A concerted evolution of supramolecular interactions in a {cation; metal complex; π-acid; solvent} anion-π system
Résumé
Combined Single-Crystal XRD, solution 13 C and 195 Pt NMR, solid-state 195 Pt NMR and UV-vis measurements, together with comprehensive (TD)DFT calculations, are used to describe the supramolecular interactions and sequential concerted structural transformation occurring in a {PPh4 + ;[Pt(CN)4] 2-;TCP;CH2Cl2} supramolecular system (TCP-tetracyanopyrazine). In the solid-state, a mixture of needle-like co-crystals first appears, (PPh4)2{[TCP][Pt(CN)4]} (1) and (PPh4)2{[TCP][Pt(CN)4]}•2CH2Cl2 (2), and subsequent recrystallization leads to block-shaped co-crystals of (PPh4)2{[TCP]2[Pt(CN)4]}•2CH2Cl2 (3), wherein double {Pt(CN)4] 2-;TCP} and triple {[Pt(CN)4] 2-;TCP;CH2Cl2} and {PPh4 + ;[Pt(CN)4] 2-;TCP} synthons present either in 1 or 2 are reproduced in 3. The structural pathway (1/2→3) is accompanied by a 1D-to-2D modular evolution of anion-π interactions between [Pt(CN)4] 2and π-acidic TCP that seems to be driven, as indicated by the calculations, not by maximizing their strength but rather optimizing other crystal interactions, e.g. between PPh4 + cations. Formation of the corresponding {[Pt(CN)4] 2-;π-acid} anion-π contacts in solution is evidenced by 13 C NMR shifts and by new low-energy electronic absorption in the visible region (UV-vis). Finally, a combined solution/solid-state 195 Pt NMR approach is used for the first time to shed light on the geometry and interactions involving such aggregates; it shows that the degree of trapping of [Pt(CN)4] 2near a π-acidic surface can be monitored by 195 Pt NMR chemical shifts. The results give fresh insight into block arrangement tactics and characterization of hybrid organic-inorganic co-crystal salts, and into aggregation controlled properties.
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