Synthesis, crystal structure, and electronic structure of Li₂PbSiS₄: a quaternary thio­silicate with a compressed chalcopyrite-like structure

The new quaternary thio­silicate, Li₂PbSiS₄ (dilithium lead silicon tetra­sulfide), was prepared in an evacuated fused-silica tube via high-temperature, solid-state synthesis at 800 °C, followed by slow cooling. The crystal structure was solved and refined using single-crystal X-ray diffraction data. By strict definition, the title compound crystallizes in the stannite structure type; however, this type of structure can also be described as a compressed chalcopyrite-like structure. The Li⁺ cation lies on a crystallographic fourfold rotoinversion axis, while the Pb²⁺ and Si⁴⁺ cations reside at the inter­section of the fourfold rotoinversion axis with a twofold axis and a mirror plane. The Li⁺ and Si⁴⁺ cations in this structure are tetra­hedrally coordinated, while the larger Pb²⁺ cation adopts a distorted eight-coordinate dodeca­hedral coordination. These units join together via corner- and edge-sharing to create a dense, three-dimensional structure. Powder X-ray diffraction indicates that the title compound is the major phase of the reaction product. Electronic structure calculations, performed using the full potential linearized augmented plane wave method within density functional theory (DFT), indicate that Li₂PbSiS₄ is a semiconductor with an indirect bandgap of 2.22 eV, which compares well with the measured optical bandgap of 2.51 eV. The noncentrosymmetric crystal structure and relatively wide bandgap designate this compound to be of inter­est for IR nonlinear optics.

Computing details

Data collection: APEX2 (Bruker, 2012); cell refinement: SAINT (Bruker, 2012); data reduction: SAINT (Bruker, 2012); program(s) used to solve structure: SHELXS2018 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018 (Sheldrick, 2015b); molecular graphics: shelXle (Hübschle et al., 2011) and CrystalMaker (Palmer, 2014); software used to prepare material for publication: publCIF (Westrip, 2010).

Dilithium lead silicon tetrasulfide

Crystal data

Li2PbSiS4	Dx = 3.882 Mg m^−3
Mr = 377.40	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I42m	Cell parameters from 1002 reflections
a = 6.4618 (1) Å	θ = 4.1–25.4°
c = 7.7333 (2) Å	µ = 27.47 mm^−1
V = 322.90 (1) Å^3	T = 296 K
Z = 2	Square plate, yellow
F(000) = 332	0.06 × 0.06 × 0.02 mm

Data collection

Bruker SMART APEXII diffractometer	235 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.041
φ and ω Scans scans	θmax = 28.5°, θmin = 4.1°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −8→8
Tmin = 0.295, Tmax = 0.435	k = −8→8
1559 measured reflections	l = −10→10
236 independent reflections

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)] = 0.016	w = 1/[σ^2(Fo^2)] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.028	(Δ/σ)max < 0.001
S = 1.01	Δρmax = 0.44 e Å^−3
236 reflections	Δρmin = −0.46 e Å^−3
14 parameters	Absolute structure: Refined as an inversion twin
0 restraints	Absolute structure parameter: 0.062 (15)

Special details

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.

Refinement. Refined as a 2-component inversion twin.

The following programs were utilized for single-crystal data collection, cell refinement; data reduction, absorption correction, structure solution, structure refinement and molecular graphics, respectively: APEXII (Bruker, 2012); SAINT; SAINT (Bruker, 2012); SADABS (Sheldrick, 1996); SHELXS97 (Sheldrick, 2015); SHELXL97 (Sheldrick, 2015); ShelXle (Hübschle, 2011). CrystalMaker (Palmer, 2014) was used to generate the figures of the cyrstal structure and publCIF (Westrip, 2010) was used to prepare the manuscript.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Li	0.000000	0.500000	0.250000	0.024 (3)
Pb	0.000000	0.000000	0.500000	0.02611 (17)
Si	0.000000	0.000000	0.000000	0.0098 (6)
S	0.19091 (19)	0.19091 (19)	0.1569 (2)	0.0140 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Li	0.016 (4)	0.016 (4)	0.039 (8)	0.000	0.000	0.000
Pb	0.0247 (2)	0.0247 (2)	0.0290 (3)	0.000	0.000	0.000
Si	0.0086 (8)	0.0086 (8)	0.0121 (13)	0.000	0.000	0.000
S	0.0126 (5)	0.0126 (5)	0.0167 (9)	−0.0030 (7)	−0.0018 (5)	−0.0018 (5)

Geometric parameters (Å, º)

Li—S^i	2.4554 (6)	Pb—S^ix	3.0743 (18)
Li—S^ii	2.4554 (6)	Pb—S^ii	3.0743 (18)
Li—S^iii	2.4554 (6)	Pb—S^x	3.1752 (17)
Li—S	2.4554 (6)	Pb—S^xi	3.1752 (17)
Li—Pb^iv	3.7652 (1)	Pb—S^xii	3.1752 (17)
Li—Pb^v	3.7652 (1)	Pb—S	3.1752 (17)
Li—Pb	3.7652 (1)	Si—S	2.1252 (17)
Li—Pb^vi	3.7652 (1)	Si—S^xiii	2.1253 (17)
Pb—S^vii	3.0743 (18)	Si—S^xiv	2.1253 (17)
Pb—S^viii	3.0743 (18)	Si—S^x	2.1253 (17)
S^i—Li—S^ii	145.91 (8)	S^ix—Pb—S^x	70.74 (2)
S^i—Li—S^iii	94.93 (2)	S^ii—Pb—S^x	70.74 (2)
S^ii—Li—S^iii	94.93 (2)	S^vii—Pb—S^xi	70.74 (2)
S^i—Li—S	94.93 (2)	S^viii—Pb—S^xi	70.74 (2)
S^ii—Li—S	94.93 (2)	S^ix—Pb—S^xi	146.58 (6)
S^iii—Li—S	145.91 (8)	S^ii—Pb—S^xi	79.924 (19)
S^i—Li—Pb^iv	148.05 (4)	S^x—Pb—S^xi	134.28 (4)
S^ii—Li—Pb^iv	56.80 (4)	S^vii—Pb—S^xii	70.74 (2)
S^iii—Li—Pb^iv	54.44 (4)	S^viii—Pb—S^xii	70.74 (2)
S—Li—Pb^iv	106.30 (4)	S^ix—Pb—S^xii	79.924 (19)
S^i—Li—Pb^v	54.44 (4)	S^ii—Pb—S^xii	146.58 (6)
S^ii—Li—Pb^v	106.30 (4)	S^x—Pb—S^xii	134.28 (4)
S^iii—Li—Pb^v	56.80 (4)	S^xi—Pb—S^xii	66.66 (6)
S—Li—Pb^v	148.05 (4)	S^vii—Pb—S	79.924 (19)
Pb^iv—Li—Pb^v	105.287 (1)	S^viii—Pb—S	146.58 (6)
S^i—Li—Pb	106.30 (4)	S^ix—Pb—S	70.74 (2)
S^ii—Li—Pb	54.44 (4)	S^ii—Pb—S	70.74 (2)
S^iii—Li—Pb	148.05 (4)	S^x—Pb—S	66.66 (6)
S—Li—Pb	56.80 (4)	S^xi—Pb—S	134.28 (4)
Pb^iv—Li—Pb	105.287 (1)	S^xii—Pb—S	134.28 (4)
Pb^v—Li—Pb	118.209 (2)	S—Si—S^xiii	109.03 (5)
S^i—Li—Pb^vi	56.80 (4)	S—Si—S^xiv	109.03 (5)
S^ii—Li—Pb^vi	148.05 (4)	S^xiii—Si—S^xiv	110.35 (9)
S^iii—Li—Pb^vi	106.30 (4)	S—Si—S^x	110.35 (9)
S—Li—Pb^vi	54.44 (4)	S^xiii—Si—S^x	109.03 (5)
Pb^iv—Li—Pb^vi	118.209 (1)	S^xiv—Si—S^x	109.03 (5)
Pb^v—Li—Pb^vi	105.287 (1)	Si—S—Li^xv	110.36 (4)
Pb—Li—Pb^vi	105.287 (1)	Si—S—Li	110.36 (4)
S^vii—Pb—S^viii	133.49 (6)	Li^xv—S—Li	137.01 (7)
S^vii—Pb—S^ix	98.97 (2)	Si—S—Pb^vi	121.92 (7)
S^viii—Pb—S^ix	98.97 (2)	Li^xv—S—Pb^vi	85.05 (4)
S^vii—Pb—S^ii	98.97 (2)	Li—S—Pb^vi	85.05 (4)
S^viii—Pb—S^ii	98.97 (2)	Si—S—Pb	91.50 (6)
S^ix—Pb—S^ii	133.49 (6)	Li^xv—S—Pb	82.87 (4)
S^vii—Pb—S^x	146.58 (6)	Li—S—Pb	82.87 (4)
S^viii—Pb—S^x	79.923 (19)	Pb^vi—S—Pb	146.58 (6)

Symmetry codes: (i) −y+1/2, x+1/2, −z+1/2; (ii) y−1/2, −x+1/2, −z+1/2; (iii) −x, −y+1, z; (iv) x−1/2, y+1/2, z−1/2; (v) x, y+1, z; (vi) x+1/2, y+1/2, z−1/2; (vii) −x+1/2, −y+1/2, z+1/2; (viii) x−1/2, y−1/2, z+1/2; (ix) −y+1/2, x−1/2, −z+1/2; (x) −x, −y, z; (xi) −y, x, −z+1; (xii) y, −x, −z+1; (xiii) −y, x, −z; (xiv) y, −x, −z; (xv) −x+1/2, y−1/2, −z+1/2.