Neodymium oxychloride is an inorganic compound composed of neodymium, oxygen, and chlorine, typically represented by the formula NdOCl. It belongs to the family of rare-earth oxychlorides, which are intermediate compounds formed by the partial hydrolysis of rare-earth chlorides. Neodymium oxychloride usually appears as a crystalline solid with colors ranging from violet to pink, a characteristic hue imparted by the electronic transitions of the Nd³⁺ ion.
This compound can be prepared by gently heating neodymium trichloride (NdCl₃) in the presence of limited oxygen or water vapor, leading to controlled hydrolysis. It is often obtained as a stable intermediate when neodymium oxide reacts with hydrogen chloride gas at high temperatures. Neodymium oxychloride is moderately hygroscopic, gradually absorbing moisture and further hydrolyzing to neodymium oxide and hydrochloric acid upon prolonged exposure.
Properties
The compound forms crystals of tetragonal system, space group P4/nmm. It exhibits paramagnetic susceptibility and structural stability. The compound is moderately hygroscopic and soluble in water, forming aquo complexes. Like other rare-earth oxychlorides, it can be prepared through thermal decomposition of neodymium chloride hydrates or by controlled hydrolysis of neodymium chloride.
- Chemical formula: NdOCl
- Molar mass: 195.69 g/mol
- Appearance: crystals
- Crystal structure: tetragonal
Structurally, NdOCl often crystallizes in layered arrangements similar to other lanthanide oxyhalides, where neodymium cations are coordinated by oxygen and chlorine atoms. It shows stability at high temperatures but decomposes under strong heating, yielding neodymium oxide (Nd₂O₃) and gaseous chlorine compounds.
Synthesis
NdOCl can be synthesized by reacting neodymium oxide (Nd2O3) and calcium dichloride (CaCl2).[2]
Nd2O3 + CaCl2 → 2NdOCl + CaO
Chemical properties
NdOCl can be reduced to metallic neodymium through high-temperature electrolysis, specifically within the FFC (Fray-Farthing-Chen) process.
NdOCl + 1.5Ca → Nd + CaO + 0.5CaCl2
Occurrences
Neodymium oxychloride does not occur naturally; it is produced synthetically in laboratories and industry. Its occurrence is tied to the chemistry of neodymium, which is mainly extracted from rare-earth minerals such as monazite and bastnäsite. During refining processes, neodymium salts, including chlorides and oxychlorides, are generated as intermediates. NdOCl and related compounds find interest in materials science, especially in optical, catalytic, and luminescent applications due to neodymium’s unique electronic structure. They also serve as precursors in the preparation of high-purity neodymium oxide and in specialized glass and laser materials.
Uses
NdOCl has been investigated as a cathode material for the extraction of metallic neodymium.
In terms of applications, neodymium oxychloride is mainly of interest in materials science and inorganic chemistry. It can serve as a precursor for the synthesis of high-purity neodymium oxide, which is vital in glass coloring, ceramics, catalysts, and the production of powerful neodymium magnets. Like other rare-earth oxychlorides, NdOCl also provides insight into the structural chemistry of lanthanides, showing layered crystalline arrangements with both ionic and covalent bonding features.
