Effect of Hydrogen Bonding on the Pyramidalization of the Amino Group: Structure of 3,4-diaminobenzamidinium Chloride

Ivana Stolić,Miroslav Bajić,Dubravka Matković-Čalogović

doi:10.5562/cca2224

Abstract

3, 4-diaminobenzamidinium was synthesized and spectroscopically and structurally characterized, both at room temperature and at 150 K. The crystal structure consists of two 3, 4- diaminobenzamidinium cations and two chloride anions. The planar amidinium group is inclined by 35.35(5)° and 28.96(7)° in respect to the diaminobenzene moiety in the two crystallographically independent cations. The ions are interconnected by a large network of hydrogen bonds into a threedimensional structure. Pyramidalization of the amino group in relation to the hydrogen bond length in which the amino group is an acceptor is analized. Two amino groups are acceptors of N–H···N hydrogen bonds of 2.9565(14) A and 2.9654(15) A resulting in pyramidalization of 340(1)° and 337(1)°, respectively (the sum of the amino group bond angles is given as a measure of pyramidalization). A very weak hydrogen bond to one amino group results in a very flat pyramid (351(1)°), while one amino group is not acceptor of a hydrogen bonds and it is planar. The resonance effect has influence on the planar amino groups resulting in a shorter C–N(amino group) bond length than in the pyramidalized ones. (

Highlights

Natural products and synthetic organic cations that bind and selectively to the DNA minor groove have therapeutic potential in a wide range of applications.[1]
It was noted that the NH2 groups were calculated to be more pyramidal than the experimental values (112(4)°, 116(5)° and110(5)°) and that this fact is not surprising considering the difficulty in assigning the hydrogen atom position in the crystal structure
The molecule of 1 contains three groups that are capable of forming hydrogen bonds: amino group, nitro group and amidino whereas that of 2 has only the amino and amidino groups

Summary

Introduction

Natural products and synthetic organic cations that bind and selectively to the DNA minor groove have therapeutic potential in a wide range of applications.[1]. Structure of 3,4-diaminobenzamidinium chloride shows a very interesting influence of hydrogen bonding on the pyramidalization of the amino group and deserves a detailed analysis. A wide signal around 3100–3300 cm–1 is associated with N–H stretching of hydrogen bonded amino groups which is in agreement with the crystal structure.

Results

Conclusion