RESUMO
We isolated a coordination polymer with the formula [Eu3(3,5-dcba)9(H2O)(dmf)3]·2dmf, with three unique EuIII coordination sites in the asymmetric unit, with the EuIII ions bridged by 3,5-dichlorobenzoato (3,5-dcba) ligands. The coordination polymer crystallized in the triclinic space group P1Ì with unit cell dimensions a = 12.4899(15), b = 16.326(2), and c = 25.059(3) Å, α = 84.271(3)°, ß = 84.832(3)°, and γ = 68.585(3)° and V = 4725.2(10) Å3. The characteristic 5D0 â 7F J ( J = 0-4) EuIII transitions were observed upon ligand-centered excitation. Emission lifetimes of 0.825 ± 0.085 and 1.586 ± 0.057 ms were observed and were attributed to the sites with coordination of water or dimethylformamide (dmf) molecules to each ion, respectively. Through a combination of spectroscopy and calculations, we determined the photophysical properties of each unique EuIII site. Energy-transfer rates ligand â EuIII were determined for each unique site using the overlapped polyhedra method. The rates depend on the coordinated water molecules and the different donor-acceptor distances. The two sites without coordinated water molecules and shortest donor-acceptor distance display the fastest energy-transfer rate ligand â EuIII, whereas the site with coordinated water molecules and longest donor-acceptor distance displays the slowest energy-transfer rate. Donor-acceptor distances were estimated computationally and were confirmed by calculating the frontier orbitals in the asymmetric units of the polymer using density functional theory.
RESUMO
The influence of the donor-acceptor distance RL on the photophysical properties, including the emission quantum yield, of two europium complexes with the same coordination number, and thus similar microsymmetries, was investigated by spectroscopic and computational methods. K3[Eu(dipicCbz)3] was synthesized using the new ligand dipicCbz and its photophysical properties compared to Cs3[Eu(dipic)3]. We found that a 50% increase in RL from 4.1 to 6.5 Å results in a substantial decrease in the emission efficiency from 24 to 1.8%.