Pillar chemistry. Part 5. Intercalation of 2,2′-bipyridine, 1,10-phenanthroline, and 2,9-dimethyl-1,10-phenanthroline into γ-zirconium phosphate and formation of interlayer copper(II) complexes

Abstract

2,2′-Bipyridine (bipy), 1,10-phenanthroline (phen), and 2,9-dimethyl-1,10-phenanthroline (dmphen) can be intercalated into γ-Zr(HPO₄)₂·2H₂O as such (i.e. without first pre-swelling the matrix) to give materials having the final formulation γ-Zr(HPO₄)₂L_x·n H₂O (x= 0.48–0.50). With dmphen, if the γ-Zr(HPO₄)₂·2H₂O is first pre-swelled using ethanol, a further, pure layered phase of composition γ-Zr(HPO₄)₂(dmphen)_0.28·2H₂O is obtained; bipy and phen do not give this latter phase. Indirect evidence, X-ray diffraction and i.r. spectroscopy, indicates that the orientations of the amines in the interlayer are different from those in the α-Zr(HPO₄)₂·H₂O analogues, probably due to the presence of specific hydrogen bonding by the interlayer water molecules. All four materials exchange Cu^II. As expected, given its lower interlayer ligand density compared with the other materials, γ-Zr(HPO₄)₂(dmphen)_0.28·2H₂O takes up Cu^II most readily. Further, within the series γ-Zr(HPO₄)₂L_x·n H₂O the order of uptake, phen > dmphen > bipy, is not that expected from ligand steric requirements alone and the uptake is in all cases slower than that in the α-Zr(HPO₄)₂·H₂O analogues, both results indicating the importance of ligand–matrix interactions. The final pure layered materials obtained have [Cu²⁺]: [] ratios of 1:1 [γ-(dmphen)_0.28] and 1:2 [γ-dmphen)_0.48 and γ-(bipy)_0.48]; γ-(phen)_0.50 gave [Cu²⁺] : []= 0.8:1. Spectroscopic evidence shows that Cu^II co-ordinates to the amine ligand only in the bipy and phen cases, whereas both dmphen-containing materials exchange Cu²⁺ into cavities widened by the dmphen but without co-ordination to the intercalated ligand.