Hollandite with Cr(III) in both tunnel and framework sites has been prepared hydrothermally from layered manganese oxide precursors.
Ching, S., Driscoll, P., Kieltyka, K., Marvel, M., & Suib, S. Synthesis of a new hollandite-type manganese oxide with framework and interstitial Cr(III). Chem. Commun. (Cambridge, England), 2001, 23, 2486-2487. Doi: 10.1039/B107887A
The views expressed in this paper are solely those of the author.