research communications
A 1:1 solvate structure of succinonitrile and lithium thiocyanate
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
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 [01]. Weak hydrogen-bonding interactions are also noted among the constituent molecules.
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 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 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.
may be found in the2. Structural commentary
The succinonitrile lithium thiocyanate solvate, LiSCN·NC(CH2)2CN, belongs to the P21/n with Z = 4. A displacement ellipsoid plot constituting the with the atom-labeling scheme is shown in Fig. 1. Projections of the 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 [01] (see Fig. 4).
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 − , − y, z + ]. 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 + , − y, z − ]. 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.
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 C2/m and a high-temperature phase with Pnam. The structures for LiSCN and LiSCN·2H2O, both belonging to 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 . 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.
details are summarized in Table 2Supporting information
CCDC reference: 2220707
https://doi.org/10.1107/S2056989022011094/zl5037sup1.cif
contains datablock I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989022011094/zl5037Isup2.hkl
Data collection: APEX3 (Bruker, 2018); cell
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).[Li(NCS)(C4H4N2)] | F(000) = 296 |
Mr = 145.11 | Dx = 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 |
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 | Rint = 0.097 |
ω and φ scans | θmax = 31.5°, θmin = 3.1° |
Absorption correction: multi-scan (SADABS; Krause et al., 2015) | h = −11→11 |
Tmin = 0.403, Tmax = 0.490 | k = −17→17 |
33422 measured reflections | l = −12→12 |
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(Fo2) + (0.0936P)2 + 0.2195P] where P = (Fo2 + 2Fc2)/3 |
S = 1.04 | (Δ/σ)max = 0.001 |
2400 reflections | Δρmax = 0.41 e Å−3 |
92 parameters | Δρmin = −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) |
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. |
x | y | z | Uiso*/Ueq | ||
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) |
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) |
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. |
D—H···A | D—H | H···A | D···A | D—H···A |
C2A—H2AA···S1iv | 0.99 | 2.93 | 3.5212 (15) | 120 |
C2A—H2AB···N1v | 0.99 | 2.63 | 3.4159 (17) | 137 |
C3A—H3AA···N2Avi | 0.99 | 2.61 | 3.4232 (17) | 140 |
C3A—H3AB···N1vi | 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).
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