5-Amino-1-naphthol: two-dimensional sheets built up from R₄⁴(18) rings formed by O—H...N, N—H...O and π–π inter­actions

The crystal structure of the title compound, C₁₀H₉NO, (I), contains inter­molecular O—H...N and N—H...O hydrogen bonds which together form sheets parallel to the (001) plane containing rings with an unusual R₄⁴(18) motif. These rings are additionally stabilized by an inter­molecular π–π stacking inter­action. The significance of this study lies in the comparison drawn between the mol­ecular structure of (I) and those of related compounds (1,5-diamino­naphthalene, 8-amino-2-naphthol, 3-amino-2-naphthol and aniline), which shows a close similarity in the noncoplanar orientation of the amine group and the aromatic moiety. Comparison of the crystal structures of (I) and several of its simple analogues (1-naphthol, naphthalene-1,4-­diol, naphthalene-1,5-­diol and 4-chloro-1-naphthol) shows a close similarity in the packing of the mol­ecules, which form π-stacks along the shortest crystallographic axes with a substantial spatial overlap between adjacent mol­ecules.

S1. Comment

5-Amino-1-naphthol, (I), is a bifunctional monomer containing two functional groups, i.e. OH and NH₂ groups, and thus it is a suitable candidate for polymerization which, depending on the electrolytic medium, can lead to different interesting materials (Ohsaka et al., 1991). In a basic medium, polymerization occurs via the hydroxyl groups, leading to the formation of a poly(naphthalene oxide) structure, while in either organic or aqueous acidic media polymerization takes place via the oxidation of the amine group, leading to the formation of poly(5-amino-1-naphthol) (PAN) (Cintra et al., 2003; Rubinger et al., 2006). This polymerization product belongs to the important class of conducting polymers, which are used as functional materials for applications in electrodes, sensors etc. and which have attracted much attention as an immobilization matrix for biomaterials, such as enzymes and proteins (Takahashi & Córdobe de Torresi, 2008). Moreover, PAN has been used as the active layer in an electronic pulse generator (Toniolo et al., 2004).

A search of the Cambridge Structural Database (CSD, Version 5.30, November 2008; Allen, 2002) for aminonaphthols revealed only two reports of two isomers of aminonaphthol, 8-amino-2-naphthol (CSD refcode MATCEQ; Dey et al., 2005) and 3-amino-2-naphthol (CSD refcode QEPGAU; Dey et al., 2006), and no prior reports on the structures of amino-substituted 1-naphthols. We present here the structure of 5-amino-1-naphthol, (I) (Fig. 1, Table 1), and compare it with those of its simple analogues, naphthalene, (II), 1-hydroxynaphthalene, (III), 1,5-dihydroxynaphthalene, (IV), 1,5-diaminonaphthalene, (V), 1,4-dihydroxynaphthalene, (VI) and 4-chloro-1-naphthol, (VII) [CSD refcodes NAPHTA15 (Oddershede & Larsen, 2004), NAPHOL01 (Rozycka-Sokolowska et al., 2004), VOGRUE (Belskii et al., 1990), ZZZKNU01 (Bernès et al., 2004), NPHHQU10 (Gaultier & Hauw, 1967) and BOTSOT (Rozycka-Sokolowska & Marciniak, 2009), respectively].

In (I), the two substituents at positions 1 and 5 of the naphthalene ring system exert an influence on the geometric parameters in the aromatic rings, and especially on the lengths of the C3—C4, C8—C9, C4—C5 and C9—C10 bonds. Thus, the C3—C4 and C8—C9 bonds are shorter by ca 0.05 Å than the corresponding distances in (II) (1.374 Å), while the C4—C5 and C9—C10 bonds are longer by ca 0.05 Å than those in (II) (1.417 Å). The other C—C bond distances in (I), in the range 1.390 (4)–1.419 (5) Å (Table 1), are similar to those found in (II) and to the typical aromatic bond length of 1.384 (13) Å (Allen et al., 1987). The valence angles within the rings lie in the range 114.2 (3)–124.0 (3)°.

Despite the variations in bond lengths and angles, the naphthalene ring system remains planar, with the largest out-of-plane deviation being -0.011 (3) Å for atom C9. Atoms O1 and N1 attached to this ring are coplanar with it, deviating from the plane of this ring by only 0.038 (2) and -0.080 (3) Å, respectively. The dihedral angle between this plane and the plane formed by the atoms of the amine group is 44 (2)°. This angle, significantly different from 0°, is in close agreement with those observed for MATCEQ [48 (2)°], QEPGAU [42 (1)°] and ZZZKNU01 [29 (2), 44 (2) and 33 (2)°], and also with the values of the dihedral angles between the amino and ring planes observed in the two independent molecules of aniline [37 (4) and 38 (4)°; CSD refcode BAZGOY (Fukuyo et al., 1982)]. It is noteworthy that this noncoplanar orientation of the amine group and the naphthalene ring, and the sum of the C6—N1—H1A, C6—N1—H1B and H1A—N1—H1B valence angles [334 (7)°], indicate that the geometry around atom N1 of molecule (I) is pyramidal, as previously found for aniline (Fukuyo et al., 1982). This pyramidalization of the NH₂ group is associated with a lengthening of the C6—N1 bond [1.424 (4) Å], which compares well with the bonds observed in related compounds such as MATCEQ and QEPGAU [1.416 (2) and 1.415 (2) Å, respectively], but it is somewhat elongated in comparison with the C—N distances observed in aniline [1.386 (6) and 1.398 (6) Å] and ZZZKNU01 [1.385 (3)–1.407 (3) Å] and with the value given by Allen et al. (1987) for a C_ar—NH₂ (Nsp³ pyramidal) bond [1.394 (11) Å]. The C1—O1 bond length [1.379 (4) Å] is in a close agreement with the corresponding distances in the simple analogues of (I), such as (III), (IV), (VI) and (VII) [1.376 (1), 1.385, 1.377 and 1.394 (3) Å, respectively].

The crystal structure of (I) contains two strong nearly linear O1—H1···N1 and N1—H1A···O1 hydrogen bonds (Table 2), which connect each molecule with four others. Hydroxy atom O1 in the molecule at (x, y, z) acts as a hydrogen-bond donor, via atom H1, to atom N1 in the molecule at (2 - x, 1/2 + y, 1/2 - z), so forming a zigzag C(7) chain (Bernstein et al., 1995) (motif m in Fig. 2) running parallel to [010]. A zigzag chain with the same C(7) descriptor and parallel to the same direction is also formed by the N1—H1···O1ⁱⁱ hydrogen bond [motif n in Fig. 2; symmetry code: (ii) 1 - x, -1/2 + y, 1/2 - z]. Together these two hydrogen bonds produce a sheet parallel to the (001) plane and built up from the R₄⁴(18) rings (Fig. 2). The non-H atoms belonging to the (001) sheets lie in domains (0.09 + z/2) < c < (0.41 + z/2), where z is zero or an integer, and there are no direction-specific interactions betwen the molecules of adjacent sheets. The R₄⁴(18) rings are additionally stabilized by intermolecular π–π interactions between the C1–C5/C10 (centroid Cg1) and C5–C10 (centroid Cg2) benzene rings which connect molecules related by translation along the [100] direction into stacks parallel to the shortest crystallographic axis, i.e. axis a (Fig. 3). The perpendicular distances of the ring centroids Cg1 and Cg2 from the planes containing the symmetry-related centroids Cg2 at (1 + x, y, z) and Cg1 at (-1 + x, y, z), respectively, are 3.453 and 3.465 Å, and the centroid-to-centroid separation is 3.690 (2) Å. The planes of the C1–C5/C10 and C5–C10 rings are nearly parallel, making an angle of only 0.55°.

The formation of molecular stacks parallel to the shortest crystallographic axis and the presence of strong interstack interactions are common characteristics of the crystal packing in (I) and its two simple analogues, (III) [see Fig. 3(a) in Rozycka-Sokolowska & Marciniak (2009)] and (IV) (Fig. 4), as well as in the 4-substituted derivatives of 1-naphthol, (VII) and (VI) [see Figs. 2 and 3(d), respectively, in Rozycka-Sokolowska & Marciniak (2009)]. It is also worth noting that in the crystal packing in (I), and in 1,4- and 1,5-naphthalenediol which crystallize with Z' = 0.5 in the space groups Pnma and P2₁/n, respectively, there is an additional common feature, namely the formation of a continuous two-dimensional framework containing rings based upon an unusual R₄⁴(18) structural motif. Such sheets are also found in the structure of 1,5-diaminonaphthalene, (V) (space group P2₁/c, Z' = 1.5), although they were not discussed in the original report (Bernès et al., 2004). The sheets in (V) lie parallel to (102) and are built up from R₈⁸(46) rings formed by two N—H···N hydrogen bonds (Fig. 5). Moreover, the supramolecular aggregation in (I) differs significantly from the pattern found in (III) and (VII), where single O—H···O hydrogen bonds connect molecules of each of these compounds into simple one-dimensional C(2) chains [see Figs. 2 and 3(a) in Rozycka-Sokolowska & Marciniak (2009)].

Analysis of the values of `pitch' and `roll' parameters [pitch (P) and roll (R) angles and pitch (dp) and roll (dr) distances] estimated according to Curtis et al. (2004), and the extent of area overlap of adjacent π-stacked molecules (AO) calculated according to a model proposed by Janzen et al. (2004), indicates that the solid-state packing of (I) provides a spatial overlap between molecules in the π-stack (P = 44.71° > R = 15.98°, dp = 3.42 Å > dr = 0.99 Å, AO = 19.4%), similar to what was found previously for (III), (VI) and (VII) (Rozycka-Sokolowska & Marciniak, 2009). Moreover, a comparison of these values with the parameters estimated for (IV) (P = 43.85° > R = 10.77°, dp = 3.28 Å > dr = 0.65 Å, AO = 24.7%) and (V) [P₁ = 25.38° < R₁ = 48.01°, dp₁ = 1.64 Å < dr₁ = 3.84 Å, P₂ = 22.84° < R₂ = 47.82°, dp₂ = 1.46 Å < dr₂ = 3.81 Å (1 and 2 denote two independent columns of molecules running along the crystallographic a axis; no π-overlap between adjacent molecules)] leads to the conclusion that the modification of the molecular structure of (V) by the replacement of one or two NH₂ groups at the 1 or 1 and 5 positions, respectively, by one or two hydroxy groups results in the appearance of π–π stacking interactions and in a transformation of the arrangement of the aromatic rings of the naphthalene moiety, from the typical herringbone arrangement in (V) (dp < dr) to practically parallel π-stacking with a spatial overlap between adjacent molecules in (I) and (IV) (dp > dr). Taking this into account, we can additionally conclude that the parallel arrangement of 5-amino-1-naphthol molecules in the solid state is caused by the presence of a hydroxy substituent at position 1.

In summary, we note that (I), as a material yielding π-stacking with substantial spatial overlap in the solid state [similar to (VI); Rozycka-Sokolowska & Marciniak, 2009], is an attractive candidate for electronic applications, including devices with high charge-carrier mobilities (Anthony et al., 2002; Li et al., 1998; Horowitz et al., 1996; Laquindanum et al., 1997; Chen et al., 2006).

S2. Experimental

Crystals of (I) were obtained from the commercially available 5-amino-1-naphthol (Aldrich, purity 97%) by slow evaporation of a methanol solution at a constant temperature of 279 K.

S3. Refinement

All aromatic H atoms were positioned geometrically and constrained to ride on their parent atoms, with C—H = 0.93 Å and with U_iso(H) = 1.2U_eq(C). The H atoms of the hydroxyl and amine groups were located in a difference Fourier map and refined with U_iso(H) = 1.5U_eq(O,N). Friedel equivalent reflections were merged using MERG4 in SHELXL97 (Sheldrick, 2008), according to the standard procedure for X-ray measurements of chemical compounds with no atoms heavier than Si.

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2008); cell refinement: CrysAlis RED (Oxford Diffraction, 2008); data reduction: CrysAlis RED (Oxford Diffraction, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2009).

Figures

	Fig. 1. A view of the molecule of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. Part of the crystal structure of (I), showing the intermolecular O—H···N (m) and N—H···O (n) hydrogen bonds (dashed lines), which can be described by the graph-set notation C(7), and together produce a sheet parallel to the (001) plane and built up from the R4^4(18) rings. All aromatic H atoms have been omitted for clarity. [Symmetry codes: (i) 2 - x, 1/2 + y, 1/ 2 - z; (ii) 1 - x, -1/2 + y.]
	Fig. 3. Part of the crystal structure of (IV), showing the intermolecular π–π interactions (dashed lines) linking the molecules into stacks parallel to the crystallographic a axis. All aromatic H atoms have been omitted for clarity. Cg1 and Cg2 are the centroids of the C1–C5/C10 and C5–C10 benzene rings, respectively, and are denoted by small spheres. [Symmetry codes: (iii) 1 + x, y, z; (iv) -1 + x, y, z.]
	Fig. 4. Part of the crystal structure of (IV), showing a sheet of R4^4(18) rings lying parallel to the (110) plane. O—H···O hydrogen bonds are shown as dashed lines. All aromatic H atoms have been omitted for clarity.
	Fig. 5. Part of the crystal structure of (V), showing the formation of a sheet parallel to the (102) plane and built up from the R8^8(46) rings formed by the N—H···N hydrogen bonds (dashed lines). All aromatic H atoms have been omitted for clarity.

5-amino-1-naphthol

Crystal data

C10H9NO	F(000) = 336
Mr = 159.18	Dx = 1.331 Mg m^−3
Orthorhombic, P212121	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 5049 reflections
a = 4.8894 (10) Å	θ = 2.3–26.4°
b = 12.404 (3) Å	µ = 0.09 mm^−1
c = 13.096 (3) Å	T = 290 K
V = 794.2 (3) Å^3	Plate, violet-brown
Z = 4	0.23 × 0.06 × 0.02 mm

Data collection

Oxford Xcalibur3 CCD diffractometer	978 independent reflections
Radiation source: Enhance (Mo) X-ray Source	516 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.092
ω scans	θmax = 26.4°, θmin = 2.3°
Absorption correction: multi-scan CrysAlis RED (Oxford Diffraction, 2008)	h = −6→3
Tmin = 0.966, Tmax = 1.000	k = −15→15
5049 measured reflections	l = −16→16

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.051	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.059	w = 1/[σ^2(Fo^2) + (0.0156P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.89	(Δ/σ)max < 0.001
978 reflections	Δρmax = 0.13 e Å^−3
119 parameters	Δρmin = −0.13 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0111 (16)

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
O1	1.0086 (5)	0.32326 (18)	0.1526 (2)	0.0526 (8)
H1	1.157 (7)	0.351 (3)	0.154 (3)	0.079*
N1	0.5296 (7)	−0.0546 (2)	0.3610 (3)	0.0452 (11)
H1A	0.369 (7)	−0.086 (2)	0.352 (3)	0.068*
H1B	0.541 (7)	−0.031 (2)	0.434 (3)	0.068*
C1	0.9876 (7)	0.2543 (3)	0.2348 (3)	0.0375 (11)
C2	1.1305 (7)	0.2604 (3)	0.3267 (3)	0.0418 (11)
H2	1.2569	0.3157	0.3349	0.050*
C3	1.0938 (7)	0.1869 (3)	0.4082 (3)	0.0468 (12)
H3	1.1947	0.1923	0.4681	0.056*
C4	0.9095 (6)	0.1101 (3)	0.3952 (3)	0.0392 (10)
H4	0.8776	0.0609	0.4474	0.047*
C5	0.7546 (6)	0.1013 (3)	0.2997 (3)	0.0314 (10)
C6	0.5579 (8)	0.0228 (3)	0.2813 (3)	0.0360 (11)
C7	0.4150 (7)	0.0188 (3)	0.1881 (3)	0.0432 (12)
H7	0.2848	−0.0351	0.1795	0.052*
C8	0.4572 (8)	0.0916 (3)	0.1069 (3)	0.0460 (11)
H8	0.3585	0.0863	0.0464	0.055*
C9	0.6438 (6)	0.1679 (3)	0.1205 (3)	0.0415 (11)
H9	0.6797	0.2172	0.0687	0.050*
C10	0.7935 (7)	0.1744 (3)	0.2176 (3)	0.0334 (10)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0458 (17)	0.0355 (17)	0.076 (2)	−0.0063 (16)	−0.0025 (17)	0.0139 (15)
N1	0.045 (2)	0.027 (2)	0.064 (3)	−0.0058 (18)	0.012 (3)	0.0024 (17)
C1	0.037 (2)	0.031 (2)	0.045 (3)	0.006 (2)	0.007 (2)	0.007 (2)
C2	0.042 (2)	0.033 (3)	0.051 (3)	−0.003 (2)	−0.006 (2)	−0.003 (2)
C3	0.047 (3)	0.041 (3)	0.051 (3)	0.003 (2)	−0.010 (2)	−0.007 (2)
C4	0.038 (2)	0.029 (2)	0.050 (3)	−0.001 (2)	0.002 (2)	0.001 (2)
C5	0.027 (2)	0.028 (2)	0.039 (3)	0.0050 (19)	0.001 (2)	−0.0024 (19)
C6	0.031 (3)	0.023 (2)	0.055 (3)	0.005 (2)	0.006 (2)	0.002 (2)
C7	0.039 (3)	0.033 (3)	0.057 (4)	−0.004 (2)	−0.005 (3)	−0.009 (2)
C8	0.050 (3)	0.045 (3)	0.043 (3)	0.000 (2)	−0.011 (2)	−0.003 (2)
C9	0.043 (2)	0.035 (3)	0.047 (3)	0.000 (2)	0.000 (2)	0.002 (2)
C10	0.025 (2)	0.027 (2)	0.049 (3)	0.0036 (19)	0.000 (2)	−0.003 (2)

Geometric parameters (Å, º)

O1—C1	1.379 (4)	C4—C5	1.466 (4)
O1—H1	0.81 (3)	C4—H4	0.9300
N1—C6	1.424 (4)	C5—C6	1.389 (4)
N1—H1A	0.88 (3)	C5—C10	1.419 (4)
N1—H1B	1.00 (4)	C6—C7	1.408 (5)
C1—C10	1.390 (4)	C7—C8	1.410 (4)
C1—C2	1.393 (4)	C7—H7	0.9300
C2—C3	1.415 (5)	C8—C9	1.327 (4)
C2—H2	0.9300	C8—H8	0.9300
C3—C4	1.322 (4)	C9—C10	1.469 (5)
C3—H3	0.9300	C9—H9	0.9300
C1—O1—H1	108 (3)	C6—C5—C4	123.9 (4)
C6—N1—H1A	106 (2)	C10—C5—C4	122.0 (3)
C6—N1—H1B	119.8 (18)	C5—C6—C7	121.2 (4)
H1A—N1—H1B	108 (3)	C5—C6—N1	114.4 (4)
O1—C1—C10	111.5 (3)	C7—C6—N1	124.3 (4)
O1—C1—C2	127.1 (3)	C6—C7—C8	124.0 (3)
C10—C1—C2	121.4 (3)	C6—C7—H7	118.0
C1—C2—C3	123.6 (3)	C8—C7—H7	118.0
C1—C2—H2	118.2	C9—C8—C7	117.1 (4)
C3—C2—H2	118.2	C9—C8—H8	121.4
C4—C3—C2	117.0 (4)	C7—C8—H8	121.4
C4—C3—H3	121.5	C8—C9—C10	119.9 (4)
C2—C3—H3	121.5	C8—C9—H9	120.1
C3—C4—C5	121.0 (4)	C10—C9—H9	120.1
C3—C4—H4	119.5	C1—C10—C5	115.1 (4)
C5—C4—H4	119.5	C1—C10—C9	121.3 (4)
C6—C5—C10	114.2 (3)	C5—C10—C9	123.6 (3)
O1—C1—C2—C3	179.1 (3)	C6—C7—C8—C9	0.0 (6)
C10—C1—C2—C3	0.7 (5)	C7—C8—C9—C10	−0.7 (5)
C1—C2—C3—C4	−1.1 (5)	O1—C1—C10—C5	−178.6 (3)
C2—C3—C4—C5	0.9 (5)	C2—C1—C10—C5	0.0 (4)
C3—C4—C5—C6	−179.8 (3)	O1—C1—C10—C9	1.6 (4)
C3—C4—C5—C10	−0.4 (5)	C2—C1—C10—C9	−179.7 (3)
C10—C5—C6—C7	0.3 (4)	C6—C5—C10—C1	179.3 (3)
C4—C5—C6—C7	179.7 (3)	C4—C5—C10—C1	−0.1 (4)
C10—C5—C6—N1	176.5 (3)	C6—C5—C10—C9	−0.9 (4)
C4—C5—C6—N1	−4.1 (5)	C4—C5—C10—C9	179.6 (3)
C5—C6—C7—C8	0.2 (6)	C8—C9—C10—C1	−179.1 (3)
N1—C6—C7—C8	−175.6 (4)	C8—C9—C10—C5	1.2 (5)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···N1^i	0.80 (4)	1.94 (4)	2.725 (4)	166 (4)
N1—H1A···O1^ii	0.88 (3)	2.16 (3)	3.042 (3)	172 (3)

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