The interaction of lead(II) with oxa-aza macrocycles: the X-ray crystal structures of lead(II) complexes of an N3O3 Schiff-base macrocycle and of the corresponding saturated macrocycle

Abstract

The complexes [PbL¹(NO₃)₂]·H₂O, (1)·H₂O, and [PbL²(NO₃)₂]·H₂O, (2)·H₂O, where L¹ and L² are corresponding di-imino- and diamino-macrocycles containing an N₃O₃ donor set, have been synthesized and characterised. X-Ray structural analyses of the anhydrous form of (1) and (2) have revealed significantly different co-ordination environments for the lead(II) ion in the complexes. In (1), L¹ utilises all six possible donors in a ten-co-ordinate complex, with no apparent stereochemical activity of the lone pair on lead(II). Crystals of (1) were monoclinic, space group P2₁/n(alternative no. 14) with a= 30.245(6), b= 10.271 (2), c= 16.246(3)Å, β= 95.05(3)°, and Z= 8. 2 872 Independent reflections above background were measured and the structure refined to R= 0.0648. In contrast, L² employs only the three nitrogen donor atoms of the macrocycle in a six-co-ordinate complex, apparently with a stereochemically active lone pair. Crystals of (2) were triclinic, space group P(no. 2) with a= 15.117(3), b= 9.658(2), c= 9.182(2)Å, α= 76.24(2), β= 105.03(3), γ= 92.19(3)°, and Z= 2.3214 Independent reflections above background were measured and the structure refined to R= 0.0508.