Acetate exchange mechanism on a Zr₁₂ oxo hydroxo cluster: relevance for reshaping Zr–carboxylate coordination adaptable networks

Abstract

The kinetics and mechanism of the acetate ligand exchange with free acetic acid in [Zr6O4(OH)4(O2CCH3)12]2, used as a molecular model of crosslink migration in [Zr6O4(OH)4(carboxylate)12-n(OH)n]-based coordination adaptable networks with vitrimer-like...

Hafnium coordination vitrimer based on carboxylate exchange: synthesis, properties, and mechanistic investigations on the [Hf6O4(OH)4(O2CMe)12]2 model compound

“…The 1 H NMR spectra in CD 2 Cl 2 and in C 6 D 6 (shown in Figure 5) are quite similar to those of the corresponding Zr compound in the same solvents. [11] The spectrum of the Hf 12 compound in CD 2 Cl 2 has also been described in a previous contribution, [7d] though without the identification of the μ 3 -OH resonances, while the spectrum in C 6 D 6 is reported here for the first time. The resonance assignments are based on those previously made for the Zr analogue and are backed up by variable-temperature, DOSY and EXSY NMR analyses, as shown below.…”

“…The investigations outlined below mirror more or less exactly those recently published by us for the analogous [Zr 6 O 4 (OH) 4 (O 2 CMe) 12 ] 2 system. [11] For each equivalent Hf 6 subunit of [Hf 6 O 4 (OH) 4 (O 2 CMe) 12 ] 2 , the molecular C 2h symmetry splits the twelve acetate ligands into seven magnetically inequivalent sets (chelating, 2 : 1; beltbridging, 2 : 2 : 2; inner-face-bridging, 1; intercluster-bridging, 2) and the four μ 3 -OH ligands into three sets (1 : 1 : 2). The 1 H NMR spectra in CD 2 Cl 2 and in C 6 D 6 (shown in Figure 5) are quite similar to those of the corresponding Zr compound in the same solvents.…”

“…We have also reported a detailed kinetico-mechanistic study, based on variable-temperature and variable-concentration 1 H NMR spectra, on the model [Zr 6 O 4 (OH) 4 (O 2 CMe) 12 ] 2 compound (C 2h À Zr 12 structure of Figure 1), which demonstrated an operationally associative exchange mechanism for the chelating acetates and for most of the intracluster-bridging acetates. [11] The rate-determining step, however, consists of partial acetate dissociation with assistance of a neighboring bridging hydroxide ligand, which provides a stabilizing Hbonding interaction (Scheme 1).…”

“…[16] A view of the [Hf 6 O 4 (OH) 4 (O 2 CMe) 12 ] 2 molecule is shown in Figure 2 and an additional view highlighting the H-bonding interactions of the metal complex with the interstitial acids is available in . [11] Scheme 2. Synthesis of HgÀ CooAN-10.…”

Coordination Adaptable Networks: Introducing Vitrimer Properties Using Dynamic Coordination Bonds

“…Variabletemperature and variable-ratio 1 H NMR studies, in combination with DFT calculations, were carried out for the exchange of acetates with free acetic acid in the model C 2h -symmetric [Zr 6 O 4 (OH) 4 (O 2 CMe) 12 ] 2 compound. [48] The results indicate that both chelating and belt-bridging acetates exchange rapidly (resonance coalescence on the NMR timescale) with a ratedetermining partial dissociation (zero order in free CH 3 COOH), assisted by the cluster triply bridging hydroxide ligand (μ 3 -OH) to yield an H-bonded intermediate, followed by rapid associative scrambling (Scheme 4). Hence, the exchange processes are operationally associative.…”