4-{[3-(4-Hydroxy­benzyl­ideneamino)-2,2-dimethyl­propyl]iminiomethyl}phenolate dihydrate

Reza Kia; Hoong-Kun Fun; Hadi Kargar

doi:10.1107/S1600536809013804

. 2009 Apr 18;65(Pt 5):o1071–o1072. doi: 10.1107/S1600536809013804

4-{[3-(4-Hydroxybenzylideneamino)-2,2-dimethylpropyl]iminiomethyl}phenolate dihydrate

Reza Kia ^a,^‡, Hoong-Kun Fun ^a,^*,^§, Hadi Kargar ^b

PMCID: PMC2977751 PMID: 21583887

Abstract

The asymmetric unit of the title compound, C₁₉H₂₂N₂O₂·2H₂O, comprises a zwitterionic form of the Schiff base compound and two water molecules of crystallization. Intermolecular N—H⋯O, C—H⋯O and O—H⋯N hydrogen bonds involving one of the water molecules in the asymmetric unit generate seven- and eight-membered rings, with R ₂ ¹(7) and R ₂ ²(8) ring motifs, respectively. The dihedral angle beween the two aromatic rings is 86.5 (2)°. The imino and iminium groups are coplanar with the benzene rings to which they are attached, making dihedral angles (N—C—C—C) of −179.3 (5) and −179.2 (4)°, respectively. Validation software indicates the higher symmetry space group Pnma for this structure. However, this process ignores H atoms and the zwitterionic configuration of the main molecule breaks the higher symmetry. Solution in Pna2₁ provides a chemically sensible zwitterionic compound with improved residuals. In the crystal structure, molecules are linked together through intermolecular O—H⋯O, O—H⋯N, N—H⋯O and C—H⋯O interactions, forming a three-dimensional network. The crystal structure is further stabilized by intermolecular C—H⋯π interactions.

Related literature

For hydrogen-bond motifs, see: Bernstein et al. (1995 ▶). For information on Schiff base ligands and their complexes and applications, see: Calligaris & Randaccio (1987 ▶); Li et al. (2005 ▶); Bomfim et al. (2005 ▶); Glidewell et al. (2005 ▶, 2006 ▶); Sun et al. (2004 ▶). For details of the synthesis, see: Fun et al. (2008 ▶). For the stability of the temperature controller used for data collection, see: Cosier & Glazer (1986 ▶).

Experimental

Crystal data

C₁₉H₂₂N₂O₂·2H₂O
M _r = 346.42
Orthorhombic,
a = 13.0336 (4) Å
b = 11.5242 (3) Å
c = 12.4132 (4) Å
V = 1864.49 (10) Å³
Z = 4
Mo Kα radiation
μ = 0.09 mm⁻¹
T = 100 K
0.34 × 0.21 × 0.11 mm

Data collection

Bruker SMART APEXII CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2005 ▶) T _min = 0.971, T _max = 0.991
10183 measured reflections
2237 independent reflections
1753 reflections with I > 2σ(I)
R _int = 0.056

Refinement

R[F ² > 2σ(F ²)] = 0.047
wR(F ²) = 0.116
S = 1.05
2237 reflections
235 parameters
3 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.27 e Å⁻³
Δρ_min = −0.20 e Å⁻³

Data collection: APEX2 (Bruker, 2005 ▶); cell refinement: APEX2; data reduction: SAINT (Bruker, 2005 ▶); program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809013804/sj2615sup1.cif

e-65-o1071-sup1.cif^{(20.5KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809013804/sj2615Isup2.hkl

e-65-o1071-Isup2.hkl^{(110KB, hkl)}

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

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

Cg1 and Cg2 are the centroids of the C1–C6 and C12–C17 benzene rings, respectively.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1W—H1W1⋯O1ⁱ	0.93	1.91	2.830 (5)	171
O1W—H2W1⋯O2ⁱⁱ	0.86	1.90	2.751 (4)	168
O2W—H1W2⋯O1Wⁱⁱⁱ	0.84	2.00	2.774 (3)	153
O2W—H2W2⋯N1	0.86	2.22	2.826 (4)	127
N2—H1N2⋯O2W	0.95 (4)	1.90 (4)	2.832 (4)	170 (3)
O1—H1O1⋯O2ⁱⁱ	0.83 (4)	1.74 (5)	2.565 (5)	174 (5)
C17—H17A⋯O2W	0.93	2.52	3.408 (6)	161
C10—H10B⋯Cg1^iv	0.97	2.69	3.422 (5)	133
C8—H8A⋯Cg2^v	0.97	2.74	3.497 (5)	136

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

Acknowledgments

HKF and RK thank the Malaysian Government and Universiti Sains Malaysia for the Science Fund (grant No. 305/PFIZIK/613312). RK thanks Universiti Sains Malaysia for the award of a postdoctoral research fellowship. HK thanks PNU for financial support. HKF also thanks Universiti Sains Malaysia for Research University Golden Goose Grant No. 1001/PFIZIK/811012.

supplementary crystallographic information

Comment

In the field of coordination chemistry, Schiff base compounds are among the most prevalent and versatile ligands. They have received much attention due to their important roles in the development of coordination chemistry related to catalysis and enzymatic reactions, magnetism, and supramolecular architectures. In comparison to the Schiff base metal complexes, only a relatively small number of free Schiff base ligands have been structurally characterized (Calligaris & Randaccio, 1987). Structures of Schiff bases derived from substituted benzaldehydes have been reported (Li et al., 2005; Bomfim et al., 2005; Glidewell et al., 2005, 2006; Sun et al., 2004).

The asymmetric unit of the title compound, Fig. 1, comprises a zwitterionic Schiff base compound and two water molecules of crystallization. The zwitterion results from protonation of the imine N2 atom with the O2 hydroxy group deprotonated resulting in the formation of iminium and phenolate groups. Intermolecular N—H···O and C—H···O hydrogen bonds involving the O2W O atom as a bifurcated acceptor generate an R₂¹(7) ring motif (Bernstein et al., 1995). Intermolecular N—H···O and O—H···N hydrogen bonds, again involving O2W, generate an R₂²(8) ring motif. The dihedral angle beween the two phenyl rings is 86.5 (2)°. The imino and iminium groups are coplanar with the benzene rings to which they are attached making dihedral angles of -179.3 (5) and -179.2 (4)° for N1—C7—C6—C5 and N2—C11—C12—C13, respectively. This structure requires differentiating between the Pna21 and Pnma space groups to achieve a correct solution. The solution based on the higher symmetry space group (Pnma) gives a chemically nonsensible polymeric chain as the program PLATON/ADDSYM has not taken into account H atoms in determining the symmetry elements. The solution in Pna21 gives a chemically sensible zwitterionic compound with lower R values. In the crystal structure, the molecules are linked together through intermolecular O—H···O, O—H···N, N—H···O and C—H···O interactions, forming a three-dimensional network (Fig. 2). The crystal structure is further stabilized by intermolecular C—H···π interactions [Cg1 and Cg2 are the centroids of the C1–C6 and C12–C17 benzene rings] (Table 1).

Experimental

The synthetic method has been described earlier (Fun et al., 2008), except that 4-hydroxybenzaldehyde (2 mmol, 244 mg) and 2,2-dimethylpropane diamine (1 mmol, 102 mg) were used. Single crystals suitable for X-ray diffraction were obtained by evaporation of an ethanol solution at room temperature.