Crystal structure of N,N,N′,N′,N′′,N′′-hexa­methyl­guanidinium cyanate 1.5-hydrate

Ioannis Tiritiris; Willi Kantlehner

doi:10.1107/S2056989015024317

. 2015 Dec 24;71(Pt 12):o1076–o1077. doi: 10.1107/S2056989015024317

Crystal structure of N,N,N′,N′,N′′,N′′-hexamethylguanidinium cyanate 1.5-hydrate

Ioannis Tiritiris ^a, Willi Kantlehner ^a,^*

PMCID: PMC4719987 PMID: 26870506

Abstract

The title hydrated salt, C₇H₁₈N₃ ⁺·OCN⁻.1.5H₂O, was synthesized starting from N,N,N′,N′,N′′,N′′-hexamethylguanidinium chloride by a twofold anion-exchange reaction. The asymmetric unit contains two cations, two cyanate anions and three water molecules. One cation shows orientational disorder and two sets of N-atom positions were found related by a 60° rotation, with an occupancy ratio of 0.852 (6):0.148 (6). The C—N bond lengths in both guanidinium ions range from 1.329 (2) to 1.358 (10) Å, indicating double-bond character, pointing towards charge delocalization within the NCN planes. Strong O—H⋯N hydrogen bonds between the crystal water molecules and the cyanate ions and strong O—H⋯O hydrogen bonds between the water molecules are present, resulting in a two-dimensional hydrogen bonded network running parallel to the (001) plane. The hexamethylguanidinium ions are packed in between the layers built up by water molecules and cyanate ions.

Keywords: crystal structure, cyanate, hexamethylguanidinium, salt, O—H⋯O hydrogen bonds, O—H⋯N hydrogen bonds

Related literature

For the synthesis of hexasubstituted guanidinium salts with different anions, see: Kantlehner et al. (1984 ▸). For the crystal structure of N,N,N′,N′,N′′,N′′-hexamethylguanidinium chloride, see: Oelkers & Sundermeyer (2011 ▸). For the crystal structure of N,N,N′,N′,N′′,N′′-hexamethylguanidinium difluorotrimethylsilicate, see: Röschenthaler et al. (2002 ▸). For the crystal structure of N,N,N′,N′,N′′,N′′-hexamethylguanidinium tetraphenylborate, see: Frey et al. (1998 ▸). For the crystal structure of N,N,N′,N′,N′′,N′′-hexamethylguanidinium fluoride, see: Kolomeitsev et al. (2000 ▸). For the crystal structure of N,N,N′,N′,N′′,N′′-hexamethylguanidinium hexafluorosilicate hexahydrate, see: Zhang et al. (1999 ▸). For the crystal structures of [C(NMe₂)₃][Mn(CO)₅] and [C(NMe₂)₃][Co(CO)₄], see: Petz & Weller (1991 ▸). For a neutron diffraction studie of deuterated ammonium cyanate, see: MacLean et al. (2003 ▸). For the use of intensity quotients and differences in absolute structure refinement, see: Parsons et al. (2013 ▸).

Experimental

Crystal data

2C₇H₁₈N₃ ⁺·2CNO⁻·3H₂O
M _r = 426.58
Monoclinic,
a = 8.3245 (5) Å
b = 22.536 (2) Å
c = 13.2580 (12) Å
β = 108.092 (7)°
V = 2364.2 (3) Å³
Z = 4
Mo Kα radiation
μ = 0.09 mm⁻¹
T = 100 K
0.40 × 0.25 × 0.10 mm

Data collection

Bruker Kappa APEXII DUO diffractometer
19766 measured reflections
5588 independent reflections
5279 reflections with I > 2σ(I)
R _int = 0.025
Standard reflections: 0

Refinement

R[F ² > 2σ(F ²)] = 0.034
wR(F ²) = 0.089
S = 1.02
5588 reflections
328 parameters
2 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.40 e Å⁻³
Δρ_min = −0.19 e Å⁻³

Data collection: APEX2 (Bruker, 2008 ▸); cell refinement: SAINT (Bruker, 2008 ▸); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▸); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015 ▸); molecular graphics: DIAMOND (Brandenburg & Putz, 2005 ▸); software used to prepare material for publication: SHELXL2014.

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S2056989015024317/rz5180sup1.cif

e-71-o1076-sup1.cif^{(600.9KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989015024317/rz5180Isup2.hkl

e-71-o1076-Isup2.hkl^{(306.3KB, hkl)}

Click here for additional data file.^{(1.1MB, tif)}

. DOI: 10.1107/S2056989015024317/rz5180fig1.tif

The structure of the title compound with displacement ellipsoids at the 50% probability level. All hydrogen atoms are omitted for clarity. Only the major component of the disordered cation is shown.

Click here for additional data file.^{(1.8MB, tif)}

. DOI: 10.1107/S2056989015024317/rz5180fig2.tif

The structure of the orientationally disordered cation. The nitrogen atoms are disordered between the opaque and dark positions.

Click here for additional data file.^{(1.1MB, tif)}

c . DOI: 10.1107/S2056989015024317/rz5180fig3.tif

O—H⋯N and O—H⋯O hydrogen bonds (black dashed lines) between anions and water molecules and between the water molecules (view down the c axis).

Click here for additional data file.^{(1.1MB, tif)}

c . DOI: 10.1107/S2056989015024317/rz5180fig4.tif

View down the c axis of the two-dimensional O—H⋯N and O—H⋯O hydrogen-bonding network (all hydrogen bonds are indicated by black dashed lines).

Click here for additional data file.^{(1.2MB, tif)}

a . DOI: 10.1107/S2056989015024317/rz5180fig5.tif

Packing of the guanidinium ions in between the layers build up by water molecules and cyanate ions (down the a axis).

CCDC reference: 867308

Additional supporting information: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O3—H31⋯N2	0.78 (3)	2.00 (3)	2.780 (3)	176 (3)
O3—H32⋯O5ⁱ	0.86 (4)	2.00 (4)	2.858 (4)	172 (3)
O4—H42⋯O3ⁱⁱ	0.83 (4)	2.04 (4)	2.852 (4)	164 (3)
O4—H41⋯N1ⁱⁱ	0.84 (3)	2.00 (3)	2.833 (3)	173 (3)
O5—H51⋯O2ⁱⁱⁱ	0.85 (3)	1.92 (3)	2.761 (3)	175 (3)
O5—H52⋯O1^iv	0.74 (4)	2.10 (4)	2.840 (4)	177 (3)

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) ; (iv) .

Acknowledgments

The authors thank Dr W. Frey (Institut für Organische Chemie, Universität Stuttgart) for measuring the diffraction data.

supplementary crystallographic information

S1. Comment

The reaction of phosgene with N,N,N',N'-tetramethylurea yields N,N,N',N'-tetramethylchloroformamidinium chloride, which can be transformed by a mixture of dimethylamine and triethylamine into a mixture of N,N,N',N',N'',N''-hexamethylguanidinium chloride and triethylamine hydrochloride. Treating the salt mixture with an aqueous sodium hydroxide solution leads after work up to the pure guanidinium chloride. Conversion of the chloride to the tetrafluoroborate salt occurs by heating it with BF₃O(C₂H₅)₂ (Kantlehner et al., 1984). A further anion exchange was possible by reacting N,N,N',N',N'',N''-hexamethylguanidinium tetrafluoroborate with potassium cyanate in water. According to the structure analysis of the title compound, the asymmetric unit contains two N,N,N',N',N'',N''-hexamethylguanidinium (HMG⁺) ions, two cyanate ions and three water molecules (Fig. 1). One cation (cation I) shows an orientational disorder and two sets of N positions were found related by a 60° rotation, with an occupancy ratio of 0.852 (6):0.148 (6). This leads to the characteristic star-shaped appearance of the HMG⁺ ion (Fig. 2). The second cation (cation II) is not disordered. Searching for known crystal structures in literature of N,N,N',N',N'',N''-hexamethylguanidinium salts [see, for example: chloride salt (Oelkers & Sundermeyer, 2011), difluorotrimethylsilicate salt (Röschenthaler et al., 2002), tetraphenylborate salt (Frey et al., 1998), fluoride salt (Kolomeitsev et al., 2000), hexafluorosilicate hexahydrate salt (Zhang et al., 1999), [Mn(CO)₅] and [Co(CO)₄] salts (Petz & Weller, 1991)], it is obvious that in all those compounds the HMG⁺ ions are orientationally disordered too. In the title salt, the C–N bond lengths of both cations are in a range from 1.329 (2) and 1.358 (10) Å, indicating double bond character. The CN₃ units are planar and the N–C–N angles are ranging from 118.0 (7)° to 121.8 (7)°. The positive charge is completely delocalized in the CN₃ plane. The N–C bond lengths in the non-disordered guanidinium ion (cation II) are in a typical range from 1.453 (3) to 1.475 (2) Å, characteristic for a N–C single bond. In the disordered one (cation I), some N–C bond lengths deviate from their typical values and appear to be slightly longer [d(N–C) = 1.464 (3) − 1.655 (10) Å]. The N–C and C–O bond lengths in both cyanate ions [d(N–C) = 1.165 (3) and 1.172 (3) Å; d(C–O) = 1.213 (3) and 1.230 (3) Å] are in very good agreement with the data determined from a neutron diffraction study of deuterated ammonium cyanate (ND₄OCN) at 14 K [d(N–C) = 1.191 (5) Å and d(C–O) =) 1.215 (5) Å (MacLean et al., 2003)]. Strong O–H···N hydrogen bonds between the crystal water molecules and the cyanate ions [d(H···N) = 2.00 (3) Å (Tab. 1)] and strong O–H···O hydrogen bonds between the water molecules are present [d(H···O) = 1.92 (3) − 2.10 (4) Å (Tab. 1)] (Fig. 3), resulting in a two-dimensional hydrogen bonded network parallel to the (0 0 1) plane (Fig. 4). Additionally, C–H···N and C–H···O interactions between the H atoms of the guanidinium –N(CH₃)₂ groups and the cyanate ions are present [d(H···N) = 2.52 – 2.61 Å; d(H···O) = 2.46 – 2.60 Å]. The hexamethylguanidinium ions are packed in between the layers build up by water molecules and cyanate ions (Fig. 5).

S2. Experimental

To a solution of 10 g (0.043 mol) N,N,N',N',N'',N''-hexamethylguanidinium tetrafluoroborate in water, 3.51 g (0.043 mol) potassium cyanate in 20 ml water was added. The solution was kept for twelve hours at 273 K and the precipitated potassium tetrafluoroborate was removed by filtration. After removing of the water, the residue was redissolved in acetonitrile and the solution was filtered again to remove the insoluble residue. The title compound crystallized from a saturated acetonitrile solution after several days at 273 K, forming colorless single crystals. Yield: 7.05 g (88%).