Thiophene-linked azacryptand sites for dicopper and disilver; thiophene sulfur as an inert spacer?

Abstract

Two disilver cryptates of the thiophene-spaced azacryptand hexa Schiff bases N[(CH₂)_nNCHRHCN(CH₂)_n]₃N (n= 2 or 3, R = thiophene-2,5-diyl) and with the dicopper(I) cryptate where n= 2 have been structurally characterised. The dinuclear separation increases by 0.36 Å on going from the disilver complex of the n= 2 cryptand, to the n= 3 analogue, with that in the dicopper(I) cryptate intermediate, but little difference in cryptand conformation is observed in the three complexes. Proton NMR spectra show three-bond (H–CN–Ag) coupling of each imino CH proton to ^109,107Ag, confirmed by an ¹⁰⁹Ag insensitive nuclei enhanced by polarisation transfer experiment. No copper(II) cryptates were obtained with the hexa(Schiff-base) cryptands. The analogous octaamino compounds generate dicopper(II) cryptates which accommodate bridging anions in cascade fashion, with a bridging disposition collinear, Cu–NNN–Cu, in the µ-azido-, but non-linear, Cu–O(H)–Cu, in the µ-hydroxo-cryptate. Both the hexa(Schiff-base) and octaamino cryptates are very similar to inert-spacer azacryptates and give no evidence for hemico-ordination of thiophene sulfur.