Growth and characterization of a new inorganic metal–halide crystal structure, InPb₂Cl₅

A new solid-state inorganic compound, indium dilead penta­chloride, InPb₂Cl₅, was synthesized by melting InCl and PbCl₂ in a vacuum-sealed quartz ampoule. The ampoule was heated to 793 K and then slowly cooled to room temperature to induce crystallization of InPb₂Cl₅. InPb₂Cl₅ crystallizes in the monoclinic crystal system adopting a space group of type P2₁/c, which is isostructural with other metal halides such as RbPb₂Cl₅, KPb₂Cl₅ and TlPb₂Cl₅. The bulk InPb₂Cl₅ exhibits a metallic black/grey colour, allowing it to be separated from white/yellow PbCl₂ crystals. Due to the incongruent nature of the compound, the pure bulk InPb₂Cl₅ was not obtained. The black/grey InPb₂Cl₅ crystals were characterized by powder and single-crystal X-ray diffraction. InPbCl₃ was also explored, however the growth was unsuccessful.

1. Chemical context

Indium lead chloride, InPb₂Cl₅ is a metal halide that has been studied as a new material to be used in optoelectronic semiconducting applications. Other isostructural metal halides that have the structure APb₂Cl₅ (where A = K, Rb, Tl) have gained inter­est in fields such as optoelectronics (Vu et al., 2020), and photovoltaics as a tunable laser (Isaenko et al., 2013; Khyzhun et al., 2014; Brown et al., 2013). There has been success in growing metal-halide semiconducting crystals such as RbPb₂Cl₅ and KPb₂Cl₅ (Isaenko et al., 2013; Rowe et al., 2014; Isaenko et al., 2009), however single-crystal InPb₂Cl₅ has not been reported and has only been computationally studied as the InPbCl₃ phase (Khan et al., 2022). Similar to RbPb₂Cl₅, KPb₂Cl₅, and TlPb₂Cl₅, InPb₂Cl₅ crystallizes in a monoclinic structure and has a space group of type P2₁/c. Bulk InPb₂Cl₅ samples were prepared, which contained a mixture of black/grey metallic polycrystalline InPb₂Cl₅ at the bottom of the ampoule and white/yellow PbCl₂ crystals above. When the black/grey crystals were broken up, the crystals appeared to have a much clearer and lighter green hue. The broken-up crystal was examined under an optical microscope and clear colourless crystal pieces were seen. The clear colourless single-crystal pieces were handpicked and characterized by single-crystal X-ray diffraction (XRD). The bulk material was ground using a mortar and pestle and the powder was characterized by powder-XRD. The powder-XRD pattern had low intensity peaks of In₇Cl₉ and PbCl₂ impurities, but matched closely with the InPb₂Cl₅ phase. When InPb₂Cl₅ was left in ambient conditions over four months, the bulk absorbed moisture over time and left a light-grey film around the bulk with moisture build up on the side of the material.

2. Structural commentary

The single-crystal structure of InPb₂Cl₅ was found to adopt a monoclinic P2₁/c space group. The single-crystal structure refinement confirmed the composition as InPb₂Cl₅. The bond lengths in the asymmetric unit (Fig. 1) of InPb₂Cl₅ are listed in Table 1. The unit cell of InPb₂Cl₅ (Fig. 2) has four symmetry-related formula units. The Pb atoms in the unit cell (Fig. 2) coordinate multiple chlorine atoms that give a range of bond lengths from 2.868 (5)–3.3145 (15) Å. The Pb1 atoms coordinate with seven chlorine atoms in the structure, with bond lengths ranging from 2.868 (5)–3.1371 (14) Å. The Pb1 atoms form a nine-face polyhedron with a volume of 37.374 ų (Fig. 3). The Pb2 atoms have a coordination number of 8 with bond lengths from 2.916 (7)–3.3145 (15) Å. The Pb2 atoms form a 12-face dodeca­hedron with a volume of 49.796 ų (Fig. 3). The shortest bond length is between Cl1 and Pb1, which is 2.868 (5) Å. The largest bond lengths are between the Pb2 atom and a Cl3 atom at 3.3145 (15) Å. The typical bond length between Pb and Cl atoms is 2.44 Å in the binary structure. There is an increase in bond lengths from the binary PbCl₂ to the InPb₂Cl₅ structure. The indium atom inter­stitially coordinates eight chlorine atoms in a distorted octa­hedral geometry. The range of indium–chlorine bonds range from 3.1447 (18)–3.588 (8) Å. The indium atom forms a 12-face dodeca­hedron with a volume of 62.568 ų (Fig. 3). The typical In—Cl bond length is around 2.56 Å, indicating that the indium–chlorine bonds have a much weaker inter­action in the InPb₂Cl₅ structure. The largest bond angles seen in the unit cell (Fig. 2) are between the Cl1ⁱⁱⁱ—Pb1—Cl2 atoms at 156.02 (3)° (symmetry codes as per Fig. 2). The shortest bond angle in the structure is between the Cl4ⁱⁱ—In1—Cl5ⁱ atoms at 63.2587 (3)°. The Pb atoms have stronger inter­actions with the chlorine atoms resulting in shorter bond lengths and a wide range of bond lengths from 69.7087 (3)–156.02 (3)°. The indium atoms have weaker inter­actions and are inter­stitially located throughout the structure. The weaker inter­actions of the indium atoms is evident because of the shorter bond lengths and smaller range of bond angles from 63.2587 (3)–144.1653 (3)°. A complete list of bond lengths and bond angles is given in the supporting information.

Table 1
Bond lengths (Å) in the InPb₂Cl₅ asymmetric unit (Fig. 1)

Bond	Distance
Cl1—Pb1	2.8677 (12)
Cl2—Pb1	2.9214 (10)
Cl3—Pb1	2.8744 (12)
Cl3—Pb2	2.9156 (12)
Cl4—Pb2	2.9236 (11)
Cl5—Pb2	2.9760 (12)

Figure 1 A view of the asymmetric unit. Ellipsoids are drawn at the 50% probability level.

Figure 2 A partial packing plot viewed down the b-axis. Ellipsoids are drawn at the 50% probability level. Symmetry codes: (i) x, y, z; (ii) −x, y + , −z + ; (iii) −x, −y, −z; (iv) x, −y − , z − .

Figure 3 A polyhedron view of the crystal structure packing, viewed down the b-axis.

3. Database survey

The InPb₂Cl₅ structure is isostructural with other compounds such as RbPb₂Cl₅ (Isaenko et al., 2013; Isaenko et al., 2009), KPb₂Cl₅ (Rowe et al., 2014; Isaenko et al., 2009) and TlPb₂Cl₅ (Khyzhun et al., 2014). The cell dimensions of the monoclinic InPb₂Cl₅ cell are compared with the isostructural compounds in Table 2. The cell dimensions for InPb₂Cl₅ match very closely with TlPb₂Cl₅. There is no significant difference between the InPb₂Cl₅ structure and the isostructural structures in Table 2, the small difference is due to the atomic size difference for indium. The indium atom has the smallest atom size, so it is expected to fit tighter into the unit cell compared to the other structures, so we see that InPb₂Cl₅ has the smallest unit cell volume. The thallium atom is most comparable to the indium atom size, which is why its cell dimensions are most similar.

Table 2
InPb₂Cl₅ unit-cell parameters compared with isostructural compounds.

Compound	a (Å)	b (Å)	c (Å)	β (°)	Volume (Å^3)
InPb2Cl5	8.9681 (11)	7.9033 (9)	12.4980 (16)	90.254 (6)	885.82 (19)
TlPb2Cl5	8.9561	7.9204	12.4908	90.073	886.0
RbPb2Cl5	8.9900	7.9963	12.541	90.20	901.5
KPb2Cl5	8.864	7.932	12.491	90.153	878.2

4. Synthesis and crystallization

Stoichiometric amounts of the binary compounds In^ICl (4g, ThermoFisher Scientific 99.995%, metals basis) and Pb^IICl₂ [3.7278 (5)g, Acros Organics 99%] were mixed in a glove box under an argon environment (<0.1ppm O₂ and H₂O). The binary compounds were ground together with a mortar and pestle and then loaded into a quartz ampoule. The quartz ampoule was flame sealed under high vacuum (5.5 × 10⁻⁵ mbar). The loaded quartz ampoule was heated at 3K min⁻¹ in a vertical furnace to 793K. The ampoule was cooled at 0.5 K min⁻¹ to room temperature. A 1 mm³ piece of the metallic black and grey crystal was separated from the excess yellow Pb^IICl₂ crystals and sent for characterization by powder-XRD and single-crystal XRD.

5. Refinement

The crystallographic data, data collection and structure refinement are summarized in Table 3.

Table 3
Experimental details

Crystal data
Chemical formula	In2Pb4Cl10
Mr	1412.9
Crystal system, space group	Monoclinic, P21/c
Temperature (K)	298
a, b, c (Å)	8.9681 (11), 7.9033 (9), 12.4980 (16)
β (°)	90.254 (6)
V (Å^3)	885.82 (19)
Z	2
Radiation type	Mo Kα
μ (mm^−1)	41.91
Crystal size (mm)	0.22 × 0.18 × 0.13
Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Krause et al., 2015)
Tmin, Tmax	0.378, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	20682, 2699, 2423
Rint	0.051
(sin θ/λ)max (Å^−1)	0.715
Refinement
R[F^2 > 2σ(F^2)], wR(F^2), S	0.021, 0.042, 1.08
No. of reflections	2699
No. of parameters	74
Δρmax, Δρmin (e Å^−3)	1.22, −1.13
Computer programs: APEX2 and SAINT (Bruker, 2012), SHELXT (Sheldrick, 2015a), SHELXL (Sheldrick, 2015b), CrystalMaker (Palmer, 2014), WinGX (Farrugia, 2012) and publCIF (Westrip, 2010).

Supporting information

Computing details

Cell refinement: APEX2 (Bruker, 2012); data reduction: SAINT (Bruker, 2012); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL (Sheldrick, 2015b); molecular graphics: CrystalMaker (Palmer, 2014); software used to prepare material for publication: WinGX (Farrugia, 2012) and publCIF (Westrip, 2010).

Indium dilead pentachloride

Crystal data

In2Pb4Cl10	F(000) = 1192
Mr = 1412.9	Dx = 5.297 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 9997 reflections
a = 8.9681 (11) Å	θ = 2.3–30.5°
b = 7.9033 (9) Å	µ = 41.91 mm^−1
c = 12.4980 (16) Å	T = 298 K
β = 90.254 (6)°	Transparent square, colourless
V = 885.82 (19) Å^3	0.22 × 0.18 × 0.13 mm
Z = 2

Data collection

Bruker APEXII CCD diffractometer	2699 independent reflections
Radiation source: sealed X-ray tube, Incoatec Iµs	2423 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.051
Detector resolution: 7.9 pixels mm^-1	θmax = 30.6°, θmin = 2.3°
φ and ω scans	h = −12→12
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	k = −11→11
Tmin = 0.378, Tmax = 0.746	l = −17→17
20682 measured reflections

Refinement

Refinement on F^2	0 constraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F^2 > 2σ(F^2)] = 0.021	w = 1/[σ^2(Fo^2) + (0.0083P)^2 + 1.8133P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.042	(Δ/σ)max = 0.002
S = 1.08	Δρmax = 1.22 e Å^−3
2699 reflections	Δρmin = −1.13 e Å^−3
74 parameters	Extinction correction: SHELXL-2018/3 (Sheldrick 2015b), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.00232 (8)

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.

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

	x	y	z	Uiso*/Ueq
Cl1	0.04109 (12)	0.67574 (15)	0.41739 (11)	0.0316 (3)
Cl2	0.45758 (11)	0.66555 (13)	0.40434 (9)	0.0226 (2)
Cl3	0.27835 (14)	0.65746 (14)	0.68735 (10)	0.0304 (3)
Cl4	0.72918 (12)	0.68702 (14)	0.72264 (9)	0.0252 (2)
Cl5	0.28105 (12)	0.45943 (14)	1.00167 (9)	0.0232 (2)
In1	0.98678 (5)	0.45346 (6)	0.83468 (4)	0.04410 (11)
Pb1	0.24664 (2)	0.43551 (2)	0.50647 (2)	0.02229 (6)
Pb2	0.49498 (2)	0.48805 (2)	0.82509 (2)	0.02538 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl1	0.0194 (5)	0.0309 (6)	0.0445 (7)	0.0009 (4)	0.0017 (5)	0.0137 (5)
Cl2	0.0192 (5)	0.0201 (4)	0.0285 (6)	−0.0008 (4)	−0.0002 (4)	0.0059 (4)
Cl3	0.0364 (6)	0.0283 (5)	0.0263 (6)	0.0084 (5)	−0.0081 (5)	−0.0063 (4)
Cl4	0.0259 (5)	0.0254 (5)	0.0243 (6)	−0.0027 (4)	0.0021 (4)	0.0025 (4)
Cl5	0.0251 (5)	0.0240 (5)	0.0205 (5)	0.0004 (4)	0.0005 (4)	0.0009 (4)
In1	0.0418 (2)	0.0432 (2)	0.0472 (3)	0.00874 (18)	−0.00359 (19)	−0.00495 (19)
Pb1	0.01876 (9)	0.02412 (9)	0.02399 (10)	−0.00042 (6)	−0.00025 (6)	−0.00142 (6)
Pb2	0.02614 (10)	0.02526 (9)	0.02473 (10)	−0.00304 (7)	0.00037 (7)	0.00179 (6)

Geometric parameters (Å, º)

Cl1—Pb1	2.8677 (12)	Cl3—Pb2	2.9156 (12)
Cl1—Pb1^i	2.8912 (11)	Cl4—Pb2	2.9236 (11)
Cl2—Pb1	2.9214 (10)	Cl4—Pb1^iii	3.0314 (12)
Cl2—Pb2^ii	2.9311 (10)	Cl5—Pb2	2.9394 (11)
Cl2—Pb1^iii	2.9817 (11)	Cl5—Pb2^iv	2.9760 (12)
Cl3—Pb1	2.8744 (12)
Pb1—Cl1—Pb1^i	104.12 (4)	Cl2—Pb1—Cl2^iii	75.72 (3)
Pb1—Cl2—Pb2^ii	143.53 (4)	Cl1—Pb1—Cl4^iii	83.88 (4)
Pb1—Cl2—Pb1^iii	104.28 (3)	Cl3—Pb1—Cl4^iii	158.52 (3)
Pb2^ii—Cl2—Pb1^iii	105.88 (3)	Cl1^i—Pb1—Cl4^iii	106.34 (4)
Pb1—Cl3—Pb2	104.33 (4)	Cl2—Pb1—Cl4^iii	74.75 (3)
Pb2—Cl4—Pb1^iii	107.24 (4)	Cl2^iii—Pb1—Cl4^iii	101.55 (3)
Pb2—Cl5—Pb2^iv	95.44 (3)	Cl3—Pb2—Cl4	88.42 (4)
Cl1—Pb1—Cl3	87.85 (4)	Cl3—Pb2—Cl2^v	72.16 (3)
Cl1—Pb1—Cl1^i	75.88 (4)	Cl4—Pb2—Cl2^v	74.28 (3)
Cl3—Pb1—Cl1^i	90.69 (4)	Cl3—Pb2—Cl5	92.48 (3)
Cl1—Pb1—Cl2	80.49 (3)	Cl4—Pb2—Cl5	147.44 (3)
Cl3—Pb1—Cl2	84.37 (4)	Cl2^v—Pb2—Cl5	75.06 (3)
Cl1^i—Pb1—Cl2	156.02 (3)	Cl3—Pb2—Cl5^iv	144.23 (3)
Cl1—Pb1—Cl2^iii	153.09 (3)	Cl4—Pb2—Cl5^iv	76.10 (3)
Cl3—Pb1—Cl2^iii	77.57 (3)	Cl2^v—Pb2—Cl5^iv	72.65 (3)
Cl1^i—Pb1—Cl2^iii	126.11 (3)	Cl5—Pb2—Cl5^iv	84.56 (3)

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