Gradual Size Enlargement of Aluminum-Oxo Clusters and the Photochromic Properties.

Metallic clusters, assembled by functional motifs, possess the attribute of regulating the properties by changing inorganic and organic components. In this work, a series of aluminum-oxo clusters, [AlO(dmp)(Hdmp)]·2PrOH [, Hdmp = 2,2-bis(hydroxymethyl)propionic acid], [Al(Hthmmg)]·2DMF·2HO [, Hthmmg = -tris(hydroxymethyl)methylglycine], [Al(OH)(NAP-OH)(MeO)(MeOH)]Cl·7MeCN·3MeOH (, HNAP-OH = 3-hydroxy-2-naphthoic acid), and [Al(NA)(MeO)] (, HNA = nicotinic acid), were obtained based on different carboxylic acids, realizing metallic ring size enlargement from 5.91 to 9.32 Å. They all exhibit good chemical stability. Importantly, the cluster displays obvious photochromic behavior from pale yellow to orange yellow, originating from the generation of photoinduced radicals in the metal-assisted ligand-ligand electron transfer process of 3-hydroxy-2-naphthoic acid (HNAP-OH). This work enriches the metal ring cluster chemistry and reports the example of the aluminum-oxo cluster-based photochromic material, developing a novel system of photochromic materials.