The incorporation and stabilization of copper(II) complexes in silica sol-gel matrices

The incorporation and thermal stabilization of copper(II) complexes into siloxane sol-gels has been studied using the electron paramagnetic resonance of the copper(II) cation. In separate experiments, copper(II) chloride and copper(II) chloride complexed with 1,10-phenanthroline have been introduced during the initial hydrolysis of tetraethoxysilane. The EPR spectra of the incorporated copper(II) complexes have been followed during the subsequent drying and heating of the resulting siloxane gels. It has been determined that some of the copper(II) complexes are incorporated into the siloxane network, residing in the small isolated molecular spaces of diameter less than 16 A. Excess copper(II) complexes remain solvated in the large open pores of diameter greater than 1000 A. The EPR results indicate that copper(II) complexes incorporated into the small isolated molecular spaces maintain their ligation environment when heated in flowing argon to temperatures as high as 446{dollar}spcirc{dollar}C, whereas those incorporated into the large open pores do not.; Heating the doped siloxane gels in flowing argon also causes radical color center formation and glass blackening at temperatures as low as 278{dollar}spcirc{dollar}C. It has been determined that these effects can be eliminated by heating the siloxane gels in flowing oxygen, although the ligation environment of the copper(II) complexes incorporated in the small molecular spaces then becomes unstable between 300 and 340{dollar}spcirc{dollar}C.; Applying these results to a siloxane gel doped with copper(II)-1,10-phenanthroline complexes, it has been determined that heating the gel initially in flowing argon to 340{dollar}spcirc{dollar}C and then subsequently in flowing oxygen to 420{dollar}spcirc{dollar}C protects the incorporated complexes, prevents glass blackening and produces a unique, optically active molecular composite glass.