Synthesis and characterisation of the first organotin complex of piroxicam. An extended network system via non-hydrogen, hydrogen bonding linkages and C–H· · ·π contacts

Abstract

The organotin complex, [SnBu₂(pir)]_n, of the potent and widely used anti-inflammatory drug piroxicam, H₂pir, was obtained and a crystal structure determination showed that in this complex the ligand is doubly deprotonated at the oxygen and amide nitrogen atoms. There are two similar molecules in the asymmetric unit. The isolated molecules of Sn(1) or Sn(2) are arranged in polymers in a head to tail fashion with a stacking of alternate parallel chains. Extended networks of Sn–O–Sn, C–H· · ·O and C–H· · ·π contacts lead to aggregation and a supramolecular assembly. Real concentration protonation constants for the zwitterionic form (pyridyl group) and the protonated piroxicam (enolic group) were determined spectrophotometrically in pure aqueous solutions of constant ionic strength. It is the first example where piroxicam is proved to act as a doubly deprotonated tridentate ligand.