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Molecular structure of 1:1 complex of 1,4-dimethylpiperazine di-betaine with l -tartaric acid studied by X-ray diffraction, FTIR, Raman and NMR spectroscopy and DFT calculations
Journal of Molecular Structure 891 (2008) 258–265
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Molecular structure of 1:1 complex of 1,4-dimethylpiperazine di-betaine with L-tartaric acid studied by X-ray diffraction, FTIR, Raman and NMR spectroscopy and DFT calculations Z. Dega-Szafran *, A. Katrusiak, M. Szafran ´ , Poland Faculty of Chemistry, Adam Mickiewicz University, ul. Grunwaldzka 6, 60-780 Poznan
a r t i c l e
i n f o
Article history: Received 28 February 2008 Received in revised form 27 March 2008 Accepted 27 March 2008 Available online 14 April 2008 Keywords: 1, 4-Dimethylpiperazine di-betaine L-Tartaric acid Hydrogen bonds X-ray diffraction FTIR Raman and NMR spectra
a b s t r a c t Crystal structure of the 1:1 complex of 1,4-dimethylpiperazine di-betaine (1,4-dicarboxymethyl-1,4dimethylpiperazinium inner salt, DBPZ) with L-tartaric acid (TA) has been determined by X-ray diffraction. The crystals are triclinic, space group P1. TA and DBPZ are linked by two asymmetric COOHOOC hydrogen bonds of 2.485(3) and 2.566(3) Å into chains. The piperazine ring has a chair conformation with the methyl groups in the axial positions and the CH2COO substituents in the equatorial ones. In the theoretically optimized structure of isolated DBPZTA at the B3LYP/6-31G(d,p) level of theory the non-linear complex, with DBPZ in the same conformation as in the crystal, is formed. The 1H and 13C magnetic isotropic shielding tensors have been analyzed in order to confirm the CAHO contacts, which stabilize the optimized structure of DBPZTA. The FTIR spectrum of the solid complex is consistent with the X-ray results. Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction L-Tartaric acid is a naturally occurring chiral dicarboxylic acid [1]. Different isomers of tartaric acid, pure enantiomers, racemic and meso forms, were subjects of crystallographic studies [2–9]. The study of the molecular packing and hydrogen bonding in tartaric acid and its derivatives is relevant to the development of approaches in crystal engineering [10–13]. Salts of TA with amines and amino acids were studied by X-ray diffraction and their structures are stored in the Cambridge Crystallographic DataBase [14]. In complexes of organic bases with tartaric acid, one or two protons can be transferred from the carboxylic groups of TA to form the monovalent (semi-tartrate) or divalent (tartrate) anions, respectively. A structural study of organic salts of semi-L-tartrate shows that the anionic network is remarkably consistent, regardless of the nature of the cation [10– 13]. L-Tartaric-amine complexes have been chosen for the study as a potential organic material for non-linear optics. Their second harmonic generation (SHG) activity depends on the crystal structure and the type of amine [15–18]. One of such complex is piperazinium L-tartrate, which crystallizes in the monoclinic P21 space group. The piperazinium divalent cation is surrounded by four L-tartrate
* Tel.: +48 61 8291216; fax: +48 61 8291505. E-mail address: [email protected] (Z. Dega-Szafran). 0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2008.03.057
anions through the NAHO hydrogen bonds of the lengths between 2.688(2) and 2.780(2) Å [19]. Recently, we have studied the 2:1 complex of N-carboxymethyl-N-methylmorpholinium inner salt (N-methylmorpholine betaine) with L-tartaric acid [20] and the 4:2 complex of N-carboxymethyl-N-methylpiperidinium inner salt (N-methylpiperidine betaine) with L-tartaric acid [21], which belong to a new family of zwitterionic-L-tartaric acid compounds (betaine–tartaric acid), differing from that of amino acids–L-tartaric acid complexes [17,18,22–29]. In betaines (R3N+CH2COO ) only the carboxylate group can interact with tartaric acid, through COOHOOC hydrogen bond, without proton transfer. In continuation of our previous investigation, the present work is focused on the structure, hydrogen bonds and conformation of the complex formed between 1,4-dimethylpiperazine di-betaine (1,4-dimethyl-1,4-dicarboxymethyl-piperazinium inner salt, DBPZ) and L-tartaric acid (TA), which is a new example of the interaction of zwitterionic compound with L-tartaric acid. 2. Experimental 1,4-Dimethylpiperazine di-betaine (DBPZ) was prepared according the procedure described in Ref. [30]. DBPZ crystallizes with two water molecules [31]. The 1:1 complex of DBPZ with Ltartaric acid (TA) was obtained by mixing one equivalent of DBPZ with one equivalent of TA in water. The complex decomposes at
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222 °C, [a]D = +5.74° in H2O. The crystals of DBPZTA are formed in the 1:1 stoichiometry as anhydrous sample. Analysis for C14H24N2O10: calculated: %C, 44.21; %H, 6.36; %N, 7.37; required: %C, 43.90; %H, 6.36; %N, 7.26. The crystal structure was determined from X-ray diffraction, measured with a KUMA KM-4 CCD diffractometer [32]. The structure was solved by direct methods using SHELXS-97 [33] and refined on F2 by full-matrix least-squares with the SHELXL-97 programs [34]. The crystal data, details of data collection and structure refinement are given in Table 1, and the final atomic coordinates are listed in Table 2. The complete set of structural parameters in CIF format is available as an Electronic Supplementary Publication from the Cambridge Crystallographic Data Centre (CCDC 679313). The DFT calculations were performed with the GAUSSIAN-03 program package [35]. The calculations employed the B3LYP exchange-correlation functional, which combines the hybrid exchange functional of Becke [36,37] with the gradient-correlation functional of Lee, Yang and Parr [38], and the splitvalence polarized 6-31G(d,p) basis set [39]. The magnetic isotropic shielding tensors (r) were calculated using the Gauge Independent Atomic Orbitals (GIAO) approach with the GAUSSIAN 03 package. The X-ray geometry was used as the input file. FTIR spectra were measured on a Bruker IFS 66v/S instrument, evacuated to avoid water and CO2 absorptions. Solid state spectra were recorded in Nujol and Fluorolube suspensions using KBr plates. Each spectrum consisted of 64 scans. The Raman spectrum was measured on a Bruker IFS 66 instrument. The NMR spectra were recorded on a Varian Gemini 300 VT spectrometer operating at 300.07 and 75.46 MHz for 1H and 13 C, respectively. The spectra were measured in D2O relative to internal standard of 3-(trimethylsilyl)propionic-d4 acid sodium salt.
Table 1 Crystal data and structure refinement for the DBPZTA complex Molecular formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions
Volume Z Calculated density Absorption coefficient F(0 0 0) Crystal size h Range for data collection Limiting indices
Reflections collected/unique Completeness to h = 29.21° Absorption correction Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2rI] R indices (all data) Absolute structure parameter Largest diff. peak and hole
C14H24N2O10 380.35 293(2) K 0.71073 Å Triclinic P1 a = 6.8439(16) Å b = 8.372(3) Å c = 8.424(2) Å a = 104.84(3)° b = 109.29(2)° c = 101.19(2)° 419.3(2) Å3 1 1.506 g/m3 0.129 mm 1 202 0.3 0.2 0.18 mm 2.64°–29.21° 96h68 11 6 k 6 8 10 6 l 6 11 3098/2272 [Rint = 0.0111] 86.2% None Full-matrix least-squares on F2 2272/3/310 0.926 R1 = 0.0296, wR2 = 0.0651 R1 = 0.0430, wR2 = 0.0687 0.4(10) 0.187 and 0.175 e. Å 3
Table 2 Atomic coordinates and equivalent isotropic displacement parameters (Å2 103) of the DBPZTA complex Atom N(1) C(2) C(3) N(4) C(5) C(6) C(7) C(8) C(9) C(10) O(1) O(2) C(11) C(12) O(3) O(4) O(5) O(6) C(21) C(22) O(7) C(23) O(8) C(24) O(9) O(10) H(2A) H(2B) H(3A) H(3B) H(5A) H(5B) H(6A) H(6B) H(7A) H(7B) H(7C) H(8A) H(8B) H(8C) H(9A) H(9B) H(11A) H(11B) H(5) H(22) H(7) H(23) H(8) H(9)
x
y 0.4022(3) 0.2777(4) 0.3428(4) 0.5841(3) 0.7059(4) 0.6435(4) 0.3377(5) 0.6402(5) 0.3661(4) 0.1353(4) 0.1375(3) 0.0224(3) 0.6332(4) 0.8737(4) 0.8922(3) 1.0235(3) 0.7543(3) 0.9273(3) 0.7861(4) 0.6235(4) 0.6741(3) 0.3941(4) 0.4021(3) 0.2314(4) 0.1356(4) 0.2019(3) 0.2910(40) 0.1240(50) 0.3160(40) 0.2590(40) 0.6650(40) 0.8620(40) 0.6840(40) 0.7140(40) 0.1710(60) 0.4090(50) 0.3870(60) 0.5400(50) 0.7980(50) 0.6170(50) 0.4130(40) 0.4570(40) 0.5740(40) 0.5450(40) 0.8620(50) 0.6200(40) 0.7560(50) 0.3510(40) 0.2980(50) 0.0260(70)
0.8888(2) 0.9923(3) 1.0229(4) 1.1173(2) 1.0076(3) 0.9779(3) 0.7029(3) 1.3009(3) 0.8976(4) 0.8159(3) 0.8289(2) 0.7513(2) 1.1241(4) 1.2096(3) 1.2255(2) 1.2493(3) 0.3881(2) 0.2592(2) 0.3726(3) 0.5158(3) 0.5053(2) 0.5021(3) 0.3326(2) 0.6501(3) 0.6029(2) 0.7985(2) 1.1020(30) 0.9240(30) 0.9240(40) 1.0910(40) 0.9050(30) 1.0610(30) 1.0840(30) 0.9060(30) 0.6580(40) 0.6390(40) 0.6970(50) 1.3470(40) 1.3550(40) 1.3000(40) 1.0140(40) 0.8350(30) 0.9890(30) 1.1800(40) 0.3260(50) 0.6250(40) 0.4190(40) 0.5300(30) 0.3120(40) 0.7000(60)
z
U(eq)/U(iso) 0.0789(2) 0.0156(3) 0.1652(3) 0.0988(2) 0.0117(3) 0.1378(3) 0.0402(4) 0.0265(4) 0.2500(3) 0.2317(4) 0.3876(2) 0.0862(3) 0.2617(3) 0.2258(3) 0.3668(2) 0.0787(3) 0.6252(2) 0.3271(2) 0.4579(3) 0.4434(3) 0.2626(2) 0.5259(3) 0.4291(2) 0.5160(3) 0.4109(3) 0.6055(3) 0.0670(30) 0.0690(30) 0.2650(40) 0.2160(40) 0.1110(30) 0.0390(30) 0.2320(30) 0.1770(30) 0.0730(40) 0.0250(50) 0.1350(40) 0.0360(40) 0.0660(40) 0.1310(40) 0.3170(30) 0.3070(40) 0.3630(30) 0.3180(40) 0.6280(40) 0.5120(40) 0.2030(40) 0.6630(40) 0.4890(50) 0.4000(60)
23(1) 26(1) 30(1) 22(1) 24(1) 25(1) 41(1) 35(1) 26(1) 30(1) 42(1) 44(1) 28(1) 28(1) 41(1) 40(1) 39(1) 46(1) 28(1) 27(1) 40(1) 26(1) 32(1) 28(1) 55(1) 51(1) 31 31 36 36 29 29 30 30 62 62 62 52 52 52 32 32 33 33 56(10) 32 42 32 66(12) 106(14)
U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.
3. Results and Discussion 3.1. Crystal structure 1,4-Dimethylpiperazine di-betaine (DBPZ) has two equivalent proton-acceptor centres; pKa = 2.10 [30], while L(+)-tartaric acid (TA) has four proton-donor centres; two carboxylic and two hydroxyl groups; pKa1 = 3.03 and pKa2 = 4.46 [40]. However, DBPZ forms a crystalline complex in the 1:1 stoichiometry with L-tartaric acid (TA). DBPZTA crystals belong to the triclinic system, space group P1 (Table 1). This low-symmetry space group P1 has been already established in four complexes of tartaric acid: bis(quinolinium-2carboxylate)–L-tartaric acid [28], ephedrine–L–hemitartrate trihydrate [41], L-malic–L-tartaric co-crystals [42] and bis(4’-pyridyl)ethane–tartaric acid [43] complexes. Bond lengths, bond and torsion angles for title compound are given in Tables 3 and 4. Fig. 1 shows the atomic numbering system.
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Table 3 Experimental and calculated bond lengths (Å) and angles (°) for the DBPZTA complex X-ray Bond lengths N(1)AC(2) C(2) AC(3) C(3) AN(4) N(4) AC(5) C(5) AC(6) N(1) AC(6) N(1) AC(7) N(4) AC(8) N(1) AC(9) C(9) AC(10) C(10) AO(1) C(10) AO(2) N(4) AC(11) C(11) AC(12) C(12) AO(3) C(12) AO(4) C(21) AC(22) C(21) AO(5) C(21) AO(6) C(22) AC(23) C(22) AO(7) C(23) AO(8) C(23) AC(24) C(24) AO(9) C(24) AO(10) Bond angles N(1) AC(2) AC(3) C(2) AC(3) AN(4) C(3) AN(4) AC(5) N(4) AC(5) AC(6) C(5) AC(6) AN(1) C(2) AN(1) AC(6) C(7) AN(1) AC(2) C(7) AN(1) AC(6) C(2) AN(1) AC(9) C(6) AN(1) AC(9) C(7) AN(1) AC(9) N(1) AC(9) AC(10) O(1) AC(10) AC(9) O(2) AC(10) AC(9) O(2) AC(10) AO(1) C(8) AN(4) AC(3) C(8) AN(4) AC(5) C(3) AN(4) AC(11) C(5) AN(4) AC(11) C(8) AN(4) AC(11) N(4) AC(11) AC(12) O(3) AC(12) AC(11) O(4) AC(12) AC(11) O(3) AC(12) AO(4) C(21) AC(22) AC(23) O(5) AC(21) AC(22) O(6) AC(21) AC(22) O(6) AC(21) AO(5) C(22) AC(23) AC(24) O(7) AC(22) AC(21) O(7) AC(22) AC(23) O(8) AC(23) AC(22) O(8) AC(23) AC(24) O(9) AC(24) AC(23) O(10) AC(24) AC(23) O(10) AC(24) AO(9)
1.517(3) 1.531(3) 1.523(3) 1.521(3) 1.518(3) 1.523(3) 1.505(3) 1.515(3) 1.527(3) 1.534(4) 1.285(3) 1.232(3) 1.529(3) 1.554(3) 1.272(3) 1.231(3) 1.529(3) 1.320(3) 1.206(3) 1.534(3) 1.421(3) 1.424(3) 1.537(3) 1.294(3) 1.215(3) 113.0(2) 112.9(2) 106.5(2) 111.9(2) 114.3(2) 107.5(2) 111.9(2) 110.9(2) 109.8(2) 106.4(2) 110.3(2) 118.1(2) 109.4(2) 122.8(2) 127.7(2) 110.5(2) 113.6(2) 108.0(2) 109.2(2) 109.0(2) 116.9(2) 111.5(2) 122.3(2) 126.1(2) 109.3(2) 113.1(2) 121.9(2) 125.0(2) 108.8(2) 111.7(2) 109.7(2) 106.1(2) 114.4(2) 115.6(2) 118.8(2) 125.6(2)
B3LYP/6-31G(d,p) 1.527 1.524 1.505 1.516 1.514 1.528 1.508 1.517 1.527 1.546 1.300 1.223 1.544 1.592 1.231 1.258 1.523 1.348 1.211 1.549 1.406 1.407 1.538 1.273 1.257 113.04 114.08 108.15 112.72 113.11 107.18 112.01 111.71 108.83 107.36 109.59 112.88 114.81 120.50 124.67 111.60 111.56 109.75 107.90 107.80 116.06 110.02 116.84 133.13 109.62 112.73 123.52 123.74 108.98 109.57 111.81 109.99 111.50 114.90 118.69 126.40
The piperazine ring has a chair conformation with the methyl groups in the axial positions and the CH2COO substituents in the equatorial ones. The reverse orientation of the substituents has been found in the 1:1 complex of DBPZ with HCl [30]. In the complex investigated DBPZ exists in its zwitterionic form, with two slightly different CAO bonds: the C(10/12)AO(1/3) bonds, of 1.285(3) and 1.272(3) Å, are longer than the C(10/12)AO(2/4) bonds,
Table 4 Experimental and calculated torsion angles (°) for the DBPZTA complex Torsion angles N(1) AC(2) AC(3) AN(4) C(2) AC(3) AN(4) AC(5) C(3) AN(4) AC(5) AC(6) N(4) AC(5) AC(6) AN(1) C(2) AN(1) AC(6) AC(5) C(6) AN(1) AC(2) AC(3) C(7) AN(1) AC(2) AC(3) C(7) AN(1) AC(6) AC(5) C(7) AN(1) AC(9) AC(10) C(9) AN(1) AC(2) AC(3) C(9) AN(1) AC(6) AC(5) C(2) AN(1) AC(9) AC(10) C(6) AN(1) AC(9) AC(10) N(1) AC(9) AC(10) AO(1) N(1) AC(9) AC(10) AO(2) C(8) AN(4) AC(3) AC(2) C(8) AN(4) AC(5) AC(6) C(8) AN(4) AC(11) AC(12) C(2) AC(3) AN(4) AC(11) C(6) AC(5) AN(4) AC(11) C(3) AN(4) AC(11) AC(12) C(5) AN(4) AC(11) AC(12) N(4) AC(11) AC(12) AO(3) N(4) AC(11) AC(12) AO(4) C(21) AC(22) AC(23) AC(24) O(5) AC(21) AC(22) AC(23) O(6) AC(21) AC(22) AC(23) O(7) AC(22) AC(23) AC(24) O(7) AC(22) AC(21) AO(5) O(7) AC(22) AC(21) AO(6) O(8) AC(23) AC(22) AC(21) O(8) AC(23) AC(22) AO(7) O(9) AC(24) AC(23) AC(22) O(9) AC(24) AC(23) AO(8) O(10) AC(24) AC(23) AC(22) O(10) AC(24) AC(23) AO(8)
X-ray 58.1(3) 57.3(3) 56.9(2) 58.5(3) 53.3(3) 52.4(2) 69.6(3) 69.2(3) 59.3(3) 167.7(2) 170.9(2) 64.4(3) 179.6(2) 177.3(2) 3.5(4) 66.4(3) 64.9(3) 62.1(3) 174.5(2) 173.3(2) 177.8(2) 62.4(3) 172.8(2) 9.6(4) 178.2(2) 63.9(3) 116.2(3) 58.9(2) 174.5(2) 5.4(3) 58.3(2) 64.5(2) 113.3(2) 5.1(3) 67.1(3) 174.5(2)
B3LYP/6-31G(d,p) 55.55 53.26 54.41 58.52 55.17 53.18 69.68 67.88 73.86 168.99 171.95 48.94 164.64 137.43 44.05 69.82 68.69 63.90 170.74 173.08 174.36 93.98 179.98 0.42 178.54 67.75 111.19 56.82 169.20 11.86 56.02 65.70 123.96 2.36 56.98 178.59
of 1.232(3), 1.231(3) Å, respectively (Table 3). In the DBPZTA complex the proton is not transferred from TA to DBPZ, however the molecules are linked by a short non-symmetric O(9)AHO(1) hydrogen bond of 2.485(3) Å (Table 5). The other carboxylate oxygen atom of DBPZ is involved in significantly longer O(3)HAO(5) hydrogen bond of 2.566(3) Å with the neighboring molecule of the complex. The Donohue angles of the hydrogen bonds agree with the angular criteria for the H-atom sites [44,45]. These two hydrogen bonds link the complex molecules into an infinite chain. The chains are linked to the neighboring ones by the O(7)AHO(4) and O(8)AHO(3) hydrogen bonds of 2.886(3) and 2.650(2) Å, respectively, between the hydroxyl groups of TA and the carboxylate groups of DBPZ (Fig. 2, Table 5). The intramolecular O(7)AHO(6) hydrogen bond of 2.712(3) Å and the OAHO angle of 118(3)° (Table 5) stabilizes the TA conformation. It appears that the significant difference of 0.081 Å in the lengths of the hydrogen bonds, the shorter O(9)AHO(1) and the longer O(5)AHO(3) one, results from the involvement of the O(3) atom of the DBPZ moiety in bifurcated hydrogen bonds to the hydroxyl group, O(8)-H, and to the oxygen atom O(5) of the carboxylic group of TA (Table 5). There are no other strong interactions disturbing the short O(9)AHO(1) hydrogen bond geometry. Also no hydrogen bonds are formed by the DBPZ carboxylate O(2) atom, whereas the O(4) oxygen is involved in the O(7)AHO(4) hydrogen bond to another hydroxyl group O(7)H of TA (Fig. 2, Table 5). The hydrogen bonds to the hydroxyl groups of TA link the hydrogen-bonded chains into a 3-dimensional network (Fig. 3). The interactions between the TA molecules themselves are very weak only. According to the most recent studies the spheres of interactions are considerably larger than the sums of the van der
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Fig. 1. Molecular structure and atom labeling scheme of 1,4-dimethylpiperazine di-betaine–L-tartaric acid complex. The hydrogen bonds have been shown as the dashed lines and the thermal ellipsoids at 50% probability displacement level.
Table 5 Dimensions of hydrogen bonds in the crystal and optimized structures of the DBPZTA complex DAHA
DAH (Å)
HA (Å)
DA (Å)
DAHA (°)
X-ray O(9) AH(9)O(1) O(5) AH(5)O(3)a O(7) AH(7)O(4)b O(7) AH(7)O(6) O(8) AH(8)O(3)c
1.07(2) 0.83(3) 0.75(3) 0.75(3) 0.81(3)
1.45(2) 1.75(3) 2.24(3) 2.28(3) 1.86(3)
2.485(3) 2.566(3) 2.886(3) 2.712(3) 2.650(2)
176(2) 170(2) 146(2) 118(3) 166(3)
B3LYP/6-31G(d,p) O(1) AH(9)O(9) C(9) AHO(10) C(2) AH(ax)O(10) C(6) AH(ax)O(10) C(8) AHO(10) O(7) AH(7)O(9) O(8) AH(8)O(6)
1.060 1.088 1.094 1.092 1.090 0.974 0.971
1.429 2.123 2.124 2.253 2.191 1.945 2.192
2.485 3.044 3.097 3.185 3.272 2.595 2.692
173.70 140.63 146.65 141.99 177.02 121.90 110.64
Symmetry codes: ax
Waals radii [46–49], which contribute to the effect of crystal-structure stabilization of molecules [50].
3.2. B3LYP/6-31G(d,p) calculations
2, y
1, z + 1; bx
2, y
1, z; cx
1, y
1, z.
The optimized structure of the title complex was compared to the X-ray diffraction one in Fig. 4, and the bond lengths, bond and torsion angles are listed in Tables 3 and 4. The main difference between these structures is in the arrangement of the molecules of DBPZ and TA, which are linear in the crystals and bent in the isolated complex. The O(9)O(1) distances are comparable, however the acidic proton from carboxylic group of TA is transferred to the oxygen atom of the carboxylate group of DBPZ in the optimized structure, hence the mono-protonated DBPZ molecule interacts with the semi-tartrate anion (Table 5). In the optimized structure of DBPZTA, several CAHO(10) contacts stabilize the bent structure (Table 5) and influence the NACACAO torsion angles,
Fig. 2. An autostereogram [60] of one sheet of hydrogen-bonded molecules of 1,4-dimethylpiperazine di-betaine–L-tartaric acid
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c 0
Fig. 3. The crystal structure of the 1,4-dimethylpiperazine di-betaine–L-tartaric acid complex viewed down the [001] direction, with the hydrogen bonds marked by the dashed lines.
Fig. 4. Comparison of the X-ray and optimized structures of 1,4-dimethylpiperazine di-betaine–tartaric acid complex.
which have the opposite signs than in the crystal (Table 4). The energy of the calculated DBPZTA complex is 1409.681688 a.u., and the dipole moment of 7.17 D confirms the asymmetry of the title complex. 3.3. NMR spectra The experimental proton and carbon-13 chemical shifts (d) and calculated magnetic isotropic shielding tensors (r) by the GIAO/ B3LYP/6-31G(d,p) approach for DBPZTA are listed in Table 6. In the 1H NMR spectrum two doublets at 4.44 and 4.00 ppm are
attributed to the ring piperazine protons at the equatorial and axial positions, respectively. The sharp and intensive resonance signals of CAH, N+CH2COO and CH3 protons appear at 4.46, 4.18 and 3.47 ppm, respectively. The rH values of magnetic isotropic shielding tensors are scattered, with the exception of rH of the CAH protons of tartaric acid (Fig. 5a and Table 6). These discrepancy can confirm the engagement of the ring, methyl and methylene protons in the hydrogen bonds with tartaric acid molecule in the isolated molecule (Table 5), as well as a proton-solvent interaction in aqueous solution. The 13C NMR spectrum consists of four sharp signals at 56.1, 75.1, 170.5 and 178.0 ppm, assigned to the piperazine ring carbon atoms, the skeletal tartaric acid carbon atom, the carboxylate carbon atom of DBPZ and the carbonyl carbon atom of TA, respectively (Table 6). Similarly as in the spectra of 1,4-dimethylpiperazine, tetramethylpiperazinium salts, DBPZ and its complexes with HCl and p-hydroxybenzoic acid, the signals attributed to the methyl and methylene carbon atom of N+CH3 and N+CH2COO groups are broad and of very low intensities [30,51–53]. This broadening can be caused by a quadrupole effect of the positively charged nitrogen atoms. Theoretically computed 13C chemical shifts can be obtained at a level of accuracy sufficient to allow application to configurational and conformational determination of organic molecules [54,55]. The carbon-13 chemical shifts assignments for the complex investigated were confirmed by the GIAO calculated magnetic isotropic shielding tensors (rC) (Table 6). The relation between the experimental 13C chemical shifts and the average rC values gives a linear regression described by the equation: d = a + br (Fig. 5b), where a = 206.1784, b = 1.0849, r = 0.9962.
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Chemical shifts (ppm)
4.6 4.4
150
4.2 4.0
100
3.8 3.6 3.4
50
a 24
26
b
28 30 50 Magnetic isotropic shielding tensors (ppm)
100
150
Fig. 5. Plots of the experimental chemical shifts (d) versus the magnetic isotropic shielding tensors (r) from the GIAO/B3LYP/6-31G(d,p) calculations for 1H (a) and 13C (b) for DBPZTA.
Table 6 Experimental chemical shifts (d, ppm, D2O) and calculated magnetic isotropic shielding tensors (r, ppm) by the GIAO/B3LYP/6-31G(d,p) method for the DBPZTA complex d
Atoma
H Ring (ax)
4.00
Ring (eq)
4.44
CH2
4.18
CH3
3.47
CH (TA)
4.64
2 3 5 6 2 3 5 6 9 9 11 11 7 7 7 8 8 8 23 22
28.2949 28.9105 29.2593 26.6901 25.9297 29.0452 24.0891 29.2297 25.2599 28.8485 28.6462 29.0670 26.2208 29.8595 28.7266 30.0148 26.0113 26.9173 27.4976 27.4445
2 3 5 6 9 11 7 8 23 22 10 12 24 21
140.9635 135.8245 141.5898 133.6650 127.4020 122.4029 148.4739 148.0776 114.7617 117.7610 34.3253 45.5474 18.4761 24.5260
r
1
to several bands in the 3470–2450 cm 1 region. The bands attributed to the mC@O and masCOO appear at 1732, 1672 and 1642 cm 1, respectively. The broad absorption in the 1500– 560 cm 1 region, with the centre of gravity at 1090 cm 1, arises from the stretching and bending vibrations of the OH groups, and it is characteristic of the short OAHO hydrogen bond [56]. The continuous absorption of the OHO vibration overlaps the in-plane and out-of-plane CAH, stretching and bending CAC, CAN, CAO vibrations, as well as the skeletal of TA molecule and the ring of piperazine modes. Some of these vibrations can be distinguished by the second derivative (d2) spectrum (Fig. 6b). The derivative spectroscopy can be used to determine the frequencies of the narrow bands covered by the broad absorption due to stretching and bending OAH vibrations. The minima in the d2 spectrum have the same wavenumbers as the maxima in the absorbance FTIR spectrum, but their intensities vary inversely with the fourth power of the half-width of the absorption bands [57,58]. In the Raman spectrum (Fig. 6c) the absorption bands of the OH vibration are absent, and the bands attributed to the mC@O and masCOO modes are of weak intensities [59]. 4. Conclusions
13
C Ring
56.1
CH2
68.7
CH3
49.9
CH (TA)
75.1
COO (DBPZ)
170.5
COOH (TA)
178.0
a
See Fig. 1.
In the 1:1 complex of 1,4-dimethylpiperazine di-betaine (DBPZ) with L-tartaric acid (TA) only a half of the proton-donor COOH groups of TA and proton-acceptor COO groups of DBPZ are involved in the short hydrogen bonds of 2.485(3) Å between the above molecules. The remaining COOH and COO groups link the molecules of the 1:1 complex into infinite chains, through the OAHO hydrogen bonds of 2.566(3) Å. The chains are parallel to each other and are linked by the OAHO hydrogen bonds between the hydroxyl group of TA and the carboxylate group of DBPZ. The complex is non-centrosymmetric, space group P1. In the optimized structure of the title complex by the B3LYP/6-31G(d,p) approach, the DBPZ and TA molecules are not extended but bent. Such an arrangement of molecules is stabilized by several CAHO contacts. The FTIR, 1H and 13C NMR data agree well with the X-ray structure. Acknowledgements
3.4. Vibrational spectra Fig. 6a shows a solid-state FTIR spectrum of the DBPZTA complex. The stretching type of vibration of hydrogen bonds gives rise
The DFT calculations were performed at the Poznan´ Supercomputing and Network Centre. The authors thank Prof. Maria Połomska for the Raman spectrum measurement.
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1.5
a
1.0
0.5
0.0
Intensity
0.2
b
0.0
-0.2
0.10
c
0.05
0.00 3500 3000 2500 2000
1500
1000
500
Wavenumbers (cm-1) Fig. 6. Vibrational spectra of DBPZTA: (a) FTIR; (b) FTIR second derivative; (c) Raman.
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Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
Molecular structure of 1:1 complex of 1,4-dimethylpiperazine di-betaine with L-tartaric acid studied by X-ray diffraction, FTIR, Raman and NMR spectroscopy and DFT calculations Z. Dega-Szafran *, A. Katrusiak, M. Szafran ´ , Poland Faculty of Chemistry, Adam Mickiewicz University, ul. Grunwaldzka 6, 60-780 Poznan
a r t i c l e
i n f o
Article history: Received 28 February 2008 Received in revised form 27 March 2008 Accepted 27 March 2008 Available online 14 April 2008 Keywords: 1, 4-Dimethylpiperazine di-betaine L-Tartaric acid Hydrogen bonds X-ray diffraction FTIR Raman and NMR spectra
a b s t r a c t Crystal structure of the 1:1 complex of 1,4-dimethylpiperazine di-betaine (1,4-dicarboxymethyl-1,4dimethylpiperazinium inner salt, DBPZ) with L-tartaric acid (TA) has been determined by X-ray diffraction. The crystals are triclinic, space group P1. TA and DBPZ are linked by two asymmetric COOHOOC hydrogen bonds of 2.485(3) and 2.566(3) Å into chains. The piperazine ring has a chair conformation with the methyl groups in the axial positions and the CH2COO substituents in the equatorial ones. In the theoretically optimized structure of isolated DBPZTA at the B3LYP/6-31G(d,p) level of theory the non-linear complex, with DBPZ in the same conformation as in the crystal, is formed. The 1H and 13C magnetic isotropic shielding tensors have been analyzed in order to confirm the CAHO contacts, which stabilize the optimized structure of DBPZTA. The FTIR spectrum of the solid complex is consistent with the X-ray results. Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction L-Tartaric acid is a naturally occurring chiral dicarboxylic acid [1]. Different isomers of tartaric acid, pure enantiomers, racemic and meso forms, were subjects of crystallographic studies [2–9]. The study of the molecular packing and hydrogen bonding in tartaric acid and its derivatives is relevant to the development of approaches in crystal engineering [10–13]. Salts of TA with amines and amino acids were studied by X-ray diffraction and their structures are stored in the Cambridge Crystallographic DataBase [14]. In complexes of organic bases with tartaric acid, one or two protons can be transferred from the carboxylic groups of TA to form the monovalent (semi-tartrate) or divalent (tartrate) anions, respectively. A structural study of organic salts of semi-L-tartrate shows that the anionic network is remarkably consistent, regardless of the nature of the cation [10– 13]. L-Tartaric-amine complexes have been chosen for the study as a potential organic material for non-linear optics. Their second harmonic generation (SHG) activity depends on the crystal structure and the type of amine [15–18]. One of such complex is piperazinium L-tartrate, which crystallizes in the monoclinic P21 space group. The piperazinium divalent cation is surrounded by four L-tartrate
* Tel.: +48 61 8291216; fax: +48 61 8291505. E-mail address: [email protected] (Z. Dega-Szafran). 0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2008.03.057
anions through the NAHO hydrogen bonds of the lengths between 2.688(2) and 2.780(2) Å [19]. Recently, we have studied the 2:1 complex of N-carboxymethyl-N-methylmorpholinium inner salt (N-methylmorpholine betaine) with L-tartaric acid [20] and the 4:2 complex of N-carboxymethyl-N-methylpiperidinium inner salt (N-methylpiperidine betaine) with L-tartaric acid [21], which belong to a new family of zwitterionic-L-tartaric acid compounds (betaine–tartaric acid), differing from that of amino acids–L-tartaric acid complexes [17,18,22–29]. In betaines (R3N+CH2COO ) only the carboxylate group can interact with tartaric acid, through COOHOOC hydrogen bond, without proton transfer. In continuation of our previous investigation, the present work is focused on the structure, hydrogen bonds and conformation of the complex formed between 1,4-dimethylpiperazine di-betaine (1,4-dimethyl-1,4-dicarboxymethyl-piperazinium inner salt, DBPZ) and L-tartaric acid (TA), which is a new example of the interaction of zwitterionic compound with L-tartaric acid. 2. Experimental 1,4-Dimethylpiperazine di-betaine (DBPZ) was prepared according the procedure described in Ref. [30]. DBPZ crystallizes with two water molecules [31]. The 1:1 complex of DBPZ with Ltartaric acid (TA) was obtained by mixing one equivalent of DBPZ with one equivalent of TA in water. The complex decomposes at
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222 °C, [a]D = +5.74° in H2O. The crystals of DBPZTA are formed in the 1:1 stoichiometry as anhydrous sample. Analysis for C14H24N2O10: calculated: %C, 44.21; %H, 6.36; %N, 7.37; required: %C, 43.90; %H, 6.36; %N, 7.26. The crystal structure was determined from X-ray diffraction, measured with a KUMA KM-4 CCD diffractometer [32]. The structure was solved by direct methods using SHELXS-97 [33] and refined on F2 by full-matrix least-squares with the SHELXL-97 programs [34]. The crystal data, details of data collection and structure refinement are given in Table 1, and the final atomic coordinates are listed in Table 2. The complete set of structural parameters in CIF format is available as an Electronic Supplementary Publication from the Cambridge Crystallographic Data Centre (CCDC 679313). The DFT calculations were performed with the GAUSSIAN-03 program package [35]. The calculations employed the B3LYP exchange-correlation functional, which combines the hybrid exchange functional of Becke [36,37] with the gradient-correlation functional of Lee, Yang and Parr [38], and the splitvalence polarized 6-31G(d,p) basis set [39]. The magnetic isotropic shielding tensors (r) were calculated using the Gauge Independent Atomic Orbitals (GIAO) approach with the GAUSSIAN 03 package. The X-ray geometry was used as the input file. FTIR spectra were measured on a Bruker IFS 66v/S instrument, evacuated to avoid water and CO2 absorptions. Solid state spectra were recorded in Nujol and Fluorolube suspensions using KBr plates. Each spectrum consisted of 64 scans. The Raman spectrum was measured on a Bruker IFS 66 instrument. The NMR spectra were recorded on a Varian Gemini 300 VT spectrometer operating at 300.07 and 75.46 MHz for 1H and 13 C, respectively. The spectra were measured in D2O relative to internal standard of 3-(trimethylsilyl)propionic-d4 acid sodium salt.
Table 1 Crystal data and structure refinement for the DBPZTA complex Molecular formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions
Volume Z Calculated density Absorption coefficient F(0 0 0) Crystal size h Range for data collection Limiting indices
Reflections collected/unique Completeness to h = 29.21° Absorption correction Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2rI] R indices (all data) Absolute structure parameter Largest diff. peak and hole
C14H24N2O10 380.35 293(2) K 0.71073 Å Triclinic P1 a = 6.8439(16) Å b = 8.372(3) Å c = 8.424(2) Å a = 104.84(3)° b = 109.29(2)° c = 101.19(2)° 419.3(2) Å3 1 1.506 g/m3 0.129 mm 1 202 0.3 0.2 0.18 mm 2.64°–29.21° 96h68 11 6 k 6 8 10 6 l 6 11 3098/2272 [Rint = 0.0111] 86.2% None Full-matrix least-squares on F2 2272/3/310 0.926 R1 = 0.0296, wR2 = 0.0651 R1 = 0.0430, wR2 = 0.0687 0.4(10) 0.187 and 0.175 e. Å 3
Table 2 Atomic coordinates and equivalent isotropic displacement parameters (Å2 103) of the DBPZTA complex Atom N(1) C(2) C(3) N(4) C(5) C(6) C(7) C(8) C(9) C(10) O(1) O(2) C(11) C(12) O(3) O(4) O(5) O(6) C(21) C(22) O(7) C(23) O(8) C(24) O(9) O(10) H(2A) H(2B) H(3A) H(3B) H(5A) H(5B) H(6A) H(6B) H(7A) H(7B) H(7C) H(8A) H(8B) H(8C) H(9A) H(9B) H(11A) H(11B) H(5) H(22) H(7) H(23) H(8) H(9)
x
y 0.4022(3) 0.2777(4) 0.3428(4) 0.5841(3) 0.7059(4) 0.6435(4) 0.3377(5) 0.6402(5) 0.3661(4) 0.1353(4) 0.1375(3) 0.0224(3) 0.6332(4) 0.8737(4) 0.8922(3) 1.0235(3) 0.7543(3) 0.9273(3) 0.7861(4) 0.6235(4) 0.6741(3) 0.3941(4) 0.4021(3) 0.2314(4) 0.1356(4) 0.2019(3) 0.2910(40) 0.1240(50) 0.3160(40) 0.2590(40) 0.6650(40) 0.8620(40) 0.6840(40) 0.7140(40) 0.1710(60) 0.4090(50) 0.3870(60) 0.5400(50) 0.7980(50) 0.6170(50) 0.4130(40) 0.4570(40) 0.5740(40) 0.5450(40) 0.8620(50) 0.6200(40) 0.7560(50) 0.3510(40) 0.2980(50) 0.0260(70)
0.8888(2) 0.9923(3) 1.0229(4) 1.1173(2) 1.0076(3) 0.9779(3) 0.7029(3) 1.3009(3) 0.8976(4) 0.8159(3) 0.8289(2) 0.7513(2) 1.1241(4) 1.2096(3) 1.2255(2) 1.2493(3) 0.3881(2) 0.2592(2) 0.3726(3) 0.5158(3) 0.5053(2) 0.5021(3) 0.3326(2) 0.6501(3) 0.6029(2) 0.7985(2) 1.1020(30) 0.9240(30) 0.9240(40) 1.0910(40) 0.9050(30) 1.0610(30) 1.0840(30) 0.9060(30) 0.6580(40) 0.6390(40) 0.6970(50) 1.3470(40) 1.3550(40) 1.3000(40) 1.0140(40) 0.8350(30) 0.9890(30) 1.1800(40) 0.3260(50) 0.6250(40) 0.4190(40) 0.5300(30) 0.3120(40) 0.7000(60)
z
U(eq)/U(iso) 0.0789(2) 0.0156(3) 0.1652(3) 0.0988(2) 0.0117(3) 0.1378(3) 0.0402(4) 0.0265(4) 0.2500(3) 0.2317(4) 0.3876(2) 0.0862(3) 0.2617(3) 0.2258(3) 0.3668(2) 0.0787(3) 0.6252(2) 0.3271(2) 0.4579(3) 0.4434(3) 0.2626(2) 0.5259(3) 0.4291(2) 0.5160(3) 0.4109(3) 0.6055(3) 0.0670(30) 0.0690(30) 0.2650(40) 0.2160(40) 0.1110(30) 0.0390(30) 0.2320(30) 0.1770(30) 0.0730(40) 0.0250(50) 0.1350(40) 0.0360(40) 0.0660(40) 0.1310(40) 0.3170(30) 0.3070(40) 0.3630(30) 0.3180(40) 0.6280(40) 0.5120(40) 0.2030(40) 0.6630(40) 0.4890(50) 0.4000(60)
23(1) 26(1) 30(1) 22(1) 24(1) 25(1) 41(1) 35(1) 26(1) 30(1) 42(1) 44(1) 28(1) 28(1) 41(1) 40(1) 39(1) 46(1) 28(1) 27(1) 40(1) 26(1) 32(1) 28(1) 55(1) 51(1) 31 31 36 36 29 29 30 30 62 62 62 52 52 52 32 32 33 33 56(10) 32 42 32 66(12) 106(14)
U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.
3. Results and Discussion 3.1. Crystal structure 1,4-Dimethylpiperazine di-betaine (DBPZ) has two equivalent proton-acceptor centres; pKa = 2.10 [30], while L(+)-tartaric acid (TA) has four proton-donor centres; two carboxylic and two hydroxyl groups; pKa1 = 3.03 and pKa2 = 4.46 [40]. However, DBPZ forms a crystalline complex in the 1:1 stoichiometry with L-tartaric acid (TA). DBPZTA crystals belong to the triclinic system, space group P1 (Table 1). This low-symmetry space group P1 has been already established in four complexes of tartaric acid: bis(quinolinium-2carboxylate)–L-tartaric acid [28], ephedrine–L–hemitartrate trihydrate [41], L-malic–L-tartaric co-crystals [42] and bis(4’-pyridyl)ethane–tartaric acid [43] complexes. Bond lengths, bond and torsion angles for title compound are given in Tables 3 and 4. Fig. 1 shows the atomic numbering system.
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Table 3 Experimental and calculated bond lengths (Å) and angles (°) for the DBPZTA complex X-ray Bond lengths N(1)AC(2) C(2) AC(3) C(3) AN(4) N(4) AC(5) C(5) AC(6) N(1) AC(6) N(1) AC(7) N(4) AC(8) N(1) AC(9) C(9) AC(10) C(10) AO(1) C(10) AO(2) N(4) AC(11) C(11) AC(12) C(12) AO(3) C(12) AO(4) C(21) AC(22) C(21) AO(5) C(21) AO(6) C(22) AC(23) C(22) AO(7) C(23) AO(8) C(23) AC(24) C(24) AO(9) C(24) AO(10) Bond angles N(1) AC(2) AC(3) C(2) AC(3) AN(4) C(3) AN(4) AC(5) N(4) AC(5) AC(6) C(5) AC(6) AN(1) C(2) AN(1) AC(6) C(7) AN(1) AC(2) C(7) AN(1) AC(6) C(2) AN(1) AC(9) C(6) AN(1) AC(9) C(7) AN(1) AC(9) N(1) AC(9) AC(10) O(1) AC(10) AC(9) O(2) AC(10) AC(9) O(2) AC(10) AO(1) C(8) AN(4) AC(3) C(8) AN(4) AC(5) C(3) AN(4) AC(11) C(5) AN(4) AC(11) C(8) AN(4) AC(11) N(4) AC(11) AC(12) O(3) AC(12) AC(11) O(4) AC(12) AC(11) O(3) AC(12) AO(4) C(21) AC(22) AC(23) O(5) AC(21) AC(22) O(6) AC(21) AC(22) O(6) AC(21) AO(5) C(22) AC(23) AC(24) O(7) AC(22) AC(21) O(7) AC(22) AC(23) O(8) AC(23) AC(22) O(8) AC(23) AC(24) O(9) AC(24) AC(23) O(10) AC(24) AC(23) O(10) AC(24) AO(9)
1.517(3) 1.531(3) 1.523(3) 1.521(3) 1.518(3) 1.523(3) 1.505(3) 1.515(3) 1.527(3) 1.534(4) 1.285(3) 1.232(3) 1.529(3) 1.554(3) 1.272(3) 1.231(3) 1.529(3) 1.320(3) 1.206(3) 1.534(3) 1.421(3) 1.424(3) 1.537(3) 1.294(3) 1.215(3) 113.0(2) 112.9(2) 106.5(2) 111.9(2) 114.3(2) 107.5(2) 111.9(2) 110.9(2) 109.8(2) 106.4(2) 110.3(2) 118.1(2) 109.4(2) 122.8(2) 127.7(2) 110.5(2) 113.6(2) 108.0(2) 109.2(2) 109.0(2) 116.9(2) 111.5(2) 122.3(2) 126.1(2) 109.3(2) 113.1(2) 121.9(2) 125.0(2) 108.8(2) 111.7(2) 109.7(2) 106.1(2) 114.4(2) 115.6(2) 118.8(2) 125.6(2)
B3LYP/6-31G(d,p) 1.527 1.524 1.505 1.516 1.514 1.528 1.508 1.517 1.527 1.546 1.300 1.223 1.544 1.592 1.231 1.258 1.523 1.348 1.211 1.549 1.406 1.407 1.538 1.273 1.257 113.04 114.08 108.15 112.72 113.11 107.18 112.01 111.71 108.83 107.36 109.59 112.88 114.81 120.50 124.67 111.60 111.56 109.75 107.90 107.80 116.06 110.02 116.84 133.13 109.62 112.73 123.52 123.74 108.98 109.57 111.81 109.99 111.50 114.90 118.69 126.40
The piperazine ring has a chair conformation with the methyl groups in the axial positions and the CH2COO substituents in the equatorial ones. The reverse orientation of the substituents has been found in the 1:1 complex of DBPZ with HCl [30]. In the complex investigated DBPZ exists in its zwitterionic form, with two slightly different CAO bonds: the C(10/12)AO(1/3) bonds, of 1.285(3) and 1.272(3) Å, are longer than the C(10/12)AO(2/4) bonds,
Table 4 Experimental and calculated torsion angles (°) for the DBPZTA complex Torsion angles N(1) AC(2) AC(3) AN(4) C(2) AC(3) AN(4) AC(5) C(3) AN(4) AC(5) AC(6) N(4) AC(5) AC(6) AN(1) C(2) AN(1) AC(6) AC(5) C(6) AN(1) AC(2) AC(3) C(7) AN(1) AC(2) AC(3) C(7) AN(1) AC(6) AC(5) C(7) AN(1) AC(9) AC(10) C(9) AN(1) AC(2) AC(3) C(9) AN(1) AC(6) AC(5) C(2) AN(1) AC(9) AC(10) C(6) AN(1) AC(9) AC(10) N(1) AC(9) AC(10) AO(1) N(1) AC(9) AC(10) AO(2) C(8) AN(4) AC(3) AC(2) C(8) AN(4) AC(5) AC(6) C(8) AN(4) AC(11) AC(12) C(2) AC(3) AN(4) AC(11) C(6) AC(5) AN(4) AC(11) C(3) AN(4) AC(11) AC(12) C(5) AN(4) AC(11) AC(12) N(4) AC(11) AC(12) AO(3) N(4) AC(11) AC(12) AO(4) C(21) AC(22) AC(23) AC(24) O(5) AC(21) AC(22) AC(23) O(6) AC(21) AC(22) AC(23) O(7) AC(22) AC(23) AC(24) O(7) AC(22) AC(21) AO(5) O(7) AC(22) AC(21) AO(6) O(8) AC(23) AC(22) AC(21) O(8) AC(23) AC(22) AO(7) O(9) AC(24) AC(23) AC(22) O(9) AC(24) AC(23) AO(8) O(10) AC(24) AC(23) AC(22) O(10) AC(24) AC(23) AO(8)
X-ray 58.1(3) 57.3(3) 56.9(2) 58.5(3) 53.3(3) 52.4(2) 69.6(3) 69.2(3) 59.3(3) 167.7(2) 170.9(2) 64.4(3) 179.6(2) 177.3(2) 3.5(4) 66.4(3) 64.9(3) 62.1(3) 174.5(2) 173.3(2) 177.8(2) 62.4(3) 172.8(2) 9.6(4) 178.2(2) 63.9(3) 116.2(3) 58.9(2) 174.5(2) 5.4(3) 58.3(2) 64.5(2) 113.3(2) 5.1(3) 67.1(3) 174.5(2)
B3LYP/6-31G(d,p) 55.55 53.26 54.41 58.52 55.17 53.18 69.68 67.88 73.86 168.99 171.95 48.94 164.64 137.43 44.05 69.82 68.69 63.90 170.74 173.08 174.36 93.98 179.98 0.42 178.54 67.75 111.19 56.82 169.20 11.86 56.02 65.70 123.96 2.36 56.98 178.59
of 1.232(3), 1.231(3) Å, respectively (Table 3). In the DBPZTA complex the proton is not transferred from TA to DBPZ, however the molecules are linked by a short non-symmetric O(9)AHO(1) hydrogen bond of 2.485(3) Å (Table 5). The other carboxylate oxygen atom of DBPZ is involved in significantly longer O(3)HAO(5) hydrogen bond of 2.566(3) Å with the neighboring molecule of the complex. The Donohue angles of the hydrogen bonds agree with the angular criteria for the H-atom sites [44,45]. These two hydrogen bonds link the complex molecules into an infinite chain. The chains are linked to the neighboring ones by the O(7)AHO(4) and O(8)AHO(3) hydrogen bonds of 2.886(3) and 2.650(2) Å, respectively, between the hydroxyl groups of TA and the carboxylate groups of DBPZ (Fig. 2, Table 5). The intramolecular O(7)AHO(6) hydrogen bond of 2.712(3) Å and the OAHO angle of 118(3)° (Table 5) stabilizes the TA conformation. It appears that the significant difference of 0.081 Å in the lengths of the hydrogen bonds, the shorter O(9)AHO(1) and the longer O(5)AHO(3) one, results from the involvement of the O(3) atom of the DBPZ moiety in bifurcated hydrogen bonds to the hydroxyl group, O(8)-H, and to the oxygen atom O(5) of the carboxylic group of TA (Table 5). There are no other strong interactions disturbing the short O(9)AHO(1) hydrogen bond geometry. Also no hydrogen bonds are formed by the DBPZ carboxylate O(2) atom, whereas the O(4) oxygen is involved in the O(7)AHO(4) hydrogen bond to another hydroxyl group O(7)H of TA (Fig. 2, Table 5). The hydrogen bonds to the hydroxyl groups of TA link the hydrogen-bonded chains into a 3-dimensional network (Fig. 3). The interactions between the TA molecules themselves are very weak only. According to the most recent studies the spheres of interactions are considerably larger than the sums of the van der
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261
Fig. 1. Molecular structure and atom labeling scheme of 1,4-dimethylpiperazine di-betaine–L-tartaric acid complex. The hydrogen bonds have been shown as the dashed lines and the thermal ellipsoids at 50% probability displacement level.
Table 5 Dimensions of hydrogen bonds in the crystal and optimized structures of the DBPZTA complex DAHA
DAH (Å)
HA (Å)
DA (Å)
DAHA (°)
X-ray O(9) AH(9)O(1) O(5) AH(5)O(3)a O(7) AH(7)O(4)b O(7) AH(7)O(6) O(8) AH(8)O(3)c
1.07(2) 0.83(3) 0.75(3) 0.75(3) 0.81(3)
1.45(2) 1.75(3) 2.24(3) 2.28(3) 1.86(3)
2.485(3) 2.566(3) 2.886(3) 2.712(3) 2.650(2)
176(2) 170(2) 146(2) 118(3) 166(3)
B3LYP/6-31G(d,p) O(1) AH(9)O(9) C(9) AHO(10) C(2) AH(ax)O(10) C(6) AH(ax)O(10) C(8) AHO(10) O(7) AH(7)O(9) O(8) AH(8)O(6)
1.060 1.088 1.094 1.092 1.090 0.974 0.971
1.429 2.123 2.124 2.253 2.191 1.945 2.192
2.485 3.044 3.097 3.185 3.272 2.595 2.692
173.70 140.63 146.65 141.99 177.02 121.90 110.64
Symmetry codes: ax
Waals radii [46–49], which contribute to the effect of crystal-structure stabilization of molecules [50].
3.2. B3LYP/6-31G(d,p) calculations
2, y
1, z + 1; bx
2, y
1, z; cx
1, y
1, z.
The optimized structure of the title complex was compared to the X-ray diffraction one in Fig. 4, and the bond lengths, bond and torsion angles are listed in Tables 3 and 4. The main difference between these structures is in the arrangement of the molecules of DBPZ and TA, which are linear in the crystals and bent in the isolated complex. The O(9)O(1) distances are comparable, however the acidic proton from carboxylic group of TA is transferred to the oxygen atom of the carboxylate group of DBPZ in the optimized structure, hence the mono-protonated DBPZ molecule interacts with the semi-tartrate anion (Table 5). In the optimized structure of DBPZTA, several CAHO(10) contacts stabilize the bent structure (Table 5) and influence the NACACAO torsion angles,
Fig. 2. An autostereogram [60] of one sheet of hydrogen-bonded molecules of 1,4-dimethylpiperazine di-betaine–L-tartaric acid
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c 0
Fig. 3. The crystal structure of the 1,4-dimethylpiperazine di-betaine–L-tartaric acid complex viewed down the [001] direction, with the hydrogen bonds marked by the dashed lines.
Fig. 4. Comparison of the X-ray and optimized structures of 1,4-dimethylpiperazine di-betaine–tartaric acid complex.
which have the opposite signs than in the crystal (Table 4). The energy of the calculated DBPZTA complex is 1409.681688 a.u., and the dipole moment of 7.17 D confirms the asymmetry of the title complex. 3.3. NMR spectra The experimental proton and carbon-13 chemical shifts (d) and calculated magnetic isotropic shielding tensors (r) by the GIAO/ B3LYP/6-31G(d,p) approach for DBPZTA are listed in Table 6. In the 1H NMR spectrum two doublets at 4.44 and 4.00 ppm are
attributed to the ring piperazine protons at the equatorial and axial positions, respectively. The sharp and intensive resonance signals of CAH, N+CH2COO and CH3 protons appear at 4.46, 4.18 and 3.47 ppm, respectively. The rH values of magnetic isotropic shielding tensors are scattered, with the exception of rH of the CAH protons of tartaric acid (Fig. 5a and Table 6). These discrepancy can confirm the engagement of the ring, methyl and methylene protons in the hydrogen bonds with tartaric acid molecule in the isolated molecule (Table 5), as well as a proton-solvent interaction in aqueous solution. The 13C NMR spectrum consists of four sharp signals at 56.1, 75.1, 170.5 and 178.0 ppm, assigned to the piperazine ring carbon atoms, the skeletal tartaric acid carbon atom, the carboxylate carbon atom of DBPZ and the carbonyl carbon atom of TA, respectively (Table 6). Similarly as in the spectra of 1,4-dimethylpiperazine, tetramethylpiperazinium salts, DBPZ and its complexes with HCl and p-hydroxybenzoic acid, the signals attributed to the methyl and methylene carbon atom of N+CH3 and N+CH2COO groups are broad and of very low intensities [30,51–53]. This broadening can be caused by a quadrupole effect of the positively charged nitrogen atoms. Theoretically computed 13C chemical shifts can be obtained at a level of accuracy sufficient to allow application to configurational and conformational determination of organic molecules [54,55]. The carbon-13 chemical shifts assignments for the complex investigated were confirmed by the GIAO calculated magnetic isotropic shielding tensors (rC) (Table 6). The relation between the experimental 13C chemical shifts and the average rC values gives a linear regression described by the equation: d = a + br (Fig. 5b), where a = 206.1784, b = 1.0849, r = 0.9962.
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Chemical shifts (ppm)
4.6 4.4
150
4.2 4.0
100
3.8 3.6 3.4
50
a 24
26
b
28 30 50 Magnetic isotropic shielding tensors (ppm)
100
150
Fig. 5. Plots of the experimental chemical shifts (d) versus the magnetic isotropic shielding tensors (r) from the GIAO/B3LYP/6-31G(d,p) calculations for 1H (a) and 13C (b) for DBPZTA.
Table 6 Experimental chemical shifts (d, ppm, D2O) and calculated magnetic isotropic shielding tensors (r, ppm) by the GIAO/B3LYP/6-31G(d,p) method for the DBPZTA complex d
Atoma
H Ring (ax)
4.00
Ring (eq)
4.44
CH2
4.18
CH3
3.47
CH (TA)
4.64
2 3 5 6 2 3 5 6 9 9 11 11 7 7 7 8 8 8 23 22
28.2949 28.9105 29.2593 26.6901 25.9297 29.0452 24.0891 29.2297 25.2599 28.8485 28.6462 29.0670 26.2208 29.8595 28.7266 30.0148 26.0113 26.9173 27.4976 27.4445
2 3 5 6 9 11 7 8 23 22 10 12 24 21
140.9635 135.8245 141.5898 133.6650 127.4020 122.4029 148.4739 148.0776 114.7617 117.7610 34.3253 45.5474 18.4761 24.5260
r
1
to several bands in the 3470–2450 cm 1 region. The bands attributed to the mC@O and masCOO appear at 1732, 1672 and 1642 cm 1, respectively. The broad absorption in the 1500– 560 cm 1 region, with the centre of gravity at 1090 cm 1, arises from the stretching and bending vibrations of the OH groups, and it is characteristic of the short OAHO hydrogen bond [56]. The continuous absorption of the OHO vibration overlaps the in-plane and out-of-plane CAH, stretching and bending CAC, CAN, CAO vibrations, as well as the skeletal of TA molecule and the ring of piperazine modes. Some of these vibrations can be distinguished by the second derivative (d2) spectrum (Fig. 6b). The derivative spectroscopy can be used to determine the frequencies of the narrow bands covered by the broad absorption due to stretching and bending OAH vibrations. The minima in the d2 spectrum have the same wavenumbers as the maxima in the absorbance FTIR spectrum, but their intensities vary inversely with the fourth power of the half-width of the absorption bands [57,58]. In the Raman spectrum (Fig. 6c) the absorption bands of the OH vibration are absent, and the bands attributed to the mC@O and masCOO modes are of weak intensities [59]. 4. Conclusions
13
C Ring
56.1
CH2
68.7
CH3
49.9
CH (TA)
75.1
COO (DBPZ)
170.5
COOH (TA)
178.0
a
See Fig. 1.
In the 1:1 complex of 1,4-dimethylpiperazine di-betaine (DBPZ) with L-tartaric acid (TA) only a half of the proton-donor COOH groups of TA and proton-acceptor COO groups of DBPZ are involved in the short hydrogen bonds of 2.485(3) Å between the above molecules. The remaining COOH and COO groups link the molecules of the 1:1 complex into infinite chains, through the OAHO hydrogen bonds of 2.566(3) Å. The chains are parallel to each other and are linked by the OAHO hydrogen bonds between the hydroxyl group of TA and the carboxylate group of DBPZ. The complex is non-centrosymmetric, space group P1. In the optimized structure of the title complex by the B3LYP/6-31G(d,p) approach, the DBPZ and TA molecules are not extended but bent. Such an arrangement of molecules is stabilized by several CAHO contacts. The FTIR, 1H and 13C NMR data agree well with the X-ray structure. Acknowledgements
3.4. Vibrational spectra Fig. 6a shows a solid-state FTIR spectrum of the DBPZTA complex. The stretching type of vibration of hydrogen bonds gives rise
The DFT calculations were performed at the Poznan´ Supercomputing and Network Centre. The authors thank Prof. Maria Połomska for the Raman spectrum measurement.
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1.5
a
1.0
0.5
0.0
Intensity
0.2
b
0.0
-0.2
0.10
c
0.05
0.00 3500 3000 2500 2000
1500
1000
500
Wavenumbers (cm-1) Fig. 6. Vibrational spectra of DBPZTA: (a) FTIR; (b) FTIR second derivative; (c) Raman.
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