XAFS studies and computational simulation of calixcrowns-caesium complexes in solution

Caesium L-3-edge XANES (X-ray absorption near-edge structure) and EXAFS (extended X-ray absorption fine structure) have been evaluated as means of probing the local structure and the interaction of caesium ions with BPC6 {1,3-alternate bis(2-propyloxy)calix[4]arenecrown-6}, BOC6 {1,3-alternate bis(octyl-oxy)calix[4]arenecrown-6} and BisC6 (1,3-alternate calix[4] arene bis-crown-6) in NPME (o-nitrophenyl methyl ether) or OA (n-octyl alcohol). The XANES results indicate that the molecular symmetry is enhanced as the caesium ions are embedded. The EXAFS spectra demonstrate that the coordination numbers (N) and average distances ( R) from the central caesium ion to the O atoms are: for BPC6, N = 7.0, R = 3.22 angstrom (in NPME), and N = 7.0, R = 3.23 angstrom (in OA); for BOC6, N = 6.8, R = 3.28 angstrom (in NPME), and N = 6.9, R = 3.27 angstrom (in OA); for BisC6, N = 6.9, R = 3.21 angstrom (in NPME). Density functional theory at the triple-zeta adding polarization basis set level was used to simulate the BPC6, BOC6 and BisC6 coordination with the caesium ions. Data show that the seven-oxygen-configuration average distances from the central caesium ion to the O atoms are R = 3.38 for BPC6, R = 3.40 for BisC6 and R = 3.39 for BOC6.