N 2-(4-Meth­oxy­salicyl­idene)arginine hemihydrate

M Sethuram; G Bhargavi; M Dhandapani; G Amirthaganesan; M NizamMohideen

doi:10.1107/S1600536813019727

. 2013 Jul 24;69(Pt 8):o1301–o1302. doi: 10.1107/S1600536813019727

N ²-(4-Methoxysalicylidene)arginine hemihydrate

M Sethuram ^a, G Bhargavi ^b, M Dhandapani ^a, G Amirthaganesan ^a, M NizamMohideen ^c,^*

PMCID: PMC3793792 PMID: 24109379

Abstract

The title compound, C₁₄H₂₀N₄O₄·0.5H₂O [systematic name: (2S)-5-{[amino(iminiumyl)methyl]amino}-2-{[(1Z)-4-methoxy-2-oxidobenzylidene]azaniumyl}pentanoate hemihydrate], has been synthesized by the reaction of l-arginine and 4-methoxysalicylaldehyde and crystallizes with two independent substituted l-arginine molecules and one water molecule of solvation in the asymmetric unit. Each molecule exists as a zwitterion and adopts a Z configuration about the central C=N. The molecular conformation is stabilized by strong intramolecular N—H⋯O hydrogen bonds that generate S(6) and S(10) ring motifs. Intermolecular N—H⋯O and O—H⋯O hydrogen bonds involving also the water molecule and weak intermolecular C—H⋯O_water interactions link the molecules into an infinite one-dimensional ribbon structure extending along the b axis. The known (2S) absolute configuration for l-arginine was invoked. Weak intermolecular C—H⋯π interactions are also present.

Related literature

For the synthesis of similar compounds, see: Srinivasan et al. (1986 ▶); Moutet & Ourari (1997 ▶). For general background on Schiff bases, see: von Konig et al. (1982 ▶); Lewis et al. (2009 ▶). For hydrogen-bond motifs, see: Bernstein et al. (1995 ▶). For related structures, see: Oueslati et al. (2007 ▶). graphic file with name e-69-o1301-scheme1.jpg

Experimental

Crystal data

C₁₄H₂₀N₄O₄·0.5H₂O
M _r = 317.35
Monoclinic,
a = 10.1828 (11) Å
b = 10.3414 (11) Å
c = 15.5542 (16) Å
β = 102.688 (2)°
V = 1597.9 (3) Å³
Z = 4
Mo Kα radiation
μ = 0.10 mm⁻¹
T = 293 K
0.30 × 0.30 × 0.25 mm

Data collection

Bruker Kappa APEXII CCD-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2004 ▶) T _min = 0.971, T _max = 0.976
18648 measured reflections
7483 independent reflections
5859 reflections with I > 2σ(I)
R _int = 0.036

Refinement

R[F ² > 2σ(F ²)] = 0.072
wR(F ²) = 0.167
S = 1.10
7483 reflections
452 parameters
14 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.25 e Å⁻³
Δρ_min = −0.21 e Å⁻³

Data collection: APEX2 (Bruker, 2004 ▶); cell refinement: APEX2 and SAINT (Bruker, 2004 ▶); data reduction: SAINT and XPREP (Bruker, 2004 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012 ▶) and Mercury (Macrae et al., 2008 ▶); software used to prepare material for publication: WinGX (Farrugia, 2012 ▶) and PLATON (Spek, 2009 ▶).

Supplementary Material

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S1600536813019727/zs2267sup1.cif

e-69-o1301-sup1.cif^{(38.3KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536813019727/zs2267Isup2.hkl

e-69-o1301-Isup2.hkl^{(358.7KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1⋯O2	0.89 (1)	1.94 (3)	2.638 (4)	134 (3)
N4—H4A⋯O4	0.90 (1)	2.06 (1)	2.935 (4)	165 (3)
N5—H5⋯O6	0.90 (1)	1.90 (3)	2.600 (4)	134 (3)
N8—H8A⋯O7	0.90 (1)	2.03 (1)	2.914 (4)	166 (3)
N2—H2⋯O2ⁱ	0.86	1.92	2.758 (4)	166
N3—H3A⋯O3ⁱ	0.89 (1)	2.58 (3)	3.333 (4)	142 (3)
N3—H3B⋯O4ⁱⁱ	0.89 (1)	1.93 (1)	2.817 (4)	175 (4)
N4—H4B⋯O3ⁱⁱ	0.89 (1)	2.03 (1)	2.912 (4)	171 (3)
N6—H6⋯O6ⁱⁱⁱ	0.86	1.89	2.705 (4)	158
N7—H7A⋯O8ⁱⁱⁱ	0.89 (1)	2.50 (3)	3.202 (4)	135 (3)
N7—H7B⋯O7^iv	0.90 (1)	1.91 (1)	2.800 (4)	173 (3)
N8—H8B⋯O8^iv	0.89 (1)	2.05 (2)	2.911 (4)	161 (3)
O1W—H2W⋯O3^v	0.94 (1)	1.98 (2)	2.881 (5)	159 (6)
C15—H15C⋯O1W ⁱ	0.96	2.56	3.451 (7)	155
C22—H22⋯O1W	0.93	2.53	3.359 (6)	149
C1—H1C⋯Cg1^vi	0.96	2.96	3.669 (4)	132
C15—H15C⋯Cg2^vii	0.96	2.98	3.762 (5)	139

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) ; (iv) ; (v) ; (vi) ; (vii) .

Acknowledgments

MS thanks the UGC Networking Centre, School of Chemistry, University of Hyderabad, India, for the award of a Visiting Research Fellowship to use the facilities at the School. The authors also thank for access to the X-ray diffraction equipment.

supplementary crystallographic information

Comment

The Schiff base ligands derived from salicylaldehyde derivatives have been found to be excellent chelating agents for most applications in coordination chemistry such as in catalysis (Srinivasan et al., 1986) and electrocatalysis (Moutet & Ourari, 1997). Schiff bases of the general type p-R'-C₆H₄—CH═N—C₆H₄—R"-p are well known reagents that find their practical application in various areas, e.g. photography (von Konig et al., 1982) and medicinal and pharmaceutical chemistry (Lewis et al., 2009). Here, we report the synthesis of the title compound, C₁₄H₂₀N₄O₄. 0.5H₂O [systematic name: (2S)-5- {[amino(iminio)methyl]amino}-2-{[(1Z)-(4-methoxy-2-oxidophenyl) methylene]ammonio}pentanoate hemihydrate] and the structure is reported herein.

This compound crystallizes with two independent substituted L-arginine molecules (A and B), together with one water molecule of solvation in the asymmetric unit (Fig. 1). Each molecule exists as a zwitterion and adopts a Z configuration about the central iminium C═N functional group which is coplanar with the adjacent benzene ring. The known (2S) absolute configuration for L-arginine was invoked for the trivially named chiral centres at C9 and C23. The C—N bond distances of the NH₂ groups(N3—C14, N4—C14, N7—C28 and N8—C28) are 1.332 (6), 1.319 (6), 1.328 (6) and 1.322 (5) Å, respectively, which is short for a C—N single bond, but still not quite as contracted as one would expect for a fully established C═N. These bond length features are consistent with an imino resonance form as is commonly found for C—N single bonds involving sp² hybridized C and N atoms (Oueslati et al., 2007). The bond distances C6—O2, C10—O3, C10—O4, C20—O6, C24—O7 and C24—O8 [1.284 (5), 1.248 (6), 1.239 (5), 1.285 (5), 1.253 (5) and 1.237 (5) Å, respectively], clearly indicate the presence of C═O double bonds, including those also generated through resonance. The H atoms attached to the phenolic groups (O2 and O6) are transferred to the basic centres N1 and N5 respectively, generating the iminium groups. Also, the carboxylic H-atoms on O4 and O7 have been transferred to N4 and N8, respectively, to generate the common amino acid zwitterions.

In both molecules A and B, all nitrogen H-atoms are involved in hydrogen bonding (Table 1). In each, intramolecular N—H···O hydrogen bonds lead to the formation of a six- and a ten-membered ring motif [S(6) and S(10), respectively (Bernstein et al., 1995)] (Fig.1). Intermolecular N—H···O and O—H···O hydrogen bonds involving also the water molecule and weak intermolecular C—H···O_water interactions link the molecules into an infinite one-dimensional ribbon structure extending along the b axis (Fig. 2). Present also are weak intermolecular C—H..π interactions.

Experimental

L-Arginine and 4-methoxy salicylaldehyde (E-Merck- analar grades) were mixed in 1:1 stoichiometric proportions and dissolved in a triply distilled water–ethanol mixture using a mechanical stirrer for about four hours. The raw reaction product was removed by filtration, then re-dissolved in a water–ethanol solvent mixture and kept aside to allow crystal growth at ambient temperature. Bright yellowish crystals formed in 3 days and on removal were recrystallized several times to obtain the crystal specimen used in the X-ray analysis.