CrCl63

CrCl63 refers to the hexachlorochromate(III) anion, [CrCl6]3−, an octahedral coordination complex of chromium in the +3 oxidation state bound to six chloride ligands. This anion is encountered in salts such as K3[CrCl6], (NH4)3[CrCl6], and related hydrates. In idealized form, the chromium center sits at the center of an octahedron formed by six chloride ligands, giving Oh symmetry.

Electronically, Cr3+ is a d3 ion. In an octahedral field, the three electrons occupy the t2g set with three unpaired spins, making [CrCl6]3− a paramagnetic species with three unpaired electrons (approximately 3.8–3.9 μB). Spectroscopically, Cr(III) octahedral complexes exhibit characteristic ligand-field transitions, and the observed color of CrCl6^3− salts depends on the ligand field strength and counterions. The presence of chloride ligands typically yields colors that reflect Cr(III) d–d transitions and charge-transfer interactions.

Preparation and stability are linked to chloride concentration. In highly chloride-rich media, CrCl3 can be converted to [CrCl6]3−, and salts such as K3[CrCl6] can be prepared by metathesis with suitable cations. In aqueous solution, equilibria among hexachloro, aquated, and mixed-ligand chromium(III) species depend on chloride concentration and pH; high chloride stabilizes the hexachlorometalate relative to aquated forms. The complex is generally stable in concentrated chloride media but hydrolyzes under dilute or basic conditions.

Applications include use as a laboratory reagent and a model system for studying ligand-field effects in Cr(III) octahedral complexes. It is primarily of academic and spectroscopic interest rather than a widely used industrial commodity. Safety follows standard precautions for chromium(III) salts; handle with care to avoid skin contact and inhalation.