We assembled eight cofacial porphyrin prisms using MTPyP (M = Co­(II) or Zn­(II), TPyP = 4-tetrapyridylporphyrin) and functionalized ruthenium-based “molecular clips” using coordination-driven self-assembly. Our approach allows for the rapid synthesis of these architectures in isolated yields as high as 98% for the assembly step. Structural and reactivity studies provided a deeper understanding of the role of the building blocks on the oxygen reduction reaction (ORR). Catalytic efficacy was probed by using cyclic and hydrodynamic voltammetry on heterogeneous catalyst inks in aqueous media. The reported prisms showed outstanding selectivity (>98%) for the kinetically hindered 4e–/4H+ reduction of O2 to H2O over the kinetically more accessible 2e–/2H+ reduction to H2O2. Furthermore, we have demonstrated significant cofacial enhancement in the observed catalytic rate constant k s (∼5 orders of magnitude) over the mononuclear analogue. We conclude that the steric bulk of the clip plays an important role in the structural dynamics of these prisms, which in turn modulates the ORR reactivity with respect to selectivity and kinetics.

Cofacial porphyrin catalysts for the Oxygen Reduction Reaction (ORR) formed via coordination-driven self-assembly have so far been limited to designs with fourfold symmetry, where four molecular clips bridge two porphyrin sites. We have synthesized six Py n Ph m (Py = pyridyl, Ph = phenyl) metalloporphyrin prisms (Co 2+ , Zn 2+ ) bridged by molecular clips containing two Rh 3+ centers. Four of these structures are lower symmetry, with the Py 3 Ph and Py 2 Ph 2 prisms containing three and two molecular clips, respectively. The Co 2+ species were evaluated for their ORR activity. Cyclic and hydrodynamic voltammetry studies of heterogeneous catalyst inks in aqueous media revealed marked differences in selectivity from ∼5% (Py 3 Ph) to ∼37% (Py 2 Ph 2 ) for the formation of H 2 O 2 . The single-crystal X-ray structure of the Zn 2 Py 2 Ph 2 prism shows an offset between the porphyrin faces. This structural feature may be responsible for the change in selectivity, consistent with previous studies of covalently tethered cofacial porphyrins that have shown that geometry is a critical determinant of two-electron/two-proton versus four-electron/four-proton pathways. Extraction of standard rate constants k s for the ORR revealed a cofacial enhancement of ∼2 orders of magnitude over mononuclear Co 2+ tetrapyridyl porphyrin. Even though all the prisms described here use the same molecular clip, the resultant structures, and thus the reactivity for the ORR, differ significantly based on the number and orientation of pyridyl donor groups on the porphyrins, highlighting how coordination-driven self-assembly can be used to rapidly tune dinuclear catalysts.

A self-assembled porphyrin cube can be metalated/transmetalated to contain fourteen cobalt ions in two different environments. The Co(ii) metalloporphyrin sites are electrocatalytically active to selectively generate hydrogen peroxide from oxygen.

Urbanization, which is accompanied by the flow of various production factors, leads to increasingly close spatial linkages between cities, and exerts profound influences on water resource use. This study focuses on the three major urban agglomerations in China’s Yangtze River Economic Belt, and examines the temporal changes and spatial variations of its water resource use based on an improved water ecological footprints (WEFs) model that uses city-level data to calculate yield factors and considers the recycling of water resources. Moreover, this study investigates the spatial autocorrelation of WEFs and explores the spatial correlations between WEFs and three dimensions of urbanization (population, economy, land) in three urban agglomerations. The results show that the WEF is the highest in the downstream of the Yangtze River and the lowest in the upper stream. City-level WEFs have significant spatial autocorrelations, and cities with high water use are often concentrated. In some regions, urbanization and WEFs have significant spatial correlations, indicating the environmental externality of urbanization on water resource use. This study contributes to the methodology of developing localized water use evaluation indices, and provides insights into the driving factors of WEFs and the environmental externality of urbanization at different spatial scales. Its findings provide empirical support for formulating and implementing more targeted water resources protection measures in the upper, middle, and lower reaches of the Yangtze River.

We report the electrocatalytic Oxygen Reduction Reaction on a rigid Co(II) porphyrin prism scaffold bridged by Ag(I) ions. The reactivity of this scaffold differs significantly from previous prism catalysts in...