A Systematic Crystallographic Study of the Host–Guest Interactions between Amines and Ti8 Polyoxotitanium Clusters

Host–guest interaction is a core concept in supramolecular chemistry. Amine is one of the most studied guest molecules, thanks to its abundant types and versatility as a hydrogen bonding donor. A thorough understanding of how the types of amines (primary, secondary, and tertiary) can affect the host–guest interaction is yet to be fully realized. Herein, we study crystallographically Ti8 polyoxotitanium clusters that host primary, secondary, and tertiary amines and diamines. The number of guests in each cluster, the hydrogen bonding mode and number, and even the host structure all critically depend on the types of amines. For a tertiary amine (triethylamine), there are two guests for the [Ti8O8(OOCPh)14(OiPr)4]2– host. For a secondary amine (dimethylamine), [Ti8O8(OOCPh)15(OiPr)2]− accommodates one guest. For primary amines (n-butylamine and benzylamine), there are four guests inhabiting in each host. Introducing more guests causes a greater distortion of the host structure. Remarkably, when diamines (such as 1,4-diaminobutane and ethylenediamine) are used instead, they have shown interesting reactivity with benzoic acid to yield new guests. This enriches the host–guest systems composed of amines and polyoxotitanium clusters.