An S4-symmetric mixed-valent decacopper cage comprised of [CuII(L-S2N2)] complexes bridged by CuI(MeCN)n (n = 1 or 2) cations

Abstract

Oxidative addition of 1,2,11,12-tetrathia-5,8,15,19-tetra(N-methylamino)cycloicosane, the bis(disulfide) form of N,N′-dimethyl-N,N′-bis(2-mercaptoethyl)ethylenediamine (L-N₂S₂) to [Cu(MeCN)₄][BF₄] (2.5 eq.) in MeCN produces good yields of the decacopper cage compound [(Cu^II(L-N₂S₂))₄(μ₂-Cu^I(MeCN)₂)₂(μ₃-Cu^I(MeCN))₄][BF₄]₆·2.25MeCN, [1][BF₄]₆·2.25MeCN. This mixed-valent hexacation shows idealized S₄ point group symmetry and is composed of four [Cu^II(L-N₂S₂] centers held in distorted four-coordinate environments and joined by μ₂-Cu^I(MeCN)₂/μ₃-Cu^I(MeCN) ions that bridge their thiolate sulfur atoms. Each four-coordinate [Cu^II(L-N₂S₂)] center is related to the other three by successive executions of the S₄ operation. A dark violet color is observed for [1]⁶⁺ and attributed to a combination of metal-to-ligand (S), ligand (S)-to-metal, and, at lower energy, intermetal charge transfer transitions, as found for Cu₅ cage compounds with a compositional relationship to [1]⁶⁺.