Effect of bulkiness on reversible substitution reaction at Mn^II center with concomitant movement of the lattice DMF: observation through single-crystal to single-crystal fashion

Abstract

The porous coordination polymer ({[Mn(L)H₂O](H₂O)_1.5(dmf)}_n, 1) (DMF=N,N-dimethylformamide) exhibits variety of substitution reactions along with movement of lattice DMF molecule depending upon bulkiness of the external guest molecules. If pyridine or 4-picoline is used as a guest, both lattice and coordinated solvent molecules are simultaneously substituted (complexes 6 and 7, respectively). If a bulky guest like aniline is used, a partial substitution at the metal centers and full substitution at the channels takes place (complex 8). If the guest is 2-picoline (by varying the position of bulky methyl group with respect to donor N atom), one Mn^II center is substituted by 2-picoline, whereas the remaining center is substituted by a DMF molecule that migrates from the channel to the metal center (complex 9). Here, the lattice solvent molecules are substituted by 2-picoline molecules. For the case of other bulky guests like benzonitrile or 2,6-lutidine, both the metal centers are substituted by two DMF molecules, again migrating from the channel, and the lattice solvent molecules are substituted by these guest molecules (complex 10 and 11, respectively). A preferential substitution of pyridine over benzonitrile (complex 12) at the metal centers is observed only when the molar ratio of PhCN:Py is 95:5 or less. For the case of an aliphatic dimethylaminoacetonitrile guest, the metal centers remain unsubstituted (complex 13); rather substitutions of the lattice solvents by the guest molecules take place. All these phenomena are observed through single crystal to single crystal (SC-SC) phenomena.