Conformationally locked pentadentate macrocycles containing the 1,10-phenanthroline unit.: Synthesis and crystal structure of 5-oxa-2,8-dithia[9](2,9)-1,10-phenanthrolinophane (L) and its coordination properties to NiII, PdII, PtII, RhIII and RuII

The complexation of the new mixed thia-aza-oxa macrocycle 5-oxa-2,8-dithia[9](2,9)-1,10-phenanthrolinophane (L) containing the 1,10-phenanthroline unit with Ni-II, Pd-II, Pt-II, Rh-III and Ru-II has been investigated. The results have been compared with those obtained with the structurally related ligand 2,5,8-trithia[9](2,9)-1,10-phenanthrolinophane (L'). The most stable conformations of both ligands have been calculated in order to understand their change upon metal complexation and for L good agreement has been found with the conformations observed in the crystal structure of L .1/2H(2)O. The single-crystal structures of [Ni(L)Cl]BF4 and [Ru(L)(PPh3)][PF6](2).1/4MeCN reveal a N2S2O coordination sphere about Ni-II and Ru-II, with the macrocyclic ligand in a folded conformation and with the sixth coordination site taken up by Cl- or PPh3, respectively. For [Pd(L)][BF4](2) an [N2S2 + O] coordination is observed, with the O-donor interacting weakly with the metal centre at the apical position of a square-based coordination sphere. C-13 and H-1 NMR spectroscopic studies indicate that the complexes are not fluxional in solution, with the ligand imposing the same coordination sphere as observed in the solid state. C-13 NMR spectroscopy has also helped in elucidating the stereochemistry of [Rh(L)Cl-2]BF4 for which no suitable crystals could be grown: the two Cl- ligands are mutually trans with the N2S2 donor set of the macrocyclic ligand occupying the equatorial positions of an octahedral coordination sphere and with the O-donor atom left un-coordinated. The redox properties of all the complexes in MeCN have been studied.