Comments on proton cascade in a molecular solid: H/D exchange on mobile and immobile water

Abstract

Following a previous report of proton transport in a channel-free molecular solid possessing a complex set of water wires, the mechanisms implied by the available neutron diffraction measurements are further developed. Three specific proton transfer pathways along an experimentally observed water wire are proposed. The first is proton transfer involving two aqua ligands coordinated to the same Mn(II) unit and one free water acting as a shuttle. The second mechanism consists of proton transfer between coordinated aqua ligands of distinct molecules, with no shuttle. The third mechanism involves a component of vehicle transport, involving a water molecule that changes position during the process. Geometric parameters of the proposed mechanisms are given.