Microwave-assisted synthesis of lanthanide coordination polymers with 2-bromobenzoic acid as ligand from hexa-lanthanide molecular precursors

Abstract

Microwave-assisted reactions, between 2-bromobenzoic acid (2-bbH) and hexa-lanthanide molecular precursors of general chemical formula Ln6(µ6-O)(µ3-OH)8(NO3)6(H2O)12·2NO3·2H2O [Ln6], lead to iso-structural 1D coordination polymers of general chemical formula [Ln(2-bb)3]∞ with Ln = Eu, Tb or Dy. These compounds crystallize in the monoclinic system, space group P21/c (n°14), with the following cell parameters (for the Dy-derivative): a = 12.3809(10) Å, b = 21.8653(16) Å, c = 7.9119(7) Å, β = 98.709(3)°, V = 2117.2(3) Å3 and Z = 4. The influence of the hexa-nuclear precursors over the final coordination polymer is demonstrated. Indeed, while the hexa-nuclear complexes collapse during the synthetic process their progressive destruction affords a unique 1D coordination polymer that cannot be readily obtained otherwise. Additionally, some iso-structural hetero-lanthanide derivatives with general chemical formulas [EuxTb1-x(2-bb)3]∞ and [YxTb1-x(2-bb)3]∞ with 0 ≤ x ≤ 1 have been prepared from the corresponding hexa-nuclear complexes [Eu6xTb6-6x] and [Y6xTb6-6x], respectively. Luminescent properties have been recorded and colorimetric coordinates have been calculated for all the compounds. These measurements indicate that the molecular chains host strong intermetallic energy transfers.