Molybdenum oxydichloride
| Identifiers | |
|---|---|
3D model (JSmol) |
|
| |
| |
| Properties | |
| Cl2MoO | |
| Molar mass | 182.85 g·mol−1 |
| Density | 3.6–3.8 g/cm3 |
| Structure[1] | |
| monoclinic (100 K) | |
| C2/m (No. 12) | |
a = 1.280 nm, b = 0.378 nm, c = 0.657 nm α = 90°, β = 105.78°, γ = 90° | |
Lattice volume (V) |
0.30332 nm3 |
Formula units (Z) |
4 units per cell |
| Related compounds | |
Related compounds |
Molybdenum dichloride dioxide |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references | |
Molybdenum oxydichloride (MoOCl2) is a layered van der Waals material. Its molybdenum is in the +4 oxidation state. It is notable for its extreme in-plane optical anisotropy (hyperbolic behavior in the visible range).[2]
Structure
MoOCl2 has a monoclinic crystal system with a layered van der Waals structure. It features quasi-one-dimensional Mo chains with orbital-selective Peierls distortion: Mo–Mo dimerization along the b-axis (leading to more localized/insulating character) versus metallic/dispersive behavior along the a-axis (Mo–O chains). This creates strong in-plane anisotropy—metallic-like (ε₁ < 0) along *a*, dielectric (ε₁ > 0) along b and c.
The structure consists of interconnected Mo-centered octahedra (Mo bonded to O and Cl), forming easily exfoliable layers held by weak van der Waals forces.
Preparation
Common methods include:
- Chemical transport reaction for high-quality single crystals: This typically involves reacting MoCl3 with MoO3 (molar ratio ~2:1) in a sealed quartz ampoule under argon or mild vacuum, with a temperature gradient (e.g., source at ~400 °C, sink at ~300 °C, then controlled cooling). Needle-like crystals form, with a metallic sheen.
- Direct chlorination: Molybdenum oxides (MoO2 or MoO3) can be combined with Cl2 gas at elevated temperatures. This is common for bulk/powder forms but can yield fluffy, low-density material; post-processing (sublimation/re-aggregation under reduced pressure) improves density and purity for CVD/ALD precursors.
Reactions
- Coordination chemistry: Acts as a precursor or forms adducts/complexes with ligands (e.g., phosphines like PMe3 yielding mer-MoOCl2(PMe3)3 or chalcogenoethers). It can undergo redox or ligand exchange. Related Mo(V) species like MoOCl3 are more commonly studied in coordination contexts.
- Hydrolysis/solvolysis: MoOCl2 is sensitive to moisture. It can dissolve in water (depending on form—compact vs. fluffy) forming molybdate species. The crystals are relatively stable in ambient conditions for optical studies.
- Precursor: It is used in material synthesis (e.g., for other Mo compounds) or as a CVD/ALD source for molybdenum-containing films (though MoO2Cl2 is more common for some applications).
- Its "bad metal" electronic structure influences solid-state behavior more than solution reactivity.
- Stability: Air-stable as bulk/exfoliated flakes for many experiments; inert conditions are required or long-term purity.
Anistropy
MoOCl2 exhibits broadband in-plane hyperbolicity that spans the visible to near-infrared spectrum, driven by a Drude-like response. Thin MoOCl2 (∼100–200 nm) flakes achieve >80% reflectivity along the metallic axis and >50% transmission along the perpendicular dielectric axis. This enables polarization extinction with minimal loss. In-plane dielectric permittivity anisotropy exceeds |Δ(ε∥)| > 10 for wavelengths above 600 nm.[2]
Spectroscopic ellipsometry, Mueller matrix, and reflectance measurements reveal MoOCl2's optical duality: a metallic optical response (ε1 < 0) along the crystallographic a-axis and a dielectric response (ε1 > 0) along the orthogonal directions. This dichotomy drives an epsilon-near-zero (ENZ) condition at ≈512 nm and results in a giant in-plane birefringence of Δn ≈ 2.2 for MoOCl2.[3]
Time-resolved photoemission electron microscopy allows nanoscale visualization of long-range anisotropic plasmon polariton (LRAPP) dynamics with propagation lengths larger than 10 µm on a flake of MoOCl2, some three times longer than previously reported with lower loss.[4]
Applications
MoOCl2's low-loss, miniaturized polarization offers potential in photonic systems.[3]
References
- ↑ "MoOCl2 (MoCl2O mon) (Von Schnering, 1963, C12/m1) Crystal St". materials.springer.com. Retrieved 2026-06-17.
- 1 2 Melchioni, Nicola; Mancini, Andrea; Nan, Lin; Efimova, Anastasiia; Venturi, Giacomo; Ambrosio, Antonio (2025-07-15). "Giant Optical Anisotropy in a Natural van der Waals Hyperbolic Crystal for Visible Light Low-Loss Polarization Control". ACS Nano. 19 (27): 25413–25421. Bibcode:2025ACSNa..1925413M. doi:10.1021/acsnano.5c07323. ISSN 1936-086X. PMC 12269362. PMID 40590966.
- 1 2 Ermolaev, Georgy; Toksumakov, Adilet; Slavich, Aleksandr; Minnekhanov, Anton; Tselikov, Gleb; Mazitov, Arslan; Kruglov, Ivan; Tikhonowski, Gleb; Mironov, Mikhail; Radko, Ilya P.; Grudinin, Dmitriy; Fradkin, Ilia; Vyshnevyy, Andrey; Sofer, Zdeněk; Arsenin, Aleksey (2026-04-08). "Giant Optical Anisotropy and Visible-Frequency Epsilon-near-Zero in Hyperbolic van der Waals MoOCl2". Nano Letters. 26 (13): 4329–4338. arXiv:2512.06495. Bibcode:2026NanoL..26.4329E. doi:10.1021/acs.nanolett.5c06153. ISSN 1530-6984. PMC 13067380. PMID 41839189.
- ↑ Mohan, Aishani; Munawar, Muneeza; Rieger, Janek; King, Sarah B. (February 27, 2026). "Spatiotemporal Visualization of Long-Range Anisotropic Plasmon Polaritons in Hyperbolic MoOCl2". Nature Communications. 17 (1) 3884. doi:10.1038/s41467-026-70565-2. PMC 13125215. PMID 41826319.