Capturing the Heptaniobate {Nb7O22}9– Anion by Covalent Bond Formation: Synthesis, Crystal Structure, and Selected Properties of {[Fe(cyclam)]3Nb7O22}· ≈ 19 H2O

Abstract

The new compound {[Fe(cyclam)]3Nb7O22}· ≈ 19 H2O (I) was synthesized at room temperature reacting aqueous solutions of K8{Nb6O19}·16 H2O, Fe(NO3)3·9 H2O and cyclam (1,4,8,11‐tetraazacyclotetradecane). In the crystal structure the heptaniobate {Nb7O22}9– anion is observed which is expanded by three [Fe(cyclam)]3+ complexes, thus suppressing further condensations into larger aggregates. The complexes are solely bound to the three terminal O2– anions of the NbO6 octahedron which expands the hexaniobate {Nb6O19}8– anion to form the heptaniobate cluster. The two O atoms in the FeN4O2 octahedron are in cis position leading to a severe distortion of the cyclam ligand with one of the CH2–CH2–CH2–N–CH2–CH2 fragments being rotated by about 90°. The {[Fe(cyclam)]3Nb7O22} units are arranged to form channels which host the crystal water molecules. The crystal water molecules can be removed by thermal treatment. Storing the sample on air the pristine sample is recovered.