Spectroscopic Identification of Hydrogen Bond Vibrations and Quasi-Isostructural Polymorphism in N-Salicylideneaniline.

Łukasz Hetmańczyk,Mikhail V Vener,Peter M Tolstoy,Eugene A Goremychkin,Aleksander Filarowski,Paweł Lipkowski,Janusz Waliszewski

doi:10.3390/molecules26165043

Abstract

The ortho-hydroxy aryl Schiff base 2-[(E)-(phenylimino)methyl]phenol and its deutero-derivative have been studied by the inelastic incoherent neutron scattering (IINS), infrared (IR) and Raman experimental methods, as well as by Density Functional Theory (DFT) and Density-Functional Perturbation Theory (DFPT) simulations. The assignments of vibrational modes within the 3500–50 cm−1 spectral region made it possible to state that the strong hydrogen bond in the studied compound can be classified as the so-called quasi-aromatic bond. The isotopic substitution supplemented by the results of DFT calculations allowed us to identify vibrational bands associated with all five major hydrogen bond vibrations. Quasi-isostructural polymorphism of 2-[(E)-(phenylimino)methyl]phenol (SA) and 2-[(E)-(phenyl-D5-imino)methyl]phenol (SA-C6D5) has been studied by powder X-ray diffraction in the 20–320 K temperature range.

Highlights

This paper dwells on the studies of one of the most popular photo-thermochromic compounds, 2-[(E)-(phenylimino)methyl]phenol (N-salicylideneaniline), from the group of the ortho-hydroxy aryl Schiff bases
The paper presents the synthesis of 2-[(E)-(phenylimino)methyl]phenol (SA) and its two deutero-derivatives (SA-OD and s0p4–8e4]c8.t]r.a of non-deuterated (SA)-C6D5)
The bands corresponding to hydrogen bond vibrational modes were assigned in experimental IR, inelastic incoherent neutron scattering (IINS) and Raman spectra

Summary

Introduction

This paper dwells on the studies of one of the most popular photo-thermochromic compounds, 2-[(E)-(phenylimino)methyl]phenol (N-salicylideneaniline), from the group of the ortho-hydroxy aryl Schiff bases. TThhee rreecceenntt ccoommpprreehheennssiivvee ssttuuddiieess sseeeemm ttoo iinnddiiccaattee tthhaatt tthhee pprroottoonn ttrraannssffeerr iinn tthhee iinnttrraammoolleeccuullaarr OOHHNN hhyyddrrooggeenn bboonndd aanndd tthhee iissoommeerriizzaattiioonn ooff tthhee aallddiimmiinnee ffrraaggmmeenntt ((CChhaarrtt bb,, FFiigguurree 11)) iiss iinn cchhaarrggee ooff tthhee aappppeeaarraannccee ooff pphhoottoo--tthheerrmmoocchhrroommiicc pprrooppeerrttiieess iinn oorrtthhoo--hhyyddrrooxxyy aarryyllSScchhififffbbaasesses[2[82].8N]. Upon deuteration in the hydrogen bridge site (SA-OD), the intensity of the b5aonfd13s assigned to the γ(OH) and νσ(OHN) vibrations (848 cm−1 and 449 cm−1, respectively) is decreasing (Figure 4A), while the IINS spectrum of the SA-C6D5 derivative features a more complicated picture (Figure 4B). The band at 449 cm−1, which is assigned to νσ(OHN) vibration ( marked by the red arrow in Figure 4B), is sensitive to deuteration in the aldimine ring: the band broadens and its peak intensity decreases Such a long-range H/D isotope effect on hydrogen bond vibrations is reported here for the first time.

Spectral Manifestations of Polymorphism

X-ray Powder Diffraction

Calculations

Conclusions