Stable Heterometallic Cluster Ions based on Werner's Hexol

Abstract

Large aqueous ions are interesting because they are useful in materials science (for example to generate thin films) but also because they serve as molecular models for the oxideaqueous mineral interface where spectroscopyisdifficult. Here we showt hat new clusters of the type M[(m-OH) 2 Co(NH 3 ) 4 ] 3 -(NO 3 ) 6 (M = Al, Ga) can be synthesized using Werners century-old cluster as as ubstitutable framework. We substituted Group 13 metals into the hexol Co[(m-OH) 2 Co-(NH 3 ) 4 ] 3 6+ ion to make diamagnetic heterometallic ions.T he solid-state structure of the hexol-type derivatives were determined by single-crystal XRD and NMR spectroscopya nd confirmed that the solid-state structure persists in solution after dissolution into either D 2 Oor [D 6 ]DMSO.Other compositions besides these diamagnetic ions can undoubtedly be made using asimilar approach,whichconsiderably expands the number of stable aqueous heteronuclear ions. Nanoscale inorganic clusters have been shown to be useful precursors for solution processing of high-quality thin films. [1,2] Clusters are desirable precursors for thin films that can be included in devices and test structures due to their solubility in environmentally benign solvents,e ase of deposition on surfaces,pre-organized structure,and lower temperatures of decomposition. [3] While various sol-gel based approaches satisfy these conditions,m any use hybrid inorganic-organic mixtures that require large amounts of energy to process and have the potential to leave behind organic/ carbon contaminants.B ecause of this,t here is an eed for precursors with minimal organic components that can be deposited from solution, to realize alow-energy and efficient method for producing thin films for avariety of applications. [4] Thew ell-known, venerable "Werner hexol" cluster (M = Co in Scheme 1) was originally synthesized in 1898 by Jçrgensen, [5] and later studied by Alfred Werner to provide the first evidence for molecular chirality in the absence of carbon. [6,7] Later synthetic work by Kauffman and others developed methods to prepare additional salts and hydrates of this structure type. [7b] This cluster contained only cobalt ions and inorganic ligands such as hydroxide and ammine,and provided awealth of information about coordination chemistry and the structure of inorganic molecules. [7] Importantly, this cluster-through its D and L twisted isomers-provided definitive proof that chirality was not solely the domain of organic molecules.Despite spectacular examples of historically significant inorganic coordination clusters,t he rational design of allinorganic clusters can be challenging,w ith clusters often resulting from serendipity.T his likely results from undesirable reactions (or precipitation) that produce the thermodynamically more stable bulk metal oxide/hydroxide. [8] It is for this reason that many successful strategies use organic ligands to suppress continued polymerization, resulting in elegant ligand-supported aqueous coordination clusters, [9] which are typically undesirable as...