Diammonium hexa­kis­(thio­cyanato-κN)rhenate(IV) dimethyl sulfone tetra­solvate

The title compound, (NH₄)₂[Re(NCS)₆]·4C₂H₆O₂S, was ob­tained by solvothermal synthesis as part of a project on rhenium thio­cyanate catalysts and starting materials for further aggregation to mol­ecular magnets. The compound is the ammonium salt of octa­hedral hexa­kis­(thio­cyanato-κN)rhenate(IV) anions, which lie on centres of inversion. The dimethyl sulfone solvent mol­ecules are involved in R₄²(8) and D N—H...O hydrogen-bonded motifs. N—H...S and S...S short contacts are also present. Hydrogen-bonded ammonium–dimethyl sulfone layers alternate with layers formed by the complex anion (with S...S short contacts) parallel to (100).

S1. Comment

Rhenium thiocyanate complexes possess catalytic activity, which makes them an alternative to the expensive catalyst methyltrioxidorhenium (MTO) (Dinda et al., 2009). Synthetic routes for the synthesis of such catalysts are still being explored, in particular through reductive thiocyanolysis (Dinda et al., 2009) or ligand exchange in hexachloridorhenates(IV) (Gonzalez et al., 2008). Synthetic difficulties arise in connection with product purification.

The title compound, (I), was obtained as part of a project on synthetic routes for new rhenium catalysts and reagents for further syntheses of new polynuclear materials. Compound (I) is a product of the reaction of ammonium thiocyanate and ammonium hexachloridorhenate(IV), carried out under solvothermal conditions (see reaction scheme). The solvent, dimethyl sulfone (m.p. 382 K), proves to be suitable under these conditions for ligand exchange in the hexachloridorhenate(IV) anion.

The structure of (I) contains rare centrosymmetric hexakis(thiocyanato-κN)rhenate(IV) anions (Fig. 1). To date, a modest amount of crystal data has been reported for this anion, namely for a tetraphenylphosphonium salt (Dinda et al., 2009), and for a tetrabutylammonium salt along with its linkage isomer (Gonzalez et al., 2008). In both these cases the anions are also centrosymmetric. Spectroscopic and magnetic data for a tetraphenylarsonium salt are available (Małecka et al., 2002). Reports of dimethyl sulfone are scarce in the literature; it has been observed on its own (Sands, 1963; Langs et al., 1970; Fronczek, 2006, 2007), as a solvent (Bandy et al., 1981; Coles et al., 2003) and as a ligand (Cotton & Felthouse, 1981; Dikarev et al., 2003; Biagini et al., 2004), and has been observed to participate in discrete hydrogen-bonded motifs.

The octahedral geometry of the anion of (I) (Table 1) can be compared with those found for the tetraphenylphosphonium and tetrabutylammonium salts (Dinda et al., 2009; Gonzalez et al., 2008). In (I), all Re—N bond lengths are equal, while in both of the previously reported structures some degree of anion axial distortion was observed, probably resulting from the influence of intermolecular interactions. For the tetrabutylammonium salt, Re—N = 2.043 (6), 2.012 (5) and 2.000 (5) Å, and 2.045 (6), 2.016 (4) and 2.155 (7) Å for two symmetry-independent anions. The long bond is in a thiocyanate ligand involved in a short S···S contact. For the tetraphenylphosphonium salt, Re—N = 2.025 (7) and 1.943 (5) Å (Re on a site of 4/m symmetry). All thiocyanate ligands bonded to the Re^IV centre in (I) are linear, with bond lengths comparable with previously observed values [e.g. for the tetraphenylphosphonium salt, C—N = 1.154 (10)–1.197 (11) Å and C—S = 1.604 (8)–1.607 (10) Å]. This geometry can be best understood in terms of one of the possible ligand resonance forms (see scheme).

The ammonium atoms H2–H4 participate as donors in N—H···O hydrogen bonds with dimethyl sulfone O atoms (Table 2). This does not seem to affect the S—O bond lengths, which, along with other molecular parameters, are as expected (Table 1). They are also comparable with, for example, the values found for 1,4,7,10,13,16-hexaoxacyclooctadecane-bis(dimethyl sulfone) (Bandy et al., 1981), where the relevant S—O bond lengths are 1.439 (2) and 1.440 (2) Å. The remaining H atom is involved in an N4—H1···S1^vi short contact [N···S = 3.551 (3) Å and N—H···S = 170°; symmetry code: (vi) -x + 1, y - 1/2, -z + 1/2]. N4—H3···O1ⁱⁱⁱ and N4—H4···O1^iv hydrogen bonds participate in R₄²(8) graph-set motifs (Etter et al., 1990), whereas the bifurcated N4—H2···O2ⁱⁱ and N4—H2···O4ⁱⁱ hydrogen bond constitutes two D graph-set motifs (Fig. 2; symmetry codes as in Table 2). These motifs all occur within hydrogen-bonded layers formed by dimethyl sulfone molecules and ammonium cations parallel to (100), alternating with anion layers with S···S interanion short contacts (Fig. 3). It has been shown that such S···S contacts can dominate crystal structure packing in thiocyanate complex salts, even in the presence of hydrogen bonds (Jana et al., 2007). In (I), all thiocyanate S atoms are involved in such contacts, of which two types are present: S1···S3^vii = 3.470 (2) Å within the anion layer (Fig. 3), and S2···S2^iv, an interlayer contact [symmetry codes: (iv) -x, -y + 1, -z; (vii) x, y + 1, z]. We note that the C—S bond for the thiocyanate involved in the latter contact, S2···S2^iv, is slightly longer than those in the other thiocyanate ligands (Table 1). Similar S···S contacts [but longer, 4.114 (4) Å] were observed for the tetrabutylammonium salt (Gonzalez et al., 2008).

Compound (I) will be used as a starting material in reactions with amines, with possible further aggregation to products of interest for their magnetic and/or catalytic properties.

Related literature

For related literature, see: Bandy et al. (1981); Biagini et al. (2004); Coles et al. (2003); Cotton & Felthouse (1981); Dikarev et al. (2003); Dinda et al. (2009); Etter et al. (1990); Fronczek (2006, 2007); Gonzalez et al. (2008); Jana et al. (2007); Langs et al. (1970); Małecka et al. (2002); Sands (1963); Watt & Thompson (1963).

S2. Experimental

The synthesis was carried out in a Berghoff BF-100 autoclave under a nitrogen atmosphere. A 150 ml Teflon vessel was charged with (NH₄)₂ReCl₆ (1.20 g) [prepared according to Watt & Thompson (1963)], dimethyl sulfone (15 g) and NH₄SCN (3.50 g). The vessel was sealed under nitrogen at a primary pressure of 0.5 bar (1 bar = 100 000 Pa). The reaction was carried out at 393 K. During the reaction, the pressure rose to 3.5 bar. After 20 h of continuous stirring and heating at 393 K. the reaction mixture was cooled to room temperature and extracted with distilled water in order to remove part of the solvent. The remaining solid product (4.50 g) was dried over P₄O₁₀ in a desiccator. The solid was dissolved in acetonitrile (100 ml) and concentrated on a rotary evaporator. From the cooled solution, a red–brown precipitate (2.01 g) was obtained, which was soluble in acetone, acetonitrile, dimethylformamide and chloroform. Product homogeneity was checked by means of thin-layer chromatography on a silica-gel-coated plate (0.2 mm layer) using dichloromethane as a developing solvent, and the product was found to be a mixture of different compounds. Separation was carried out using column chromatography on a column filled with silica gel 60 (0.063–0.20 mm, MN Kieselgel 60; height 50 cm, diameter 1.5 cm). The product mixture, dissolved in dichloromethane (30 ml), was introduced onto the column and the eluent used was dichloromethane–methanol–acetonitrile (20:3:2 v/v). In the course of the separation, one orange fraction and one yellow fraction were obtained (the yellow fraction appeared second, in small quantity). Compound (I) crystallized from the first fraction (yield 75%). The yellow by-product was characterized by elemental analysis and IR spectroscopy, but the results were ambiguous. Spectroscopic analysis for the title compound, (I): IR bands (Medium?, ν, cm^-1): 547 (m), 494 (vs), 458 (vs), 301 (vs), 182 (m), 87 (s), 2916 (vs), 2844 (vs), 2399 (m), 2324 (m) 2259 (m) 2192 (m), 2053 (vs), 1641 (s), 1454 (vs), 1375 (vs), 1130 (vs), 934 (s), 760 (s), 697 (s), 494 (m), 459 (s). Interpretation of selected bands: 2399–2053 cm^-1: stretching M-NCS modes; 934–760 cm^-1 stretching M-NCS modes; 494 and 459 cm^-1: deformation M-NCS modes. Elemental analysis, calculated: C 17.74, H 3.40, N 11.82, S 33.84%; found: C 17.01, H 3.20, N 11.10, S 33.56%.

S3. Refinement

Methyl H atoms were initially placed at positions determined on the basis of a local difference Fourier map and then refined as riding atoms (C—H 0.98 Å), with rotational freedom about their respective local C—S bonds, and with U_iso(H) = 1.5U_eq(C). Ammonium H atoms were found in a difference Fourier map, adjusted to N—H = 0.910 (3) Å and H···H = 1.50 (1) Å using restraints, and then refined as riding atoms, with U_iso(H) = 1.2U_eq(N). The highest peak in the final difference Fourier map (0.88 e Å^-3) was found 0.97 Å from atom Re1.

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2009); cell refinement: CrysAlis RED (Oxford Diffraction, 2009); data reduction: CrysAlis RED (Oxford Diffraction, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2010) and SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. The hexakis(thiocyanato-κN)rhenate(IV) anion of (I). Displacement ellipsoids are drawn at 30% probability level. [Symmetry code: (i) -x + 1, -y + 1, -z.]
	Fig. 2. Hydrogen-bonded cation–solvent layers, with the ring graph-set motif indicated. Hydrogen bonds are displayed as dashed lines. C and H atoms are shown as sticks for clarity. [Symmetry codes: (ii) -x, y - 1/2, -z + 1/2; (iii) x, y - 1, z; (iv) -x, -y + 1, -z; (v) -x, -y, -z.]
	Fig. 3. Puckered hydrogen-bonded layers containing dimethyl sulfone molecules and ammonium cations, alternating with hexakis(thiocyanato-κN)rhenate(IV) anion layers with S···S contacts, both parallel to (100). Hydrogen bonds are drawn as dashed lines.

Diammonium hexakis(thiocyanato-κN)rhenate(IV) dimethyl sulfone tetrasolvate

Crystal data

(NH4)2[Re(NCS)6]·4C2H6O2S	F(000) = 942
Mr = 947.28	Dx = 1.787 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 3295 reflections
a = 13.128 (3) Å	θ = 2.9–28.7°
b = 9.493 (3) Å	µ = 4.09 mm^−1
c = 15.412 (4) Å	T = 100 K
β = 113.57 (3)°	Plate, red
V = 1760.5 (8) Å^3	0.15 × 0.12 × 0.05 mm
Z = 2

Data collection

Oxford KM-4 CCD area-detector diffractometer	4234 independent reflections
Radiation source: fine-focus sealed tube	3483 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.025
ω scans	θmax = 28.7°, θmin = 2.9°
Absorption correction: analytical (CrysAlis RED; Oxford Diffraction, 2009)	h = −16→17
Tmin = 0.789, Tmax = 0.956	k = −11→12
11719 measured reflections	l = −20→18

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)] = 0.023	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.057	H-atom parameters constrained
S = 1.00	w = 1/[σ^2(Fo^2) + (0.0355P)^2] where P = (Fo^2 + 2Fc^2)/3
4234 reflections	(Δ/σ)max < 0.001
191 parameters	Δρmax = 0.88 e Å^−3
0 restraints	Δρmin = −0.74 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
Re1	0.5000	0.5000	0.0000	0.01558 (5)
S1	0.68450 (6)	0.75836 (8)	0.28721 (5)	0.02761 (16)
S2	0.14184 (6)	0.48764 (7)	0.01508 (5)	0.02210 (14)
S3	0.60694 (6)	0.09692 (8)	0.20140 (5)	0.02721 (16)
N1	0.57362 (18)	0.6110 (2)	0.11976 (15)	0.0198 (5)
N2	0.3534 (2)	0.4999 (2)	0.01489 (16)	0.0186 (4)
N3	0.54292 (18)	0.3228 (2)	0.07720 (15)	0.0198 (5)
C1	0.6206 (2)	0.6722 (3)	0.19103 (18)	0.0191 (5)
C2	0.2655 (2)	0.4937 (3)	0.01572 (17)	0.0167 (5)
C3	0.5698 (2)	0.2285 (3)	0.13033 (18)	0.0197 (5)
S4	0.04600 (5)	0.82492 (7)	0.21610 (4)	0.01637 (13)
O1	−0.00998 (14)	0.88909 (19)	0.12332 (12)	0.0207 (4)
O2	−0.01961 (15)	0.8121 (2)	0.27206 (12)	0.0251 (4)
C4	0.0937 (2)	0.6585 (3)	0.20212 (18)	0.0240 (6)
H4A	0.0303	0.5984	0.1655	0.036*
H4B	0.1347	0.6162	0.2645	0.036*
H4C	0.1429	0.6672	0.1685	0.036*
C5	0.1674 (2)	0.9218 (3)	0.27910 (18)	0.0226 (6)
H5A	0.2103	0.8745	0.3392	0.034*
H5B	0.1472	1.0168	0.2916	0.034*
H5C	0.2124	0.9282	0.2416	0.034*
S5	0.25241 (5)	0.57269 (7)	0.51536 (4)	0.01698 (13)
O3	0.17912 (16)	0.5437 (2)	0.56340 (13)	0.0227 (4)
O4	0.20792 (16)	0.6655 (2)	0.43481 (13)	0.0247 (4)
C6	0.2918 (2)	0.4133 (3)	0.47956 (19)	0.0241 (6)
H6A	0.3425	0.4327	0.4486	0.036*
H6B	0.2255	0.3649	0.4351	0.036*
H6C	0.3292	0.3534	0.5351	0.036*
C7	0.3755 (2)	0.6439 (3)	0.59830 (19)	0.0275 (6)
H7A	0.3593	0.7327	0.6226	0.041*
H7B	0.4274	0.6614	0.5681	0.041*
H7C	0.4090	0.5774	0.6507	0.041*
N4	0.03350 (17)	0.1804 (2)	0.06881 (14)	0.0177 (4)
H1	0.1069	0.2025	0.0990	0.021*
H2	−0.0071	0.2370	0.0907	0.021*
H3	0.0240	0.0888	0.0818	0.021*
H4	0.0111	0.1926	0.0053	0.021*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Re1	0.01127 (8)	0.01794 (8)	0.01593 (7)	0.00087 (6)	0.00376 (5)	0.00062 (6)
S1	0.0290 (4)	0.0239 (4)	0.0205 (3)	0.0036 (3)	0.0000 (3)	−0.0025 (3)
S2	0.0151 (3)	0.0285 (4)	0.0246 (3)	−0.0019 (3)	0.0100 (3)	0.0005 (3)
S3	0.0250 (4)	0.0234 (4)	0.0312 (4)	0.0013 (3)	0.0090 (3)	0.0092 (3)
N1	0.0133 (11)	0.0228 (12)	0.0208 (11)	0.0024 (9)	0.0043 (9)	0.0011 (9)
N2	0.0155 (11)	0.0196 (11)	0.0203 (11)	0.0011 (10)	0.0066 (8)	0.0008 (9)
N3	0.0149 (11)	0.0208 (12)	0.0218 (11)	0.0004 (9)	0.0054 (9)	0.0002 (9)
C1	0.0156 (13)	0.0187 (14)	0.0213 (12)	0.0043 (11)	0.0056 (10)	0.0050 (11)
C2	0.0193 (13)	0.0147 (12)	0.0142 (11)	0.0018 (11)	0.0048 (9)	0.0014 (10)
C3	0.0133 (13)	0.0225 (14)	0.0217 (13)	−0.0013 (11)	0.0055 (10)	−0.0049 (11)
S4	0.0147 (3)	0.0211 (3)	0.0134 (3)	−0.0001 (3)	0.0057 (2)	0.0023 (2)
O1	0.0177 (10)	0.0272 (11)	0.0151 (8)	0.0002 (8)	0.0045 (7)	0.0056 (8)
O2	0.0221 (10)	0.0366 (12)	0.0220 (9)	0.0040 (9)	0.0146 (8)	0.0086 (8)
C4	0.0228 (15)	0.0244 (15)	0.0228 (13)	0.0018 (12)	0.0069 (11)	−0.0032 (11)
C5	0.0223 (14)	0.0229 (15)	0.0189 (12)	−0.0054 (12)	0.0044 (11)	−0.0022 (11)
S5	0.0141 (3)	0.0186 (3)	0.0175 (3)	0.0007 (3)	0.0055 (2)	0.0025 (3)
O3	0.0199 (10)	0.0272 (10)	0.0233 (10)	−0.0028 (8)	0.0112 (8)	0.0001 (8)
O4	0.0270 (11)	0.0249 (11)	0.0212 (9)	0.0053 (9)	0.0084 (8)	0.0079 (8)
C6	0.0210 (15)	0.0227 (15)	0.0295 (14)	0.0044 (12)	0.0110 (12)	−0.0004 (12)
C7	0.0200 (15)	0.0277 (16)	0.0288 (14)	−0.0042 (12)	0.0034 (12)	0.0010 (12)
N4	0.0183 (11)	0.0175 (11)	0.0188 (10)	−0.0001 (9)	0.0092 (9)	−0.0026 (9)

Geometric parameters (Å, º)

Re1—N1	2.006 (2)	C4—H4C	0.9800
Re1—N1^i	2.006 (2)	C5—H5A	0.9800
Re1—N2	2.027 (2)	C5—H5B	0.9800
Re1—N3	2.006 (2)	C5—H5C	0.9800
Re1—N3^i	2.007 (2)	S5—O4	1.4415 (19)
Re1—N2^i	2.027 (2)	S5—O3	1.456 (2)
S1—C1	1.605 (3)	S5—C7	1.747 (3)
S2—C2	1.621 (3)	S5—C6	1.758 (3)
S3—C3	1.603 (3)	C6—H6A	0.9800
N1—C1	1.175 (3)	C6—H6B	0.9800
N2—C2	1.160 (4)	C6—H6C	0.9800
N3—C3	1.169 (3)	C7—H7A	0.9800
S4—O1	1.4545 (18)	C7—H7B	0.9800
S4—O2	1.4472 (18)	C7—H7C	0.9800
S4—C4	1.745 (3)	N4—H1	0.9114
S4—C5	1.758 (3)	N4—H2	0.9114
C4—H4A	0.9800	N4—H3	0.9114
C4—H4B	0.9800	N4—H4	0.9094
N1—Re1—N1^i	180.0	H4B—C4—H4C	109.5
N1—Re1—N3	88.69 (8)	S4—C5—H5A	109.5
N1^i—Re1—N3	91.31 (8)	S4—C5—H5B	109.5
N1—Re1—N3^i	91.31 (8)	H5A—C5—H5B	109.5
N1^i—Re1—N3^i	88.69 (8)	S4—C5—H5C	109.5
N3—Re1—N3^i	180.0	H5A—C5—H5C	109.5
N1—Re1—N2	91.49 (9)	H5B—C5—H5C	109.5
N1^i—Re1—N2	88.51 (9)	O4—S5—O3	115.53 (12)
N3—Re1—N2	89.24 (9)	O4—S5—C7	109.37 (14)
N3^i—Re1—N2	90.76 (9)	O3—S5—C7	107.90 (13)
N1—Re1—N2^i	88.51 (9)	O4—S5—C6	108.93 (13)
N1^i—Re1—N2^i	91.49 (9)	O3—S5—C6	109.50 (13)
N3—Re1—N2^i	90.76 (9)	C7—S5—C6	105.11 (14)
N3^i—Re1—N2^i	89.24 (9)	S5—C6—H6A	109.5
N2—Re1—N2^i	180.0	S5—C6—H6B	109.5
C1—N1—Re1	177.1 (2)	H6A—C6—H6B	109.5
C2—N2—Re1	173.9 (2)	S5—C6—H6C	109.5
C3—N3—Re1	172.9 (2)	H6A—C6—H6C	109.5
N1—C1—S1	178.9 (2)	H6B—C6—H6C	109.5
N2—C2—S2	178.7 (3)	S5—C7—H7A	109.5
N3—C3—S3	178.7 (2)	S5—C7—H7B	109.5
O2—S4—O1	115.71 (11)	H7A—C7—H7B	109.5
O2—S4—C4	109.05 (13)	S5—C7—H7C	109.5
O1—S4—C4	108.85 (12)	H7A—C7—H7C	109.5
O2—S4—C5	109.81 (13)	H7B—C7—H7C	109.5
O1—S4—C5	108.29 (12)	H1—N4—H2	109.3
C4—S4—C5	104.54 (14)	H1—N4—H3	108.5
S4—C4—H4A	109.5	H2—N4—H3	109.2
S4—C4—H4B	109.5	H1—N4—H4	109.9
H4A—C4—H4B	109.5	H2—N4—H4	109.8
S4—C4—H4C	109.5	H3—N4—H4	110.1
H4A—C4—H4C	109.5

Symmetry code: (i) −x+1, −y+1, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N4—H2···O2^ii	0.91	2.12	2.823 (3)	133
N4—H2···O4^ii	0.91	2.60	3.151 (3)	120
N4—H3···O1^iii	0.91	2.11	3.010 (3)	172
N4—H4···O1^iv	0.91	2.12	2.927 (3)	147

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