Synchrotron powder diffraction in a systematic study of 4′-[2-(tosylamino)benzylideneamino]-2,3-benzo-15-crown-5 complexes

The crystal structures of two compounds, CuL ₂ and LiNCS·HL [HL = 4′-[2-(tosylamino)benzylideneamino]-2,3-benzo-15-crown-5], have been determined from synchrotron powder diffraction data. Both compounds crystallize in the monoclinic space group P2 ₁/c and with one molecule in the asymmetric unit. In CuL ₂ the four N atoms of two bidentate L ligands coordinate the Cu^II ion in a distorted tetrahedral geometry with Cu—N distances of 1.98 (5)–2.05 (5) Å, while two O atoms from two sulfoxide groups complete the distorted octahedral Cu coordination [Cu—O 2.64 (4), 2.74 (4) Å]. In LiNCS·HL, lithium is coordinated by all five ether O atoms with Li—O distances of 2.03 (3)–2.50 (3) Å and an N atom from the thiocyanate moiety [Li—N 1.98 (3) Å] in a distorted pentagonal pyramidal geometry. Preliminary potentiometric selectivity measurements for ion-selective electrodes (ISEs) based on CuL ₂ and ZnL ₂ demonstrated significant differences in their selectivity. In order to find a possible reason for this, theoretical calculations at the DFT (B3LYP) level were performed. These calculations used the crystal structures of CuL ₂, LiNCS·HL, ZnL ₂ and HL as input geometries for the minimum energy optimization in vacuo. The results indicate that in ML ₂ complexes (M = Cu, Zn) the electronic structure of the metal ion determines the spatial orientation of benzo-15-crown-5 macrocycles, and their different orientation in CuL ₂ and ZnL ₂ results in different potentiometric selectivities of ISEs based on these compounds.