4-[(2-Hydroxy­ethyl)­imino­meth­yl]-5-hydroxy­methyl-2-methyl­pyridin-3-ol

The title compound, C₁₀H₁₄N₂O₃, is a Schiff base which is derived from pyridoxal and represents, therefore, a vitamin B₆-related compound. Mol­ecules are linked into sheets by a combination of O—H...O and O—H...N hydrogen bonds.

S1. Comment

Vitamin B₆ is an essential cofactor to a large number of enzymes that catalyze many reactions of amino acids (Sykes et al., 1991). One of the active forms of vitamin B₆ is the heterocyclic aldehyde pyridoxal. Much attention has been focused on the coordination chemistry of pyridoxal Schiff bases with amino acids (Christensen, 1957; Long et al., 1980; Dawes et al., 1982; Walz et al., 1983; Rao et al. 1985; Astheimer et al. 1985; Sykes et al. 1991; Costa Pessoa et al., 1999). No X-ray structure of a free pyridoxal Schiff base has been reported to date, since the Schiff base ligand is usually generated in the coordination sphere of the transition metal. This approach is impractical for the complexation with moisture sensitive reagents, for instance halogenosilanes or organometallic derivatives. The title compound, (I), was prepared in order to supply an alternative ligand system for the preparation of vitamin B₆–Schiff base complexes. Fig. 1 shows the molecular structure of (I) and the atomic labelling scheme. Selected bond lengths are listed in Table 1.

The substituted pyridine ring has somewhat unusual bond lengths owing to the irregular substitution pattern of the pyridoxal ring. The enamine group (N2═C7) has a bond length of 1.280 (1) Å, which is typical for this type of Schiff base (Böhme & Günther, 2006, 2007; Böhme et al., 2006). The O2/C8 group is nearly coplanar with the pyridine ring, with a C3—C4—C8—O2 torsion angle of 176.28 (8)°. The same holds for the enamine group, with a C2—C3—C7—N2 torsion angle of 0.9 (1)°. Atom N2 is bonded to the O1/H1 group via a hydrogen bridge (Table 2), forming an intramolecular six-membered pseudo-ring. The 2-hydroxyethyl group (C9/C10/O3) is rotated out of the molcecule plane with an N2—C9—C10—O3 torsion angle of 74.5 (1)°. The O3/H3 group forms a hydrogen bridge with the pyridine N atom of another molecule, giving pairs of molecules which are connected `head-to-tail' (see Fig. 2). These pairs are further stabilized by π–π interactions between π-conjugated units, with a distance of 3.030 Å between the planes formed by atoms N1, C1–C8, N2 and O1. The crystal packing is further stabilized by O—H···O hydrogen bonds, which generate a sheet structure parallel to the crystallographic ab plane (Fig. 3).

Compound (I) represents a potentially useful ligand for the preparation of complexes with main group and transition metals. Furthermore, the preparation of coordination polymers seems to be feasible because of the presence of three OH groups and two nitrogen donor positions in the molecule.

Related literature

For related literature, see: Astheimer et al. (1985); Böhme & Günther (2006, 2007); Böhme, Wiesner & Günther (2006); Christensen (1957); Costa Pessoa, Cavaco, Correia, Duarte, Gillard, Henriques, Higes, Madeira & Tomaz (1999); Dawes et al. (1982); Dubs et al. (2000); Hopfl et al. (1998); Long et al. (1980); Pradeep (2005); Rao et al. (1985); Sykes et al. (1991); Walz et al. (1983).

S2. Experimental

Pyridoxal hydrochloride (4.07 g, 20 mmol) and sodium methanolate (1.08 g, 20 mmol) were mixed in ethanol (200 ml). The suspension was stirred at room temperature and treated with 2-aminoethanol (1.22 g, 1.2 ml, 20 mmol). The reaction mixture was boiled at reflux temperature for 2 h. After that time, a yellow solution and a white precipitate were formed. The precipitate (NaCl) was filtered off and washed with ethanol. The filtrate was reduced in a vacuum to 50 ml. The product was precipitated by adding n-hexane (30 ml) and was isolated by filtration (3.6 g, 85.6% yield, m.p. 421 K). NMR (DMSO-D₆, 298 K, TMS): ¹H δ 2.37 (s, Me, H6), 3.70, 3.72 (2 × t, CH₂, H9, H10), 4.64 (s, CH₂, H8), 4.87 (s broad, O3—H3), 5.37 (s broad, O2—H2), 7.86 (s, C5—H5), 8.86 (s, N═C7—H7), 14.49 (s broad, O1—H1); ¹³C δ 18.9 (C6), 58.5, 60.5, 60.9 (C8, C9, C10), 118.9, 132.9, 136.9, 148.8, 155.2 (C1–C5), 164.5 (C7).

S3. Refinement

There are few structure reports of Schiff bases with oxygen in the ortho-position where the intramolecular bridging H atom is localized at the N atom (e.g. Pradeep, 2005; Dubs et al., 2000; Hopfl et al., 1998). Therefore, atom H1 was located by difference Fourier synthesis and refined without constraints. All other H atoms were placed in geometrically idealized positions and treated as riding atoms with C—H distances of 0.95–0.99 Å and O—H of 0.84 Å. For all H atoms, U_iso(H) = kU_eq(carrier), where k = 1.5 for methyl and hydroxy groups and k = 1.2 for all other H atoms.

Computing details

Data collection: SMART (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP in SHELXTL-Plus (Sheldrick, 1991); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).

Figures

	Fig. 1. The molecular structure of (I), drawn with 50% probability displacement ellipsoids.
	Fig. 2. Head-to-tail dimers of (I), formed by O3—H3···N1A hydrogen bonds and π–π interactions. [The suffix A corresponds to symmetry code ii in Table 2.]
	Fig. 3. The packing of (I) in the c direction, showing the sheet structure which is build up by intermolecular hydrogen bridges between the dimers. (The lower part of the hydrogen-bridged dimers is shown shaded; atoms have been omitted for clarity.)

5-Hydroxymethyl-4-[(2-hydroxyethyl)iminomethyl]-2-methylpyridin-3-ol

Crystal data

C10H14N2O3	F(000) = 896
Mr = 210.23	Dx = 1.428 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 4942 reflections
a = 16.2739 (5) Å	θ = 2.5–32.4°
b = 9.6403 (3) Å	µ = 0.11 mm^−1
c = 13.5513 (4) Å	T = 153 K
β = 113.069 (2)°	Needle, yellow
V = 1955.99 (10) Å^3	0.60 × 0.16 × 0.10 mm
Z = 8

Data collection

Bruker SMART CCD area-detector diffractometer	2858 independent reflections
Radiation source: sealed tube	2292 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.029
ϕ and ω scans	θmax = 30.0°, θmin = 3.3°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −22→22
Tmin = 0.935, Tmax = 0.989	k = −13→13
16737 measured reflections	l = −19→19

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.038	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.109	H atoms treated by a mixture of independent and constrained refinement
S = 1.05	w = 1/[σ^2(Fo^2) + (0.06P)^2 + 0.9077P] where P = (Fo^2 + 2Fc^2)/3
2858 reflections	(Δ/σ)max < 0.001
140 parameters	Δρmax = 0.46 e Å^−3
0 restraints	Δρmin = −0.20 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
N1	0.65785 (6)	0.52717 (10)	0.25154 (7)	0.01770 (18)
N2	0.33566 (6)	0.49096 (9)	−0.00010 (7)	0.01753 (18)
O1	0.46598 (5)	0.32461 (8)	0.09744 (6)	0.01973 (17)
H1	0.4115 (11)	0.3544 (16)	0.0579 (12)	0.030*
O2	0.57535 (6)	0.93319 (8)	0.18094 (7)	0.02501 (19)
H2	0.6035	0.9568	0.1432	0.038*
O3	0.18125 (5)	0.52286 (9)	0.07119 (6)	0.02220 (18)
H3	0.2322	0.5200	0.1209	0.033*
C1	0.60476 (7)	0.41931 (10)	0.20927 (8)	0.0163 (2)
C2	0.51541 (7)	0.43875 (10)	0.13658 (8)	0.01492 (19)
C3	0.48196 (6)	0.57359 (10)	0.10808 (7)	0.01446 (19)
C4	0.54023 (6)	0.68621 (10)	0.15161 (8)	0.01564 (19)
C5	0.62627 (7)	0.65734 (11)	0.22254 (8)	0.0172 (2)
H5	0.6655	0.7330	0.2527	0.021*
C6	0.64074 (8)	0.27566 (12)	0.23967 (9)	0.0226 (2)
H6A	0.6479	0.2314	0.1784	0.034*
H6B	0.5991	0.2213	0.2602	0.034*
H6C	0.6988	0.2803	0.3003	0.034*
C7	0.38825 (7)	0.59429 (11)	0.03632 (8)	0.01614 (19)
H7	0.3662	0.6858	0.0166	0.019*
C8	0.50918 (7)	0.83479 (11)	0.12447 (8)	0.0196 (2)
H8A	0.4913	0.8495	0.0465	0.024*
H8B	0.4559	0.8502	0.1412	0.024*
C9	0.24215 (7)	0.51547 (12)	−0.06790 (8)	0.0193 (2)
H9A	0.2286	0.4765	−0.1402	0.023*
H9B	0.2305	0.6165	−0.0755	0.023*
C10	0.18219 (7)	0.44817 (11)	−0.01926 (8)	0.0190 (2)
H10A	0.1206	0.4427	−0.0745	0.023*
H10B	0.2032	0.3523	0.0030	0.023*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0152 (4)	0.0228 (4)	0.0153 (4)	0.0016 (3)	0.0062 (3)	0.0004 (3)
N2	0.0137 (4)	0.0227 (4)	0.0155 (4)	−0.0002 (3)	0.0050 (3)	−0.0014 (3)
O1	0.0187 (4)	0.0169 (3)	0.0218 (4)	−0.0021 (3)	0.0060 (3)	−0.0018 (3)
O2	0.0288 (4)	0.0204 (4)	0.0277 (4)	−0.0087 (3)	0.0132 (3)	−0.0045 (3)
O3	0.0145 (3)	0.0301 (4)	0.0204 (4)	0.0008 (3)	0.0051 (3)	−0.0041 (3)
C1	0.0165 (4)	0.0196 (5)	0.0144 (4)	0.0028 (4)	0.0077 (4)	0.0012 (3)
C2	0.0158 (4)	0.0167 (4)	0.0135 (4)	−0.0005 (3)	0.0071 (3)	−0.0005 (3)
C3	0.0128 (4)	0.0182 (4)	0.0129 (4)	0.0004 (3)	0.0056 (3)	0.0001 (3)
C4	0.0152 (4)	0.0179 (4)	0.0152 (4)	−0.0004 (3)	0.0073 (4)	0.0002 (3)
C5	0.0147 (4)	0.0203 (5)	0.0161 (4)	−0.0019 (4)	0.0055 (3)	−0.0013 (4)
C6	0.0227 (5)	0.0217 (5)	0.0223 (5)	0.0065 (4)	0.0077 (4)	0.0019 (4)
C7	0.0146 (4)	0.0199 (5)	0.0139 (4)	0.0014 (3)	0.0055 (3)	0.0013 (3)
C8	0.0187 (5)	0.0163 (5)	0.0224 (5)	−0.0013 (4)	0.0066 (4)	0.0008 (4)
C9	0.0135 (4)	0.0253 (5)	0.0163 (4)	−0.0002 (4)	0.0028 (4)	−0.0008 (4)
C10	0.0146 (4)	0.0188 (5)	0.0215 (5)	−0.0006 (4)	0.0048 (4)	−0.0031 (4)

Geometric parameters (Å, º)

N1—C1	1.330 (1)	C4—C5	1.381 (1)
N1—C5	1.355 (1)	C4—C8	1.516 (1)
N2—C7	1.280 (1)	C5—H5	0.95
N2—C9	1.456 (1)	C6—H6A	0.98
O1—C2	1.343 (1)	C6—H6B	0.98
O1—H1	0.885 (17)	C6—H6C	0.98
O2—C8	1.414 (1)	C7—H7	0.95
O2—H2	0.84	C8—H8A	0.99
O3—C10	1.427 (1)	C8—H8B	0.99
O3—H3	0.84	C9—C10	1.520 (2)
C1—C2	1.413 (1)	C9—H9A	0.99
C1—C6	1.497 (1)	C9—H9B	0.99
C2—C3	1.404 (1)	C10—H10A	0.99
C3—C4	1.410 (1)	C10—H10B	0.99
C3—C7	1.466 (1)
C1—N1—C5	119.40 (9)	H6A—C6—H6C	109.5
C7—N2—C9	119.52 (9)	H6B—C6—H6C	109.5
C2—O1—H1	106.0 (10)	N2—C7—C3	120.98 (9)
C8—O2—H2	109.5	N2—C7—H7	119.5
C10—O3—H3	109.5	C3—C7—H7	119.5
N1—C1—C2	120.93 (9)	O2—C8—C4	113.07 (9)
N1—C1—C6	119.13 (9)	O2—C8—H8A	109.0
C2—C1—C6	119.94 (9)	C4—C8—H8A	109.0
O1—C2—C3	122.84 (9)	O2—C8—H8B	109.0
O1—C2—C1	117.38 (9)	C4—C8—H8B	109.0
C3—C2—C1	119.78 (9)	H8A—C8—H8B	107.8
C2—C3—C4	118.25 (9)	N2—C9—C10	110.29 (8)
C2—C3—C7	119.93 (9)	N2—C9—H9A	109.6
C4—C3—C7	121.81 (9)	C10—C9—H9A	109.6
C5—C4—C3	117.93 (9)	N2—C9—H9B	109.6
C5—C4—C8	120.67 (9)	C10—C9—H9B	109.6
C3—C4—C8	121.37 (9)	H9A—C9—H9B	108.1
N1—C5—C4	123.68 (9)	O3—C10—C9	112.44 (8)
N1—C5—H5	118.2	O3—C10—H10A	109.1
C4—C5—H5	118.2	C9—C10—H10A	109.1
C1—C6—H6A	109.5	O3—C10—H10B	109.1
C1—C6—H6B	109.5	C9—C10—H10B	109.1
H6A—C6—H6B	109.5	H10A—C10—H10B	107.8
C1—C6—H6C	109.5
C5—N1—C1—C2	−1.48 (14)	C2—C3—C4—C8	179.84 (8)
C5—N1—C1—C6	178.57 (9)	C7—C3—C4—C8	−1.24 (14)
N1—C1—C2—O1	−179.93 (8)	C1—N1—C5—C4	1.04 (15)
C6—C1—C2—O1	0.02 (14)	C3—C4—C5—N1	0.73 (15)
N1—C1—C2—C3	0.18 (14)	C8—C4—C5—N1	178.93 (9)
C6—C1—C2—C3	−179.86 (9)	C9—N2—C7—C3	177.67 (8)
O1—C2—C3—C4	−178.32 (8)	C2—C3—C7—N2	0.9 (1)
C1—C2—C3—C4	1.56 (14)	C4—C3—C7—N2	−178.05 (9)
O1—C2—C3—C7	2.74 (14)	C5—C4—C8—O2	−1.86 (13)
C1—C2—C3—C7	−177.38 (9)	C3—C4—C8—O2	176.28 (8)
C2—C3—C4—C5	−1.97 (13)	C7—N2—C9—C10	−122.62 (10)
C7—C3—C4—C5	176.95 (9)	N2—C9—C10—O3	74.5 (1)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···N2	0.89 (2)	1.77 (2)	2.573 (1)	151 (2)
O2—H2···O3^i	0.84	1.98	2.817 (1)	173
O3—H3···N1^ii	0.84	1.94	2.775 (1)	172

Symmetry codes: (i) x+1/2, y+1/2, z; (ii) −x+1, y, −z+1/2.