Spectrochimica Acta Part A 79 (2011) 529–532 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa Experimental and theoretical study on the structure and vibrational spectra of -2-aminopyridinium dihydrogenphosphate C ¸a˘ grı C ¸ ırak a,∗ , Selc ¸ uk Demir b , Fatih Ucun c , Osman C ¸ ubuk d a Department of Physics, Faculty of Arts and Sciences, Erzincan University, 24100 Erzincan, Turkey b Department of Chemistry, Faculty of Arts and Sciences, Rize University, 53100 Rize, Turkey c Department of Physics, Faculty of Arts and Sciences, Süleyman Demirel University, 32100 Isparta, Turkey d Department of Chemistry, Faculty of Arts and Sciences, Erzincan University, 24100 Erzincan, Turkey article info Article history: Received 25 November 2010 Received in revised form 28 February 2011 Accepted 11 March 2011 Keywords: 2-Aminopyridinium dihydrogenphosphate HF DFT Vibrational analysis abstract Experimental and theoretical vibrational spectra of -2-aminopyridinium dihydrogenphosphate (- 2APDP) have been investigated. The FT-IR spectrum of -2APDP was recorded in the region 4000–400 cm -1 . The optimized molecular structure and theoretical vibrational frequencies of -2APDP have been investigated using ab initio Hartree–Fock (HF) and density functional B3LYP method with 6-311++G(d,p) basis set. The optimized geometric parameters (bond lengths and bond angles) and the- oretical frequencies have been compared with the corresponding experimental data and it is found that they agree well with each other. All the assignments of the theoretical frequencies were performed by potential energy distributions using VEDA 4 program. Furthermore, the used scale factors were obtained from the ratio of the frequency values of the strongest peaks in the experimental and theoretical IR spectra. From the results it was concluded that the B3LYP method is superior to the HF method for the vibrational frequencies. © 2011 Elsevier B.V. All rights reserved. 1. Introduction 2-Aminopyridine (2AP) (a.k.a. 2-pyridinamine), (C 5 H 4 N)NH 2 , is used in the synthesis of pharmaceuticals and polymer industry. 2AP and phosphoric acid system show rich polymorphism depending on crystallization conditions. Three anhydrate phases and one mono- hydrate form were isolated earlier [1,2]. It is reported that -form of 2-aminopyridinium dihydrogenphosphate (2APDP) displays fer- roelectric phase transition and this phenomenon is important for technologic materials [1,2]. Pyridine derivatives are widely used to synthesize many organic and organo-metallic compounds such as coordination com- pounds and metal phosphates. Metal phosphates are a member of open-framework materials family; the preparation of phosphate containing materials is attracting much more interest because of their application areas, such as catalysts, ion-exchangers and optic materials [3,4]. Although ammonium phosphates are known to occur as by-products in the synthesis of metal phosphates [5], it is believed that they could act as intermediates in the formation of metal phosphates and they can be used in order to synthe- size metal-phosphates under relatively mild conditions [6–8]. They exhibit interesting crystal packing motifs strongly influenced by hydrogen bonds, also [9–13]. ∗ Corresponding author. Tel.: +90 446 2243097; fax: +90 446 2243016. E-mail address: ccirak@erzincan.edu.tr (C ¸.C ¸ ırak). Complementary to our earlier works [9–13], herein we present our results on the experimental and theoretical IR study of -2APDP. The optimized molecular geometry and vibrational fre- quencies have been calculated using ab initio Hartree–Fock (HF) and density functional theory (B3LYP) methods with 6-311++G(d,p) basis set level. The calculated optimized geometric parameters and vibrational frequencies have been compared with the correspond- ing experimental data. 2. Experimental details -2APDP can be synthesized according to the literature [2,14]. We have used the same sample synthesized and characterized in our earlier work [14]. The FT-IR spectra were recorded from KBr pellets in the range 4000–400 cm -1 using a JASCO FT/IR-430 spec- trophotometer. Single crystal X-ray data collection and structure solution procedures were explained earlier [14]. 3. Computational methods The optimized structure parameters and vibrational frequen- cies of -2APDP have been calculated using ab initio Hartree–Fock and density function theory (B3LYP) method at 6-311++G(d,p) basis set level. All computations have been performed using Gaus- sian 03 program package on high performance computing system [15]. The calculated vibrational frequencies were scaled with some scale factors which we have found using the ratio of the fre- 1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2011.03.026