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Inducing Structural Diversity in Anionic Metal–Tetraoxolene Coordination Polymers Using Templating Methyl Viologen Countercations

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journal contribution
posted on 18.01.2022, 13:33 authored by Martin P. van Koeverden, Brendan F. Abrahams, Carol Hua, Timothy A. Hudson, Richard Robson
Controlling the connectivity of coordination polymers is an important scientific goal, as the physicochemical properties of these compounds are often intimately linked to the network topology. Using redox-active methyl viologen (MeV2+) countercations, a series of one-, two-, and three-dimensional anionic coordination polymers are described in which MnII or CdII centers are bridged with tetraoxolene ligands derived from 3,6-dihalo-2,5-dihydroxy-1,4-benzoquinone (H2Xan, X = F, Cl). Using MeV2+ countercations and either MnII or CdII yields nonporous anionic diamond networks of the general composition (MeV)­[M­(Clan)2] in which eight-coordinate divalent metal centers are linked by Clan2– ligands. Changing the solvent mixture from acetone/water to acetonitrile/water (MeCN/H2O) afforded the same product in the case of CdII, but an anionic 2D honeycomb network with the composition (MeV)­[Mn2(Clan)3]·6MeCN was obtained in the case of MnII. In contrast, the use of Fan2– ligands affords 1D ladder-type anionic coordination polymers (MeV)­[M2(Fan)3(H2O)2] (M = MnII, CdII) despite the chemical and structural similarity of Fan2– and Clan2– ligands. In the case of the diamond and 2D networks, MeV2+ countercations play a key structural role, arising from C–H···O hydrogen bonding extending from the cation to the anionic network. For the 1D ladder-type structures formed with Fan2–, O–H···O hydrogen bonding between anionic [M2(Fan)3(H2O)2]2– ladders is largely responsible for directing the crystal packing. For these compounds, MeV2+ cations play a more nuanced structural role, only occupying the void space between layers of H-bonded anionic [M2(Fan)3(H2O)2]2– ladders.