Insight into the Structural and Emissive Behavior of a Three-Dimensional Americium(III) Formate Coordination Polymer.

Abstract

We report the structural, vibrational, and optical properties of americium formate (Am(CHO2 )3 ) crystals synthesized via the in situ hydrolysis of dimethylformamide (DMF). The coordination polymer features Am3+ ions linked by formate ligands into a three-dimensional network that is isomorphous to several lanthanide analogs, (e. g., Eu3+ , Nd3+ , Tb3+ ). Structure determination revealed a nine-coordinate Am3+ metal center that features a unique local C3v symmetry. The metal-ligand bonding interactions were investigated by vibrational spectroscopy, natural localized molecular orbital calculations, and the quantum theory of atoms in molecules. The results paint a predominantly ionic bond picture and suggest the metal-oxygen bonds increase in strength from Nd-O<Eu-O<Am-O. The optical properties were probed using diffuse reflectance and photoluminescence spectroscopies. Notably, the rarely reported 5 D1' →7 F0' emission band is observed and dominates the emission spectrum. This behavior is unusual and is attributed to the C3v coordination environment of the metal center.