UV-visible transmission microscope spectrophotometry on x-type zeolites: Part I. Formation of different nickel complexes in zeolite X

Abstract

Comparative UV-visible spectroscopic investigations on single crystals of nickel(II) salts of D 4h symmetry and of NiNaX zeolites with various nickel contents were carried out. The transmission spectra were recorded by means of a microcomputer-controlled microscope spectrophotometer (MMSP method). The absorption curves of NiNaX zeolites showed different symmetries of nickel(II) complexes within zeolites depending on the degree of ion exchange. An absorption maximum of 260 nm characteristic for nickel(II) complexes of D 4h symmetry was detected only at low degrees of ion exchange, whereas the spectra of highly-exchanged NiNaX zeolites were almost identical to those of octahedral nickel complexes obtained from aqueous solutions of nickel(II) salts. The formation of differently coordinated nickel complexes is discussed in terms of graph theory, assuming various molecular complexes whose graphs represent all relations between the cations and the surrounding zeolite lattice.