A 1:1 solvate structure of succino­nitrile and lithium thio­cyanate

Burba, C.M.; Powell, D.R.

doi:10.1107/S2056989022011094

research communications

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 78| Part 12| December 2022| Pages 1284-1287

https://doi.org/10.1107/S2056989022011094

Open

access

A 1:1 solvate structure of succinonitrile and lithium thiocyanate

Christopher M. Burba ^a ^* and Douglas R. Powell ^b

^aDepartment of Natural Sciences, Northeastern State University, 611 N. Grand Ave., Tahlequah, OK 74464, USA, and ^bDepartment of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson Parkway, Norman, OK 73019, USA
^*Correspondence e-mail: burba@nsuok.edu

Edited by M. Zeller, Purdue University, USA (Received 5 October 2022; accepted 18 November 2022; online 30 November 2022)

A 1:1 solvate structure of succinonitrile and lithium thiocyanate, namely, catena-poly[lithium-di-μ-thiocyanato-lithium-di-μ-butanedinitrile], [Li(NCS)(C₄H₄N₂)]_n or LiSCN·NC(CH₂)₂CN, was isolated and its structure was solved. Lithium ions are tetrahedrally coordinated by two nitrile groups from separate succinonitrile molecules, as well as S and N atoms of separate SCN⁻ anions. The succinonitrile molecules and Li⁺ ions form double-chain one-dimensional coordination polymers that are bridged by Li₂(SCN)₂ dimers. The coordination network extends along [ $[\overline{1}]$ 01]. Weak hydrogen-bonding interactions are also noted among the constituent molecules.

Keywords: lithium battery; plastic crystalline electrolyte; X-ray diffraction; crystal structure.

CCDC reference: 2220707

1. Chemical context

Most commercial lithium-ion batteries employ liquid-phase electrolyte solutions that are composed of organic solvents and lithium salts. It is now well documented, however, that these materials can present consumer safety risks (Chen et al., 2021 ). For example, internal electrical shortages may lead to thermal runaway and solvent combustion. The battery community has responded to this problem by pursuing safer alternatives to `traditional' electrolyte solutions, such as all-solid-state polymer electrolytes (Armand, 1994 ; Zhou et al., 2019 ). Despite the advantages provided by solid-state electrolytes, there are significant technological issues preventing their widespread commercialization (Zhou et al., 2019). For example, lithium-ion batteries require highly conductive electrolyte systems (>10⁻³ S cm⁻¹) to support rapid charging and discharging rates. This requirement is probably the most formidable challenge currently facing polymer electrolytes since most candidate materials simply do not have high enough ionic conductivities to be commercially competitive.

Alternative solid-state ion conductors, such as those created from plastic crystalline materials (Zhou et al., 2019; Zhu et al., 2019 ), are able to deliver high ionic conductivities without sacrificing mechanical integrity. Plastic crystalline materials possess long-range translational order with some degree of orientational or conformational disorder. Alarco and coworkers (2004 ) examined a family of plastic crystalline electrolytes based on succinonitrile, a highly polar compound (dielectric constant ɛ = 66; Williams & Smyth, 1962 ) capable of solvating lithium ions. These materials deliver good electrochemical performance and are promising candidates for lithium battery applications (Alarco et al., 2004).

Our contribution to this field is the isolation and analysis of a solvate structure formed between lithium thiocyanate and succinonitrile that we collected from a mixture of the two components. Additional details about the crystalline material and subsequent structure determination may be found in the Synthesis and Crystallization section. The crystallographic information reveals cation–solvent and cation–anion interaction motifs that may guide the design of next generation plastic crystalline electrolytes for lithium-ion battery applications.

2. Structural commentary

The succinonitrile lithium thiocyanate solvate, LiSCN·NC(CH₂)₂CN, belongs to the P2₁/n space group with Z = 4. A displacement ellipsoid plot constituting the asymmetric unit with the atom-labeling scheme is shown in Fig. 1. Projections of the unit cell along the a, b, and c crystallographic axes are provided in Fig. 2, and the Li⁺ coordination environment and cation–succinonitrile interactions are depicted in Fig. 3. Lithium ions are tetrahedrally coordinated in LiSCN·NC(CH₂)₂CN. Two of the ligating N atoms originate from two different succinonitrile molecules, yielding one-dimensional coordination polymer chains composed of cations and succinonitrile. Each Li⁺ ion is also coordinated by S and N atoms from two different thiocyanate anions to produce Li₂(SCN)₂ dimers that link adjacent lithium–succinonitrile polymer chains. The resulting double-chain network is oriented along [ $[\overline{1}]$ 01] (see Fig. 4).

Figure 1
The asymmetric unit of LiSCN·NC(CH₂)₂CN solvate structure. Displacement ellipsoids are shown at the 50% probability level.

Figure 2
Projections of the unit cell for LiSCN·NC(CH₂)₂CN along the a (left), b (center), and c (right) axes. Hydrogen atoms are omitted for clarity.

Figure 3
Coordination environments for Li⁺, SCN⁻, and succinonitrile with atom labeling. Symmetry codes: (i) 1 − x, 1 − y, 2 − z; (ii) x − $[{1\over 2}]$ , $[{3\over 2}]$ − y, z + $[{1\over 2}]$ ; (iii) x + $[{1\over 2}]$ , $[{3\over 2}]$ − y, z − $[{1\over 2}]$ ; (vii) $[{3\over 2}]$ − x, y − $[{1\over 2}]$ , $[{3\over 2}]$ − z; (viii) $[{3\over 2}]$ − x, $[{1\over 2}]$ + y, $[{3\over 2}]$ − z.

Figure 4
Double-chain structure of LiSCN·NC(CH₂)₂CN when viewed along the b axis. Hydrogen atoms are omitted for clarity.

The cation–anion Li1—N1 bond [1.985 (3) Å] is shorter than either Li–N bond formed between Li⁺ and the nitrile groups of succinonitrile [Li1—N1A = 2.028 (3) Å and Li1—N2Aⁱⁱ = 2.093 (2) Å; symmetry code: (ii) x − $[{1\over 2}]$ , $[{3\over 2}]$ − y, z + $[{1\over 2}]$ ]. By way of comparison, Li1—S1ⁱ is relatively longer at 2.572 (3) Å [symmetry code: (i) 1 − x, 1 − y, 2 − z]. The tetrahedral coordination environment about Li⁺ is somewhat distorted with bond angles centered on the cation ranging from 125.75 (13) to 98.67 (9)°. The Li1—N1A—C1A bond angle approaches a linear geometry [170.60 (13)°], whereas Li1ⁱⁱⁱ—N2A—C4A is noticeably bent [155.39 (13)°; symmetry code: (iii) x + $[{1\over 2}]$ , $[{3\over 2}]$ − y, z − $[{1\over 2}]$ ]. By way of comparison, the Li1—N1—C1 and Li1—S1ⁱ—C1ⁱ bond angles are 159.26 (12) and 96.67 (6)°, respectively. The succinonitrile molecules adopt a gauche conformation with a 66.04 (13)° C1A—C2A—C3A—C4A torsion angle and comparable C≡N bond lengths. Both are similar to the low-temperature α phase of pure succinonitrile (Hore et al., 2009 ; Whitfield, et al., 2008 ).

3. Supramolecular features

Possible hydrogen bonds between C—H groups of succinonitrile and N or S atoms are detected in LiSCN·NC(CH₂)₂CN (Table 1). These interactions have relatively long distances and are of low directionality. Hence, we classify the hydrogen bonds as weak.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C2A—H2AA⋯S1^iv	0.99	2.93	3.5212 (15)	120
C2A—H2AB⋯N1^v	0.99	2.63	3.4159 (17)	137
C3A—H3AA⋯N2A^vi	0.99	2.61	3.4232 (17)	140
C3A—H3AB⋯N1^vi	0.99	2.54	3.4257 (17)	150
Symmetry codes: (iv) ; (v) ; (vi) $[x-{\script{1\over 2}}, -y+{\script{3\over 2}}, z-{\script{1\over 2}}]$ .

4. Database survey

The structure of the SCN⁻ anion in our solvate structure may be compared against the LiSCN·xH₂O (x = 0, 1, and 2) family of compounds. Joos et al. (2022 ) report crystallographic data for two phases of LiSCN·H₂O: a room-temperature phase with space group C2/m and a high-temperature phase with space group Pnam. The structures for LiSCN and LiSCN·2H₂O, both belonging to space group Pnma, are provided by Reckeweg et al. (2014 ). Structural parameters for the anions in these compounds are similar to each other and to LiSCN·NC(CH₂)₂CN. The C1=S1 and C1=N1 bond lengths in LiSCN·NC(CH₂)₂CN [1.646 (1) and 1.167 (2) Å, respectively] are comparable to those found in LiSCN (1.643 and 1.162 Å, respectively). Furthermore, the C1=N1 bond length is only slightly longer than those reported for the LiSCN hydrates (e.g., the average length is 1.167 Å for LiSCN·xH₂O). Finally, the 178.0 (1)° S1—C1—N1 bond angle in LiSCN·NC(CH₂)₂CN only deviates slightly from a linear geometry and is closest in value to that found in LiSCN·2H₂O (177.55°).

5. Synthesis and crystallization

Succinonitrile (NC(CH₂)₂CN, CAS# 110–61-2) and lithium thiocyanate hydrate (LiSCN·xH₂O, CAS# 123333–85-7) were both obtained from Sigma Aldrich. The LiSCN·xH₂O was dehydrated in a vacuum oven. The two reagents were then stored inside a <1 p.p.m. H₂O, argon-filled dry box. A total of 0.3005 g of LiSCN was mixed with 0.5550 g of succinonitrile, and gentle heating on a hot plate promoted dissolution of the salt into the solvent. The resulting solution was stored under argon gas until crystals of sufficient size formed. A colorless, block-shaped crystal of dimensions 0.272 mm × 0.274 mm × 0.368 mm was selected for structural analysis.

6. Refinement

Crystal data, data collection, and structure refinement details are summarized in Table 2. The positions of hydrogen atoms bonded to carbon atoms were initially determined by geometry and were refined using a riding model. Non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atom displacement parameters were set to 1.2 times the isotropic equivalent displacement parameters of the bonded atoms.

Table 2
Experimental details

Crystal data
Chemical formula	[Li(NCS)(C₄H₄N₂)]
M_r	145.11
Crystal system, space group	Monoclinic, P2₁/n
Temperature (K)	100
a, b, c (Å)	7.5802 (13), 11.868 (3), 8.2724 (16)
β (°)	104.155 (7)
V (Å³)	721.6 (3)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.36
Crystal size (mm)	0.37 × 0.27 × 0.27

Data collection
Diffractometer	Area detector κ–geometry diffractometer
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.403, 0.490
No. of measured, independent and observed [I > 2σ(I)] reflections	33422, 2400, 2210
R_int	0.097
(sin θ/λ)_max (Å⁻¹)	0.735

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.049, 0.140, 1.04
No. of reflections	2400
No. of parameters	92
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.41, −0.36
Computer programs: APEX3 (Bruker, 2018 ), SAINT (Bruker, 2016 ), SHELXT2014/5 (Sheldrick, 2015a ), SHELXL2018/3 (Sheldrick, 2015b ), and Mercury (Macrae et al., 2020 ).

Supporting information

CCDC reference: 2220707

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989022011094/zl5037sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989022011094/zl5037Isup2.hkl

checkCIF report

Computing details top

Data collection: APEX3 (Bruker, 2018); cell refinement: SAINT (Bruker, 2016); data reduction: SAINT (Bruker, 2016); program(s) used to solve structure: SHELXT2014/5 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015b); molecular graphics: Mercury (Macrae et al., 2020); software used to prepare material for publication: SHELXL2018/3 (Sheldrick, 2015b).

catena-Poly[lithium-di-µ-thiocyanato-lithium-di-µ-butanedinitrile] top

Crystal data top

[Li(NCS)(C₄H₄N₂)]	F(000) = 296
M_r = 145.11	D_x = 1.336 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 7.5802 (13) Å	Cell parameters from 8809 reflections
b = 11.868 (3) Å	θ = 2.8–33.7°
c = 8.2724 (16) Å	µ = 0.36 mm⁻¹
β = 104.155 (7)°	T = 100 K
V = 721.6 (3) Å³	Block, colourless
Z = 4	0.37 × 0.27 × 0.27 mm

Data collection top

Area detector κ–geometry diffractometer	2400 independent reflections
Radiation source: microfocus sealed tube, Incoatec IµS 3.0	2210 reflections with I > 2σ(I)
Multilayer mirror monochromator	R_int = 0.097
ω and φ scans	θ_max = 31.5°, θ_min = 3.1°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −11→11
T_min = 0.403, T_max = 0.490	k = −17→17
33422 measured reflections	l = −12→12

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.049	H-atom parameters constrained
wR(F²) = 0.140	w = 1/[σ²(F_o²) + (0.0936P)² + 0.2195P] where P = (F_o² + 2F_c²)/3
S = 1.04	(Δ/σ)_max = 0.001
2400 reflections	Δρ_max = 0.41 e Å⁻³
92 parameters	Δρ_min = −0.36 e Å⁻³
0 restraints	Extinction correction: SHELXL2018/3 (Sheldrick 205b8), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: shelxt	Extinction coefficient: 0.044 (16)

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
S1	0.76963 (4)	0.62537 (2)	1.19303 (4)	0.02384 (15)
N1	0.49689 (16)	0.62469 (8)	0.89339 (15)	0.0233 (2)
C1	0.61234 (16)	0.62517 (8)	1.01617 (15)	0.0184 (2)
Li1	0.2669 (3)	0.5822 (2)	0.7318 (3)	0.0262 (4)
N1A	0.27232 (17)	0.59303 (10)	0.48836 (14)	0.0290 (3)
N2A	0.50670 (16)	0.86047 (9)	0.23500 (16)	0.0267 (2)
C1A	0.25268 (17)	0.60611 (10)	0.34831 (16)	0.0220 (2)
C2A	0.22707 (18)	0.62314 (9)	0.16912 (15)	0.0208 (2)
H2AA	0.116761	0.582051	0.109166	0.025*
H2AB	0.332380	0.590928	0.134143	0.025*
C3A	0.20743 (15)	0.74810 (10)	0.11935 (14)	0.0210 (2)
H3AA	0.174675	0.753955	−0.003771	0.025*
H3AB	0.107091	0.781563	0.160645	0.025*
C4A	0.37413 (15)	0.81229 (9)	0.18592 (14)	0.0207 (2)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
S1	0.0196 (2)	0.0238 (2)	0.0247 (2)	0.00019 (8)	−0.00112 (13)	0.00022 (9)
N1	0.0244 (5)	0.0225 (5)	0.0225 (5)	−0.0005 (3)	0.0045 (4)	0.0044 (3)
C1	0.0176 (5)	0.0168 (5)	0.0218 (5)	0.0005 (3)	0.0067 (4)	0.0020 (3)
Li1	0.0232 (10)	0.0341 (11)	0.0204 (9)	0.0029 (8)	0.0034 (7)	0.0021 (8)
N1A	0.0357 (6)	0.0275 (5)	0.0231 (5)	−0.0024 (4)	0.0061 (4)	0.0007 (4)
N2A	0.0249 (5)	0.0210 (4)	0.0318 (6)	−0.0011 (4)	0.0021 (4)	0.0008 (4)
C1A	0.0227 (5)	0.0210 (5)	0.0220 (5)	−0.0022 (4)	0.0049 (4)	−0.0018 (4)
C2A	0.0231 (5)	0.0229 (5)	0.0174 (5)	−0.0043 (4)	0.0068 (4)	−0.0040 (3)
C3A	0.0180 (4)	0.0260 (5)	0.0180 (5)	−0.0006 (4)	0.0022 (4)	0.0000 (4)
C4A	0.0219 (5)	0.0191 (5)	0.0204 (5)	0.0022 (4)	0.0043 (4)	0.0010 (3)

Geometric parameters (Å, º) top

S1—C1	1.6459 (13)	C1A—C2A	1.4611 (17)
S1—Li1ⁱ	2.572 (3)	C2A—C3A	1.5366 (17)
N1—C1	1.1674 (18)	C2A—H2AA	0.9900
N1—Li1	1.985 (3)	C2A—H2AB	0.9900
Li1—N1A	2.028 (3)	C3A—C4A	1.4628 (16)
Li1—N2Aⁱⁱ	2.093 (2)	C3A—H3AA	0.9900
N1A—C1A	1.1420 (17)	C3A—H3AB	0.9900
N2A—C4A	1.1411 (16)

C1—S1—Li1ⁱ	96.67 (6)	C1A—C2A—H2AA	109.1
C1—N1—Li1	159.26 (12)	C3A—C2A—H2AA	109.1
N1—C1—S1	177.99 (11)	C1A—C2A—H2AB	109.1
N1—Li1—N1A	115.14 (12)	C3A—C2A—H2AB	109.1
N1—Li1—N2Aⁱⁱ	125.75 (13)	H2AA—C2A—H2AB	107.8
N1A—Li1—N2Aⁱⁱ	103.89 (11)	C4A—C3A—C2A	112.56 (10)
N1—Li1—S1ⁱ	102.07 (9)	C4A—C3A—H3AA	109.1
N1A—Li1—S1ⁱ	109.28 (11)	C2A—C3A—H3AA	109.1
N2Aⁱⁱ—Li1—S1ⁱ	98.67 (9)	C4A—C3A—H3AB	109.1
C1A—N1A—Li1	170.60 (13)	C2A—C3A—H3AB	109.1
C4A—N2A—Li1ⁱⁱⁱ	155.39 (13)	H3AA—C3A—H3AB	107.8
N1A—C1A—C2A	179.80 (16)	N2A—C4A—C3A	177.96 (13)
C1A—C2A—C3A	112.68 (10)

C1A—C2A—C3A—C4A	66.04 (13)

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

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C2A—H2AA···S1^iv	0.99	2.93	3.5212 (15)	120
C2A—H2AB···N1^v	0.99	2.63	3.4159 (17)	137
C3A—H3AA···N2A^vi	0.99	2.61	3.4232 (17)	140
C3A—H3AB···N1^vi	0.99	2.54	3.4257 (17)	150

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

Acknowledgements

The authors thank Northeastern State University for access to facilities needed to prepare the crystals. The authors declare no competing financial interests.

Funding information

Funding for this research was provided by: National Science Foundation (grant No. CHE-1726630).

References

Alarco, P.-J., Abu-Lebdeh, Y., Abouimrane, A. & Armand, M. (2004). Nat. Mater. 3, 476–481. CrossRef PubMed CAS Google Scholar
Armand, M. (1994). Solid State Ionics, 69, 309–319. CrossRef CAS Google Scholar
Bruker (2016). SAINT. Bruker Nano Inc., Madison, Wisconsin, USA. Google Scholar
Bruker (2018). APEX3. Bruker Nano Inc., Madison, Wisconsin, USA. Google Scholar
Chen, Y., Kang, Y., Zhao, Y., Wang, L., Liu, J., Li, Y., Liang, Z., He, X., Li, X., Tavajohi, N. & Li, B. (2021). J. Energy Chem., 59, 83-99. CrossRef CAS Google Scholar
Hore, S., Dinnebier, R., Wen, W., Hanson, J. & Maier, J. (2009). Z. Anorg. Allg. Chem. 635, 88–93. CrossRef CAS Google Scholar
Joos, M., Conrad, M., Bette, S., Merkle, R., Dinnebier, R. E., Schleid, T. & Maier, J. (2022). J. Phys. Chem. Solids, 160, 110299. CrossRef Google Scholar
Krause, L., Herbst-Irmer, R., Sheldrick, G. M. & Stalke, D. (2015). J. Appl. Cryst. 48, 3–10. Web of Science CSD CrossRef ICSD CAS IUCr Journals Google Scholar
Macrae, C. F., Sovago, I., Cottrell, S. J., Galek, P. T. A., McCabe, P., Pidcock, E., Platings, M., Shields, G. P., Stevens, J. S., Towler, M. & Wood, P. A. (2020). J. Appl. Cryst. 53, 226–235. Web of Science CrossRef CAS IUCr Journals Google Scholar
Reckeweg, O., Schulz, A., Blaschkowski, B., Schleid, T. & DiSalvo, F. J. (2014). Z. Naturforsch. 69, 17–24. CrossRef CAS Google Scholar
Sheldrick, G. M. (2015a). Acta Cryst. A71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Sheldrick, G. M. (2015b). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Whitfield, P. S., Le Page, Y., Abouimrane, A. & Davidson, I. J. (2008). Powder Diffr. 23, 292–299. CrossRef CAS Google Scholar
Williams, D. E. & Smyth, C. P. (1962). J. Am. Chem. Soc. 84, 1808–1812. CrossRef CAS Google Scholar
Zhou, D., Shanmukaraj, D., Tkacheva, A., Armand, M. & Wang, G. (2019). Chem, 5, 2326–2352. CrossRef CAS Google Scholar
Zhu, H., MacFarlane, D. R., Pringle, J. M. & Forsyth, M. (2019). Trends Chem. 1, 126–140. CrossRef CAS Google Scholar