CRYSTAL GROWTH & DESIGN
Structure and Properties of Orthorhombic L-Arginine Formate
2006 VOL. 6, NO. 9 2041-2046
S. Haussu¨hl,† H. A. Karapetyan,‡ R. P. Sukiasyan,‡ and A. M. Petrosyan*,‡ Institut fu¨r Kristallographie, UniVersita¨t zu Ko¨ln, Zu¨lpicher Strasse 49b, D-50374 Ko¨ln, Germany, and Molecule Structure Research Center, NAS of Armenia, 26 Azatutyan AVenue, YereVan 375014, Armenia ReceiVed January 28, 2006; ReVised Manuscript ReceiVed July 5, 2006
ABSTRACT: Single crystals of orthorhombic L-arginine formate (+(NH2)2CNH(CH2)3CH(NH3+)COO-‚HCOO-) that had dimensions of ca. 30 × 30 × 40 mm and were of optical quality were grown by controlled evaporation of aqueous solutions. An X-ray structure analysis yielded space group P212121, a1 ) 7.706(2) Å, a2 ) 7.808(2) Å, a3 ) 18.594(4) Å, Z ) 4, and Fc ) 1.308 Mg/m3 at 293 K. Hydrogen bonds determine the interactions between monovalent L-arginine cations and also the interactions of these cations with formate anions. The structure is compared with that of the monoclinic polymorph. ATR FTIR and FT Raman spectra, TG, DTA, thermal expansion, and elastic and thermoelastic properties are reported. 1. Introduction
Table 1. Crystal Data and Structure Refinement Details for L-Arg‚HCOOH
Several salts of L-arginine are known to possess strong nonlinear optical properties (see, for example, the citations in ref 1). Similar remarkable nonlinear effects have been observed in certain formates, such as LiHCOO‚H2O and NaHCOO,2 Sr(HCOO)2 and Sr(HCOO)2‚2H2O,3 Ba(HCOO)2,4 and Y(HCOO)3‚2H2O.5 Therefore, we expected that L-arginine formate (L-Arg‚HCOOH) might exhibit still better nonlinear optical properties. This has already been confirmed qualitatively.6 The compound L-Arg‚HCOOH was first prepared by Monaco et al.7 in the form of a fine powder. Then Suresh, Padmanabhan, and Vijayan8 detected monoclinic crystals of L-arginine formate, a polymorph of L-Arg‚HCOOH, and determined its crystal structure. Our attempts to grow large single crystals that were of optical quality and had dimensions of several centimeters in all directions were successful.9 Recently Packiam Julius et al.10 grew and investigated single crystals of L-Arg‚HCOOH as well. In the present paper we report the results of our crystal structure analysis of orthorhombic L-Arg‚HCOOH and of investigations of its thermal, spectroscopic, and elastic properties.
empirical formula formula wt temp wavelength cryst syst space group unit cell dimens a b c R)β)γ V, Z density (calcd) density (measd) abs coeff F(000) cryst size θ range for data collecn limiting indices no. of rflns collected no. of indep rflns abs cor refinement method no. of data/restraints/params goodness of fit on F2 final R indices (I > 2σ(I)) R1 wR2 R indices (all data) R1 wR2 extinction coeff largest diff peak and hole
2. Experimental Section Single crystals of L-Arg‚HCOOH were grown from aqueous solutions by controlled evaporation at about 29 °C. The starting reagents were L-arginine (Sigma Chemical Co.) and formic acid (Merck 98-100% GR). X-ray diffraction data for the structure analysis were collected by a CAD-4 Enraf-Nonius diffractometer. For the structure solution and refinement we used the programs SHELXS 97 and SHELXL 97.11,12 For details and selected results see Tables 1-4. Attenuated total reflection Fourier transform infrared spectra (ATR FTIR) and Fourier transform Raman spectra were measured with the aid of a Nicolet “Nexus” FT-IR spectrometer with ZnSe prism (4000-650 cm-1) and the NXP FT-Raman module of a Nicolet 5700 spectrometer, respectively. The UV-vis transmittance was measured by the aid of a “Helios Gamma” UV-vis spectrophotometer (England). For the study of thermal properties we employed a 3427-904 type Paulik-Paulik-Erdey Derivatograph (MOM, Hungary) and also a
a ) 7.706(2) Å b ) 7.808(2) Å c ) 18.594(4) Å 90° 118.8(4) Å3, 4 1.308 Mg/m3 1.309(1) Mg/m3 0.107 mm-1 472 0.2 × 0.2 × 0.1 mm 2.19-23.98° -8 e h e +8 -8 e k e +8 0 e l e +20 3575 1742 (Rint ) 0.0234) none full-matrix least squares on F2 1742/0/201 1.084 0.0264 0.0629 0.0353 0.0662 0.018(3) 0.092 and -0.086 e Å-3
Boe¨tius type microscope with a heating table. For the equipment used for the measurement of thermal expansion and elastic properties, see Table 5.
3. Results and Discussion 3.1. Preparation and Crystal Growth. The formation of occurs according to the scheme
L-Arg‚HCOOH +
(H2N)2CNH(CH2)3CH(NH2)COO- + HCOOH f +
* To whom correspondence should be addressed. Tel: +37410 285139. Fax: +37410 282267. E-mail:
[email protected]. † Universita ¨ t zu Ko¨ln. ‡ NAS of Armenia.
C7H16N4O4 220.24 293(2) K 0.710 73 Å orthorhombic P212121
(H2N)2CNH(CH2)3CH(NH3+)COO-‚HCOO-
Recently we observed during crystal growth of L-Arg‚ HCOOH that at a temperature above 30 °C the compound NR-
10.1021/cg060051t CCC: $33.50 © 2006 American Chemical Society Published on Web 08/08/2006
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Table 2. Selected Bond Lengths (Å) and Angles (deg) for Orthorhombic L-Arg‚HCOOH C(1)-O(1) C(1)-O(2) C(7)-O(3) C(7)-O(4) C(2)-N(1) C(5)-N(2) N(2)-C(6)
1.244(2) 1.255(2) 1.220(2) 1.237(2) 1.491(2) 1.463(3) 1.325(2)
O(1)-C(1)-O(2) O(1)-C(1)-C(2) O(2)-C(1)-C(2) O(3)-C(7)-O(4) N(1)-C(2)-C(1) N(1)-C(2)-C(3) N(2)-C(5)-C(4)
126.1(2) 118.80(15) 115.08(14) 128.3(2) 110.89(14) 111.19(15) 113.8(2)
C(6)-N(3) C(6)-N(4) C(1)-C(2) C(2)-C(3) C(3)-C(4) C(4)-C(5)
1.325(3) 1.326(2) 1.526(3) 1.535(2) 1.518(3) 1.518(3)
N(3)-C(6)-N(4) N(3)-C(6)-N(2) N(4)-C(6)-N(2) C(1)-C(3)-C(2) C(2)-C(4)-C(3) C(3)-C(4)-C(5) C(5)-C(6)-N(2)
118.4(2) 119.7(2) 122.0(2) 110.46(14) 113.21(15) 113.9(2) 125.1(2)
Figure 1. Solubility curve of an orthorhombic crystal of L-Arg‚ HCOOH in water.
Table 3. Hydrogen Bond Parameters for Orthorhombic L-Arg‚HCOOH D-H‚‚‚Aa
d(D-H), Å
d(H‚‚‚A), Å
d(D‚‚‚A), Å
∠(DHA), deg
N(1)-H(2)‚‚‚O(3)#1 N(1)-H(1)‚‚‚O(2)#2 N(1)-H(3)‚‚‚O(4)#3 N(2)-H(4)‚‚‚O(3)#4 N(3)-H(5)‚‚‚O(1)#4 N(3)-H(6)‚‚‚O(2)#5 N(4)-H(7)‚‚‚O(1)#5 N(4)-H(8)‚‚‚O(4) #6
0.90(3) 0.98(2) 0.99(2) 0.90(2) 0.82(2) 0.89(2) 0.97(2) 0.89(2)
1.90(3) 1.79(2) 1.83(2) 1.92(2) 2.24(2) 1.97(2) 1.98(2) 2.06(2)
2.783(2) 2.760(2) 2.804(2) 2.816(2) 2.977(2) 2.841(3) 2.951(2) 2.926(2)
167(2) 168(2) 168(2) 171(2) 151(2) 166(2) 177(2) 165(2)
a Symmetry transformations used to generate equivalent atoms: (#1) x, y, z; (#2) -x + 2, y - 0.5, -z + 1.5; (#3) x + 0.5, -y + 0.5, -z + 1; (#4) x, y + 1, z; (#5) -x + 1, y + 0.5, -z + 1.5; (#6) x - 0.5, -y + 0.5, -z + 1.
Figure 2. Dependence of pH values on the ratio of HCOOH to L-arginine.
formyl-L-arginine (NFLA) can be formed13 according to +
(H2N)2CNH(CH2)3CH(NH2)COO- + HCOOH f +
(H2N)2CNH(CH2)3CH(HN(HCO))COO- + H2O
At room temperature this compound crystallizes as a monohydrate (NFLA‚H2O). A similar compound (NR-oxalyl-L-arginine) was obtained earlier.14 Detailed results on this species will be reported later. To optimize the growth conditions of L-Arg‚ HCOOH, we determined its solubility in the range between 20 and 30 °C by a method of sequential dissolution of decreasing amounts at a given temperature. Figure 1 shows that the solubility of L-Arg‚HCOOH and its temperature dependence in water are rather high. The variation of the pH value with the ratio of L-arginine to formic acid is presented in Figure 2. After our experience the optimal pH value for crystal growth is about 4, which corresponds to the ratio 1:1.5. In the range between 1:1 and 1:2 high-quality bulk crystals can be grown. Crystals obtained from equimolar solutions have a rather elongated habitus, while those grown at a ratio of 1:2 are more isometric. At about 29 °C crystals with dimensions up to 45 × 60 × 60 mm3 were grown with a rate of 0.4 mm/day. An occurrence of disturbing microorganisms was not observed during crystal growth, due to the bactericidal properties of formic acid.
Figure 3. Asymmetric part of the unit cell with the atomic numbering scheme of L-Arg‚HCOOH.
3.2. Crystal Structure of Orthorhombic L-Arg‚HCOOH and Comparison with the Monoclinic Polymorph. In Table 1 the crystal data and details of the structure determination and refinement are given. The asymmetric part of the unit cell with the atomic numbering scheme is shown in Figure 3. The structure consists of formate ions and arginine cations, in which, as is usual, guanidyl and R-amino groups are protonated while the carboxylate group is deprotonated. Selected intramolecular bond lengths and angles are given in Table 2. The bond lengths
Table 4. Selected Torsion Angles (deg) of L-Arg‚HCOOH Orthorhombic and Monoclinic8 Polymorphsa
L-Arg‚HCOOH,
P212121 P21 (I) L-Arg‚HCOOH, P21 (II) L-Arg‚HCOOH,
ψ1
χ1
χ2
χ3
χ4
χ5
-8.3(2) -4.5(7) 21.4(8)
73.9(2) -66.3(6) -70.7(7)
167.1(2) -68.7(7) -179.9(5)
-55.3(2) -174.4(5) -176.7(5)
-70.5(3) 178.9(5) 176.8(5)
172.7(2) 0.3(9) 2.3(8)
a ψ1, χ1, χ2, χ3, χ4, χ5 denote O1-C1-C2-N1, N1-C2-C3-C4, C2-C3-C4-C5, C3-C4-C5-N2, C6-N2-C5-C4, and C5-N2-C6-N3, respectively.
Orthorhombic L-Arginine Formate
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Figure 4. Stereoscopic view of the molecular packing of L-Arg‚HCOOH.
Figure 5. IR spectrum of a powder specimen of L-Arg‚HCOOH.
C(1)-O(1) and C(1)-O(2) in the carboxylate group and of C-N in the guanidyl group have values as expected. However, the bond length C(7)-O(3) in the formate ion is shorter than expected. In contrast, in the monoclinic polymorph the corresponding bond lengths C-O in the formate ions are nearly the same (1.247(7)/1.244(6) Å in the first site and 1.235(6)/1.248(7) Å in the second independent site), while there is an appreciable difference of the C-O bond lengths in one of the arginine carboxylate groups. While in one arginine cation (I) the bond lengths C-O are close and are characteristic of a carboxylate group (1.250(7) and 1.254(7) Å), for the other cation (II) these distances (1.255(7) and 1.198(6) Å) differ appreciably. The bond length of 1.198 Å is rather characteristic of a CdO bond. Bond lengths and angles of the monoclinic form missing in the article of Suresh et al.8 were calculated from the coordinates taken from the Cambridge Crystallographic Data Centre. The most important differences between the two polymorphs are found with respect to the packing schemes, conformations of cations, and hydrogen bonds, which lead to significantly different densities (1.308 and 1.422 Mg/m3 in the orthorhombic and monoclinic polymorphs, respectively). The parameters of hy-
drogen bonds of L-Arg‚HCOOH are given in Table 3, the packing of the structure is shown in Figure 4, and torsion angles of cations in both structures are given in Table 4. The most noticeable structural differences are observed in the arrangements of the arginine cations and hydrogen bond interactions with the anion. In the monoclinic polymorph, in contrast to the expectation of the authors,8 the guanidyl group interacts primarily with formate ions, while the protonated R-amino group interacts primarily with the carboxylate group. In the orthorhombic polymorph the guanidyl group interacts primarily with the carboxylate group. The nitrogen atoms N(3) and N(4) of the guanidyl group form hydrogen bonds N-H‚‚‚O with the oxygen atoms O(2) and O(1) of the carboxylate group of the neighboring arginine cation. This type of interaction was designated as type A by Salunke and Vijayan.15 The protonated R-amino group interacts mainly with the formate ion. However, there are also N(4)-H(8)‚‚‚O(4) and N(1)-H(1)‚‚‚O(2) bonds (see Table 3). Each oxygen atom of the carboxylate group and the formate ion forms two hydrogen bonds. The contact N(3)H(5)‚‚‚O(1), according to Zefirov’s criterion,16 is either a very weak hydrogen bond or a van der Waals interaction. In contrast
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Haussu¨hl et al.
Figure 6. IR spectrum of an orthorhombic crystal of L-Arg‚HCOOH.
Figure 7. Raman spectrum of an orthorhombic crystal of L-Arg‚HCOOH.
to the orthorhombic polymorph, in which all 8 active hydrogen atoms are involved in hydrogen bonds, in the monoclinic polymorph only 13 out of 16 active hydrogen atoms form hydrogen bonds. Nevertheless, here also each oxygen atom of the formate ion possesses two hydrogen bonds. 3.3. ATR FTIR and FT Raman Spectra of L-Arg‚ HCOOH. The IR spectrum of a powder specimen of L-Arg‚ HCOOH, precipitated from an aqueous solution of L-arginine
and formic acid, is shown in Figure 5, and the IR and Raman spectra of an orthorhombic crystal of L-Arg‚HCOOH are given in Figures 6 and 7. From a comparison of Figures 5 and 6 we recognize that, despite their definite similarity, powder and orthorhombic L-Arg‚HCOOH can be easily identified by their IR spectra. Characteristic frequencies of the spectra can be assigned on the basis of structural data. In the region 35002500 cm-1 the strongest lines in the Raman spectrum with peaks
Orthorhombic L-Arginine Formate
Crystal Growth & Design, Vol. 6, No. 9, 2006 2045
Figure 9. Transmittance spectrum of an orthorhombic crystal of L-Arg‚ HCOOH.
Figure 8. Cut and polished plate (with 0.8 mm thickness) of an orthorhombic L-Arg‚HCOOH crystal.
at 2980.29, 2947.98, and 2931.80 cm-1 are related to stretching vibrations of CH bonds. In the IR spectrum respective peaks are found at 2975.94, 2957.70, and 2930.96 cm-1. We assign the remaining bands in this region to stretching vibrations of NH bonds. The peak with the highest frequency at 3382.64 cm-1 in the IR spectrum and 3387.92 cm-1 in the Raman spectrum belong to the vibration of the N(3)-H(5) bond, which otherwise forms the weakest hydrogen bond. The next two peaks at 3338.74 and 3315.23 cm-1 (in the Raman spectrum the corresponding lines have wavenumbers of 3341.22 and 3298.67 cm-1) result from vibrations of the N(4)-H(7) and N(4)-H(8) bonds, which also form rather weak hydrogen bonds (see Table 3). The poorly split band near 3151.31 cm-1 (the corresponding Raman line, also split, is observed near 3138.78 cm-1) can be ascribed to vibrations of N(3)-H(6) and N(2)-H(4) bonds. The NH3+ group forms the strongest hydrogen bonds. Absorption peaks at 2706.24, 2781.54, and 2885.18 cm-1 in the IR spectrum (and Raman lines at 2708.14, 2781.92, and 2891.59 cm-1) are assigned to N(1)-H(1), N(1)-H(2), and N(1)-H(3) bonds. A characteristic weak absorption band at 2142.76 cm-1 is caused by a combinational mode. The very strong absorption band in the region 1700-1500 cm-1 with peaks at 1683.63, 1663.14, 1643.02, 1583.81, and 1544.66 cm-1 is characteristic for arginine salts. These absorption peaks are caused by asymmetric stretching vibrations of the carboxylate group (-COO-), in addition to the formate ion (HCOO-), and also by deformation vibrations of NH2 and NH3+ (δas) groups. In the Raman spectrum weak lines at 1691.28, 1665.56, and 1607.26 cm-1 are observed in this region. It is known that lines in a Raman spectrum caused by asymmetric vibrations, unlike symmetric vibrations, usually are weak or inactive. One more strong absorption band is observed at 1344.08 cm-1. Packiam Julius et al.10 assigned this band to a stretching vibration of the C-N bond. However, it appears more probable that this band is caused by a symmetric stretching vibration of the formate ion. In the Raman spectrum we find a rather strong line at 1345.59 cm-1. The absorption band at 750.40 cm-1 might be assigned to bending vibrations of COO- groups. This is confirmed by results of an IR and Raman study on Ba(HCOO)2.17 The presence of two sets of formate ions in the structure of Ba(HCOO)2 gives rise to the doubling of the internal modes and to symmetric stretching vibrations of HCOO- with very strong bands at 1352 and 1361 cm-1. 3.4. UV-Vis Transparency. From a crystal of optical quality a plate with a thickness of 0.8 mm was cut (Figure 8). In Figure 9 the transmittance spectrum in the range 200-1100 nm is shown. The absorption edge is located near 233 nm. Any absorption bands are absent in the 233-1100 nm range
Figure 10. Thermogravimetric (TG), derivative thermogravimetric (DTG), and differential thermoanalytical (DTA) curves of L-Arg‚ HCOOH.
(reflection losses are not considered). The transmittance spectrum reported by Packiam Julius et al.10 contains anomalous bands in this range, which we could not observe. 3.5. Thermal Stability. Thermogravimetric (TG), derivative thermogravimetric (DTG), and differential thermoanalytical (DTA) curves of L-Arg‚HCOOH are shown in Figure 10 (the specimen had a mass of 58 mg; the heating rate was 5 °C/min in an air atmosphere). We recognize from Figure 10 that the L-Arg‚HCOOH crystal is stable up to 180 °C. The DTG curve indicates that the decomposition process is not a single stage and has a complex character. The decomposition is accompanied by absorption of heat. Direct observation of the process by means of a Boe¨tius-type microscope near 190 °C revealed that the decomposition is accompanied by transition into a liquid state. Pakiam Julius et al.10 investigated the thermal stability by thermogravimetry (TG) and found that the sample is stable up to 200 °C and decomposition begins above 220 °C. This difference might be explained by a much higher rate of heating (20 °C/min). It is known that an increase in the heating rate shifts the peaks of thermal effects toward higher temperatures.18 3.6. Thermal Expansion, Elastic, and Thermoelastic Constants. For describing physical properties, we use a Cartesian reference system with axes ei parallel to the axes ai of the crystallographic basic system. The methods and procedures employed are given in Table 5. The results are presented in Table 6. The volume thermal expansion R of L-Arg‚HCOOH and its two invariants, the mean elastic stiffness C ) (c11 + c22 + c33 + c12 + c13 + c23 + c44 + c55 + c66)/9 and T* ) d(log C)/dT, deviate only slightly from those of the corresponding quantities of L-Arg‚HCl‚H2O and L-Arg‚HBr‚H2O.19 The values
2046 Crystal Growth & Design, Vol. 6, No. 9, 2006
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Table 5. Methods of Measurement of Physical Properties property
method and equipment
coeff of thermal expansion Rii
longitudinal dilatation of thick plates along ei employing an optical Fizeau interferometer; thickness of plates ca. 15 mm, temp range 285-295 K determination of propagation velocities of ultrasonic waves along ei and (ej + ek) with i, j ) 1-3 from resonant frequencies of thick plane-parallel plates in the range between 4 and 18 MHz; detection of resonances by the aid of a network analyzer; thickness of plates ca. 5 mm, diameter ca. 12 mm; neglecting piezoelectric coupling longitudinal piezoelectric effect along (e1 + e2 + e3) and transversal effects with uniaxial stress along (ej + ek) and charge detection on faces normal to ei by the aid of a charge amplifier shift of ultrasonic resonant frequencies of plane-parallel plates upon variation of temp between 265 and 300 K; also, investtigations (for control) by resonant ultrasound spectroscopy (RUS)
elastic constant cij
est of static piezoelectric constant dijl thermoelastic constant Tij ) d log cij/dT, T ) temp
Table 6. Coefficients of Thermal Expansion (rii, 10-6 K-1), Elastic Constants (cij, 1010 N m-2), and Thermoelastic Constants (Tij, 10-3 K-1) of L-Arg‚HCOOH at 293 K property
value
property
value
R11 R22 R33 c11 c22 c33 c12 c13 c23 c44 c55 c66
22(1) 75(3) 15(1) 1.543(11) 1.500(11) 2.349(9) 0.902(2) 1.33(2) 1.32(2) 0.823(7) 0.716(7) 0.650(7)
a C T* T11 T22 T33 T12 T13 T23 T44 T55 T66
112 1.237 -0.639 -0.55(3) -0.45(3) -0.87(3) -0.41(5) -0.70(3) -0.45(3) -0.74(2) -0.69(2) -0.84(2)
for L-Arg‚HCOOH are given in Table 6 as well. For the chloride and bromide (in parentheses), respectively, we have R ) 85.5 (99.2) × 10-6 K-1, C ) 1.789 (1.653) × 10-10 N m-2, and T* ) -0.91 (-0.96) × 103 K-1. For L-Arg‚HCOOH we found R ) 112 × 10-3 K-1, C ) 1.237 × 10-10 N m-2, and T* ) -0.639 × 10-3 K-1. We recognize that the formate ion contributes less to the elastic stiffness than the halide ion together with one water molecule. In contrast, the water molecule in connection with a halide ion is responsible for the considerably larger effect of an increase in temperature on the mean elastic stiffness. A comparison of L-Arg‚HCOOH with the compound L-Arg‚2H3PO4, where the arginine cation is doubly charged, reveals that the latter salt is by about 50% stiffer; however, with respect to thermal properties both materials exhibit a smaller difference. From Haussu¨hl et al.1 we obtain R ) 84 × 10-6 K-1, C ) 1.852 × 10-10 N m-2, and T* ) -0.59 × 10-3 K-1. This difference is mainly due to the larger number of interactions between the lattice particles per unit volume, as qualitatively expected. Preliminary qualitative measurements of the piezoelectric coefficients showed that the effects are smaller than in R-quartz. 4. Conclusions The opportunity to grow large crystals of optical quality having a series of other favorable properties and also the absence of problems with microorganisms during crystal growth make orthorhombic L-arginine formate a candidate for possible applications. In this respect a more detailed investigation on the monoclinic polymorph as a new nonlinear optical material might be also of interest; we are currently involved in this study.
Acknowledgment. This publication was made possible in part due to CRDF Award No. AE2-2533-YE-03. A.M.P. is grateful to Dr. T. S. Kurtikyan for the opportunity of using spectroscopic equipment. Supporting Information Available: A CIF file giving crystal data for L-Arg‚HCOOH. This material is available free of charge via the Internet at http://pubs.acs.org. CCDC 215202 also contains supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, U.K.; fax +44 1223 336033).
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CG060051T
