M6O8 metal oxo clusters: A key structural motif across the periodic table
Ajmal Roshan Unniram Parambil, Jikson Pulparayil Mathew, Muhammed Jibin Parammal, Jonathan De Roo
Abstract
Octahedral M 6 O 8 clusters represent a versatile class of compounds formed by a wide range of elements across the periodic table. They stand out due to their prevalence among 23 metals and their use as nodes in metal–organic frameworks. In this review, we examine their structural features, synthetic strategies, and characterization methods, with a focus on highlighting the trends and parallels among oxo clusters of different metals. We begin with an analysis of cluster core, identifying the metals capable of adopting the M 6 O 8 architecture and the electronic and geometric factors that enable its formation. We then discuss surface functionalization of clusters, focusing on key ligand classes and their influence on cluster geometry and stability. Following this general analysis, we proceed per element, emphasizing group 4 metals, lanthanides, actinides, p-block elements, and selected s- and d-block metals. Finally, we explore emerging directions in the field, particularly mixed-metal M 6 O 8 clusters and their synergistic potential in cluster chemistry and metal–organic frameworks (MOFs).