A Concerted Evolution Of Supramolecular Interactions In A {Cation; Metal Complex; Pi-Acid; Solvent} Anion-Pi System

Combined Single-Crystal XRD, solution C-13 and Pt-195 NMR, solid-state Pt-195 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)upramolecular 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)])center dot 2CH(2)Cl(2) (2), and subsequent recrystallization leads to block-shaped co-crystals of (PPh4)(2)([TCP](2)[Pt(CN)(4)])center dot 2CH(2)Cl2 (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-pi interactions between [Pt(CN)(4)](2-)- and pi-acidic TCP that seems to be driven, as indicated by calculations, not by maximizing their strength but rather by optimizing other crystal interactions, e.g. between PPh2 cations. Formation of the corresponding {[Pt(CN)(4)](2-); pi-acid) anion-pi contacts in solution is evidenced by C-13 NMR shifts and by new low-energy electronic absorption in the visible region (UV-vis). Finally, a combined solution/solid-state Pt-195 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)](2) near a pi-acidic surface can be monitored by Pt-195 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.