Pyridine-based macrocycles containing N, O, and S and their use as ion-selective electrodes. Crystal structures of 15-aza-6-oxa-3,9-dithiabicyclo[9.3.1]pentadeca-1(15),11,13-triene and (15-aza-6-oxa-3,9-dithiabicyclo[9.3.1]pentadeca-1(15),11,13-triene)dichlorocopper(II)