Pillaring of layers in α-zirconium phosphate by 1,10-phenanthroline and bis(1,10-phenanthroline)copper(II): formation of complex pillars in situ

Abstract

The complex [Cu(phen)₂]²⁺(phen = 1,10-phenanthroline) can be diffused between the layers of α-zirconium phosphate only if the layers are first pre-swelled by preparing the diethanol intercalate, α-Zr(HPO₄)₂(EtOH)₂. At maximum uptake a material of formula α-ZrH_1.6[Cu(phen)₂]_0.20(PO₄)₂·3H₂O is obtained and no further complex can be intercalated. X-Ray and spectroscopic evidence show that the [Cu(phen)₂]²⁺ remains intact after intercalation, and probably has a tetragonal-octahedral geometry. A ‘complex pillared’ layer structure is still present after the zeolitic water has been removed. However, the geometry adopted by the [Cu(phen)₂]²⁺ is now square-based pyramidal, and it is bonded asymmetrically between the phosphate layers. Further ions (Cu²⁺, Pd²⁺, or Ag⁺) can be exchanged into the pillared cavities, to form solid solutions. 1,10-Phenanthroline itself diffuses into α-Zr(HPO₄)₂(EtOH)₂ to form the ‘intercalated ligand’ phase α-Zr(HPO₄)₂(phen)_0.50·2H₂O at maximum uptake. This is a pure, well ordered Stage I phase with an interlayer distance of 13.58 Å, and it is suggested that the phen is ordered throughout the layers in a ‘slanted’ fashion. This phase exchanges Co²⁺, Ni²⁺, and Cu²⁺(in the order Cu²⁺ Co²⁺ > Ni²⁺) much more slowly than does the 2,2′-bipyridyl analogue, due to the steric hindrance caused by the bulkier ligand backbone and higher pillar density. Only in the case of Cu²⁺ does subsequent co-ordination to the phen proceed to complete formation of α-ZrH [Cu(phen)]_0.50(PO₄)₂·3H₂O. In the cobalt and nickel analogues there is competition between phen-co-ordinated and cavity-co-ordinated metal ion. Spectroscopic evidence (u.v.–visible, e.s.r.) is presented which shows that these complex pillars formed in situ have very distorted geometries, caused by the steric constraints imposed by the interlayer region.