Formation processes of high-dimensional MoO frameworks in tetrakis(2-hydroxypropane-1,3-diaminium) hexatriacontamolybdate hydrate (C3H12N2O)4[Mo36O112(H2O)16-m]·nH2O crystals: Solid-phase structural conversions under restricted dehydration conditions

Abstract

We found that the hexatriacontamolybdate [Mo36O112(H2O)16]8− ({Mo36}) compound of 1,3-diamino-2-propanol (βOHC3-DA) forms seven structural phases with the formula (βOHC3-DA)4{Mo36}·nH2O. They showed a range of dimensionality: three zero-dimensional (0D), two 1D, and two 2D MoO framework structures consisting of {Mo36} anions. Two of the phases have 0D framework structures crystallized in the mother solution. The remaining five phases were obtained when the crystals of these two 0D phases were aged in resin. The dense 2D framework ({Mo36}-nanosheet) of the title compound was formed via solid-phase condensation reactions under restricted dehydration conditions such as in resin-coated crystals, unlike the loose {Mo36}-nanosheet of the (C3DA)4{Mo36}·nH2O. The formation processes of the related high-dimensional MoO frameworks were guided by hydrogen-bonding contacts initially formed between {Mo36} anions in the crystal. There were two different conversion routes: the one starting from the phase consisting of {Mo36} hydrogen-bonded at their head/foot parts lead to the dense 2D nanosheet, while the other originating from the phase consisting of {Mo36} hydrogen-bonded at their trunk parts, to 1D {Mo36}-nanochain with rare triple oxygen bridges. These routes had neither branching nor intercrossing.