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Molecular structures and hydrogen bonding in the crystalline hydrates of two flexible double betaines with different quarternary ammonio groups in the adipic acid skeleton
Journal of
ELSEVIER
MOLECULAE STRUCTURE Journal of Molecular Structure 372 (1995) 187-193
Molecular structures and hydrogen bonding in the crystalline hydrates of two flexible double betaines with different quaternary ammonio groups in the adipic acid skeleton De-Dong Wu, Thomas C.W. Mak* Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong
Received 12 June 1995;accepted 10 July 1995
Abstract
Crystalline dihydrates of two flexible double betaines -O2CCH(R)CH2CH2CH(R)CO~- (1, R = Me3N +, 2, R = C5HsN +) have been characterized by single-crystal X-ray analysis. Both compounds crystallize in the monoclinic space group P2 t/c with a = 7.463(4), b = 10.312(6), c = 9.978(5) A, ~ = 90.18(5) °, Z = 2 for 1.2H20 and a = 9.063(2), b = 7.665(1), c = 11.962(1) A, B = 94.89(1) °, Z = 2 for 2.2H20. Both betaine molecules occupy i sites but differ with regard to the orientation of the carboxylate groups and ammonio groups. In each crystal structure, the formation of donor hydrogen bonds from the water molecules to adjacent carboxylate groups gives rise to an infinte two-dimensional network composed of a packing of identical 26-membered rings.
1. Introduction
Betaine (Me3N+CH2CO2; IUPAC name, trimethylammonioacetate), as a zwitterion containing an anionic carboxylate group and a positivelycharged quaternary ammonio group [1], is a good proton acceptor and easily forms acceptor hydrogen bonds with water molecules and hydrohalic acids. Some betaine compounds of this type, such as Me3NCHECOE-H20 [2], (Me3NCH2COEH)C1 [3,4], (Eta NCH2 CO2 H)C1.2H20 [5], (Et 3NCH 2CH 2CO 2H)B r ' H 2 0 [6], [(Me3NCH2CO2)EH]CI'H20 [7] and [(C5HsNCHECO2)2H]CI'H20 [8], have been structurally characterized via single-crystal X-ray analysis to elucidate the interaction of protons with the carboxylate groups. Intermolecular hydrogen bonding * Corresponding author.
between C5H4(CO2)NCH2CO2H molecules has also been investigated in the crystalline state [9]. Recent studies have shown that a double betaine, which comprises pairs of ammonio and carboxylate moieties in the same molecule, exhibits interesting features with regard to the mode of hydrogen bonding and molecular packing. The hydrated form of the olefinic double betaine l',l-(dicarboxy1,2-ethylenediyl)bis(4-dimethylaminopyridinium), in which functional groups of the same charge bear a cis relationship, has C2 molecular symmetry, and the carboxylate groups and pyridine rings are twisted out of the plane of the central double bond in a conrotatory fashion [10]. However, the hydrated l : l adducts of this olefinic double betaine with perchloric and nitric acids conform approximately to idealized C2v symmetry, and the two carboxylate group are coplanar with the central
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double bond, whereas the pyridine rings are orientated nearly perpendicular to this plane [11]. The site symmetries of the crystalline hydrates of three flexible double betaines 3, 4 and 5 with polymethylene bridges of different lengths inserted between the quaternary nitrogen atoms (-O2CCH2N+(CH3)2 (CH2)n-N+(CHa)2CH2CO~-; n = 2, 3 and 4 for 3, 4 and 5, respectively) are C2, C1 and Ci, respectively. The hydrogen bonds generated by water molecules bridging neighboring carboxy oxygen atoms in different modes lead to polymeric zigzag chains in the dihydrates of 3 and 5, and a layer structure in the trihydrate of 4 [1211 In the present study, we have prepared two novel dihydrated flexible double betaines with different quaternary ammonio group attached to the adipic acid skeleton, namely meso-2,5-bis(trimethylammonio)adipate (- O2CCH (Me3N+) CH2CH2CH (Me3N+) CO2, 1) and meso-2,5-bis(pyridinio)adipate (-O2CCH(CsHsN+)CH2CH2CH(CsHsN+)CO~, 2), and carried out a single-crystal X-ray analysis to determine
their molecular structures as well as details of the mode of hydrogen bonding.
©.
1
°
2
2. Experimental
2.1. Synthesis The flexible double betaines were prepared by the reaction of meso-2,5-dibromoadipic acid with trimethylamine or pyridine according to the method described previously [13]. The colorless polyhedral
Table 1 Crystallographic data and parameters for hydrates 1-2H20 and 2"2H20 a
Mol. formula Mol. weight Crystal size (mm3) Crystal system Space group a (,~,) b (,/~) c (,~,) /3 (deg) V (.~3) Z p (calcd) (gcm -3) F (000) # (mm-I) Transm. coeff. 20 range (deg) No. of data collected No. of unique data No. of data used (I >/4tr(I)), n No. of variables, p R Rs S(GOF) Residual extremes in final difference map (e,A-3)
1-2H20
2"2H20
Ct2H24N204"2H20 296.4 0.20 x 0.30 x 0.40 Monoclinic P21/c (No. 14) 7.463(4) 10.312(6) 9.978(5) 90.18(5) 767.9(7) 2 1.282 324 0.10 0.934/1.000 4.0-52.0 1598 1507 1168 92 0.044 0.062 2.19 +0.20, -0.20
CI6HIrN204"2H20 336.3 0.20 x 0.20 x 0.25 Monoclinie P2j/c (No. 14) 9.063(2) 7.665(1) 11.962(1) 94.89(1) 828.0(4) 2 1.349 356 0.10 0.973/1.000 4.0-50.0 1550 1453 1073 110 0.047 0.063 1.95 +0.24, -0.22
' R = ZA/Z~IFol,Rg = (~wA2/F_~IFol2)'/2 and S = [wA2/(n_ p)]l/2 where w = [o2(Fo)+ 0.00021F012]-', A = IIFoll- [IF¢II.
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crystals of 1.2H20 were obtained by slow evaporation of its methanol solution, and the colorless prismatic crystals of 2.H20 were obtained by slow evaporation of its methanol/water (1 : 1 v/v) solution.
2.2. CITstal data Information concerning the crystal data and structure refinements of the compounds is summarized in Table 1. The intensities were recorded in the variable w-scan mode on a Rigaku AFC7R fourcircle diffractometer using M o - K a radiation (A -- 0.71073 ,/k, 50 kV, 90 mA) at 293 K. An empirical absorption correction based on ~b-scan data was applied in processing the raw data [14]. All calculations were performed on a PC 486 computer with the SHELXTL-PCprogram package [15]. Direct methods yielded the positions of all non-hydrogen atoms. The hydrogen atoms in the double betaines were placed in calculated positions with C - H = 0.96 ,~, and allowed to ride on their respective parent carbon atoms. The hydrogen atoms of the water molecules were derived from subsequent Fourier difference syntheses. The last refinement cycles were performed by full-matrix least-squares fitting with anisotropic thermal parameters for all non-hydrogen atoms and fixed isotropic thermal parameters for all hydrogen atoms. Analytical expressions of neutral-atom scattering factors were employed [16]. Lists of anisotropic thermal parameters and hydrogen atomic coordinates have been deposited with the B.L.L.D. as Supplementary Publication number SUP26550 (11 pages).
3. Results and discussion
The fractional atomic coordinates and equivalent isotropic thermal parameters for the crystal structures of the hydrated double betaines 1"2H20 and 2"2H20, along with their estimated standard deviations, are presented in Table 2. The bond lengths and bond angles are listed in Table 3. As illustrated in Fig. l(a), the molecular structure of I has Ci symmetry and the molecular backbone is fully extended so that maximum separation of the ammonio groups is achieved. Unlike free
betaine [2,3] and three other flexible double betaines [12], in which one cal:boxy oxygen atom lies close to the positively-charged nitrogen atom to facilitate internal charge neutralization, both oxygen atoms in each carboxylate group of 1 are nearly equidistant to a positively-charge nitrogen atom (N(1) • .. O(1) 3.316(2), N(1)..-0(2) 3.104(2) ,~), the torsion angles O(1)-C(1)-C(2)-N(1) and O(2)-C(1)C(2)-N(1) being - 104.0 ° and 77.1 °, respectively. It is noted that the pair of positively-charged nitrogen atoms, along with two terminal methyl carbon atoms, are coplanar with the four carbon atoms in the molecular backbone (the mean deviation from their least-squares plane for atoms C(4), N(1), C(2), C(3), C(3a), C(2a), N(la) and C(4a) is 0.045 A), and the carboxylate group is close to being perpendicular to this plane with an dihedral angle of 83.5 ° .
Table 2 Atomic coordinates (x 104) and equivalent isotropic thermal parameters (Aft x 103)a Atom
x
y
z
U~q
1"2H20 O(1) O(2) N(I) C(I) C(2) C(3) C(4) C(5) C(6) O(IW)
2978(2) 3863(2) 7356(2) 4011(2) 5644(2) 5818(2) 7036(3) 7942(3) 8851(3) 1115(2)
637(2) 2275(2) 814(1) 1175(2) 355(2) 335(2) 796(2) 2149(2) -122(2) 2325(2)
3070(2) 1777(2) 2543(1) 2270(2) 1828(2) 314(2) 4025(2) 2136(2) 2284(2) 4809(2)
65(1) 63(1) 32(1) 40(I) 31(I) 36(1) 46(1) 51(I) 49(I) 60(I)
2.2H20 O(I) 0(2) N(1) C(l) C(2) C(3) C(4) C(5) C(6) C(7) C(8) O(lW)
4737(2) 6882(2) 3094(2) 5502(3) 4728(3) 5357(3) 2516(3) 1025(3) 103(3) 694(3) 2202(3) 1942(2)
4976(2) 3542(2) 2074(2) 3637(3) 1878(3) 899(3) 2989(3) 3138(4) 2374(4) 1457(4) 1320(3) 6051(4)
6385(2) 6489(2) 5834(2) 6322(2) 6048(2) 5110(2) 4938(2) 4724(2) 5423(3) 6338(3) 6535(2) 6970(2)
48(1) 46(I) 33(1) 35(1) 37(1) 45(I) 39(I) 48(1) 56(1) 56(1) 44(1) 106(1)
a Equivalent isotropic Ueq defined as one third of the trace of the orthogonalized Uq tensor.
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Table 3 Bond lengths (/k) and bond angles (deg) a 1.2H20 O(l)-C(l) N(I)-C(2) N(1)-C(5) C(1)-C(2) C(3)-C(3a) O(IW) . . - O ( I ) O(1)-C(I)-O(2) O(2)-C(1)-C(2) C(2)-N(1)-C(5) C(2)-N(1)-C(6) C(5)-N(1)-C(6) N(1)-C(2)-C(3) C(2)-C(3)-C(3a) O(1) ... O(IW) ... O(2b) O(1)-C(I)-C(2)-N(1)
1.242(2) 1.536(2) 1.501(2) 1.548(2) 1.535(3) 2.827(3) 127.4(2) 117.1(2) 113.6(1) 109.9(1) 109.0(1) 113.2(1) 110.1(2) 99.0(2) -104.0
O(2)-C(I) N( 1)-C(4) N(I)-C(6) C(2)-C(3) O(IW) ..-O(2b) O(1)-C(I)-C(2) C(2)-N( 1)-C(4) C(4)-N(1)-C(5) C(4)-N(1)-C(6)
N(1)-C(2)-C(1) C(1)-C(2)-C(3)
O(2)-C(I)-C(2)-N(I)
1.242(3) 1.499(2) 1.498(2) 1.516(2) 2.865(3) 115.5(2) 108.6( 1) 109.0(1) 106.5 I) 110.7(1) 111.2(1)
77.1
1.2H20
O(1)-C(1) N(1)-C(2) N(1)-C(8) C(2)-C(3) C(4)-C(5) C(6)-C(7) O(IW) ... O(I) O( I )-C( I )-0(2) O(2)-C(I)-C(2) C(2)-N(I)-C(8) N(1)-C(2)-C(1) C(I)-C(2)-C(3) N(I)-C(4)-C(5) C(5)-C(6)-C(7) N(I)-C(8)-C(7) O(I) ... O(IW) ... O(2b) O(I)-C(1)-C(2)-N(1)
1.244(3) 1.489(3) 1.344(3) 1.502(4) 1.359(4) 1.370(4) 2.809(4) 126.3(2) 114.4(2) 119.4(2) 112. I(2) 113.6(2) , ]20.4(2) I 19.5(3 ) 120.2(2) 93.6(3) 2.9
O(2)-C(1) N(I)-C(4) C(1)-C(2) C(3)-C(3a) C(5)-C(6) C(7)-C(8) O(I W)... O(2b) O(1)-C(1)-C(2) C(2)-N(1)-C(4) C(4)-N(1)-C(8) N( 1)-C(2)-C(3) C(2)-C(3)-C(3a) C(4)-C(5)-C(6) C(6)-C(7)-C(8) O(2)-C(1)-C(2)-N(1)
1.252(3) 1.348(3) 1.543(3) 1.536(5) 1.364(4) 1.371(4) 2.801(4) 119.2(2) 120.2(2) 120.4(2) 110.9(2) 113.3(3) 119.9(3) 119.6(3) - 178.8
a Symmetry transformation: 1 a: 1 - x, - y , - z ; b: x, 1/2 - y, 1/2 + z; 2 a: 1 - x, - y , 1 - z; b: 1 - x, 1/2 + y, 3/2 - z. The donor atom is given first in each hydrogen bond.
In the crystal structure of 1"2H20 (Fig. l(b)), the independent water molecule forms donor hydrogen bonds (OIlW) ... O(1) 2.827(3), O(lW) ... O(2b) 2.865(3) A; O(1) ... O(1W) .-. O(2b) 99.0(2) °) to carboxy oxygen atoms of two neighboring double betaine molecules to generate an infinite twodimensional network comprising a herringbone arrangement of identical 26-membered rings. This lies parallel to the bc plane, with trimethylammonio moieties protruding on both sides of the layer. The crystal structure is made up of a stacking of these layers such that their interactions are mainly of van der Waals type.
The molecular structure of 2 also possesses Ci symmetry (Fig. 2(a)). However, the conformation of 2 is significantly different from that of 1. As is the case in most betaine compounds, the close proximity of O(1) to N(1) (O(1) ... N(1) 2.726 ,~) facilitates internal charge neutralization. The torsion angles O(1 )-C(1)-C(2)-N(1) and O(2)-C(1 )C(2)-N(1) are 2.9 and -178.8 °, respectively, indicating that the positively-charged nitrogen atom is nearly coplanar with the carboxymethyl group. The molecular backbone is fully extended to achieve maximum separation of the carboxylate groups, and all carbon atoms in the adipic acid
D.-D. Wu, T.C.W. Mak/Journal of Molecular Structure 372 (1995) 187-193
O(ll
O~
(a)
,
191
0(lal
g (b)
Fig. I. (a) Molecular structure (35% thermal ellipsoids) of double betaine 1 with atom labeling. (b) Crystal structure of 1'2H20 showing the mode of hydrogen bonding and molecular packing with hydrogen bonds indicated by broken lines.
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D.-D. Wu. T.C.W. Mak/Journal of Molecular Structure 372 (1995) 187-193
(a)
9 ~,-4,,
?
,,
(b) Fig. 2. (a) Molecular structure (35% thermal ellipsoids) of double betaine 2 with atom labeling. (b) Crystal structure of 2"2H20 showing the mode of hydrogen bonding and molecular packing with hydrogen bonds indicated by broken lines.
D.-D. Wu, T.C.W. Mak/Journal of Molecular Structure 372 (1995) 187-193
skeleton (C(1), C(2), C(3), C(3a), C(2a) and C(la)) are coplanar (mean deviation from coplanarity: 0.019 A). The pyridinio ring is nearly exactly perpendicular to this plane (dihedral angle 91.0°), and the carboxylate group makes a dihedral angle of 51.2° with the plane of the aliphatic carbon skeleton. The crystal structure of 2"2H20 (Fig. 2(b)) is also characterized by an infinite two-dimensional network comprising a herringbone arrangement of identical 26-membered rings parallel to the bc plane. These are generated by the aliphatic carbon skeleton and the formation of donor hydrogen bonds from the water molecules to adjacent carboxylate groups (O(lW) ... O(1) 2.809(4), O(1W) ... O(2b) 2.801(4) A; O(1) ... (OlW) ... O(2b) 93.6(3)°). All pyridinio rings are oriented nearly parallel to the a axis and protrude on both sides of the layer. The equivalence of two carboxy C-O bondlengths in 1 and the small bond-length difference of the C-O bonds (AC-O = 0.008 A) in 2, together with the small bond-angle difference of the C - C - O angles ( A C - C - O = 1.6 and 3.8 ° for 1 and 2, respectively), suggest that the carboxylate groups of 1 and 2 resemble the ideal free carboxylate anion. This should be compared with the corresponding geometrical parameters in the hydrates of betaines and three other flexible double betaines (see Table 5 in Ref. [12]: average A C - O = 0.011 A,, range 0.008-0.015 A; average A C - C - O = 8.8 °, range 7.5-10.4°). ~
Acknowledgment This work is supported by a Hong Kong Research Grants Council Earmark Grant (Ref. No. CUHK 89/93E).
193
References [1] A. Leifer and E.R. Lippincott, J. Am. Chem. Soc., 79 (1957) 598. [2] T.C.W. Mak, J. Mol. Struct., 220 (1990) 13. [3] M.S. Fischer, D.H. Templeton and A. Zalkin, Acta Crystallogr., Sect. B, 26 (1970) 1392. [4] W.-H. Yip, R.-J. Wang and T.C.W. Mak, Acta Crystallogr., Sect. C, 46 (1990) 717. [5] W.-Y. Hung, X.-M. Chen, B.-H. Yang and T.C.W. Mak, J. Mol. Struct., 22 (1990) 479. [6] X.-M. Chen and T.C.W. Mak, J. Mol. Struct., 245 (1991), 301. [7] X.-M. Chen and T.C.W. Mak, J. Mol. Struct., 240 (1990), 69. [8] X.-M. Chen and T.C.W. Mak, J. Mol. Struct., 221 (1990), 256. [9] X.-M. Chen and T.C.W. Mak, J. Mol. Struct., 249 (1991), 135. [10] R. Weiss, R. Roth, R.H. Lowack and M. Bremer, Angew. Chem. Int. Ed. Engl., 29 (1990) 1132. [11] D.-D. Wu and T.C.W. Mak, J. Chem. Crystallogr, 24 (1994) 689. [12] D.-D. Wu and T.C.W. Mak, J. Mol. Struct., 326 (1994), 193. [13] D.-D. Wu and T.C.W. Mak, J. Chem. Soc., Dalton Trans., (1995) 2671. [14] MSC/AFC Diffractometer Control Software, Molecular Structure Corporation, Texas, 1988. [15] (a) G.M. Sheldrick, in D. Sayre (Ed.), Computational Crystallography, Oxford University Press, New York, 1982, p. 506. (b) G.M. Sheldrick, in G.M. Sheldrick, C. Kruger and R. Goddard (Eds.), Crystallographic Computing 3: Data Collection, Structure Determination, Proteins, and Databases, Oxford University Press, New York, 1985, p. 175. (c) G.M. Sheldrick, SHELXTL°PC, Program Package for X-ray Crystal Structure Determination, Siemens Analytical Instruments Inc., Madison, WI, 1990. [16] J.A. Ibers and W.C. Hamilton (Eds.), International Tables for X-ray Crystallography, Vol. IV, Kynoch Press, Birmingham (now distributed by Kluwer Academic Press, Dodrecht, The Netherlands), 1974, pp. 55, 99, 149.
ELSEVIER
MOLECULAE STRUCTURE Journal of Molecular Structure 372 (1995) 187-193
Molecular structures and hydrogen bonding in the crystalline hydrates of two flexible double betaines with different quaternary ammonio groups in the adipic acid skeleton De-Dong Wu, Thomas C.W. Mak* Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong
Received 12 June 1995;accepted 10 July 1995
Abstract
Crystalline dihydrates of two flexible double betaines -O2CCH(R)CH2CH2CH(R)CO~- (1, R = Me3N +, 2, R = C5HsN +) have been characterized by single-crystal X-ray analysis. Both compounds crystallize in the monoclinic space group P2 t/c with a = 7.463(4), b = 10.312(6), c = 9.978(5) A, ~ = 90.18(5) °, Z = 2 for 1.2H20 and a = 9.063(2), b = 7.665(1), c = 11.962(1) A, B = 94.89(1) °, Z = 2 for 2.2H20. Both betaine molecules occupy i sites but differ with regard to the orientation of the carboxylate groups and ammonio groups. In each crystal structure, the formation of donor hydrogen bonds from the water molecules to adjacent carboxylate groups gives rise to an infinte two-dimensional network composed of a packing of identical 26-membered rings.
1. Introduction
Betaine (Me3N+CH2CO2; IUPAC name, trimethylammonioacetate), as a zwitterion containing an anionic carboxylate group and a positivelycharged quaternary ammonio group [1], is a good proton acceptor and easily forms acceptor hydrogen bonds with water molecules and hydrohalic acids. Some betaine compounds of this type, such as Me3NCHECOE-H20 [2], (Me3NCH2COEH)C1 [3,4], (Eta NCH2 CO2 H)C1.2H20 [5], (Et 3NCH 2CH 2CO 2H)B r ' H 2 0 [6], [(Me3NCH2CO2)EH]CI'H20 [7] and [(C5HsNCHECO2)2H]CI'H20 [8], have been structurally characterized via single-crystal X-ray analysis to elucidate the interaction of protons with the carboxylate groups. Intermolecular hydrogen bonding * Corresponding author.
between C5H4(CO2)NCH2CO2H molecules has also been investigated in the crystalline state [9]. Recent studies have shown that a double betaine, which comprises pairs of ammonio and carboxylate moieties in the same molecule, exhibits interesting features with regard to the mode of hydrogen bonding and molecular packing. The hydrated form of the olefinic double betaine l',l-(dicarboxy1,2-ethylenediyl)bis(4-dimethylaminopyridinium), in which functional groups of the same charge bear a cis relationship, has C2 molecular symmetry, and the carboxylate groups and pyridine rings are twisted out of the plane of the central double bond in a conrotatory fashion [10]. However, the hydrated l : l adducts of this olefinic double betaine with perchloric and nitric acids conform approximately to idealized C2v symmetry, and the two carboxylate group are coplanar with the central
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D.-D. Wu, T.C.W. Mak/Journal of Molecular Structure 372 (1995) 187-193
double bond, whereas the pyridine rings are orientated nearly perpendicular to this plane [11]. The site symmetries of the crystalline hydrates of three flexible double betaines 3, 4 and 5 with polymethylene bridges of different lengths inserted between the quaternary nitrogen atoms (-O2CCH2N+(CH3)2 (CH2)n-N+(CHa)2CH2CO~-; n = 2, 3 and 4 for 3, 4 and 5, respectively) are C2, C1 and Ci, respectively. The hydrogen bonds generated by water molecules bridging neighboring carboxy oxygen atoms in different modes lead to polymeric zigzag chains in the dihydrates of 3 and 5, and a layer structure in the trihydrate of 4 [1211 In the present study, we have prepared two novel dihydrated flexible double betaines with different quaternary ammonio group attached to the adipic acid skeleton, namely meso-2,5-bis(trimethylammonio)adipate (- O2CCH (Me3N+) CH2CH2CH (Me3N+) CO2, 1) and meso-2,5-bis(pyridinio)adipate (-O2CCH(CsHsN+)CH2CH2CH(CsHsN+)CO~, 2), and carried out a single-crystal X-ray analysis to determine
their molecular structures as well as details of the mode of hydrogen bonding.
©.
1
°
2
2. Experimental
2.1. Synthesis The flexible double betaines were prepared by the reaction of meso-2,5-dibromoadipic acid with trimethylamine or pyridine according to the method described previously [13]. The colorless polyhedral
Table 1 Crystallographic data and parameters for hydrates 1-2H20 and 2"2H20 a
Mol. formula Mol. weight Crystal size (mm3) Crystal system Space group a (,~,) b (,/~) c (,~,) /3 (deg) V (.~3) Z p (calcd) (gcm -3) F (000) # (mm-I) Transm. coeff. 20 range (deg) No. of data collected No. of unique data No. of data used (I >/4tr(I)), n No. of variables, p R Rs S(GOF) Residual extremes in final difference map (e,A-3)
1-2H20
2"2H20
Ct2H24N204"2H20 296.4 0.20 x 0.30 x 0.40 Monoclinic P21/c (No. 14) 7.463(4) 10.312(6) 9.978(5) 90.18(5) 767.9(7) 2 1.282 324 0.10 0.934/1.000 4.0-52.0 1598 1507 1168 92 0.044 0.062 2.19 +0.20, -0.20
CI6HIrN204"2H20 336.3 0.20 x 0.20 x 0.25 Monoclinie P2j/c (No. 14) 9.063(2) 7.665(1) 11.962(1) 94.89(1) 828.0(4) 2 1.349 356 0.10 0.973/1.000 4.0-50.0 1550 1453 1073 110 0.047 0.063 1.95 +0.24, -0.22
' R = ZA/Z~IFol,Rg = (~wA2/F_~IFol2)'/2 and S = [wA2/(n_ p)]l/2 where w = [o2(Fo)+ 0.00021F012]-', A = IIFoll- [IF¢II.
189
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crystals of 1.2H20 were obtained by slow evaporation of its methanol solution, and the colorless prismatic crystals of 2.H20 were obtained by slow evaporation of its methanol/water (1 : 1 v/v) solution.
2.2. CITstal data Information concerning the crystal data and structure refinements of the compounds is summarized in Table 1. The intensities were recorded in the variable w-scan mode on a Rigaku AFC7R fourcircle diffractometer using M o - K a radiation (A -- 0.71073 ,/k, 50 kV, 90 mA) at 293 K. An empirical absorption correction based on ~b-scan data was applied in processing the raw data [14]. All calculations were performed on a PC 486 computer with the SHELXTL-PCprogram package [15]. Direct methods yielded the positions of all non-hydrogen atoms. The hydrogen atoms in the double betaines were placed in calculated positions with C - H = 0.96 ,~, and allowed to ride on their respective parent carbon atoms. The hydrogen atoms of the water molecules were derived from subsequent Fourier difference syntheses. The last refinement cycles were performed by full-matrix least-squares fitting with anisotropic thermal parameters for all non-hydrogen atoms and fixed isotropic thermal parameters for all hydrogen atoms. Analytical expressions of neutral-atom scattering factors were employed [16]. Lists of anisotropic thermal parameters and hydrogen atomic coordinates have been deposited with the B.L.L.D. as Supplementary Publication number SUP26550 (11 pages).
3. Results and discussion
The fractional atomic coordinates and equivalent isotropic thermal parameters for the crystal structures of the hydrated double betaines 1"2H20 and 2"2H20, along with their estimated standard deviations, are presented in Table 2. The bond lengths and bond angles are listed in Table 3. As illustrated in Fig. l(a), the molecular structure of I has Ci symmetry and the molecular backbone is fully extended so that maximum separation of the ammonio groups is achieved. Unlike free
betaine [2,3] and three other flexible double betaines [12], in which one cal:boxy oxygen atom lies close to the positively-charged nitrogen atom to facilitate internal charge neutralization, both oxygen atoms in each carboxylate group of 1 are nearly equidistant to a positively-charge nitrogen atom (N(1) • .. O(1) 3.316(2), N(1)..-0(2) 3.104(2) ,~), the torsion angles O(1)-C(1)-C(2)-N(1) and O(2)-C(1)C(2)-N(1) being - 104.0 ° and 77.1 °, respectively. It is noted that the pair of positively-charged nitrogen atoms, along with two terminal methyl carbon atoms, are coplanar with the four carbon atoms in the molecular backbone (the mean deviation from their least-squares plane for atoms C(4), N(1), C(2), C(3), C(3a), C(2a), N(la) and C(4a) is 0.045 A), and the carboxylate group is close to being perpendicular to this plane with an dihedral angle of 83.5 ° .
Table 2 Atomic coordinates (x 104) and equivalent isotropic thermal parameters (Aft x 103)a Atom
x
y
z
U~q
1"2H20 O(1) O(2) N(I) C(I) C(2) C(3) C(4) C(5) C(6) O(IW)
2978(2) 3863(2) 7356(2) 4011(2) 5644(2) 5818(2) 7036(3) 7942(3) 8851(3) 1115(2)
637(2) 2275(2) 814(1) 1175(2) 355(2) 335(2) 796(2) 2149(2) -122(2) 2325(2)
3070(2) 1777(2) 2543(1) 2270(2) 1828(2) 314(2) 4025(2) 2136(2) 2284(2) 4809(2)
65(1) 63(1) 32(1) 40(I) 31(I) 36(1) 46(1) 51(I) 49(I) 60(I)
2.2H20 O(I) 0(2) N(1) C(l) C(2) C(3) C(4) C(5) C(6) C(7) C(8) O(lW)
4737(2) 6882(2) 3094(2) 5502(3) 4728(3) 5357(3) 2516(3) 1025(3) 103(3) 694(3) 2202(3) 1942(2)
4976(2) 3542(2) 2074(2) 3637(3) 1878(3) 899(3) 2989(3) 3138(4) 2374(4) 1457(4) 1320(3) 6051(4)
6385(2) 6489(2) 5834(2) 6322(2) 6048(2) 5110(2) 4938(2) 4724(2) 5423(3) 6338(3) 6535(2) 6970(2)
48(1) 46(I) 33(1) 35(1) 37(1) 45(I) 39(I) 48(1) 56(1) 56(1) 44(1) 106(1)
a Equivalent isotropic Ueq defined as one third of the trace of the orthogonalized Uq tensor.
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Table 3 Bond lengths (/k) and bond angles (deg) a 1.2H20 O(l)-C(l) N(I)-C(2) N(1)-C(5) C(1)-C(2) C(3)-C(3a) O(IW) . . - O ( I ) O(1)-C(I)-O(2) O(2)-C(1)-C(2) C(2)-N(1)-C(5) C(2)-N(1)-C(6) C(5)-N(1)-C(6) N(1)-C(2)-C(3) C(2)-C(3)-C(3a) O(1) ... O(IW) ... O(2b) O(1)-C(I)-C(2)-N(1)
1.242(2) 1.536(2) 1.501(2) 1.548(2) 1.535(3) 2.827(3) 127.4(2) 117.1(2) 113.6(1) 109.9(1) 109.0(1) 113.2(1) 110.1(2) 99.0(2) -104.0
O(2)-C(I) N( 1)-C(4) N(I)-C(6) C(2)-C(3) O(IW) ..-O(2b) O(1)-C(I)-C(2) C(2)-N( 1)-C(4) C(4)-N(1)-C(5) C(4)-N(1)-C(6)
N(1)-C(2)-C(1) C(1)-C(2)-C(3)
O(2)-C(I)-C(2)-N(I)
1.242(3) 1.499(2) 1.498(2) 1.516(2) 2.865(3) 115.5(2) 108.6( 1) 109.0(1) 106.5 I) 110.7(1) 111.2(1)
77.1
1.2H20
O(1)-C(1) N(1)-C(2) N(1)-C(8) C(2)-C(3) C(4)-C(5) C(6)-C(7) O(IW) ... O(I) O( I )-C( I )-0(2) O(2)-C(I)-C(2) C(2)-N(I)-C(8) N(1)-C(2)-C(1) C(I)-C(2)-C(3) N(I)-C(4)-C(5) C(5)-C(6)-C(7) N(I)-C(8)-C(7) O(I) ... O(IW) ... O(2b) O(I)-C(1)-C(2)-N(1)
1.244(3) 1.489(3) 1.344(3) 1.502(4) 1.359(4) 1.370(4) 2.809(4) 126.3(2) 114.4(2) 119.4(2) 112. I(2) 113.6(2) , ]20.4(2) I 19.5(3 ) 120.2(2) 93.6(3) 2.9
O(2)-C(1) N(I)-C(4) C(1)-C(2) C(3)-C(3a) C(5)-C(6) C(7)-C(8) O(I W)... O(2b) O(1)-C(1)-C(2) C(2)-N(1)-C(4) C(4)-N(1)-C(8) N( 1)-C(2)-C(3) C(2)-C(3)-C(3a) C(4)-C(5)-C(6) C(6)-C(7)-C(8) O(2)-C(1)-C(2)-N(1)
1.252(3) 1.348(3) 1.543(3) 1.536(5) 1.364(4) 1.371(4) 2.801(4) 119.2(2) 120.2(2) 120.4(2) 110.9(2) 113.3(3) 119.9(3) 119.6(3) - 178.8
a Symmetry transformation: 1 a: 1 - x, - y , - z ; b: x, 1/2 - y, 1/2 + z; 2 a: 1 - x, - y , 1 - z; b: 1 - x, 1/2 + y, 3/2 - z. The donor atom is given first in each hydrogen bond.
In the crystal structure of 1"2H20 (Fig. l(b)), the independent water molecule forms donor hydrogen bonds (OIlW) ... O(1) 2.827(3), O(lW) ... O(2b) 2.865(3) A; O(1) ... O(1W) .-. O(2b) 99.0(2) °) to carboxy oxygen atoms of two neighboring double betaine molecules to generate an infinite twodimensional network comprising a herringbone arrangement of identical 26-membered rings. This lies parallel to the bc plane, with trimethylammonio moieties protruding on both sides of the layer. The crystal structure is made up of a stacking of these layers such that their interactions are mainly of van der Waals type.
The molecular structure of 2 also possesses Ci symmetry (Fig. 2(a)). However, the conformation of 2 is significantly different from that of 1. As is the case in most betaine compounds, the close proximity of O(1) to N(1) (O(1) ... N(1) 2.726 ,~) facilitates internal charge neutralization. The torsion angles O(1 )-C(1)-C(2)-N(1) and O(2)-C(1 )C(2)-N(1) are 2.9 and -178.8 °, respectively, indicating that the positively-charged nitrogen atom is nearly coplanar with the carboxymethyl group. The molecular backbone is fully extended to achieve maximum separation of the carboxylate groups, and all carbon atoms in the adipic acid
D.-D. Wu, T.C.W. Mak/Journal of Molecular Structure 372 (1995) 187-193
O(ll
O~
(a)
,
191
0(lal
g (b)
Fig. I. (a) Molecular structure (35% thermal ellipsoids) of double betaine 1 with atom labeling. (b) Crystal structure of 1'2H20 showing the mode of hydrogen bonding and molecular packing with hydrogen bonds indicated by broken lines.
192
D.-D. Wu. T.C.W. Mak/Journal of Molecular Structure 372 (1995) 187-193
(a)
9 ~,-4,,
?
,,
(b) Fig. 2. (a) Molecular structure (35% thermal ellipsoids) of double betaine 2 with atom labeling. (b) Crystal structure of 2"2H20 showing the mode of hydrogen bonding and molecular packing with hydrogen bonds indicated by broken lines.
D.-D. Wu, T.C.W. Mak/Journal of Molecular Structure 372 (1995) 187-193
skeleton (C(1), C(2), C(3), C(3a), C(2a) and C(la)) are coplanar (mean deviation from coplanarity: 0.019 A). The pyridinio ring is nearly exactly perpendicular to this plane (dihedral angle 91.0°), and the carboxylate group makes a dihedral angle of 51.2° with the plane of the aliphatic carbon skeleton. The crystal structure of 2"2H20 (Fig. 2(b)) is also characterized by an infinite two-dimensional network comprising a herringbone arrangement of identical 26-membered rings parallel to the bc plane. These are generated by the aliphatic carbon skeleton and the formation of donor hydrogen bonds from the water molecules to adjacent carboxylate groups (O(lW) ... O(1) 2.809(4), O(1W) ... O(2b) 2.801(4) A; O(1) ... (OlW) ... O(2b) 93.6(3)°). All pyridinio rings are oriented nearly parallel to the a axis and protrude on both sides of the layer. The equivalence of two carboxy C-O bondlengths in 1 and the small bond-length difference of the C-O bonds (AC-O = 0.008 A) in 2, together with the small bond-angle difference of the C - C - O angles ( A C - C - O = 1.6 and 3.8 ° for 1 and 2, respectively), suggest that the carboxylate groups of 1 and 2 resemble the ideal free carboxylate anion. This should be compared with the corresponding geometrical parameters in the hydrates of betaines and three other flexible double betaines (see Table 5 in Ref. [12]: average A C - O = 0.011 A,, range 0.008-0.015 A; average A C - C - O = 8.8 °, range 7.5-10.4°). ~
Acknowledgment This work is supported by a Hong Kong Research Grants Council Earmark Grant (Ref. No. CUHK 89/93E).
193
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