Through‐Space Spin Coupling in a Silver(II) Porphyrin Dimer upon Stepwise Oxidations: Ag II ⋅⋅⋅Ag II , Ag II ⋅⋅⋅Ag III , and Ag III ⋅⋅⋅Ag III Metallophilic Interactions

Abstract

Metallophilic interactions between closed-shell metal ions are becoming a popular tool for a variety of applications related to high-end materials. Heavier d8 transition-metal ions are also considered to have a closed shell and can be involved in such interactions. There is no systematic investigation so far to estimate the structure and energy characteristics of metallophilic interactions in AgII/AgII (d9/d9), AgIII/AgIII (d8/d8), and mixed-valent AgII/AgIII (d9/d8) complexes, which have been demonstrated in the present study. Both interporphyrinic and intermetallic interactions were investigated on stepwise oxidation by using a rigid ethene-bridged cis silver(II) porphyrin dimer and the results compared with those for highly flexible ethane-bridged analogues. By controlling the nature of chemical oxidants and their stoichiometry, both 1e and 2e oxidations were done stepwise to generate AgII/AgIII mixed-valent and AgIII/AgIII porphyrin dimers, respectively. Unlike all other ethene-bridged metalloporphyrin dimers reported earlier, in which 2e oxidation stabilizes only the trans form, such an oxidation of silver(II) porphyrin dimer stabilizes only the cis form because of the metallophilic interaction. Besides silver(II)⋅⋅⋅silver(II) interactions in cis silver(II) porphyrin dimer, stepwise oxidations also enabled us to achieve various hitherto-unknown silver(II)⋅⋅⋅silver(III) and silver(III)⋅⋅⋅silver(III) interactions, which thereby allow significant modulation of their structure and properties. The strength of Ag⋅⋅⋅Ag interaction follows the order AgII/AgII (d9/d9)<AgII/AgIII (d9/d8)<AgIII/AgIII (d8/d8). Single-crystal XRD, X-ray photoelectron spectroscopy (XPS), 1H NMR and EPR spectroscopy, and variable-temperature magnetic investigations revealed various oxidation states of silver and metallophilic interactions, which are also well supported by computational analysis.