Smoothing the single-crystal to single-crystal conversions of a two-dimensional metal-organic framework via the hetero-metal doping of the linear trimetallic secondary building unit

The two-dimensional (2D) metal-organic framework (MOF) [Cd2.25Co0.75(BTB)(2)(DEF)(4)]2(DEF)(0.5) (1a, BTB = benzene-1,3,5-tribenzolate; DEF = N,N-diethylformamide) featuring linear trimetallic cluster secondary building units (SBUs) and replaceable DEF solvates reacts smoothly with dipyridyl ligands DPS, DPDS, and BIPY (DPS = 4,4-dipyridyl sulfide; DPDS = 4,4-dipyridyl disulfide; BIPY = 4,4-bipyridine), yielding three-dimensional (3D) non-interpenetrated [Cd2.25Co0.75(BTB)(2)(DPS)(2)]<bold>xSol </bold>(2) and [Cd2.25Co0.75(BTB)(2)(DPDS)(2)]<bold>xSol </bold>(3), and interpenetrated [Cd2.25Co0.75(BTB)(2)(BIPY)(H2O)(2)]<bold>xSol </bold>(4). The smooth conversion of 1a to 3 contrasts the drastic single-crystal to single-crystal (SCSC) conversion observed for the homometallic [Cd-3(BTB)(2)(DEF)(4)]2(DEF)(0.5) (1b), presumably due to the presence of the relatively Lewis acidic Co2+ that lessens the propensity for binding by soft dipyridyl donors. Activated samples of 2-4 showed no obvious absorption of N-2 at 77 K, but reversible type I uptake of CO2 at 195 K.