Coordination Polymer Flexibility Leads to Polymorphism and Enables a Crystalline Solid–Vapour Reaction: A Multi‐technique Mechanistic Study

Abstract

Despite an absence of conventional porosity, the 1D coordination polymer [Ag4(O2C(CF2)2CF3)4(TMP)3] (1; TMP=tetramethylpyrazine) can absorb small alcohols from the vapour phase, which insert into Ag–O bonds to yield coordination polymers [Ag4(O2C(CF2)2CF3)4(TMP)3(ROH)2] (1-ROH; R=Me, Et, iPr). The reactions are reversible single-crystal-to-single-crystal transformations. Vapour-solid equilibria have been examined by gas-phase IR spectroscopy (K=5.68(9)×10−5 (MeOH), 9.5(3)×10−6 (EtOH), 6.14(5)×10−5 (iPrOH) at 295 K, 1 bar). Thermal analyses (TGA, DSC) have enabled quantitative comparison of two-step reactions 1-ROH→1→2, in which 2 is the 2D coordination polymer [Ag4(O2C(CF2)2CF3)4(TMP)2] formed by loss of TMP ligands exclusively from singly-bridging sites. Four polymorphic forms of 1 (1-ALT, 1-AHT, 1-BLT and 1-BHT; HT=high temperature, LT=low temperature) have been identified crystallographically. In situ powder X-ray diffraction (PXRD) studies of the 1-ROH→1→2 transformations indicate the role of the HT polymorphs in these reactions. The structural relationship between polymorphs, involving changes in conformation of perfluoroalkyl chains and a change in orientation of entire polymers (A versus B forms), suggests a mechanism for the observed reactions and a pathway for guest transport within the fluorous layers. Consistent with this pathway, optical microscopy and AFM studies on single crystals of 1-MeOH/1-AHT show that cracks parallel to the layers of interdigitated perfluoroalkyl chains develop during the MeOH release/uptake process.

Arene guest selectivity and pore flexibility in a metal–organic framework with semi-fluorinated channel walls

“…It is important to note that no loss of TMP ligands was detected, which may suggest that there is no facile pathway for escape of the ligand. This contrasts with our observations for monocarboxylate-containing material [Ag 4 (O 2 CCF 2 CF 2 CF 3 ) 4 (TMP) 3 ], which upon heating loses TMP and rearranges to give [Ag 4 (O 2 CCF 2 CF 2 CF 3 ) 4 (TMP) 2 ] [19,20]. Structure determination of the intermediate material would shed light on the mechanism of the solid-state rearrangement, which requires considerable reorganization of metal–ligand bonding, and again highlights the flexibility and propensity for breaking and formation of coordination bonds in the crystalline solid state.…”

“…alcohols, arenes), often without loss of crystallinity in the materials [18–22]. These processes, often followed by in situ diffraction or spectroscopic studies, are enabled by mobility of the fluoralkyl chains of the carboxylate ligands and the flexibility in coordination at the Ag(I) centres, which takes advantage of the lack of strong preferences in coordination geometry of the d 10 metal centres and the lability of the metal–ligand bonds [20].

Scheme 1.Structural analogy between ( a ) hydrogen-bonded carboxylic acid dimer (R = alkyl, aryl group) and ( b ) silver carboxylate dimer (R f  = perfluoroalkyl group).

Scheme 2.Examples of silver(I) perfluorocarboxylate dimer secondary building units, connected by neutral (ditopic) diimine ligands, L, to propagate coordination polymers.

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Reversible Encapsulation of Xenon and CH2Cl2 in a Solid‐State Molecular Organometallic Framework (Guest@SMOM)

“…While these systems also promote catalysis (e.g. [13] [6] TheC H 2 Cl 2 molecule refined to 75 %o ccupancy, is disordered over two positions (0.65:0.10), [15] and is supported by ClCH 2 Cl···F 3 C[range 2.685(3)-3.127(2) ,sum of van der Waals radii = 3.28 [16] ]a nd Cl 2 CH 2 ···F 3 C[ 2.425(2)-3.035-(4) ]n on-covalent interactions ( Figure S19,S20). [1,12] Ak ey question, then, is how substrate/product molecules move in and out of the crystalline lattice on the timescale of synthesis (minutes to hours).…”

“…This is significantly shifted from that in solution (d 5.33) reflecting ring current effects from the proximal [BAr F 4 ] À anions,aswehave noted previously for s-alkane complexes such as [1-NBA]-[BAr F 4 ]. Thes ingle resonance ( Figure S6) observed for the CH 2 Cl 2 in the 13 reflecting the different steric requirements of Cy 2 PCH 2 CH 2 PCy 2 and Cy 2 PCH 2 PCy 2 . Thes ingle resonance ( Figure S6) observed for the CH 2 Cl 2 in the 13 reflecting the different steric requirements of Cy 2 PCH 2 CH 2 PCy 2 and Cy 2 PCH 2 PCy 2 .…”

Unveiling the Mechanism of Water‐Triggered Diplex Transformation and Correlating the Changes in Structures and Separation Properties

“…The structural transformation of coordination polymers always involves the breaking and re‐making of coordinated or covalent bonds, and some novel structures that cannot be synthesized under conventional conditions may be obtained through structural transformation processes . Among the structural transformations of PCPs, two types can be identified, namely, solid‐state structural transformations (SSSTs) and dissolution‐recrystallization structural transformation (DRSTs) . In particular, SCSCs, which are the most important subset of SSSTs, and DRSTs are highly desirable to identify the structural changes by single‐crystal X‐ray crystallography .…”