Pillar chemistry. Part 4. Palladium(II)–2,2′-bipyridyl, –1,10-phenanthroline, and –2,9-dimethyl-1,10-phenanthroline complex pillars in α-zirconium phosphate

Abstract

Palladium(II) can be exchanged into the layered composites α-Zr(HPO₄)₂(bipy)_0.25·1.5H₂O (bipy = 2,2′-bipyridyl), α-Zr(HPO₄)₂(phen)_0.50·2H₂O (phen = 1,10-phenanthroline), and α-Zr(HPO₄)₂(dmphen)_0.50·2.5H₂O (dmphen = 2,9-dimethyl-1,10-phenanthroline) to give new palladium(II) amine complex–pillared materials. In all three cases, both 1 :2 and 1 :1 Pd^II:amine complexes are formed between the layers. Pillared materials with an interlayer distance as high as 17.3 Å can be obtained. Thus, using such in situ preparation methods, it is possible to prepare pillared materials with pore dimensions approaching those found in zeolite Y. Electronic spectral evidence for the presence of different geometries for the pillars is described (square planar for bipy and phen, but five-co-ordinate for both 1 :2 and 1 :1 dmphen pillared materials). All the materials exchange further metal ions, Co²⁺, Ni²⁺, and Cu²⁺, to high loading levels, a demonstration that they are indeed pillared. Evidence is presented which shows that uptake of Cu²⁺ occurs at different rates for the 1 :1 and 1 :2 complex–pillared materials, i.e. the cavities have different sizes and therefore different accessibilities. In addition, spectroscopic probing (visible–near u.v. and e.s.r.) of these cavity-exchanged ions clearly demonstrates that the new cavities formed have geometries different from those present in the parent α-Zr(HPO₄)₂·H₂O.