Estimating the Individual Spectroscopic Properties of Three Unique Eu III Sites in a Coordination Polymer.

We isolated a coordination polymer with the formula [Eu ₃ (3,5-dcba) ₉ (H ₂ O)(dmf) ₃ ]·2dmf, with three unique Eu ^III coordination sites in the asymmetric unit, with the Eu ^III ions bridged by 3,5-dichlorobenzoato (3,5-dcba) ligands. The coordination polymer crystallized in the triclinic space group P1̅ with unit cell dimensions a = 12.4899(15), b = 16.326(2), and c = 25.059(3) Å, α = 84.271(3)°, β = 84.832(3)°, and γ = 68.585(3)° and V = 4725.2(10) Å ³ . The characteristic ⁵ D ₀ → ⁷ F _J ( J = 0-4) Eu ^III 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 Eu ^III site. Energy-transfer rates ligand → Eu ^III 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 → Eu ^III , 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.