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Role of Pyrazine-N,N′‑dioxide in [W(CN)8]n-Based Hybrid Networks: Anion−π Interactions

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journal contribution
posted on 06.08.2014, 00:00 by Robert Podgajny, Dawid Pinkowicz, Bernard Czarnecki, Marcin Kozieł, Szymon Chorąży, Magdalena Wis, Wojciech Nitek, Michał Rams, Barbara Sieklucka
Pyrazine-N,N′-dioxide (pzdo) was used as a linker in the design and synthesis of hybrid octacyanometalate-based networks. Four new compounds Na6[WV(CN)8]2(pzdo)7·5H2O (1), K3[WV(CN)8]­(pzdo)2·4H2O (2), {MnII6(pzdo)4(MeOH)10[WV(CN)8]4}·4MeOH (3), and {MnII2(pzdo)­(H2O)4[WIV(CN)8]}·4H2O (4) reveal specific M-pzdo-[W­(CN)8]3–/4– (M = NaI, KI, MnII) structural arrangements where pzdo plays a significant role. Apart from typical supramolecular interactions including hydrogen bonding and van der Waals interactions, the {[M­(μ-pzdo)­M]­[W­(CN)8]x} (x = 1 or 2) structural motifs in 14 are organized by specific supramolecular interactions of the pzdo molecule and the octacyanotungstate anions: face-to-face sandwich type interactions between the plane of the pzdo aromatic ring and N4 square face of [W­(CN)8]n anions, edge-to-face interactions between the plane of the pyrazine ring and a pair of neighboring NCN atoms of the [W­(CN)8]-moiety, and end-to-face interactions between the plane of the pyrazine ring and a single NCN atoms of the [W­(CN)8]-moiety. The related intermolecular arrangements show features typical for anion−π interactions, unprecedented in the octacyanometalate chemistry. The specific interactions of the octacyanotungstate and the pzdo molecule in 1 and 2 lead to significant modification of their electronic spectra. Magnetic studies revealed that 1, 2, and 4 are paramagnetic, although 3 orders antiferromagnetically at Tc = 17.5 K.