Polyoxometalates represent a diverse range of molecular clusters with an almost unmatched range of physical properties and the ability to form structures that can bridge several length scales. The new building block principles that have been discovered are beginning to allow the design of complex clusters with desired properties and structures and several structural types and novel physical properties are examined. In this critical review the synthetic and design approaches to the many polyoxometalate cluster types are presented encompassing all the sub-types of polyoxometalates including, isopolyoxometalates, heteropolyoxometalates, and reduced molybdenum blue systems. As well as the fundamental structure and bonding aspects, the final section is devoted to discussing these clusters in the context of contemporary and emerging interdisciplinary interests from areas as diverse as anti-viral agents, biological ion transport models, and materials science.

Polyoxometalates are clusters of metal-oxide units, comprising a large diversity of nanoscale structures, and have many common building blocks; in fact polyoxometalate clusters are perhaps the largest non-biologically derived molecules structurally characterised. Not only can polyoxometalates have gigantic nanoscale molecular structures, but they also a have a vast array of physical properties, many of which can be specifically ‘engineered-in’. Here we describe how building block libraries of polyoxometalates can be used to construct systems with important catalytic, electronic, and structural properties. We also show that it is possible to construct complex chemical systems based upon polyoxometalates, manipulating the templating/self templating rules to exhibit emergent processes from the molecular to the macroscopic scale.

Scheduling hydrogen release from water: Photosynthesis splits water to provide protons and electrons for plant growth; oxygen is a by-product. When chemists split water, they're also more interested in making fuel, and the simplest product is hydrogen (a combination of protons and electrons). One challenge is keeping the reactive hydrogen and oxygen product streams separate. Rausch et al. present a scheme that captures the protons and electrons in a molecular cluster of silico-tungstic acid. Later, they expose the cluster to platinum, coaxing the acid into releasing hydrogen. Eliminating the mixing risk increases the potential for household use. Science , this issue p. 1326

Clear directions for a robotic platform: The chemistry literature contains more than a century's worth of instructions for making molecules, all written by and for humans. Steiner et al. developed an autonomous compiler and robotic laboratory platform to synthesize organic compounds on the basis of standardized methods descriptions (see the Perspective by Milo). The platform comprises conventional equipment such as round-bottom flasks, separatory funnels, and a rotary evaporator to maximize its compatibility with extant literature. The authors showcase the system with short syntheses of three common pharmaceuticals that proceeded comparably to manual synthesis. Science , this issue p. eaav2211 ; see also p. 122