Titration of Zr3(μ‐OH) Hydroxy Groups at the Cornerstones of Bulk MOF UiO‐67, [Zr6O4(OH)4(biphenyldicarboxylate)6], and Their Reaction with [AuMe(PMe3)]

Abstract The known MOF UiO‐67 of general formula [Zr 6 O 4 (OH) 4 (bpdc) 6 ] [bpdc = biphenyldicarboxylate, O 2 C(C 6 H 4 ) 2 CO 2 ] has been synthesized on a 3 g scale and characterized by BET, TGA, XRD, IR and 13 C NMR spectroscopy, and elemental analyses. The chemical accessibility of the hydroxy ligand Zr 3 (μ‐OH) was assessed by the addition of D 2 O: The expected isotopic shift of ν(OH) = 3673 cm –1 to ν(OD) = 2709 cm –1 in the IR spectrum was observed. The OH content in bulk UiO‐67, previously mildly activated at 120 °C under vacuum (10 –5 Torr) overnight, was quantitatively determined by three methods: (1) By integration of the IR ν(OH) region and comparison with calibrated spectra of MCM‐41 previously dehydroxylated at 500 °C, which gave a spectroscopically measured OH content in bulk UiO‐67 of 2.2 mmol/g (37 mg OH/g); (2) by extrapolation of the OH content from the measured weight loss between 250 and 400 °C in TGA, which corresponded to 1.6 mmol OH/g (27 mg OH/g); and (3) by chemical titration of UiO‐67 with CH 3 MgBr and GC determination of the evolved methane, which gave 1.8 mmol OH/g (31 mg OH/g). The three methods, and in particular the latter chemical titration, are in very good to excellent agreement with the nominal OH content based on the molecular formula [Zr 6 O 4 (OH) 4 (bpdc) 6 ] (expected: 1.9 mmol OH/g, 32 mg OH/g; experimental/calculated OH content = 110, 85, and 95 %, respectively, for the three methods). The weak acidity of the OH moiety in UiO‐67 was assessed by IR and 31 P NMR monitoring of the physisorption of PMe 3 in the UiO‐67 cavities. Inclusion of the organometallic Au I complex [AuMe(PMe 3 )] in a 1:1 molar ratio with respect to [Zr 6 O 4 (OH) 4 (bpdc) 6 ] was achieved. Some chemisorption at 20 % of the cornerstone hydroxy sites also occurred to yield [Zr 6 O 4 (OH) 3 (bpdc) 6 (OAuPMe 3 )].