NEt₄OH·4H₂O containing infinite hydro­xide–water ribbons

In tetraethyl­ammonium hydro­xide tetrahydrate, C₈H₂₀N⁺·­OH⁻·­4H₂O, the array of mirror symmetric NEt₄⁺ cations gives rise to a system of parallel channels which are filled with hydrogen-bonded anionic ribbons. The central part of each ribbon is constituted by a [OH⁻(HOH)_4/2] spiro-chain, with each hydro­xide ion accepting four strong linear hydrogen bonds [d(O...O) between 2.692 (1) and 2.727 (1) Å] but donating none. Additional (two-coordinate) H₂O mol­ecules bridge between the (four-coordinate) H₂O mol­ecules of the spiro-chain [d(O...O) between 2.831 (1) and 2.835 (1) Å].

S1. Comment

Higher hydrates of tetaalkylammonium hydroxides are well known to crystallize as ionic clathrate hydrates (Jeffrey, 1996). Detailed structural information about lower hydrates is however scarce. The crystal structures of both phases of dimorphic NMe₄OH^.2H₂O have been determined (Mootz & Seidel, 1990). In the course of studies on tetraalkylammonium silicate hydrates we have also prepared crystalline NEt₄OH^.4H₂O. The hydrogen-bonding system of this tetrahydrate, which is obtained by removal of water from aqueous solutions of NEt₄OH at room temperature, has previously been investigated by IR spectroscopy (Harmon et al., 1994). Here we report a single-crystal X-ray structure analysis of the title compound, (I). \sch

The NEt₄⁺ cations of approximate 42m (D_{2 d}) molecular symmetry (Fig. 1) lie with their N atoms on the crystallographic mirror planes parallel to (010) and give rise to channels extending along [100] that have approximately hexagonal cross-sections (Fig. 2). Each channel is occupied by a hydroxide-water ribbon (Fig. 1), the hydrogen-bonding geometry of which is listed in Table 1. The OH⁻ion does not act as a proton donor but its O1 atom accepts four strong linear hydrogen bonds from four water O2 molecules. The water O2 atoms form a planar rectangle with the bonded hydroxide O1 atom being slightly away from the plane [0.820 (1) Å]. Every H₂O molecule donates hydrogen bonds to two OH⁻ ions. Thus spiro chains [OH⁻(HOH)_4/2] are formed with the hydroxide protons protruding alternately to both sides. Additional (two-coordinate) water O3 molecules bridge neighbouring (four-coordinate) water O2 molecules by donating weaker linear hydrogen bonds. The two crystallographically distinct four-membered oxygen rings of the ribbons, O1—O2—O1—O2 and O1—O2—O3—O2, are nearly planar. Regarding the ribbon-cation interactions, the peripheral and two-coordinate water O3 atom builds the shortest contact distance, namely O3···H21B—C21 which may be considered as a very weak hydrogen bond [with d(C—H) normalized to 1.08 Å we find: d(O···H) = 2.35 Å, <(O···H—C) = 139° and d(O···C) = 3.251 (1) Å]. The remaining O···HC and O···C distances, including those of the OH⁻ ion, are considerably longer.

The presence of OH⁻ ions not acting as hydrogen-bond donors and two-coordinate H₂O molecules has already been inferred from IR data (Harmon et al., 1994). The coordination geometry observed for the OH⁻ ion in NEt₄OH^.4H₂O is quite common in crystalline hydroxide hydrates (for a recent review see Lutz, 1995). Similar [OH⁻(HOH)₄] surroundings exist for example in M(OH)^.2H₂O (M = K, Rb) (Rütter & Mootz, 1991, Jacobs & Schardey, 1988), CsNa₂[O(H,D)]₃·6(H,D)₂O (Mootz et al., 1994), Ba[O(H,D)]X·2(H,D)₂O (X = Cl, Br) (Lutz et al., 1989, Kellersohn et al., 1991) as well as α- and β-NMe₄OH·2H₂O (Mootz & Seidel, 1990).

NEt₄OH·4H₂O is structurally closely related to both forms of dimorphic NMe₄OH·2H₂O. The latter phases differ essentially only in the existence (β-form) and absence (α-form) of cation disorder, but have a similar array of the cations. This array gives rise to parallel channels that due to the smaller size of the NMe₄⁺ species have smaller cross-sections and are therefore filled only with spiro chains [OH⁻(HOH)_4/2] which constitute the central part of the ribbons in NEt₄OH^.4H₂O. Cooperativity of hydrogen bonding explains the shorter HOH···OH⁻ distances in the tetraethylammonium compound as compared with the tetramethylammonium compounds [α-form: d(O···O) between 2.751 and 2.762 Å].

S2. Experimental

Removal of water in vacuo from an aqueous NEt₄OH solution (Fluka, ca 40%) at room temperature yielded air-sensitive crystals of NEt₄OH·4H₂O. A suitable crystal was embedded in a droplet of a perfluorinated polyether oil for protection and freeze-fixed on the tip of a glass fibre at the low temperature of the X-ray measurements.

S3. Refinement

All H atoms were located on a difference Fourier map and refined independently. The large anisotropic displacement parameters of atom C32 and the features near this atom on the final difference Fourier map may indicate some kind of disorder of the corresponding methyl group which could however not be modelled with the X-ray data.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: SET4 in CAD-4 Software; data reduction: MolEN (Fair, 1990); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997) and DIAMOND (Brandenberg & Berndt, 1999); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. One cation (a) and part of a hydroxide-water ribbon (b) with atomic labelling (H atoms of the cation have the same numbers as the C atoms to which they are bonded and are distinguished by an additional letter). Displacement ellipsoids correspond to the 50% probability level. H atoms are represented as spheres of arbitrary radii (ORTEP-3; Farrugia, 1997). [Symmetry code: (i) −x + 1/2, y + 1/2, z + 1/2].

Fig. 2. Structure as seen along the a direction. Only non-H atoms are shown. Large open spheres are atoms of cations, small open spheres are hydroxide O atoms, black spheres are water O atoms (DIAMOND; Brandenburg & Berndt, 1999).

tetraethylammonium hydroxide-water (1/4)

Crystal data

C8H20N^+·OH^−·4H2O	Dx = 1.117 Mg m^−3
Mr = 219.32	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pnma	Cell parameters from 25 reflections
a = 7.766 (2) Å	θ = 11.4–18.1°
b = 11.670 (2) Å	µ = 0.09 mm^−1
c = 14.385 (2) Å	T = 153 K
V = 1303.7 (4) Å^3	Plate, white
Z = 4	0.42 × 0.22 × 0.06 mm
F(000) = 496

Data collection

Enraf-Nonius CAD-4 diffractometer	1627 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.052
Graphite monochromator	θmax = 34.9°, θmin = 2.3°
ω/2θ scans	h = 0→12
Absorption correction: ψ-scan (North et al., 1968)	k = 0→18
Tmin = 0.893, Tmax = 1.000	l = 0→23
2968 measured reflections	3 standard reflections every 100 reflections
2963 independent reflections	intensity decay: none

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.047	All H-atom parameters refined
wR(F^2) = 0.141	w = 1/[σ^2(Fo^2) + (0.0834P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.93	(Δ/σ)max < 0.001
2963 reflections	Δρmax = 0.50 e Å^−3
134 parameters	Δρmin = −0.27 e Å^−3
0 restraints

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	0.32820 (13)	0.2500	0.69337 (8)	0.0228 (2)
O2	0.59040 (10)	0.10616 (7)	0.73028 (6)	0.02521 (18)
O3	0.13624 (13)	0.03346 (8)	0.33488 (7)	0.0350 (2)
N	0.70268 (15)	0.2500	0.43878 (7)	0.0168 (2)
C11	0.7704 (3)	0.2500	0.53745 (11)	0.0345 (4)
C12	0.9624 (4)	0.2500	0.5462 (2)	0.0608 (8)
C21	0.76509 (13)	0.14581 (9)	0.38604 (7)	0.0219 (2)
C22	0.71382 (17)	0.03151 (10)	0.42699 (8)	0.0295 (2)
C31	0.5075 (2)	0.2500	0.44460 (15)	0.0340 (4)
C32	0.4175 (3)	0.2500	0.3505 (2)	0.0562 (7)
H11A	0.7220 (19)	0.1809 (13)	0.5649 (9)	0.034 (4)*
H12A	1.020 (3)	0.1844 (18)	0.5200 (14)	0.074 (6)*
H12B	1.000 (4)	0.2500	0.612 (2)	0.078 (9)*
H21A	0.7184 (18)	0.1546 (13)	0.3238 (10)	0.030 (4)*
H21B	0.8906 (19)	0.1509 (13)	0.3830 (10)	0.031 (4)*
H22A	0.592 (2)	0.0233 (13)	0.4249 (9)	0.035 (4)*
H22B	0.7551 (19)	0.0182 (15)	0.4881 (11)	0.040 (4)*
H22C	0.762 (2)	−0.0267 (14)	0.3893 (11)	0.044 (4)*
H31A	0.484 (2)	0.1831 (15)	0.4842 (11)	0.049 (4)*
H32A	0.447 (3)	0.173 (2)	0.3158 (14)	0.075 (6)*
H32B	0.289 (5)	0.2500	0.372 (3)	0.108 (12)*
H1	0.313 (3)	0.2500	0.6412 (18)	0.047 (7)*
H2A	0.507 (2)	0.1531 (17)	0.7151 (11)	0.054 (5)*
H2B	0.659 (3)	0.1539 (17)	0.7554 (14)	0.056 (5)*
H3A	0.060 (3)	−0.0076 (19)	0.3054 (13)	0.064 (6)*
H3B	0.222 (2)	−0.0014 (17)	0.3174 (11)	0.049 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0152 (4)	0.0260 (5)	0.0274 (5)	0.000	−0.0014 (4)	0.000
O2	0.0160 (3)	0.0205 (3)	0.0391 (4)	0.0014 (3)	−0.0017 (3)	−0.0007 (3)
O3	0.0265 (4)	0.0308 (5)	0.0478 (5)	0.0005 (4)	0.0043 (4)	−0.0134 (4)
N	0.0174 (5)	0.0164 (5)	0.0167 (4)	0.000	0.0008 (4)	0.000
C11	0.0641 (12)	0.0217 (7)	0.0178 (6)	0.000	−0.0111 (7)	0.000
C12	0.0660 (16)	0.0435 (13)	0.0729 (16)	0.000	−0.0515 (14)	0.000
C21	0.0225 (4)	0.0203 (4)	0.0230 (4)	0.0012 (4)	0.0039 (3)	−0.0040 (4)
C22	0.0362 (6)	0.0184 (5)	0.0339 (5)	−0.0003 (4)	0.0061 (5)	−0.0030 (4)
C31	0.0181 (6)	0.0255 (8)	0.0584 (11)	0.000	0.0125 (7)	0.000
C32	0.0281 (9)	0.0467 (13)	0.0938 (19)	0.000	−0.0259 (11)	0.000

Geometric parameters (Å, º)

N—C21	1.5128 (12)	C21—H21A	0.97 (1)
N—C21^i	1.5128 (12)	C21—H21B	0.98 (1)
N—C11	1.5139 (19)	C22—H22A	0.95 (1)
N—C31	1.5178 (19)	C22—H22B	0.95 (2)
C11—C12	1.496 (4)	C22—H22C	0.95 (2)
C21—C22	1.5116 (15)	C31—H31A	0.98 (2)
C31—C32	1.524 (3)	C32—H32A	1.05 (2)
C11—H11A	0.97 (1)	C32—H32B	1.05 (4)
C12—H12A	0.97 (2)	O1—H1	0.76 (3)
C12—H12B	0.99 (3)
C21—N—C21^i	106.97 (10)	H22A—C22—H22C	108 (1)
C21—N—C11	111.03 (8)	H22B—C22—H22C	106 (1)
C21^i—N—C11	111.03 (8)	N—C31—H31A	103 (1)
C21—N—C31	110.34 (8)	C32—C31—H31A	115 (1)
C21^i—N—C31	110.34 (8)	H31A—C31—H31A^i	105 (1)
C11—N—C31	107.18 (14)	C31—C32—H32A	109 (1)
C12—C11—N	115.18 (19)	C31—C32—H32B	100 (2)
C22—C21—N	115.43 (9)	H32A—C32—H32B	111 (2)
N—C31—C32	114.17 (17)	H32A—C32—H32A^i	117 (2)
C12—C11—H11A	110.5 (9)	O2^i—O1—O2	77.16 (5)
N—C11—H11A	104.2 (8)	O2^i—O1—O2^ii	144.76 (5)
H11A—C11—H11A^i	112 (1)	O2^i—O1—O2^iii	92.81 (3)
C11—C12—H12A	116 (1)	O2—O1—O2^ii	92.81 (3)
C11—C12—H12B	112 (2)	O2—O1—O2^iii	144.76 (5)
H12A—C12—H12B	103 (2)	O2^ii—O1—O2^iii	76.00 (5)
H12A—C12—H12A^i	105 (2)	O1—O2—O1^iv	102.00 (3)
C22—C21—H21A	110.7 (9)	O1—O2—O3^v	89.63 (4)
C22—C21—H21B	109.5 (9)	O1—O2—O3^vi	149.26 (5)
N—C21—H21A	104.9 (9)	O1^iv—O2—O3^v	124.14 (5)
N—C21—H21B	107.1 (9)	O1^iv—O2—O3^vi	88.85 (4)
H21A—C21—H21B	109 (1)	O3^v—O2—O3^vi	108.08 (5)
C21—C22—H22A	109.8 (9)	O2^vii—O3—O2^vi	87.65 (3)
C21—C22—H22B	115 (1)	H2A—O2—H2B	100 (2)
C21—C22—H22C	107.8 (9)	H3A—O3—H3B	98 (2)
H22A—C22—H22B	110 (1)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2A···O1	0.87 (2)	1.82 (2)	2.6919 (12)	175 (1)
O2—H2B···O1^viii	0.85 (2)	1.88 (2)	2.7267 (12)	174 (1)
O3—H3A···O2^vii	0.87 (2)	1.96 (2)	2.8314 (13)	174 (2)
O3—H3B···O2^vi	0.82 (2)	2.02 (2)	2.8355 (13)	171 (2)

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