A low-temperature phase of the 1:1 complex of 2-(6-diethylamino-3-diethyl­iminio-3H-xanthen-9-yl)benzoate with ethyl gallate at 93 K

Jin Mizuguchi

doi:10.1107/S1600536808016528

. 2008 Jun 7;64(Pt 7):o1238–o1239. doi: 10.1107/S1600536808016528

A low-temperature phase of the 1:1 complex of 2-(6-diethylamino-3-diethyliminio-3H-xanthen-9-yl)benzoate with ethyl gallate at 93 K

Jin Mizuguchi ^a,^*

PMCID: PMC2961781 PMID: 21202875

Abstract

The title compound, C₂₈H₃₀N₂O₃·C₉H₁₀O₅, is a well known red leuco complex of 2-(6-diethylamino-3-diethyliminio-3H-xanthen-9-yl)benzoate (rhodamine B base abbreviated to RBB, a leuco dye) with ethyl gallate (EG, developer). The structure of the complex at room temperature has recently been reported by Sekiguchi, Takayama, Gotanda & Sano [Chem. Lett. (2007 ▶), 36, 1010–1011]. We have found a new phase of the material with two discrete base/developer complexes (RBB-A/EG-A and RBB-B/EG-B) in the asymmetric unit at 93 K. There are no significant differences between the two developer molecules EG-A and EG-B. The lactone ring of RBB is opened in each molecule to form a zwitterionic structure. However, the xanthene system is almost flat in RBB-A (r.m.s. deviation 0.0234 Å) but is less so in RBB-B (r.m.s. deviation 0.1095 Å). Furthermore, the ethyl groups of the xanthene diethylamino substituents lie on the same side of the xanthene plane in RBB-A but on opposite sides in RBB-B. Dimeric dye/developer complexes are formed through inter- and intramolecular O—H⋯O hydrogen bonds and are linked further into dimers by additional O—H⋯O hydrogen bonds involving either EG-A or EG-B developer molecules.

Related literature

For general background literature on leuco dyes, see: Muthyala (1997 ▶). For the structure of the 1:1 RBB/EG complex at room temperature, see: Sekiguchi et al. (2007 ▶). For the related structure of n-propyl gallate, see: Iwata et al. (2005 ▶); Hitachi et al. (2005 ▶); Mizuguchi et al. (2005 ▶).

Experimental

Crystal data

C₂₈H₃₀N₂O₃·C₉H₁₀O₅
M _r = 640.71
Triclinic,
a = 11.3689 (2) Å
b = 16.3654 (3) Å
c = 17.6518 (3) Å
α = 94.1760 (7)°
β = 96.1440 (7)°
γ = 93.7790 (7)°
V = 3247.69 (10) Å³
Z = 4
Cu Kα radiation
μ = 0.76 mm⁻¹
T = 93 K
0.20 × 0.20 × 0.20 mm

Data collection

Rigaku R-AXIS RAPID diffractometer
Absorption correction: multi-scan (Higashi, 1995 ▶) T _min = 0.810, T _max = 0.860
29633 measured reflections
11011 independent reflections
7318 reflections with F ² > 2σ(F ²)
R _int = 0.039

Refinement

R[F ² > 2σ(F ²)] = 0.044
wR(F ²) = 0.115
S = 0.94
11011 reflections
881 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.23 e Å⁻³
Δρ_min = −0.25 e Å⁻³

Data collection: PROCESS-AUTO (Rigaku, 1998 ▶); cell refinement: PROCESS-AUTO; data reduction: CrystalStructure (Rigaku/MSC, 2006 ▶); program(s) used to solve structure: SIR2004 (Burla et al., 2005 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEPIII (Burnett & Johnson, 1996 ▶); software used to prepare material for publication: CrystalStructure.

Supplementary Material

Crystal structure: contains datablocks General, I. DOI: 10.1107/S1600536808016528/sj2498sup1.cif

e-64-o1238-sup1.cif^{(52KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808016528/sj2498Isup2.hkl

e-64-o1238-Isup2.hkl^{(538.4KB, 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
O6A—H6AO⋯O2A	0.94 (2)	2.72 (2)	3.4413 (18)	133.8 (18)
O6A—H6AO⋯O3A	0.94 (2)	1.72 (2)	2.6303 (17)	162 (2)
O6A—H6AO⋯O5A	0.94 (2)	2.53 (2)	2.8733 (19)	102.2 (17)
O5A—H5AO⋯O2A	0.92 (2)	1.66 (2)	2.5690 (19)	167 (2)
O5A—H5AO⋯O3A	0.92 (2)	2.62 (2)	3.1884 (18)	120.4 (18)
O4A—H4AO⋯O7Aⁱ	0.92 (2)	1.86 (2)	2.779 (2)	178.8 (10)
O6B—H6BO⋯O2B	0.94 (2)	2.72 (2)	3.4156 (18)	131.4 (16)
O6B—H6BO⋯O3B	0.94 (2)	1.68 (2)	2.5811 (17)	159 (2)
O6B—H6BO⋯O5B	0.94 (2)	2.55 (2)	2.8799 (19)	101.0 (15)
O5B—H5BO⋯O2B	0.94 (2)	1.64 (2)	2.5636 (18)	166 (2)
O5B—H5BO⋯O3B	0.94 (2)	2.66 (2)	3.2473 (18)	121.5 (19)
O4B—H4BO⋯O7Bⁱⁱ	0.97 (2)	1.83 (2)	2.7957 (19)	175 (2)

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Symmetry codes: (i) Inline graphic ; (ii) .

Acknowledgments

The author acknowledges Mr K. Sato for experimental assistance.

supplementary crystallographic information

Comment

The coloration of colorless leuco dyes by reaction with acidic developers is well known (Muthyala, 1997) and is used in practice in thermal or rewritable papers. The coloration is usually interpreted as arising from the opening of the lactone ring due to proton transfer from the developer, acting as a proton donor, to the leuco dye, a proton acceptor. The title compound [C₂₈H₃₀N₂O₃, C₉H₁₀N₂O₅] is a typical example of a leuco coloration system composed of 2-(6-diethylamino-3-diethyliminio-3H-xanthen-9-yl)benzoate [rhodamine B base (RBB): a leuco dye] with ethyl gallate (EG: a developer). The structure of the 1:1 dye:developer complex at room temperature has recently been reported by Sekiguchi et al. (2007). They found a dimer structure, in which two RBBs are connected by a sub dimer of EG through OH···O intermolecular hydrogen bonds. We have found a new phase of the material at 93 K with two discrete base/developer complexes RBB-A/EG-A and RBB-B/EG-B in the asymmetric unit, Fig. 1.

The lactone rings of each RBB are opened to form zwitterionic structures and the benzene rings with the anionic carboxylate substituents are twisted to be nearly perpendicular to the xanthene planes with dihedral angles: 84.68 (7)°) between the O1A/C4A/C5A/C7A/C12A/C13A and C14A-C19A planes of RBB-A and 73.09 (7)° between the O1B/C4B/C5B/C7B/C12B/C13B and C14B-C19B planes of RBB-B. There are no significant differences between the two developer molecules EG-A and EG-B. The xanthene moiety is nearly flat in RBB-A (deviation from the least-squares plane, 0.0234Å) and the ethyl groups of the diethylamino substituents at each extremity of the xanthene lie on the same side of the xanthene plane. On the other hand, in RBB-B, the xanthene moiety deviates slightly from planarity by 0.1095Å and the ethyl groups of the diethylamino substituents lie on opposite sides of the xanthene plane. By comparison, the room temperature phase (Sekiguchi et al., 2007) crystallises with only one type of the molecule (eqivalent to RBB-A) in the asymmetric unit and with the ethyl groups of the diethylamino substituents all on the same side of the xanthene plane.

The dye/developer complexes are formed through intermolecular O5—H5O···O2, O6—H6O···O2, O5—H5O···O3 and O6—H6O···O3 hydrogen bonds with the planar configuration of this section of the molecule supported by intramolecular O6—H6O···O5 interactions, Figs. 2 & 3. In addition, O4—H4···O7 hydrogen-bonds form centrosymmetric RBB-A···EG-A···EG-A···RBB-A (Fig. 4), and RBB-B···EG-B···EG-B···RBB-B dimers. These are similar to those found in n-propyl gallate (Iwata et al., 2005; Hitachi et al., 2005; Mizuguchi et al., 2005).

Experimental

Rhodamine B base and 4-hydroxybenzophenone were purchased from Sigma-Aldrich Corp. and and Wako Pure Chemical Industries, Ltd., respectively. Single crystals of (I) were grown by recrystallization from a toluene solution which included an equimolar quantity of both chemicals. After 24 h, a number of red crystals were obtained in the form of blocks.