Toward heteronuclear supramolecular architectures of pyridine-4-thiolate

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The reaction of Pt(d-t-bpy)(S-4-py)2 (1; d-t-bpy = 4,4′-di-tert-butyl-2,2′-bipyridine, S-4-py = pyridine-4-thiolate) with ZnX2 (X = Cl, Br, I) gave the respective heteronuclear metallocycles, [Pt(d-t-bpy)(S-4-py)2(ZnX2)]2 (X = Cl 2, Br 3, and I 4). In particular, the presence of weak intermolecular Pt(II)⋯Pt(II) (3.374 and 3.453 A for 2; 3.364 and 3.452 A for 3) and π⋯π (3.279 and 3.490 A for 2; 3.574 and 3.793 A for 3) interactions makes the heteronuclear metallocycles cooperatively stack to form a monohelical chain, and four monohelices are further stacked to give a novel bundle-of-quadruple-monohelix through nonclassical hydrogen bonding. However, 4 having only π⋯π interactions, possibly due to the larger atom size for I, cannot form a similar structural framework as those of 2 and 3. Hence, the presence of weak Pt(II)⋯Pt(II) interactions seems to play a vital role for the formation of such a novel structural motif. For the NO3 complex, [Pt2(d-t-bpy)2(S-4-py)4(Zn(NO3))2(μ-O)]n (5), a one-dimensional ladder structure is formed instead of a heteronuclear metallocycle. Therefore, a delicate anion-induced assembly has been demonstrated. In addition, the emissions of 2–5 are quite similar to that of Pt(d-t-bpy)(S-4-py)2, which has been assigned to a ligand-to-ligand charge-transfer (LLCT) transition, indicating that the coordination to Zn(II) ions through pyridyl-4-thiolate ligands of Pt(d-t-bpy)(S-4-py)2 cannot cause a significant effect on their LLCT emissions.