Single-Crystal-to-Single-Crystal Transformations of Metal–Organic-Framework-Supported, Site-Isolated Trigonal-Planar Cu(I) Complexes with Labile Ligands

Abstract

Transition-metal complexes bearing labile ligands can be difficult to isolate and study in solution because of unwanted dinucleation or ligand substitution reactions. Metal−organic frameworks (MOFs) provide a unique matrix that allows site isolation and stabilization of well-defined transition-metal complexes that may be of importance as moieties for gas adsorption or catalysis. Herein we report the development of an in situ anion metathesis strategy that facilitates the postsynthetic modification of Cu(I) complexes appended to a porous, crystalline MOF. By exchange of coordinated chloride for weakly coordinating anions in the presence of carbon monoxide (CO) or ethylene, a series of labile MOF-appended Cu(I) complexes featuring CO or ethylene ligands are prepared and structurally characterized using X-ray crystallography. These complexes have an uncommon trigonal planar geometry because of the absence of coordinating solvents. The porous host framework allows small and moderately sized molecules to access the isolated Cu(I) sites and displace the "place-holder" CO ligand, mirroring the ligand-exchange processes involved in Cu-centered catalysis.

Coordination modulated on-off switching of flexibility in a metal–organic framework

“…33 SCXRD analysis revealed a linear AuCl complex coordinated to a single N-donor site in 1 (Figure 1, Figures S15, S16), and EDX analysis of the crystals (Table S2, Figure S17) confirmed the expected Mn:Au:Cl ratio of 3:1: with NaBr or NaI in dry methanol for 24 and 48 hours, respectively. 29,30 In both cases, EDX analysis of the crystals indicated that quantitative halide exchange had occurred (see Mn:Cu:X 3:1:1 ratios; X= Br, I; Table S3, Figure S20). Single crystal quality for the bromide and iodide exchanged MOFs was excellent, permitting their examination by SCXRD.…”

“…2 (linear), 3 (trigonal planar) and 4 (tetrahedral) are known) 34 that can be interconverted under carefully controlled conditions. 30,35 In addition, we recently demonstrated that 1 can support both tetrahedral and trigonal planar geometries for Cu( i ). 30 Thus, we speculated whether a flexible MOF material could be realised by modulating the Cu( i ) coordination geometry, i.e.…”

“… 30,35 In addition, we recently demonstrated that 1 can support both tetrahedral and trigonal planar geometries for Cu( i ). 30 Thus, we speculated whether a flexible MOF material could be realised by modulating the Cu( i ) coordination geometry, i.e. switching from a rigid framework (Cu( i ) is chelated) to a flexible framework (Cu( i ) is monodentate).…”

“…27 Work in our laboratory has shown that a manganese(II)based MOF, 1 ([Mn3(L)2L'], where L=L'= bis(4-carboxyphenyl-3,5-dimethyl-pyrazol-1-yl)methane, and L' possesses a free N,N' chelating site) can retain crystallinity following post-synthetic metalation and consecutive chemical reactions at the extraneous metal site. [28][29][30][31][32] We have shown that this is primarily due to the intrinsic flexibility of the organic linker which alleviates strain on the framework caused by changes in geometry of the chelated metal ion during reactions. 33 A salient example is cobalt(II) metalated 1 which undergoes a reversible, temperature-dependent, conversion between octahedral 1•[Co(H2O)4]Cl2 and tetrahedral 1•[CoCl2] geometries at the post-synthetic metalation site (Figure 1).…”

“…Given the tailorable synthesis of MOFs and vast number of coordination complexes that are known, we believe that this work provides general design principles for the synthesis of stimuli-responsive flexible MOF materials. 30 Washing the crystals with non-polar solvents (e.g. toluene, diethyl ether, or alkanes) drives the quantitative formation of the non-solvated, trigonal planar species, 1•[CuCl] (Figure 1).…”