An Adaptable Water-Soluble Molecular Boat for Selective Separation of Phenanthrene from Isomeric Anthracene

Abstract

Anthracene crude oil is a common source of phenanthrene for its industrial use. The isolation of phenanthrene from this source is a challenging task due to very similar physical properties to its isomer anthracene. We report here a water-soluble Pd(II) molecular boat (<b>MB1</b>) with unusual structural topology that was obtained by assembling a flexible tetrapyridyl donor (<b>L</b>) with a <i>cis</i>-Pd(II) acceptor. The flexible backbone of the boat enabled it to breathe in the presence of a guest optimizing the fit within the cavity. The boat binds phenanthrene more strongly than anthracene, which enabled separation of phenanthrene with an >98% purity from an equimolar mixture of the two isomers using <b>MB1</b> as an extracting agent. <b>MB1</b> represents a unique example of a coordination receptor suitable for selective aqueous extraction of phenanthrene from anthracene with reusability of several cycles.