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, [Al 6 O(dmp) 4 (Hdmp) 2 ]·2 i PrOH [ Al 6 -1, H 3 dmp = 2,2-bis(hydroxymethyl)propionic acid], [Al 6 (H 2 thmmg) 6 ]·2DMF·2H 2 O [ Al 6 -2, H 5 thmmg = N -tris(hydroxymethyl)methylglycine], [Al 8 (OH) 4 (NAP-OH) 12 (MeO) 7 (MeOH)]Cl·7MeCN·3MeOH ( Al 8, HNAP-OH = 3-hydroxy-2-naphthoic acid), and [Al 10 (NA) 10 (MeO) 20 ] ( Al 10, 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 Al 8 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.