Isomer Interconversion Studied through Single-Crystal to Single-Crystal Transformations in a Metal–Organic Framework Matrix

Careful changes to the primary coordination sphere of an organometallic species can modify its chemical and physical properties, potentially providing accessible coordinating sites for catalysis or modifying its photophysical properties. Here we show, via a series of single-crystal to single-crystal (SC-SC) transformations, the modification of the primary coordination sphere of a Mn(CO)3Br species that has been postsynthetically incorporated into a metal–organic framework ([Mn3L2L′] (1), where L = bis(4-carboxyphenyl-3,5-dimethylpyrazolyl)methane). By simply changing the pore solvates, and hence the secondary coordination sphere from polar (EtOH) to nonpolar (toluene, THF), the MOF-tethered species is converted from an ion pair to a charge-neutral complex with a coordinated bromide ligand. Coordinating solvents such as acetonitrile and benzonitrile compete as ligands and coordinate to the Mn(I) center. The demonstration of interconversion of ionization and solvation isomers allows the preparation of materials for facile anion exchange, in the cases where bromide remains uncoordinated, or when the bromide is coordinated to the MOF-tethered Mn-carbonyl species, a charge-neutral species is generated whose spectrum is red-shifted, offering potentially lower energy photolysis for photoinduced CO release.