Competing hydrogen-bond acceptors in ethyl­enediammonium oxotrithio­tungstate(VI)

The structure of the title compound, (C₂H₁₀N₂)[WOS₃], consists of ethyl­ene­diammonium dications and tetra­hedral [WOS₃]²⁻ dianions, which are linked with the aid of four varieties of hydrogen bond, namely N—H...O, N—H...S, C—H...O and C—H...S. The strength and number of these hydrogen bonds affect the W—O and W—S bond distances.

S1. Comment

As part of an ongoing research programme, we are investigating the reactions of (NH₄)₂[WS₄] with organic amines and have structurally characterized several organic ammonium tetrathiotungstates (Srinivasan et al., 2002, 2003a,b, 2005; Srinivasan, Näther et al., 2006a,b; Srinivasan, Naik et al., 2006a). Our recent results in this area have revealed that these compounds exhibit a rich structural chemistry in terms of the N—H···S interactions between the organic ammonium cation and the tetrathiotungstate anion (Srinivasan, Näther et al., 2006a,b). In almost all these compounds, the WS₄ tetrahedron is slightly distorted with one or two of the W—S bonds elongated, which can be attributed to the strength and numbers of these S···H interactions. A competing hydrogen-bond acceptor such as oxygen in oxotrithiotungstate [WOS₃]^2- compounds offers the possibility to investigate the occurrence of N—H···O as well as N—H···S interactions in the same compound. Although the synthetic aspects of [WOS₃]^2- (Müller & Diemann 1968; McDonald et al., 1983), spectral characteristics (Müller et al., 1969; 1981), reactivity studies (Ansari et al., 1988) and medical applications (Mason et al., 1989) have been reported in the literature, only two structurally characterized monooxotrithiotungstates, K₃[WOS₃]Cl (Krebs et al., 1972) and (pipH)₄[WOS₃][WS₄] (pipH is piperidinium) (Siemeling et al., 2006), are known to date. Both reported compounds are double salts and contain anions such as Cl^- or [WS₄]^2- in addition to [WOS₃]^2- in their structures. In the present work, we describe the structure of the organic ammonium oxotrithiotungstate (enH₂)[WOS₃], (I) (enH₂ = ethylenediammonium), which does not contain any anion other than [WOS₃]^2-. The title compound was prepared by following an analogous procedure used previously for the corresponding tetrathio compound (enH₂)[WS₄] (Srinivasan et al., 2002).

The structure of (I) consists of ethylenediammonium dications and tetrahedral [WOS₃]^2- dianions, with all atoms located in general positions (Fig. 1). Both (pipH)₂[WS₄] and the double salt (pipH)₄[WOS₃][WS₄] crystallize in the monoclinic space group P2₁/n (Siemeling et al., 2006), while the tetrathio analogue of (I) (enH₂)[WS₄] crystallizes in the chiral orthorhombic space group P2₁2₁2₁ (Srinivasan et al., 2002). The geometric parameters of the (enH₂)²⁺ cation in (I) (Table 1) are in good agreement with those observed in other compounds containing the same cation (Srinivasan et al., 2002, 2003c). The bond angles around W are very close to the ideal tetrahedral angle and scatter in a small range between 108.63 (14) and 110.36 (6)°. The observed W—O and W—S bond distances are in very good agreement with those reported in the double salt (pipH)₄[WOS₃][WS₄] (Siemeling et al., 2006). Analysis of the crystal structure showed the presence of four varieties of weak interactions, namely N—H···O, N—H···S, C—H···O and C—H···S bonds. Each cation is hydrogen bonded to six different [WOS₃]^2- anions. The S and O atoms of [WOS₃]^2- function as H-atom acceptors, while the cation acts as an H-atom donor through its ammonium and methylene groups. Each anion is linked to six different cations with the aid of the same four varieties of hydrogen bonds (Fig. 2). In (I), all H atoms involved in hydrogen bonding are singly shared donors excepting H1N1, which functions as a bifurcated donor. As a result of the hydrogen-bonding pattern, the cations and anions are organized into alternating layers, resulting in the formation of a three-dimensional hydrogen-bonded network (Fig. 3).

A total of nine hydrogen bonds (Table 2) comprising six S···H and three O···H interactions are observed, and all these contacts are shorter than the sum of their van der Waals radii (Bondi, 1964). A comparison of the geometric parameters of (I) with those of K₃[WOS₃]Cl and (pipH)₄[WOS₃][WS₄] (Table 3) serves to illustrate the importance of hydrogen bonding in organic ammonium thiotungstates. In K₃[WOS₃]Cl with no hydrogen bonding, the W—S distances scatter in a narrow range between 2.196 (6) and 2.208 (5) Å. The difference Δ between the longest and shortest W—S bond is 0.012 Å, which is much less than the values in (I) and (pipH)₄[WOS₃][WS₄], with the maximum Δ value of 0.0399 Å. It is to be noted that the structure of (pipH)₄[WOS₃][WS₄] was determined at 220 K and the compound also contains an additional [WS₄]^2- anion in its structure. In (I), the shortest W—S bond length of 2.1791 (15) Å is observed for S3, which is involved in a single bifurcated S···H contact at a relatively long distance of 2.77 Å accompanied by a small N—H···S angle, which can explain the observed short W—S distance. In (pipH)₄[WOS₃][WS₄], the shortest W—S bond of 2.1666 (9) Å was explained as being due to the absence of any short S···H contact. The other two W—S bond distances in (I), at 2.2010 (14) and 2.2029 (14) Å, are identical within experimental error. Atom S2 is engaged in two short N—H···S contacts, while S1 has three hydrogen-bonding interactions (two short N—H···S and one C—H···S contact), which can explain the elongation of these bonds as compared to W—S3. The observation of longer W—S bonds at 2.2009 (10) and 2.2065 (10) Å in (pipH)₄[WOS₃][WS₄] was attributed to a singly shared hydrogen bond by each of these S atoms. [please clarify meaning]

The W—O bond distance in (I) [1.778 (4) Å] is slightly longer than that for K₃[WOS₃]Cl [1.76 (1) Å]. An elongation of the W—O bond with respect to related compounds, which do not exhibit O···H contacts, is indicated by the observed W—O stretching vibration in the IR spectrum of (I), which occurs as a strong signal centered at 828 cm^-1. For the fully alkylated organic ammonium compound [(C₂H₅)₄N]₂[WOS₃] (McDonald et al., 1983) and the pure inorganic Cs₂[WOS₃] (Müller et al., 1969) the W—O vibrational frequencies are at higher energies at 885 and 870 cm^-1, respectively. A value of 793 cm^-1 was found in (pipH)₄[WOS₃][WS₄] (Siemeling et al., 2006). In this double salt, the N—H···O contacts are slightly shorter (1.89 and 1.93 Å) and are accompanied by larger D—H···A angles of 170 and 173°, respectively, than those observed in (I). Although the W—O distances of (I) and (pipH)₄[WOS₃][WS₄] are nearly the same, it is to be noted that the O atom in (I) is involved in three hydrogen bonds, which includes two singly shared N—H···O interactions and a singly shared C—H···O contact.

The occurrence of a C—H···O and a C—H···S contact at 2.57 and 2.88 Å, respectively, in (I) prompted us to reinvestigate the known structures of (enH₂)[WS₄] and (pipH)₄[WOS₃][WS₄] for the presence of additional weak interactions. Scrutiny of the structure of (enH₂)[WS₄] revealed that in addition to the reported N—H···S bonds, the [WS₄]^2- unit is involved in three weak C—H···S contacts at 2.89, 2.92 and 2.95 Å with corresponding D—H···A angles of 148, 131 and 143°, respectively. In (pipH)₄[WOS₃][WS₄], the [WOS₃]^2- unit exhibits three weak C—H···S contacts (2.87, 2.93 and 2.96 Å) with D—H···A angles of 127, 133 and 156°, respectively. The C—H···O distance at 2.76 Å seems to be too long for significant interactions (Jeffrey, 1997). Presently, there is no direct evidence to show that C—H···S bonds affect the W—S bond distances. However, the observation of several C—H···S contacts in many tetrathiotungstates by us recently (Srinivasan, Naik et al., 2006a,b) indicates that these weak interactions may play an important role in the structural chemistry of thiotungstates.

A comparison of (I) with that of the corresponding tetrathio compound (enH₂)[WS₄] reveals that both structures are nearly identical (Fig. 4). A careful analysis of the overlaid structures demonstrates that when one S atom in (enH₂)[WS₄] is replaced by an O atom, the O atom occupies the position of that S atom in (enH₂)[WS₄] (Table 3), which exhibits two singly shared N—H···S contacts. It is to be noted that in (enH₂)[WS₄] the other three S atoms are involved in at least one bifurcated N—H···S bond. Hence, the preference of this position by the O atom can be explained due to its competing nature to engage in stronger hydrogen bonding. The incorporation of O also results in a C—H···O contact. In the tetrathio compound this bond corresponds to the weak C—H···S interaction at 2.89 Å. The structural similarity of the tetrathio and oxotrithio compounds can also explain the nearly similar hydrogen-bond surroundings around the S atoms that exhibit the longest W—S bond distances, in both compounds. It is interesting that the introduction of an O atom in the place of one S in the tetrathio compound results in about a two and half times increase in the magnitude of Δ from 0.0092 Å in (enH₂)[WS₄] to 0.0238 Å in (I). This observation adds more credence to our recent postulate that the magnitude of Δ can be considered as a useful measure of the distortion of the WS₄ tetrahedron in organic ammonium tetrathiotungstates (Srinivasan, Näther et al., 2006a).

In summary, we have shown that when an S atom in (enH₂)[WS₄] is replaced by an O atom, the resulting structure is nearly identical to that of the tetrathio compound, with the O atom occupying a position favorable for stronger N—H···O interactions. The O-atom substitution is also accompanied by a pronounced increase in the Δ value for the oxotrithio compound. In addition, the introduction of asymmetry in the form of an O atom in the WS₄ tetrahedron leads to the observation of more varieties of hydrogen bonds in a single compound. More examples of structurally characterized organic ammonium oxotrithiotungstates are essential for a better understanding of the importance of the weaker C—H···O and C—H···S interactions in the structural chemistry of oxotrithiotungstates. Efforts in this direction are currently underway in our laboratories.

Related literature

For related literature, see: Ansari et al. (1988); Bondi (1964); Jeffrey (1997); Krebs et al. (1972); Müller & Diemann (1968); Müller et al. (1969, 1981); Mason et al. (1989); McDonald et al. (1983); Siemeling et al. (2006); Srinivasan et al. (2002, 2003a, 2003b, 2003c, 2005); Srinivasan, Näther, Dhuri & Bensch (2006a, 2006b); Srinivasan, Naik, Näther & Bensch (2006a, 2006b).

S2. Experimental

(NH₄)₂[WOS₃] (664 mg, 2 mmol) was dissolved in water (10 ml) containing a few drops of aqueous ammonia and filtered. To the clear yellow filtrate, en (0.3 ml) was added dropwise at room temperature and the reaction mixture was kept aside for crystallization. After a day, crystalline blocks started to separate out slowly. These were isolated by filtration, washed well with ice-cold water (2 ml), 2-propanol (20 ml) and ether (20 ml), and air dried (yield 500 mg). The complex is quite stable in air and was analysed satisfactorily. ν_{W - O} 828 cm^-1, ν_{W - S} 484 and 455 cm^-1.

S3. Refinement

The positions of the C– and N-bound H atoms were located in a difference map; their bond lengths were set to ideal values and were refined using a riding model (C—H = 0.97 Å and N—H = 0.89 Å). The largest peak in the residual electron density map is located 0.78 Å from W1 and the deepest hole is located 0.79 Å from W1

Computing details

Data collection: DIF4 (Stoe & Cie, 1998); cell refinement: DIF4; data reduction: REDU4 (Stoe & Cie, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: CIFTAB in SHELXTL (Bruker, 1998).

Figures

	Fig. 1. The structure of the constituent ions of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. A view of the surroundings of the [WOS3]^2- anion showing the linking of each anion to six different cations via N—H···O, N—H···S, C—H···O and C—H···S interactions. Hydrogen bonds are shown as dashed lines. [Symmetry codes: (i) x + 1/2, -y + 3/2, z + 1/2; (ii) -x + 1/2, y + 1/2, -z + 1/2; (iii) -x + 3/2, y + 1/2, -z + 1/2; (iv) x + 1, y, z; (v) x + 1/2, -y + 3/2, z - 1/2.]
	Fig. 3. The packing of (I), viewed along the a axis, showing the three-dimensional hydrogen-bonded network. N—H···O, N—H···S, C—H···O and C—H···S bonds are shown as dashed lines.
	Fig. 4. An overlay diagram showing the structural similarity of (enH2)[WOS3] (blue in the online version of the journal) and (enH2)[WS4] (red).

ethylenediammonium oxotrithiotungstate(VI)

Crystal data

(C2H10N2)[WOS3]	F(000) = 664
Mr = 358.15	Dx = 2.665 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 8.8191 (14) Å	Cell parameters from 100 reflections
b = 10.7923 (18) Å	θ = 20.1–30.5°
c = 9.3793 (14) Å	µ = 13.58 mm^−1
β = 90.631 (12)°	T = 293 K
V = 892.7 (2) Å^3	Block, yellow
Z = 4	0.19 × 0.18 × 0.17 mm

Data collection

Stoe AED-II four-circle diffractometer	2052 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.027
Graphite monochromator	θmax = 30.0°, θmin = 2.9°
ω/θ scans	h = 0→12
Absorption correction: numerical (X-SHAPE; Stoe & Cie, 1998)	k = −1→15
Tmin = 0.091, Tmax = 0.135	l = −13→13
3022 measured reflections	4 standard reflections every every 120 min min
2602 independent reflections	intensity decay: none

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)] = 0.026	H-atom parameters constrained
wR(F^2) = 0.070	w = 1/[σ^2(Fo^2) + (0.0334P)^2 + 2.4809P] where P = (Fo^2 + 2Fc^2)/3
S = 1.08	(Δ/σ)max = 0.001
2602 reflections	Δρmax = 1.79 e Å^−3
85 parameters	Δρmin = −2.13 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0020 (2)

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
W1	0.23427 (2)	0.62410 (2)	0.188568 (19)	0.02179 (8)
S1	0.03782 (16)	0.61605 (15)	0.33097 (16)	0.0339 (3)
S2	0.23135 (19)	0.46562 (14)	0.04054 (15)	0.0339 (3)
S3	0.2303 (2)	0.79721 (14)	0.06900 (17)	0.0378 (3)
O1	0.4038 (4)	0.6187 (4)	0.2927 (5)	0.0327 (8)
N1	0.5718 (5)	0.8387 (5)	0.2825 (5)	0.0292 (9)
H1N1	0.6153	0.8627	0.3641	0.044*
H2N1	0.5082	0.7765	0.2994	0.044*
H3N1	0.5209	0.9019	0.2443	0.044*
N2	0.9214 (6)	0.9070 (5)	0.2668 (6)	0.0383 (12)
H1N2	0.8755	0.9298	0.3466	0.057*
H2N2	0.9897	0.9639	0.2432	0.057*
H3N2	0.9675	0.8345	0.2805	0.057*
C1	0.6906 (7)	0.7969 (6)	0.1820 (6)	0.0340 (12)
H1A	0.6423	0.7718	0.0932	0.041*
H1B	0.7414	0.7249	0.2220	0.041*
C2	0.8076 (7)	0.8948 (7)	0.1506 (7)	0.0413 (15)
H2A	0.8587	0.8739	0.0628	0.050*
H2B	0.7571	0.9738	0.1366	0.050*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
W1	0.02061 (10)	0.02227 (11)	0.02250 (11)	−0.00107 (8)	−0.00015 (6)	−0.00098 (8)
S1	0.0291 (6)	0.0346 (7)	0.0383 (7)	−0.0028 (6)	0.0095 (5)	−0.0052 (6)
S2	0.0447 (8)	0.0270 (6)	0.0300 (6)	−0.0008 (6)	0.0050 (6)	−0.0065 (5)
S3	0.0516 (9)	0.0268 (7)	0.0349 (7)	−0.0049 (6)	−0.0023 (6)	0.0070 (6)
O1	0.0265 (17)	0.0297 (19)	0.042 (2)	−0.0019 (17)	−0.0037 (16)	0.0007 (18)
N1	0.027 (2)	0.028 (2)	0.033 (2)	−0.0030 (17)	−0.0015 (18)	−0.0030 (19)
N2	0.030 (2)	0.038 (3)	0.047 (3)	−0.003 (2)	0.004 (2)	−0.004 (2)
C1	0.033 (3)	0.036 (3)	0.033 (3)	−0.003 (2)	0.002 (2)	−0.007 (2)
C2	0.034 (3)	0.053 (4)	0.037 (3)	0.001 (3)	−0.001 (2)	0.012 (3)

Geometric parameters (Å, º)

W1—O1	1.778 (4)	N2—H1N2	0.8900
W1—S3	2.1791 (15)	N2—H2N2	0.8900
W1—S1	2.2010 (14)	N2—H3N2	0.8900
W1—S2	2.2029 (14)	C1—C2	1.508 (9)
N1—C1	1.487 (7)	C1—H1A	0.9700
N1—H1N1	0.8900	C1—H1B	0.9700
N1—H2N1	0.8900	C2—H2A	0.9700
N1—H3N1	0.8900	C2—H2B	0.9700
N2—C2	1.479 (8)
O1—W1—S3	108.63 (14)	C2—N2—H3N2	109.5
O1—W1—S1	109.15 (14)	H1N2—N2—H3N2	109.5
S3—W1—S1	109.75 (7)	H2N2—N2—H3N2	109.5
O1—W1—S2	108.95 (15)	N1—C1—C2	113.5 (5)
S3—W1—S2	109.96 (6)	N1—C1—H1A	108.9
S1—W1—S2	110.36 (6)	C2—C1—H1A	108.9
C1—N1—H1N1	109.5	N1—C1—H1B	108.9
C1—N1—H2N1	109.5	C2—C1—H1B	108.9
H1N1—N1—H2N1	109.5	H1A—C1—H1B	107.7
C1—N1—H3N1	109.5	N2—C2—C1	112.2 (5)
H1N1—N1—H3N1	109.5	N2—C2—H2A	109.2
H2N1—N1—H3N1	109.5	C1—C2—H2A	109.2
C2—N2—H1N2	109.5	N2—C2—H2B	109.2
C2—N2—H2N2	109.5	C1—C2—H2B	109.2
H1N2—N2—H2N2	109.5	H2A—C2—H2B	107.9

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1N1···S2^i	0.89	2.68	3.496 (5)	153
N1—H1N1···S3^i	0.89	2.77	3.353 (5)	125
N1—H2N1···O1	0.89	1.94	2.801 (6)	163
N1—H3N1···S1^ii	0.89	2.47	3.317 (5)	159
N2—H1N2···S2^i	0.89	2.50	3.375 (6)	168
N2—H2N2···O1^iii	0.89	1.95	2.816 (7)	165
N2—H3N2···S1^iv	0.89	2.48	3.356 (6)	167
C1—H1A···S1^v	0.97	2.88	3.666 (6)	138
C2—H2A···O1^v	0.97	2.57	3.474 (8)	155

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