The　single-crystal-to-single-crystal　(SCSC)　transformations　of　metal-organic　frameworks　(MOFs)　are　fascinating　because　we　can　directly　observe　the　change　of　the　crystal　structure　during　the　transformation　process.　It　also　greatly　helps　to　understand　the　delicate　interaction　between　the　guest　molecules　and　the　skeleton　framework　and　therefore　fosters　a　deep　understanding　of　gas　storage　and　separation　within　the　frameworks.　Herein,　we　report　two　novel　MOFs,　[Cu8(BCB)4(μ3-OH)2(μ3-O)(H2O)8(Py)5]·16DMF·52H2O　(1)　and　[Cu3(BCB)2(Py)6]·DMF·11H2O　(2)　(Py　=　pyridine;　DMF　=　N,N′-dimethylformamide),　which　were　constructed　through　the　self-assembly　of　Cu2+　and　4,4′,4″-benzenetricarbonyltribenzoic　acid　(H3BCB)　by　a　solvothermal　reaction.　Although　the　structure　and　coordination　patterns　of　compound　1　are　pretty　different　from　those　of　2,　the　two　Cu-MOFs　were　prepared　from　identical　ligands　and　similar　reaction　conditions.　Interestingly,　compound　1　will　change　to　2　wholly　and　gradually　after　the　addition　of　a　certain　amount　of　Py　with　a　small　amount　of　dilute　hydrochloric　acid.　This　conversion　represents　a　scarce　example　of　SCSC　transformation　involving　transition-metal-based　MOFs.　Moreover,　with　its　microporous　nature,　compound　2　shows　large　carbon　dioxide　(CO2)　uptake　capability　and　good　selectivity　for　CO2/N2　separation.　Furthermore,　both　compounds　1　and　2　could　be　used　as　excellent　heterogeneous　catalysts　toward　the　cyanosilylation　reaction　under　solvent-free　conditions.　©　2022　American　Chemical　Society.