Supramolecular solid-state architecture formed by co-crystallization of melamine and phenylacetic acid

Journal Pre-proof Supramolecular solid-state architecture formed by co-crystallization of melamine and phenylacetic acid Jan Janczak PII:

S0022-2860(20)30157-5

DOI:

https://doi.org/10.1016/j.molstruc.2020.127833

Reference:

MOLSTR 127833

To appear in:

Journal of Molecular Structure

Received Date: 20 November 2019 Revised Date:

27 December 2019

Accepted Date: 31 January 2020

Please cite this article as: J. Janczak, Supramolecular solid-state architecture formed by cocrystallization of melamine and phenylacetic acid, Journal of Molecular Structure (2020), doi: https:// doi.org/10.1016/j.molstruc.2020.127833. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.

CRediT author statement Jan Janczak 100 %

Graphical Abstract Text Melamin-1-ium phenylacetate phenylacetic acid monohydrate supramolecular complex was obtained in the crystalline form. The hydrogen-bonded supramolecular complex was characterized by X-ray single crystal diffraction, Hirshfeld surface and analysis and vibrational spectroscopy.

Graphical Abstract Picture

Supramolecular solid-state architecture formed by co-crystallization of melamine and phenylacetic acid Jan Janczak* Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Okólna 2 str., P.O. Box 1410, 50-950 Wrocław, Poland

Abstract Crystallization of melamine with phenylacetic acid from water solution yields melamin-1-ium phenylacetate phenylacetic acid monohydrate supramolecular complex (1). The compound crystallises in the centrosymmetric space group of the triclinic system. In the crystals, beside the ionic interaction, the protonated melamin-1-ium cation (MH+) interacts with phenylacetate anion via two N−H…O hydrogen bonds with a graph of R22(8) forming supramolecular {MH…phenylacetate} complex that further interacts with neutral acid molecule by a combination of O−H...N and N−H...O hydrogen bonds with a graph of R32(10) and then with water molecule via N−H…O hydrogen bond forming supramolecular complex of 1.

The supramolecular assembly of melamin-1-ium phenylacetate

phenylacetic acid monohydrate units is driven by the noncovalent interactions with neighbours via N−H…N, N−H…O and O−H…O with a graph of R22(8), R32(8) and R43(10) into hydrogen-bonded tapes. The tapes are further organised into stacks. Hirshfeld surface and the analysis of the 2D-fingerprint plots are illustrating both qualitatively and quantitatively interactions governing the formation of the supramolecular architecture. The compound was also characterized by the FT-IR and Raman spectroscopy. Assignment of the bands have been supported by the isotropic frequency shift. Keywords: melamine; phenylacetic acid, crystal structure; supramolecular architecture, Hirshfeld surface; Vibrational spectroscopy *E-mail: [email protected]. Tel. +48 71 39 54 145. Fax: +48 71 34 410 29.

1.

Introduction Supramolecular architectures resulting from the interaction of melamine as an organic base with

organic or inorganic acids have been of interest for several decades. Melamine as a symmetric trigonal planar molecule (D3h) containing multiple hydrogen-bonding sites and is an excellent in the crystal engineering as a building blocks (Scheme 1a). It’s can acts both hydrogen donor and hydrogen acceptor in hydrogen bonding because the melamine molecule has 6 H-donors (-NH2) and 3 Hacceptors (N-ring atoms). Furthermore the π-character of its 1,3,5-triazine ring may lead to π-π interaction in solids and contributes to the stabilization of architectures with its participation [1]. The non-covalent interactions including interactions with proton transfer from various types of acids 1

to melamine as a base have been used in supramolecular chemistry the self-assembly and design a large number of architectures such as types, rosettes, layers and sheets, rectangular nets and organic-inorganic sandwich type 3D network structures [2]. Interactions between unit building blocks of the crystal can be described by the concept of supramolecular synthons, structural units formed by predictable intermolecular interactions and are powerful tools for predicting not only local interactions between individuals, but often provide insight into the global topology of the crystal architecture [3]. Melamine, a nitrogen-rich heterocyclic triazine, is an ordinary chemical compound used in the manufacture of plastics, resins, flame-retardants, adhesives, fertilizers and fabrics as well as in the production of pesticides [4], but in body is hazardous, it metabolized to cyanuric acid, a process leads to precipitation of melamine-cyanuric acid co-crystals within the kidneys, causing renal failure [5]. Contamination with melamine in food is dangerous and causes illness and death to human infants and animals [6]. The high complementarity of the melamine and cyanuric acid has been used to rationalize the stability and relatively poor aqueous solubility of melamine-cyanuric acid co-crystal [7]. Due to melamine's aromaticity, the electron density is much lower at the NH2 moiety in melamine than in aliphatic amines. As a result, in acidic media melamine is typically protonated at one or two of the triazine nitrogen atoms and not at the NH2 groups. The self-organization of melamine crystallization with various organic and inorganic acids has led to a large number of different supramolecular architectures in solids [8]. Co-crystallization of melamine and the 1,5-naphthalenedisulfonic acid from aqueous solution leads to supramolecular structure with an infinite water chains [9], whereas crystallization of melamine with 1,3,6-benzenetricarboxylic acid (trimesic acid) yields crystals with the characteristic helical assembles [10]. A porous structures of hydrogen-bonded organic frameworks have been also reported for solvent dependent crystallization of melamine [11]. Several supramolecular architectures resulting from the co-crystallization of melamine with small organic molecules illustrate that it can also forms supramolecular structures in the neutral form [12].

(a)

(b)

Scheme 1. Melamine (a) and phenyl acetic acid (b).

In the present work the supramolecular structure formed by co-crystallization of melamine with phenylacetic acid from aqueous solution has been examined (Scheme 1). This study aims to influence how the molar ratio of melamine to acid affects the composition of the crystals obtained. The 2

interactions between the components building the supramolecular arrangement have been analysed by the Hirshfeld surface and the 2D fingerprint plots. Additionally, the interactions between the melamine-phenylacetic acids were also characterized by the vibrational spectroscopy.

2.

Experimental

2.1. Materials The reagents 2,4,6-triamino-1,3,5-triazine (99%) and phenylacetic acid (99%) were purchased from Sigma-Aldrich and were used without further purification. Elemental analysis was carried out with a Perkin Elmer 240 elemental analyzer.

2.2. Synthesis 2,4,6-triamino-1,3,5-triazine and phenylacetic acid were added to hot water in a molar proportion of 1:1. When the solution became homogenous it was cooled slowly and kept at room temperature. After several days, transparent colorless crystals suitable for the X-ray single crystal analysis were obtain. The crystals have been separated by filtration and dried in air. The same procedure has been used for the melamine to phenylacetic acid used in the proportion of 2:1. However, the obtained crystals were the same in both cases. So the crystals are the most stable in the used conditions. The colorless crystals obtained are co-crystal of salts and acid: melamin-1-ium phenylacetate phenylacetic acid monohydrate, (C3H7N6)(C6H5CH2COO)(C6H5CH2COOH)(H2O) (1). Analysis: calculated for C19H24N6O5: C, 54.80; N, 20.18; O, 19.21 and H, 5.81%. Found: C, 54.68; N, 20.22; O, 19.31 and H, 5.79%.

2.2. X-ray single crystal data collection X-ray intensity data for the crystal 1 were collected using graphite monochromatic MoKα radiation on a four-circle κ geometry KUMA KM-4 diffractometer with a two-dimensional area CCD detector. The ω-scan technique with ∆ω = 1.0o for each image was used for data collection. Data collections were made using the CrysAlis CCD program [13]. Integration, scaling of the reflections, correction for Lorenz and polarisation effects and absorption corrections were performed using the CrysAlis Red program [13]. The structures were solved by the direct methods using SHELXT-2014/7 [14] and refined using SHELXL-2018/3 program [15]. The positions of hydrogen atoms involving in the hydrogen bonds were located in difference Fourier maps and were refined with Uiso=1.2Ueq of N joined H or Uiso=1.5Ueq of O atom joined H. The hydrogen atoms joined to aromatic carbon atoms were introduced in their geometrical positions and treated as rigid. The final difference Fourier maps showed no peaks of chemical significance. Details of the data collection parameters, crystallographic data and final agreement parameters are collected in Table 1. Selected geometrical parameters are 3

listed in Table S1 (in SI) and the geometry of hydrogen bonding interactions is collected in Table 2. Visualisations of the structures were made with the Diamond 3.0 program [16].

2.3. Powder X-ray Diffraction (PXRD) Powder X-ray diffraction patterns of the powdered protiated and deuterated samples of 1 were checked on

a PANanalytical X’Pert diffractometer equipped with a

Cu-Kα radiation source

(λ=1.54182 Å). The diffraction data were recorded in the range of 5-45o at room temperature. The powder diffraction patterns of H- and D-compounds are included in supporting information (Figs. S1). The obtained deuterated analogue crystallises, similar as H-compounds, in the same crystal systems with quite similar lattice parameters.

2.4. Hirshfeld surface analysis Hirshfeld surface analyses, and 2D fingerprint plots as well as percentage contributions for various intermolecular contacts in the investigated crystals were calculated using the Crystal Explorer Ver. 3.1 program package [17].

2.5. Vibrational Spectra Measurements The vibrational measurements of H-compound and its deuterated analogue were carried out at room temperature. The Fourier transform infrared spectrum was recorded from nujol mulls between 4000 and 400 cm-1 on a Bruker IFS 113 V FTIR spectrometer. Resolution was set up to 2 cm-1. The Fourier Transform Raman spectra were recorded on a FRA-106 attached to the Bruker 113 V FTIR spectrometer equipped with Ge detector cooled to liquid nitrogen temperature. Resolution was set up to 2 cm-1, signal/noise ratio was established by 32 scans. Nd3+ - YAG air-cooled diode pumped laser of power ca. 200 mW was used as an exciting source. The incident laser excitation was 1064 nm. The scattered light was collected at the angle of 180o in the region of 3600÷80 cm-1, resolution 2 cm1

, 256 scans.

3. Results and Discussion 3.1. Synthesis and preliminary characterization of 1. Initially, crystallization of melamine with phenylacetic acid taken in a molar ratio of 1:1 has been performed. Crystallization of melamine with phenylacetic acid yield hydrated ionic supramolecular complex (1). Since the melamine contains multiple hydrogen-bonding sites, the crystallization was made starting with the melamine to acid molar ratio of 1:2 and 1:3. Independent of the molar ratio of melamine to acid the formed supramolecular complex with the same composition of 1:2 which 4

crystallizes as hydrated is the most stable in applied conditions of the crystallization. Melamine is a relatively basic compound with pKa of 5.1 in an aqueous solution [18] and the pKa of the phenylacetic acid is 4.31 [19]. Depending on the acidity of the studied acid, salts or co-crystals may form. The difference between pKa of melamine and phenylacetic acid ΔpKa (ΔpKa = pKa(base) – pKa(acid) = 0.79) shows that the formation of the mixed ionic and neutral hydrogen bonded supramolecular complex takes place and is in good agreement with Brittain’s method for predicting neutral or ionic formation (salt) supramolecular complexes in aqueous solution by calculating the percentage of salt formation as a function of pKa and pKb [20]. After each synthesis attempt with melamine to phenylacetic acid rato of 1: 1, 1: 2 and 1: 3 the purity of the obtained solids was checked by elemental analysis and by the XRPD. Recrystallization of the compound 1 in heavy water yield respective deuterated analogue, which was checked by the XRPD experiment. The XRPD patterns of protiated and deuterated analogue of 1 together with the calculated one (Fig. S1, in Supporting Information) confirm that the deuterated analogue crystallizes, similar as H-compound, in the same space groups with quite similar lattice parameters.

3.2. Analysis of the X-ray supramolecular structure. Melamin-1-ium

phenylacetate-phenylacetic

acid

monohydrate

(1)

crystallises

in

the

centrosymmetric space group of the triclinic system as a co-crystal. Asymmetric unit of 1 consists of protonated melamin-1-ium cation (MH+), phenylacetate anion, neutral molecule of phenylacetic acid and one water molecule (Fig. 1). The protonation of the perfectly symmetrical melamine ring results in increasing of the C−N−C bond angle at the protonated ring N atom, which is about four degree larger when comparing with the C−N−C bond angles at the non-protonated N ring atoms (Table S1 in SI). The differences between the C−N−C bond angles between the protonated and non-protonated at the N melamine ring are in agreement with the valence-shell electron-pair repulsion model, VSEPR [21], according to which the lone pair on non-protonated aza nitrogen atoms afford a wider region than the covalent bond N−H causing the internal angle of the last to be greater than on the nonprotonated N-ring atoms. Ab-initio gas-phase geometry calculated for neutral melamine molecule and its singly protonated cation shows similar correlation between the internal C−N−C and N−C−N angles within the rings [22]. Thus the ring distortion of MH+ in comparison to neutral melamine molecule results mainly from protonation, and to a lesser degree, from the hydrogen-bonding system. The conformation of the neutral phenylacetic acid or its deprotonated unit in 1 is slightly different. The dihedral angle between the plane of aromatic ring and the planes of COOH or COOgroups is 96.0(3)o and 76.2(3)o, respectively. The neutral phenylacetic acid in crystal 1 is close to that found in the crystal of pure phenylacetic acid (94.1(2)o) [23].

5

In the crystal 1 beside the ionic interaction, the protonated melamin-1-ium cation (MH+) interacts with phenylacetate anion via two N−H…O hydrogen bonds with a graph of R22(8) forming supramolecular {MH…phenylacetate} complex that further interacts with neutral acid molecule by a combination of O−H...N and N−H...O hydrogen bonds with a graph of R23(10) and then with water molecule via N−H…O hydrogen bond forming supramolecular complex of 1 (Fig. 1). The triazine ring of MH+ is almost coplanar with the R22(8) and Rz3(10) rings formed by hydrogen bonds. The dihedral angles between the plane of triazine ring of MH+ and the planes of R22(8) the R22(10) rings are 7.0(3)o and 3.1(3)o, respectively. The hydrogen bonded supramolecular units of 1 interact each other via two N−H…N hydrogen bonds with a graph of R22(12) formed between the MH+ cations as well as via N−H…O formed by donation to O atoms of COOH and COO- groups and via O−H…O with water molecule forming extended one-dimensional tape almost parallel to (120) plane (Fig. 2a). Within the tape melamin-1-ium cations form N−H…N hydrogen bonded one dimensional chain that is typical for singly protonated melamin-1-ium cations, whereas the phenyl rings of non- and deprotonated of phenylacetic acid units lie on the both side of the plane of the of one dimensional (MH+) chain and are inclined to this plane by ~76o and 103o, respectively. Two inversion related tapes are linked together via O−H…O with water molecule forming double-tapes parallel to (120) crystallographic plane (Fig. 2b), which are further arranged along the [2-10] directions forming a stacking structure (Fig. 3). Within the stack the O−H…O hydrogen bonds between the water molecules and the deprotonated phenylacetate(-) anions of neighboring tapes are formed. In addition, the weak π…π interactions between symmetrically related melaminium(+) cations involving anti-parallel C22−N27 exocyclic amino groups of the planar N−H…N hydrogen bonded one dimensional (MH+)n adjacent chains with distances of 3.338(4) Å stabilize the stacking architecture (Fig. 3). There are no any directional interactions between the stacks, however the stacks interacts only by the van der Waals forces, like as H…H dispersive forces (Fig. 3). So the (001) crystallographic plane is a cleavage plane of the crystal.

3.3. Hirshfeld surface analysis. Hirshfeld surface is a new developed technique that allows insight into the interactions between the building blocks of the crystals [24]. This method uses visual recognition of properties of atom contacts through mapping of a range of functions (dnorm, shape index, curvedness, etc.) onto this surface [25]. The increasing popularity of this tool comes from the fact that it allows for recognition not only the hydrogen-bonding interactions but also the less directional contacts, for instance C–H…A (A=acceptor) or H…H dispersion forces. Another essential advantage is that all (di, de) contacts created by a molecule of interest can be expressed in the form of a two dimensional plot, known as the 2D 6

fingerprint plot. The di and de are defined, respectively, as the distance from the Hirshfeld surface to the nearest nucleus outwards from the surface and the distance from the surface to the nearest atom in the molecule itself. The shape of this plot, which is unique for each molecule, and is determined by dominating intermolecular contacts [26]. The Hirshfeld surface mapped with a dnorm function for the melamin-1-ium cation and for phenylacetic acid and its deprotonated anion clearly shows the red spots derived from N-H...O and O-H...N hydrogen bonding interactions (Fig. 4). The respective plots of 2D fingerprint for the melamin-1-ium, phenylacetate(-) and neutral phenylacetic acid units in crystal 1 are shown in Fig. 4. The 2D fingerprint plot for the melamin-1-ium cation (Fig. 4a) shows the most significant H...O, N…H and H…N interactions as spikes with contributions of 22.2, 17.3 and 11.1%, respectively. The H...O interaction results from the N−H…O hydrogen bonds while the N…H and H…N interactions result from N−H…N N…H−N and hydrogen bonds linking the melamin-1-ium cations into one dimensional chain. HS and the 2D fingerprint plots analysis beside these characteristic spikes interactions show also the other interactions resulting from H…H dispersive force and H…C and C…H interactions as well as the π…π within the stacks of (MH+)n chains. The contributions of the respective interactions are 26.3 % (H…H), 10.9 % (H…C + C…H) and 8.5 % (π…π). Deconvolution of fingerprint plot corresponding to respective interactions and their percentage contributions in the total interactions for the melamin-1-ium cation is shown in Fig. S2 (in SI). The respective plots of 2D fingerprint for deprotonated phenylacetate(-) and neutral phenylacetic acid units show the most significant O…H (for phenylacetate(-)) and O…H and H…O (for neutral phenylacetic acid molecule) interactions as spikes with contributions of

22.4, 15.9 and 8.3 %, respectively. Beside these

characteristic spikes interactions HS and the 2D fingerprint plots show other interactions resulting from the H…H dispersive force and C…H and H…C interactions (Fig. 4b and c). The contributions of the respective interactions for phenylacetate(-) anion are 43.0 % (H…H), 22.4 % (O…H), 16.0 % (C…H), 13.2 % (H…C) and 4.2 % for C−H…O. The remaining residual interactions (1.2%) result from insignificant interactions such as C…N, O…O and O…N. For the neutral phenylacetic acid molecule HS and 2D molecule the contributions of respective interactions are 52.2 % (H…H), 15.9 % (O…H), 15.3 % (C…H), 8.3 % (H…O) and 6.7 % (H…C). Other residual interactions (1.6 %) result from O…N, O…C, O…O and H…N interactions. Deconvolution of fingerprint plot corresponding to respective interactions and their percentage contributions in the total interactions for the phenylacetate(-) anion neutral phenylacetic acid molecule is shown in Fig. S3 and S4 (in SI). In order to gain into the interactions between the asymmetric unit of 1 i.e. melamin-1-ium phenylacetate phenylacetic acid monohydrate the Hirshfeld surface was calculated. The red spots on the HS result from the interactions between the units in the crystal (Fig. 5). The respective 2D fingerprint plot for the melamin-1-ium phenylacetate phenylacetic acid monohydrate supramolecular unit shows spikes resulting from the most significant N−H…O, N−H…N, O−H…O, C−H…C and π…π 7

interactions between the supramolecular units. The contribution of the H…O + O…H, H…N + N…H, H…C + C…H and π…π interactions are 15.7, 10.0, 17.8 and 8.5%, respectively. The contribution of the H…H dispersive forces between the supramolecular units is 47.7%. Deconvolution of fingerprint plot corresponding to respective interactions and their percentage contributions in the total interactions for melamin-1-ium phenylacetate phenylacetic acid monohydrate supramolecular unit is shown in Fig. S5.

3.5. Vibrational characterization. In order to gain an insight into the structure and the nature of the interaction between the melamine and phenylacetic acid that form from water solution co-crystal of melamin-1-ium phenylacetate - phenylacetic acid monohydrate (1) the vibrational spectra IR and Raman were measured (Fig. 6 and 7). Bands corresponding to the vibration of the functional groups were identified with the aid of infrared and Raman correlation charts [27,28]. In 1, the protonated melamine interacts via multiple N-H...O hydrogen bonds with the phenylacetic acid units (deprotonated and neutral) and water molecule with medium and weak N-H...O hydrogen bonds (2.793(3) ÷ 3.315(3) Å) result in the IR spectrum as a broad band in the spectral region of 33002350 cm-1, which is shifted to 2500-2000 cm-1 in the spectrum of deuterated analogue. In addition, the broad band in the spectral region of 1600 – 1100 cm-1, which is overlapped with several other bands confirms the presence of these hydrogen bonding interactions. In the IR spectrum of 1 the band of the hydrated water molecule that acts as a donor in two O-H...O hydrogen bonds with O…O distances of 2.768(3) and 3.064(3) Å, and as an acceptor in N-H...O hydrogen bond with distance of 2.969(3) Å is observed at 3547 cm-1, and is shifted to ~2611 cm-1 in the spectrum of its deuterated analogue. The isotopic ratio of 1.358 is consistent with the medium and weak hydrogen bonds in which the water molecule is involved. The medium-strong intensity bands of the three NH2 groups of the melamine units in the spectral region of 3500-3000 cm-1 are observed. The bands of νa(NH2) are observed at higher frequency than the νs(NH2) bands (Fig. 6a). These bands, as expected, are shifted in the spectra of deuterated analogues to the spectral region of 2650-2250 cm-1 (Fig. 6b). The protiated/deuterated isotopic ratio of these bands are ranging from 1.340 to 1.360 points on the vibration anharmonicity. Theoretical calculation of the IR spectrum of singly protonated melamin-1ium residue shows that shows that additional band with frequency between the νa(NH2) and νs(NH2) is assigned to stretching vibration of N–H bond with a proton directly bonded to triazine ring nitrogen atom [22], however in the spectrum of 1 this band is overlapped with the bands of amine groups. The spectra of phenylacetic acid, which in solid forms dimeric structure with O…O distances of 2.679(3) Å [24] show vibration bands of the COOH group contain the C=O, C-O and O-H vibration modes [29,30]. The C=O stretching appears a strong intensity band around 1700 cm-1, while for the 8

O-H involved in the hydrogen bond is observed in the frequency region ~3000 cm-1 as a broad band. Since in 1, there are both neutral and deprotonated phenylacetic acid units the bands related to COO- group should be also find in the vibrational spectra. The vibrational bands of deprotonated COO- group are observed at 1600±40 cm-1 (νaCOO- asymmetric stretching) and at 1440±50 cm-1 (νsCOO- symmetric stretching). The νaCOO- asymmetric stretching band is overlapped with the C=N stretching vibration and the νsCOO- symmetric stretching is overlapped with triazine ring vibrations. The C-H stretching modes of the methylene group (CH2) of the phenylacetic acid and phenylacetate(2-) anion are at lower frequencies than those of the aromatic C-H ring stretching. The

νa(CH2) appear at higher and νs(CH2) at lower frequency, which are clearly evidenced in the Raman spectra of protiated and deuterated analogue and are unchanged (Fig. 7). The triazine ring vibrations of melamine unit were observed and discussed by Fernandez et al [31], and the bands observed at 1552, 1440 and 1185 cm-1 are assigned to ring stretching vibrations. Attaching of proton to triazine ring of melamine and formation of melamin-1-ium cation causes changes in frequencies observed for bands originated from vibration of the ring. Generally, the bands at the range of 1565 ÷ 1534 cm-1 are assigned to side-chain antisymmetric C−N stretching, while the bands observed in the range of 14851156 cm-1 were assigned to semi-circle stretching ring vibrations, and the bands in the spectral region of 984-894 cm-1 were described as derived from characteristic breathing ring vibrations [32]. The vibrational bands of triazine ring of melamine unit are overlapped with the vibrational modes of the phenyl ring of the phenylacetic acid and phenylacetate(-) anion. Vibrational bands and their assignments are listed in Table 3.

Conclusion Upon self-recognition, a supramolecular complex of melamine with phenylacetic acid in water solution a supramolecular complex of melamin-1-ium phenylacetate is formed that co-crystallizes with neutral phenylacetic acid and water molecule yielding crystals 1. The components of the crystal 1 interact via two N−H…O hydrogen bonds with a graph of R22(8) forming supramolecular {MH…phenylacetate} complex that further interacts with neutral phenylacetic acid molecule by a combination of O−H...N and N−H...O hydrogen bonds with a graph of R23(10) and then with water molecule via N−H…O hydrogen bond forming supramolecular complex of 1. Protonation melamine residues form N−H...N hydrogen boned infinitive chains. The melamin-1-ium phenylacetate phenylacetic acid monohydrate units in the crystal form one dimensional tapes via R22(8), R32(8) and R43(10) graphs that are arranged into the stacking structure. The Hirshfeld surface and the 2D fingerprint plots clearly evidenced the differences in the interactions between the building blocks of the supramolecular complexes. The medium and weak N-H...O and O-H...N hydrogen-bonding 9

interactions have been confirmed by vibrational spectroscopy. This work confirms the usefulness of melamine as a multiple hydrogen-bonding building blocks in the crystal engineering.

Supplementary Materials Additional material comprising selected geometrical parameters (Å, o) for 1, the XRPD diagrams for protiated and deuterated analogue of 1, deconvolution of 2D fingerprint for the acid units of 1. Full details of the X-ray data collection and final refinement parameters including anisotropic thermal parameters and full list of the bond lengths and angles have been deposited with the Cambridge Crystallographic Data Center in the CIF format as supplementary publications no. CCDC 1966914 for 1. Copies of the data can be obtained free of charge on the application to CCDC, 12 Union Road, Cambridge, CB21EZ, UK, (fax: (+44) 1223-336-033; email: [email protected] ).

10

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Boca Raton: FL 2014-2015, p. 5-100. [20] H.G. Brittain, Am. Pharm. Rev. 12 (2009) 62-65. [21] R.J. Gillespie, Chem. Soc. Rev. 21 (1992) 59-69. [22] M. Drozd, M.K. Marchewka, J. Mol. Struct. THEOCHEM, 716 (2005) 175-192. [23] D.J. Hodgson, R.O. Asplund, Acta Crystallogr. Sect.C: Cryst.Struct.Commun. 47 (1991) 1986-1987. [24] A.M. Spackman, D. Jayatilaka, CrystEngComm, 11 (2009) 19-32. [25] J.J. MacKimon, M.A. Spackman, A.S. Mitchell, Acta Crystallogr., Sect. B: Struct. Sci. 60 (2004) 627668. [26] J.J. MacKimon, D. Jayatilaka, A.M. Spackman, Chem. Commun. 37 (2007) 3814-3816. [27] G. Socrates, Infrared Characteristic Group Frequencies; Wiley-Interscience: Chichester, U.K., 1980. [28] G. Socrates, Infrared and Raman Characteristic Group Frequencies Tables and Charts, 3rd ed.; Wiley: Chinchester, West Sussex, England, 2004. [29] For IR spectrum of phenylacetic acid see NIST Chemistry Web Book, (http://webbook.nist.gov/chemistry). [30] H.B. Badawi, W. Förner, Spectrochim. Acta Part A, 78 (2011) 1162-1167. [31] M. Paz Fernandez-Liencres, A. Navarro, J.J. Lopez-Gonzalez, M. Fernandez-Gomez, J. Tomkinson, G.J. Kearley, Chem. Phys. 2001, 266, 1-17 [32] (a) S. Debrus, M.K. Marchewka, M. Drozd, H. Ratajczak, Optical Materials 2007, 29, 1058-1062; (b) M.K. Marchewka, J. Baran, A. Pietraszko, A. Haznar, S. Debrus, H. Ratajczak, Solid State Sci. 2003, 3, 509-518; M.K. Marchewka, Bull. Korean Chem. Soc. 2004, 25, 466-470; (c) M.K. Marchewka, J. Janczak, S. Debrus, J. Baran, H. Ratajczak, Solid State Sci. 2003, 5, 643-652; (d) S. Viswanathan, K. Narayanan, M.K. Marchewka, G. Sethuraman, A. Gopalakrishnan, J. Phys. Sci. 2014, 25, 93-111.

13

Table 1. Crystal Data and Structure Refinement for Compound 1 1 Formula f.w. (g·mol–1) Crystal system space group a (Å)

C19H24N6O5 416.44 Triclinic P -1� 4.9682(4)

b (Å)

9.7791(6)

c (Å)

20.9398(12)

α (o )

83.827(7)

β (o )

85.322(8)

γ (o )

78.998(8)

V (Å3)

990.92(12)

Z

2

Dcalc/Dobs (g·cm–3)

1.396 / 1.39

μ (mm–1)

0.104

Crystal size (mm)

0.34 × 0.14 × 0.08

Radiation, λ (Å)

Mo Kα , 0.71073

Temp. (K)

100(1)

Tmin/Tmax

0.9677 / 1.0000

θ range, ( )

2.428 ÷ 27.997

Refls collected / unique/ observed

18136 / 4724 / 3446

Rint

0.0498

R[F2>2σ(F2)]

0.0656

wR(F2) all refls

0.1434

Goodness-of-fit, S

0.998

Δρmax; Δρmin (e Å–3)

+0.312; -0.339

o

wR={Σ [w(Fo2–Fc2)2]/ΣwFo4}½; w–1=1/[σ2(Fo2) + (0.214P)2 + 2.372P] and P = (Fo2 + 2Fc2)/3.

14

Table 2. Hydrogen-bond geometry (Å,o). D—H···A

D—H

H···A

D···A

D—H···A

O11—H11···O1

0.90 (3)

1.70 (4)

2.595 (3)

171 (3)

N21—H21···O1

0.91 (3)

1.85 (3)

2.764 (3)

172 (3)

0.91 (3)

2.63 (3)

3.301 (3)

131 (2)

0.94 (3)

2.04 (3)

2.979 (3)

178 (3)

0.91 (3)

2.61 (3)

3.315 (3)

135 (2)

0.91 (3)

2.07 (3)

2.793 (3)

135 (3)

0.89 (3)

2.11 (3)

2.996 (3)

178 (3)

N28—H28B···O1W

0.85 (3)

2.17 (3)

2.969 (3)

156 (3)

N29—H29A···N25ii

0.87 (3)

2.15 (3)

3.015 (3)

173 (3)

N29—H29B···O2

0.86 (3)

1.97 (3)

2.821 (3)

169 (3)

O1W—H1WA···O2ii

0.83 (4)

1.97 (4)

2.768 (3)

160 (3)

O1W—H1WB···O2iii

0.88 (4)

2.20 (4)

3.064 (3)

171 (3)

N21—H21···O2 N27—H27A···N23

i

N27—H27B···O1 N27—H27B···O12 N28—H28A···O12

i

Symmetry codes: (i) −x+2, −y+1, −z+1; (ii) −x, −y+2, −z+1; (iii) −x+1, −y+2, −z+1.

15

Table 3. Spectroscopic data for compound 1.a IR spectroscopy Protiated Deuterated 3547w 2611w 3469m 2558m 3419m 2525m 3355s 2484m 3240m 2383m 3132m 2337m 3094m 2282m

Raman spectroscopy Protiated Deuterated

2717w 1715m 1681vs 1670vs

1552s 1505m 1467s 1440s 1379s 1302w 1287m 1185w 1108w 1078w 1029w 997w

815m 786m 730m 711m 631m, 622w 581w 479m

ν(OH) of water νa(NH2)/νa(ND2) antisymmetric stretching νa(NH2)/νa(ND2) antisymmetric stretching νa(NH2)/νa(ND2) antisymmetric stretching νs(NH2)/νs(ND2) symmetric stretching νs(NH2)/νs(ND2) symmetric stretching νs(NH2)/νs(ND2) symmetric stretching C-H stretch νa(CH2) C-H stretch νs(CH2) C-H stretch (C-H aromatic) C-H stretch (C-H aromatic) N-H…O stretch C=O stretch ν(C-C) benzene ring ν(C-C), ν(C-N), νa(COO ) ν(C-C) benzene ring ν(C-C) benzene ring ν(C-N) stretch (triazine) ring deformation

2432w 2386w 2351m 2316w 3065m 3041w 2943w 2926w

3065m 3048m 2942w 2936w

1710w 1672s 1655s 1597vs 1532s 1496s 1465s 1377m 1351m 1316m 1288m 1186w 1142w

Assignment

1602m 1584m 1494w

1602m 1584m 1483w

1422w

1447w

νs(COO ), triazine ring stretching triazine ring stretching

1307m

1310vw

melamine ring semi-circle stretch

1202m 1182w 1156w

1200w 1188m 1156m

C-H bending, triazine ring vibration ν(C-N) stretch

1030m 1003vs 979w 946w 856w 756w

1030m 1003vs

-

1082m

838w 784m 730m 707m 667w 608w 520w 474m

ring deformation

948w 857m 772w, 752w

686m 620w 572w, 563w 477w 401w

265w 116vs a) w=weak, m=medium, s=strong, vs=very strong

C-H wag., breathing ring vibrations C-H wag., breathing ring vibrations C-N-C and N-C-N bend ring deformation ring bend

647m 619w

ring deformation

476m

ring deformation

358w

side-chain out of plane side-chain out of plane lattice vibration

140vs; 115vs

16

Figure 1. View of molecular structure of 1 with displacement ellipsoids at the 50% probability level.

17

(a)

(b) Figure 2. View of hydrogen-bonded tape (a) and two neighboring tapes of 1 (b).

18

(a)

(b) Figure 3. Molecular packing of 1 viewed along [100] (a) and along [2-10] (b) showing hydrogen bonded tapes (a) and hydrogen bonded stacks (b).

19

(a)

(b)

H...O O...H

(c) Figure 4. Hirshfeld surface (left side) and the total fingerprint plot (right side) for the melamin-1-ium cation (a), phenylacetate(-) anion (b) and phenylacetic acid (c) in 1.

20

Figure 5. Hirshfeld surface (left side) showing the N−H…O, N−H…N and O−H…O interactions ( ) between the supramolecular units and the total fingerprint plot (right side) for the supramolecular complex of melamin-1-ium phenylacetate - phenylacetic acid monohydrate (1).

21

4000

0,2

3500

0,4

3000

N

2500

22

0,6

0,0

2000

1500

Wavenumber [cm-1]

(b)

Figure 6. IR spectra of protiated (a) and deuterated analogue (b) of 1.

1000 520 474

667 608

1000

707

1500

838

2000

784

2500

1467 1440

1552

1681 1670

1302

1505

1185 1108 1029 1078 997 815 730 786 711 631 581 479

1379 1287

1715

N

730

3000

1655 1672 1597 1496 1532 1465 1377 1351 1288 1316 1186 1142 1082

3500

2383 2262

2717

0,6

2337

4000

2484

0,0

3354 3240 3132 3095

0,2

34193469

0,4

3547

Transmittance 0,8

2558 2525 2611

Transmittance 1,0

Protiated

-1

500

Wavemunber [cm ]

(a)

1,0

Deuterated

0,8

500

1003

116

1,0

Protiated

265

477 401

946 856 756 620

979

686 572 563

1182 1202 1272 1156 1030

0,2

1494 1422 1307

2926

0,4

1602

3065 2943

1584

0,6

3041

Raman Intensity

0,8

0,0 3600

3200

2800

2400

2000

1600

1200

800

400

Wavenumber [cm-1] (a)

140 115

1,0 1003

Deuterated

2432 2386 2351 2316

2936

0,4

1602 1584 1483 1447 1310 1200 1188 1156 1130 948 857 772 899 752 647 619 556 476 358

3065 3048

0,6

2942

Raman Intensity

0,8

0,2

0,0 3600

3200

2800

2400

2000

1600

1200

Wavenumber [cm-1] (b) Figure 7. Raman spectra of protiated (a) and deuterated analogue (b) of 1.

23

800

400

Highlights ► Crystallization of melamine with phenylacetic acid from water solution was made. ► Melamin-1-ium phenylacetate phenylacetic acid crystals as hydrate were obtained. ► R22(8) and R32(10) motifs linking the units into supramolecular complex. ► Hirshfeld surface and 2D fingerprint plots have been analysed. ► The characteristic vibrational bands of the H and D analogue are discussed.

Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: