Matrix isolation chemistry in a porous metal-organic framework:: Photochemical substitutions of N2 and H2 in Zn4O[(η6-1,4-benzenedicarboxylate)Cr(CO)3]3

Reaction of the microporous metal-organic framework Zn4O(BDC)(3) (BDC2- = 1,4-benzenedicarboxylate) with Cr(CO)(6) at 140 degrees C in a 6:1 mixture of dibutylether and THF affords Zn4O[(BDC)Cr(CO)(3)](3)(1). This compound retains the porous cubic structure of the parent framework, but features Cr(CO)3 groups attached in an 1 fashion to all of the benzene rings. Compound I is also microporous, exhibiting a BET surface area of 2130 m(2)/g. It can be fully decarbonylated by heating at 200 degrees C, but the resulting gray solid (2) shows little affinity for N-2 or H-2 at 298 K, suggesting aggregation of the chromium atoms. In contrast, photolysis of 1 using 450-nm light in an atmosphere of N-2 or H-2 produces solids with infrared spectra indicative of Zn4O[(BDC)Cr(CO)(2)(N-2)](3) (3) and Zn4O[(BDC)Cr(CO)(2)(H-2)]3 (4). Under an N2 atmosphere, compound 4 completely converts into compound 3 over the course of 12 h, demonstrating the lability of the Cr-0-H-2 bond. Owing to isolation of the metal centers within the rigid, evacuable framework structures, the N-2- and H-2-substituted compounds show greatly enhanced stability relative to molecular analogues generated in frozen gas matrices or supercritical fluid solutions.