Steric Effects of Alcohols on the [Mn4O4] Cubane-Type Structures

Abstract

[M4O4] (M = 3d transition metal) represents an interesting class of compounds featuring cubane-type molecular structures, and particularly, [Mn4O4] cubanes or their derivatives attract much attention by virtue of their potential applications as single-molecule magnets (SMMs) or catalysts. However, the rational design of desired cubane-related structures is still a challenging subject due to the lack of readily available methods to effectively tune the construction patterns of the molecule assembly. In this work, we report the employment of different alcohols to prepare three cubane-related molecules, Mn2(dhd)4(iPrOH)2 (1), Mn4(dhd)4(OEt)4(EtOH)4 (2) and Mn4(dhd)6(OMe)2(MeOH)2 (3) (dhd = 5,5-dimethyl-2,4-hexanedione). Interestingly, the bulkiest iPrOH leads to simple rhombic dimer molecule 1. It can be deemed a rudimentary structure oftetranuclear [Mn4O4] cubane 2, which can be realized by the use of less bulky EtOH. In addition, the least bulky MeOH promotes the assembly of the cubanes, eventually bringing about defective dicubane molecular cluster 3. The accurate crystal structures of 1–3 were modeled by single-crystal X-ray diffraction, and their electronic structures were investigated through absorption spectroscopy coupled with theoretical calculations. Overall, this work demonstrates a systematic study on controlling cubane-type structures of Mn-based compounds by applying different solvents, which provides a new means to design functional molecules for specific applications.