Anion‑π Architectures of HAT(CN)₆ and 5d Polycyanidometalates: [W(CN)₈]^3–, [Re(CN)₇]^3–, and [Pt(CN)₆]^2–

Homoleptic polycyanido-complexes of 5d metal ions with high coordination numbers (C.N.), 8 for [W­(CN)₈]^3–, 7 for [Re­(CN)₇]^3–, and 6 for [Pt­(CN)₆]^2–, are found to form supramolecular anion-π chains with the multisite anion receptor HAT­(CN)₆ (hexaazatriphenylenehexacarbonitrile). The chains adopt a zigzag topology in the case of (XPh₄)₃­[W­(CN)₈]­·HAT­(CN)₆ (X = P: 1, X = As: 2) and (PPh₄)₃­[Re­(CN)₇]­·HAT­(CN)₆ (3), and a linear arrangement in the case of (PPh₄)₂­[Pt­(CN)₆]­·HAT­(CN)₆­·0.5CH₃CN­·2Et₂O (4). The anion-π interactions consist of 3-fold {M–CN^–···^δ+centroid_{pyrazine,ring}}₃ or single {M–CN^–···^δ+centroid_{pyrazine,C–C bond}} intermolecular contacts with separation distances in the range of 2.79–3.20 Å. An M-(CN)⁻ → HAT­(CN)₆ charge transfer (CT) along these anion-π contacts is evidenced in the solid state by the appearance of new absorptions in the visible range of UV–vis electronic absorption spectra, as compared to the starting materials, and by dispersion-corrected density functional theory studies. The CT anion-π interaction is accompanied by an extended network of hydrogen bonding interactions involving cations and solvent molecules, and these are found to be key factors stabilizing the crystal structure of polycyanidometalate/HAT­(CN)₆ compounds. Structural and electronic features of one-dimensional adducts involving [W­(CN)₈]^3–, [Re­(CN)₇]^3–, Fe­(CN)₆]^3–, [Co­(CN)₆]^3–, and [Pt­(CN)₆]^2– congeners are discussed in terms of how the C.N. and charge of polycyanidometalate complex with C.N. ≥ 6 affect its corresponding anion-π network with HAT­(CN)₆.