Reactions of Rare Earth Hydrated Nitrates and Oxides with Formamide: Relevant to Recycling Rare Earth Metals

Abstract

Reactions of hydrated rare earth nitrates with formamide under mild solvothermal reaction conditions give three different rare earth formate structure types Ln(HCOO)3, Ln(HCOO)3·(HCONH2)2, and [CH(NH2)2][Ln(HCOO)4]. The conditions for the formation of a specific structure type were determined as a function of the size of the rare earth cation, the reaction time, and the reaction temperature. Thirteen previously unreported rare earth formates were obtained; nine were isostructural compounds with the composition Ln(HCOO)3·(HCONH2)2 (denoted by LnFA, Ln = Y (1Y), Sm (2Sm), Eu (3Eu), Gd (4Gd), Tb (5Tb), Ho (6Ho), Tm (7Tm), Yb (8Yb), and Lu (9Lu)), and four were isostructural compounds with the composition [CH(NH2)2][Ln(HCOO)4] (denoted by LnFMD, Ln = Sm (10Sm), Ho (11Ho), Tm (12Tm), and Lu (13Lu)). All compounds contain metal ions that are eight coordinated by oxygen atoms and are connected by anti–anti bridging formato ligands to form frameworks. The coordination geometry is bisdisphenoid in LnFA and square ...