– 473 K) and ambient pressures has been previously
demonstrated,39,40 including a prior report from our
group evidencing participation of every single MIL-100 tri-iron node
towards methanol formation,35 unlike iron-zeolites
that typically carry distributions of active and inactive
multinuclear iron centers.46–49 In this study, we use
a suite of spectroscopic, transient kinetic, and site titration tools to
relate metal oxidation state to reactive function. Specifically, the
role of Fe2+ and Fe3+ sites in
methanol and CO2 formation are identified. Altering the
identity of the metal from iron to chromium enables C-C bond formation
events that appear to involve methoxy intermediates that also mediate
methanol formation over both MIL-100(M) variants. To this end, we
elucidate in Section 3.1 the identity of sites involved in
CO2 and methanol formation, identify in Section 3.2 the
role of methoxy intermediates, demonstrate the propensity towards and
methods for controlling the prevalence of C-C bond formation over
MIL-100(Cr) in Section 3.3, before clarifying the diversity of
functionality of Fe3+-methoxies in Section 3.4 The
study captures how precise control over metal identity and oxidation
state, combined with manipulation of the relative velocity of water and
methanol concentration fronts, enables control not only over the
selectivity towards desired partial oxidation products such as methanol
(versus CO2) but also that towards C2 oxygenates (over
C1 oxygenates).