD) by more than 0.25 Å [1,7,[10][11][12][13][14].…”

Crystal and molecular structure of the complex of 2-(1-silatranylmethylthio)-4,5-benzo-1,3-thiazole with CoCl2 and MeCN

“…The coordination polyhedron of the silicon atom in complex I is a trigonal bipyramid that is common for silatranes [5]. The length of the N3→Si coordination bond of 2.089(5) Å is close to that observed in the 1-hydrosilatrane (2.071 Å) [6], N-(1-silatranylmethyl)imidazole (2.088 Å) [7], and -benzimidazole (2.088 Å) [8] moleculеs and coincides with this bond length in N-(1-silatranylmethyl) pyrrole (2.089 Å) [9], 2-(1-silatranylmethyl)-1,2,3-benzotriazole (2.089 Å) [10], differing from 1-(2′-benzothiazolylthiomethyl)silatrane (2.100 Å) [2] by only 0.011 Å.…”