AbstractThe reactivity of the complexing anthraceneâ9âcarboxylate ligand has been investigated with a niobium(IV) tetrachloride precursor (NbCl4 â 2THF) in isopropanol solvent. This resulted in the crystallization of a molecular assembly containing two distinct {Nb12O21} cores surrounded by multiple isopropanolate and anthracenoate ligands. The compound is formulated [Nb12((ÎŒ3âO)3(ÎŒâO)18(C15H9O2)8(OiPr)10] â [Nb12(ÎŒ3âO)2(ÎŒâO)19(C15H9O2)8(OiPr)10] illustrating the two different dodecameric oxoâclusters, for which the niobium(IV) precursor was oxidized in the niobium(V) state during the reactional process. The two distinct {Nb12O21} units mainly differs by the environment of the niobium centers, which exhibits unexpected fiveâfold coordination (square pyramid) for some of them, together with the classical sixâfold coordination (octahedron) as usually found for niobium(V). In the crystallization process, the. IR spectroscopy was used to analyze the esterification reaction occurring between the anthracene acid an isopropanolate ligands responsible of the production of water used in the oxoâcondensation of the niobium centers. 93Nb Solid state NMR was tentatively used to assess the occurrence of the different niobium environments.