An anisaldehyde sodium bis­ulfite derivative: poly[[μ₄-(hy­droxy)(4-meth­oxy­phenyl)methane­sulfonato]­sodium]

The title complex, [Na(C₈H₉O₅S)]_n, is polymeric and consists of broad layers parallel to (100) made up of an inner hydro­philic core of Na⁺ cations and polar SO₃C(OH)– groups, padded on both sides by two hydro­phobic layers of pendant meth­oxy­phenyl groups. The Na⁺ cations in the inner core are six-coordinated into highly distorted NaO₆ octa­hedra by four symmetry-related (hy­droxy)(4-meth­oxy­phenyl)methane­sul­fon­ate anions, leading to a tightly woven two-dimensional structure. While there are some hydrogen bonds providing inter­planar cohesion, inter­actions between adjacent layers are weak hydro­phobic ones. The present compound appears to be the first reported structure containing the (hy­droxy)(4-meth­oxy­phenyl)methane­sulfonate ligand.

S1. Comment

Aldehydes and methyl ketones are known to undergo nucleophilic addition of NaHSO₃ in aqueous solution (Clayden et al., 2012). The resulting derivatives could act as potentially good ligands in coordination complexes through the O atoms of the sulfite group, which normally exhibits several binding modes. In order to obtain these coordination compounds, we have first prepared and determined the crystal structure of the title compound, (I). A search of the Cambridge Structural Database (CSD, Version 5.33, August 2012 update; Allen, 2002) revealed that this is the first crystal structure containing this otherwise well known commercially available (hydroxy)(4-methoxyphenyl)methanesulfonate (mbs) derivative [Chemical Abstracts Service (CAS) number 33402-67-4]. However, a few closely related compounds have been published. Perhaps the most interesting one for comparison purposes is the potassium salt of (hydroxyphenyl)methanesulfonate, (II) (Kuroda et al., 1967), a ligand similar to mbs but lacking the terminal methoxy group. The two solids are almost isostructural, and here we shall analyse their similarities and differences.

The asymmetric unit of (I) consists of one Na⁺ cation and one mbs anion. Fig. 1 shows an ellipsoid plot of the structure, displaying a complete Na environment, while Table 1 presents Na—O coordination bond lengths and some Na···Na distances (see below). Compound (I) has a two-dimensional polymeric structure built up around the six-coordinated Na⁺ cations, which show a highly distorted NaO₆ octahedral environment. This is provided by four symmetry-related mbs anions (Fig. 1), two of them through two different chelating bites (atoms O1 and O5, and O2ⁱⁱⁱ and O3ⁱⁱⁱ), and the remaining two by way of two of these O atoms (O1ⁱ and O2ⁱⁱ), acting now in a bridging mode [symmetry codes: (i) -x + 1, -y + 1, -z + 1; (ii) -x + 1, y - 1/2, -z + 3/2; (iii) x, y - 1, z]. The Na—O coordination bond lengths span a narrow range [2.306 (2)–2.439 (2) Å for five of the O-atom donors, the sixth being an outlier of 2.736 (2) Å]. The fact that all four O atoms of the SO₃COH group are involved in coordination provides multiple bridging paths connecting the Na⁺ cations, though this is not necessarily reflected in particularly short Na···Na distances (see below).

The mbs anion presents a µ₄η⁴ binding mode not shown by any previous ligand containing an SO₃COH group. Fig 2 presents a summary of the different coordination modes found in the CSD, ranging from the very simple µ₁ up to the extremely complex µ₇η⁴. This diversity seems to confirm the potential of mbs in structural design.

The –SO₃ group in the ligand is extremely regular, with completely delocalized double bonds [S—O = 1.4533 (18)–1.4594 (18) Å], and the very small angular deviations from regularity are due solely to chelation. Thus, the O2—S1—O3 angle of 110.49 (11)° is 3% smaller than the remaining two O—S—O analogues. A similar relationship is encountered between C1—S1—O1 [104.84 (11)°] and its corresponding C—S—O analogues.

The bonding scheme results in a tightly woven two-dimensional array which can be described as a three-layered sandwich-like structure parallel to (100), viz. the B—A—B motif shown in Fig. 3. The inner part (A) is a hydrophilic core centred at x ~0.50 and about a/4 wide, built up by Na⁺ cations and sulfite anions. The methoxyphenyl groups, in turn, evolve upwards and downwards to form two limiting hydrophobic layers (B) sandwiching the former one (Fig. 3). Fig. 4 displays a simplified version of the central type `A' layer, built up of Na⁺ cations and sulfite anions. The wide diversity of loops linking the cations is apparent, and, as expected, those involving direct (O-atom mediated) Na—O—Na bridges lead to the shortest Na···Na distances. In the following, we refer the reader to Fig. 4 for geometric details and to Table 1 for symmetry codes. The nearest approach appears between atoms Na1 and Na1ⁱ [dark-grey shaded loop; Na···Na = 3.729 (2) Å], built up around an inversion centre and, accordingly, this results in two such Na—O—Na bridges. The second nearest are those linking 2₁-related cations, Na1···Na1ⁱⁱ [light-grey shading; Na···Na = 4.006 (1) Å], with only one such bridge. The minimum approach distance in (I) is in the range of the average found in the CSD for normal Na—O networks [3.47 (18) Å in a sample of 220 cases] but appears rather long if compared with, for instance, that in pure Na₂SO₃ [Na···Na = 3.090 (2) Å; Larsson & Kierkegaard, 1969]. As expected, Na—O—S—O—Na bridges are noticeably less effective in promoting close Na···Na contacts (see Fig. 4 and Table 1 for details).

Regarding type `B' zones, they are linked internally by weaker noncovalent interactions (Table 2), where atoms O4 and O5 present quite different behaviours. Protonated atom O5 is not only involved in coordination but also takes part in a moderately strong O—H···O hydrogen bond (first entry in Table 2), while due to its isolation in the hydrophobic region, atom O4 is neither coordinated nor involved in any relevant secondary interaction. The intralayer links are completed by significantly weaker interactions, viz. a non-conventional C—H···O hydrogen bond (second entry in Table 2) and a couple of C—H···π interactions (third and fourth entries in Table 2).

The whole three-layered B—A—B array fills one complete unit cell along the [100] direction. As suggested by Fig. 3, the interaction between neighbouring B—A—B structures is governed by weak hydrophobic B···B interactions.

As stated, (I) and the closely related potassium analogue, (II), are quasi-isostructural, crystallizing in the same space group (P2₁/c) and having similar cell parameters, although with variable relative increase when going from (I) to (II) (1.7% in a, 0.2% in b and 7.1% in c). These values correlate closely with the influence of the bulky methoxy group in (I) in the direction of each lattice parameter; this group is mainly oriented along c, only slightly along a and has no significant component along b.

The crystal structure description in terms of B—A—B zones is applicable to both (I) and (II), although, strikingly, this is where the similarities end: the B···B interactions and alignments are different in the two structures, as are the cation–sulfonate interactions in the hydrophilic zones A. This is easily revealed by inspection of the coordination modes of the ligands shown in Fig. 2, in which the modes for (I) and (II) have been encircled for clarity.

In summary, the results concerning the ligand properties of the mbs anion are encouraging, and therefore a project aimed at the synthesis of possible transition metal complexes of this ligand is under way in our laboratory.

Related literature

For related literature, see: Allen (2002); Clayden et al. (2012); Kuroda et al. (1967); Larsson & Kierkegaard (1969).

S2. Experimental

Compound (I) was synthesized by mixing a saturated aqueous solution of NaHSO₃ with 4-methoxybenzaldehyde at room temperature (molar ratio 2:1). The resulting white precipitate was first washed with the same bisulfite solution used in the preparation, then with ethanol (96%) and finally with diethyl ether. The solid powder thus obtained was dissolved in H₂O, and methanol was added until saturation was achieved. After [evaporation at room temperature for?] one month, a few crystals suitable for X-ray diffraction analysis were obtained.

S3. Refinement

All H atoms were visible in a difference map. The H atom attached to atom O5 was freely refined, whereas H atoms bonded to C atoms were idealized and allowed to ride, with C—H = 0.98 Å and U_iso(H) = 1.2U_eq(C) for tertiary, C—H = 0.93 Å and U_iso(H) = 1.2U_eq(C) for aromatic, and C—H = 0.98 Å and U_iso(H) = 1.5U_eq(C) for methyl H atoms.

Computing details

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures

Fig. 1. The structure of (I), with the atom-numbering scheme, showing the complete Na environment requiring four-symmetry related ligands. The symmetry-independent part of the structure is shown with full ellipsoids and bonds. Displacement ellipsoids are drawn at the 40% probability level. C-bound H atoms have been omitted for clarity. [What is the significance of the grey-shaded area?] [Symmetry codes: (i) -x + 1, -y + 1, -z + 1; (ii) -x + 1, y - 1/2, -z + 3/2; (iii) x, y - 1, z.]

Fig. 2. The different coordination modes found in the CSD for ligands containing the SO₃COH group. Those corresponding to structures (I) and (II) are encircled. CSD refcodes: A = JAYPEE and QEQFIC; B = PEFDAF; C = ABUMIV; D = PEFDAF; E = EDUWOZ and QACCOO; F = ODUWIT; G = (I) (this work); H = ODUWOZ; I = (II) (Kuroda et al., 1967) and KHBSLF; J = KHMSUL. [Please supply literature references for these refcodes]

Fig. 3. A side view of (I), projected down the [010] direction, showing the broad planar structures. The hydrophilic (A) part is shown with bold lines and the hydrophobic (B) part is shown with light lines.

Fig. 4. A schematic view of a type `A' layer, where only the Na⁺ cations and –SO₃ groups are drawn, showing the variety of loops linking the cations. For intercationic distances, see Table 1. The significance of the light and dark grey-shaded areas is discussed in the text. [Symmetry codes: (i) -x + 1, -y + 1, -z + 1; (ii) -x + 1, y - 1/2, -z + 3/2; (iii) x, y - 1, z; (iv) -x + 1, -y, -z + 1; (v) x, -y + 1/2, z - 1/2; (vii) x, -y + 1/2, z + 1/2; (viii) x, y + 1, z; (ix) -x + 1, y + 1/2, -z + 3/2.]

Poly[[µ₄-(hydroxy)(4-methoxyphenyl)methanesulfonato]sodium]

Crystal data

[Na(C8H9O5S)]	F(000) = 496
Mr = 240.20	Dx = 1.635 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 6270 reflections
a = 16.649 (3) Å	θ = 3.1–26.3°
b = 6.0854 (10) Å	µ = 0.37 mm^−1
c = 9.8244 (16) Å	T = 170 K
β = 101.365 (3)°	Block, colourless
V = 975.8 (3) Å^3	0.25 × 0.18 × 0.15 mm
Z = 4

Data collection

Bruker SMART CCD area-detector diffractometer	2152 independent reflections
Radiation source: fine-focus sealed tube	1553 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.068
ϕ and ω scans	θmax = 27.8°, θmin = 2.5°
Absorption correction: multi-scan (SADABS; Sheldrick, 2001)	h = −20→20
Tmin = 0.92, Tmax = 0.95	k = −7→7
9705 measured reflections	l = −12→12

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)] = 0.051	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.132	H atoms treated by a mixture of independent and constrained refinement
S = 1.05	w = 1/[σ^2(Fo^2) + 0.0255P] where P = (Fo^2 + 2Fc^2)/3
2152 reflections	(Δ/σ)max < 0.001
141 parameters	Δρmax = 0.53 e Å^−3
0 restraints	Δρmin = −0.36 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.

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

	x	y	z	Uiso*/Ueq
Na1	0.45801 (7)	0.32081 (16)	0.62318 (11)	0.0248 (3)
O1	0.44313 (12)	0.6727 (3)	0.51144 (19)	0.0262 (5)
O2	0.44279 (12)	0.9413 (3)	0.69395 (18)	0.0271 (5)
O3	0.36365 (12)	1.0086 (3)	0.46680 (17)	0.0255 (5)
O4	0.06777 (13)	0.4579 (3)	0.1499 (2)	0.0334 (5)
O5	0.34392 (12)	0.5072 (3)	0.6900 (2)	0.0255 (5)
H5	0.349 (2)	0.519 (6)	0.777 (4)	0.046 (10)*
S1	0.39701 (4)	0.84056 (10)	0.56812 (7)	0.0215 (2)
C1	0.31082 (18)	0.6947 (4)	0.6149 (3)	0.0235 (7)
H1	0.2848	0.7885	0.6747	0.028*
C2	0.24889 (17)	0.6321 (4)	0.4888 (3)	0.0228 (6)
C3	0.25539 (19)	0.4371 (5)	0.4182 (3)	0.0305 (7)
H3	0.3003	0.3462	0.4485	0.037*
C4	0.1975 (2)	0.3742 (4)	0.3047 (3)	0.0311 (7)
H4	0.2037	0.2435	0.2589	0.037*
C5	0.13000 (19)	0.5066 (4)	0.2593 (3)	0.0273 (7)
C6	0.1230 (2)	0.7047 (5)	0.3257 (3)	0.0319 (7)
H6	0.0787	0.7967	0.2935	0.038*
C7	0.18134 (19)	0.7658 (5)	0.4391 (3)	0.0308 (7)
H7	0.1756	0.8984	0.4833	0.037*
C8	0.0712 (2)	0.2521 (5)	0.0810 (3)	0.0394 (8)
H8A	0.0241	0.2376	0.0075	0.059*
H8B	0.0718	0.1344	0.1463	0.059*
H8C	0.1200	0.2461	0.0430	0.059*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Na1	0.0314 (8)	0.0149 (5)	0.0276 (6)	0.0011 (4)	0.0047 (5)	0.0005 (4)
O1	0.0329 (13)	0.0162 (9)	0.0314 (11)	0.0036 (8)	0.0105 (10)	0.0003 (8)
O2	0.0348 (13)	0.0199 (10)	0.0239 (10)	−0.0050 (9)	−0.0008 (9)	−0.0014 (8)
O3	0.0384 (13)	0.0140 (9)	0.0230 (10)	0.0049 (8)	0.0033 (9)	0.0035 (7)
O4	0.0322 (13)	0.0284 (11)	0.0362 (12)	−0.0011 (9)	−0.0015 (10)	0.0006 (9)
O5	0.0388 (13)	0.0166 (9)	0.0209 (11)	0.0025 (8)	0.0052 (10)	0.0033 (8)
S1	0.0297 (5)	0.0119 (3)	0.0229 (4)	0.0013 (3)	0.0050 (3)	0.0009 (3)
C1	0.0290 (18)	0.0145 (12)	0.0278 (15)	0.0054 (12)	0.0077 (13)	0.0006 (11)
C2	0.0253 (17)	0.0156 (13)	0.0268 (15)	0.0012 (11)	0.0030 (13)	0.0021 (11)
C3	0.0300 (19)	0.0204 (14)	0.0379 (18)	0.0064 (13)	−0.0008 (14)	−0.0041 (13)
C4	0.033 (2)	0.0186 (14)	0.0388 (18)	0.0014 (13)	0.0003 (15)	−0.0057 (13)
C5	0.0272 (18)	0.0239 (14)	0.0293 (16)	−0.0022 (13)	0.0018 (13)	0.0052 (12)
C6	0.0303 (19)	0.0277 (15)	0.0354 (18)	0.0080 (13)	0.0007 (15)	0.0000 (13)
C7	0.037 (2)	0.0211 (14)	0.0339 (17)	0.0067 (13)	0.0050 (15)	−0.0005 (12)
C8	0.046 (2)	0.0304 (16)	0.0377 (19)	−0.0059 (16)	−0.0019 (16)	−0.0020 (14)

Geometric parameters (Å, º)

Na1—O1^i	2.3060 (19)	C1—H1	0.9800
Na1—O2^ii	2.307 (2)	C2—C3	1.390 (4)
Na1—O1	2.397 (2)	C2—C7	1.396 (4)
Na1—O5	2.412 (2)	C3—C4	1.377 (4)
Na1—O2^iii	2.439 (2)	C3—H3	0.9300
Na1—O3^iii	2.736 (2)	C4—C5	1.383 (4)
O1—S1	1.4533 (18)	C4—H4	0.9300
O2—S1	1.4538 (19)	C5—C6	1.387 (4)
O3—S1	1.4584 (18)	C6—C7	1.377 (4)
O4—C5	1.370 (4)	C6—H6	0.9300
O4—C8	1.430 (3)	C7—H7	0.9300
O5—C1	1.410 (3)	C8—H8A	0.9600
O5—H5	0.85 (3)	C8—H8B	0.9600
S1—C1	1.822 (3)	C8—H8C	0.9600
C1—C2	1.497 (4)
Na1···Na1^i	3.729 (2)	Na1···Na1^v	4.939 (2)
Na1···Na1^ii	4.006 (2)	Na1···Na1^vi	4.987 (2)
Na1···Na1^iv	4.006 (2)	Na1···Na1^vii	4.987 (2)
O1^i—Na1—O2^ii	87.64 (8)	O3—S1—C1	107.51 (12)
O1^i—Na1—O1	75.11 (7)	O5—C1—C2	111.2 (2)
O2^ii—Na1—O1	93.80 (8)	O5—C1—S1	106.27 (19)
O1^i—Na1—O5	146.87 (8)	C2—C1—S1	111.33 (17)
O2^ii—Na1—O5	96.88 (7)	O5—C1—H1	109.3
O1—Na1—O5	71.86 (7)	C2—C1—H1	109.3
O1^i—Na1—O2^iii	107.80 (7)	S1—C1—H1	109.3
O2^ii—Na1—O2^iii	100.23 (6)	C3—C2—C7	117.4 (3)
O1—Na1—O2^iii	165.74 (9)	C3—C2—C1	121.5 (3)
O5—Na1—O2^iii	103.65 (7)	C7—C2—C1	121.1 (2)
O1^i—Na1—O3^iii	94.91 (7)	C4—C3—C2	122.0 (3)
O2^ii—Na1—O3^iii	154.36 (7)	C4—C3—H3	119.0
O1—Na1—O3^iii	111.53 (7)	C2—C3—H3	119.0
O5—Na1—O3^iii	94.80 (7)	C3—C4—C5	119.6 (3)
O2^iii—Na1—O3^iii	54.71 (6)	C3—C4—H4	120.2
S1—O1—Na1^i	134.30 (11)	C5—C4—H4	120.2
S1—O1—Na1	117.86 (10)	O4—C5—C4	124.6 (3)
Na1^i—O1—Na1	104.89 (7)	O4—C5—C6	115.9 (3)
S1—O2—Na1^iv	134.67 (12)	C4—C5—C6	119.6 (3)
S1—O2—Na1^viii	102.91 (10)	C7—C6—C5	120.3 (3)
Na1^iv—O2—Na1^viii	115.10 (8)	C7—C6—H6	119.9
S1—O3—Na1^viii	90.25 (9)	C5—C6—H6	119.9
C5—O4—C8	117.8 (2)	C6—C7—C2	121.1 (3)
C1—O5—Na1	119.04 (14)	C6—C7—H7	119.4
C1—O5—H5	114 (2)	C2—C7—H7	119.4
Na1—O5—H5	113 (2)	O4—C8—H8A	109.5
O1—S1—O2	113.21 (12)	O4—C8—H8B	109.5
O1—S1—O3	112.97 (10)	H8A—C8—H8B	109.5
O2—S1—O3	110.49 (11)	O4—C8—H8C	109.5
O1—S1—C1	104.83 (11)	H8A—C8—H8C	109.5
O2—S1—C1	107.34 (11)	H8B—C8—H8C	109.5

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x+1, y−1/2, −z+3/2; (iii) x, y−1, z; (iv) −x+1, y+1/2, −z+3/2; (v) −x+1, −y, −z+1; (vi) x, −y+1/2, z−1/2; (vii) x, −y+1/2, z+1/2; (viii) x, y+1, z.

Hydrogen-bond geometry (Å, º)

Cg1 is the centroid of the C2–C7 ring.

D—H···A	D—H	H···A	D···A	D—H···A
O5—H5···O3^ix	0.85 (3)	1.84 (3)	2.676 (3)	169 (3)
C3—H3···O3^iii	0.93	2.30	3.152 (3)	152
C1—H1···Cg1^ix	0.98	2.93 (3)	3.818 (3)	157
C8—H8C···Cg1^vi	0.96	2.92 (3)	3.669 (5)	131

Symmetry codes: (iii) x, y−1, z; (vi) x, −y+1/2, z−1/2; (ix) x, −y+3/2, z+1/2.