Solvation Effect on the NH Stretching Vibrations of Solvated Aminopyrazine, 2-Aminopyridine, and 3-Aminopyridine Clusters

Abstract

The vibrational spectra of the hydrated and methanol-solvated aminopyrazine, 2-aminopyridine and 3-aminopyridine in supersonic jets have been measured in terms of IR-UV double-resonance spectroscopy. Comparing the IR spectrum of aminopyrazine with those of 2-aminopyridine and 3-aminopyridine clusters, we determine the solvation structure of aminopyrazine to be a similar cyclic structure as hydrated 2-aminopyridine clusters [Wu, et al., Phys. Chem. Chem. Phys. 2004, 6, 515]. In the case of monohydrated aminopyrazine cluster, one of the normal modes composed of the hydrogen-bonded OH and NH stretching local modes gives the anomalously weak IR intensity, which is ascribed to the cancellation of the dipole moment change between the OH and NH stretching local modes. The solvated 3-aminopyridine clusters forms the hydrogen-bond between the pyridyl nitrogen atom and the OH group, but the amino group is indirectly affected to induce slight blue shift of the NH(2) stretches. This phenomenon is explained by inductive effect where the electron withdrawing from the amino group upon the solvation results in a "quinoid-like" structure of the amino group.

Excited-State Dynamics Affected by Switching of a Hydrogen-Bond Network in Hydrated Aminopyrazine Clusters

“…Figure 1 shows the LIF spectra of the sample vapor mixed with water in different cooling conditions. Two intense bands appear at 31 266 and 30 463 cm −1 , which were reported in the previous article to be an APz monomer and its monohydrated cluster (APz-W1), respectively, 40 and the asterisk indicates the hot band of the former. In the lower frequency region, two weak bands are newly observed at 30 029 and 29 851 cm −1 denoted by W2 and W3, respectively.…”

“…Figure shows the FDIR spectra of APz-W n ( n = 2–4) obtained by fixing the probe UV frequencies to 30 029, 29 851, and 29 554 cm –1 , respectively. The single free NH stretch is observed in the region of about 3540 cm –1 despite the water size, meaning that one NH bond of the amino group in all of the clusters forms the NH···O H-bond, similar to APz–(H 2 O) 1 . Another common characteristic feature is the considerably broadened band at the lowest frequency.…”

“…The single free NH stretch is observed in the region of about 3540 cm −1 despite the water size, meaning that one NH bond of the amino group in all of the clusters forms the NH•••O Hbond, similar to APz−(H 2 O) 1 . 40 Another common characteristic feature is the considerably broadened band at the lowest frequency. They are assigned as the most strongly H-bonded OH stretching modes and the closely appearing bands may be attributed to Fermi resonance with HOH bending overtones or combination bands consisting of other lower frequency modes including intermolecular vibrations.…”

“…Previously, Tembreull et al measured the electronic spectrum around 320 Å for bare aminopyrazine (APz) and assigned that the S 1 state corresponds to n π* . Our group measured the infrared (IR) spectra of the hydrated and methanol-solvated APz, which has two possibilities of the H-bond acceptor sites in the pyrazine ring, namely, the nitrogen atoms at the 1- (N1) and 4-positions (N4), corresponding to the acceptor sites of monohydrated 2AP and 3-aminopyridine (3AP) clusters, respectively, and suggested that the solvation structure of APz is a cyclic form similar to 2AP, reported by Wu et al, where the H-bond network connects between the amino group and N1. On the other hand, the recent article showed that 3AP–(H 2 O) n ( n = 3, 4) is composed of the homodromic H-bond chain starting from the amino group toward a pyridyl nitrogen acceptor, which might provide the possibility that the further hydration to APz changes the H-bond network from the 2AP-like structure to the 3AP one .…”

Hydrogen and Halogen Bond Mediated Coordination Polymers of Chloro-Substituted Pyrazin-2-Amine Copper(I) Bromide Complexes

“…Powder X-ray diffraction methods were used to demonstrate the solid-state structures and estimate the phase purity of the bulk material by using Pawley full pattern fittings. The FT-IR spectra of the isolated complexes were compared to the respective ligands, and display two specific regions from 3500-2800 cm −1 and 1200-400 cm −1 for the hydrogen-bonded N-H stretching [71] and fingerprint regions, respectively, which are distinctive for each ligand and complex (see Figures S10-S16).…”