Structure and Bonding in Nickel-Thiolate-Iodine Charge-Transfer Complexes

Abstract

The dinuclear nickel complexes [Ni₂ L(μ-O₂ CR)](ClO₄ ) [R=Me (4), R=OMe (6)], where L^2- is a 24-membered macrocyclic N₆ S₂ ligand, react readily with excess I₂ in MeCN solution at 4 °C to form stable mono-(I₂ ) and bis-(I₂ ) charge-transfer (CT) adducts of the type [Ni₂ L(μ-O₂ CR)(I₂ )_n ]⁺ (n=1 or 2) containing linear RS-I-I linkages. Three new CT compounds, namely, [Ni₂ L(OAc)(I₂ )](I₂ )(I₃ ) (5), [Ni₂ L(O₂ COMe)(I₂ )](I₅ )⋅MeCN (7⋅MeCN), and [Ni₂ L(O₂ COMe)(I₂ )₂ ](I₅ )⋅MeCN (8⋅MeCN) as well as the triiodide salt [Ni₂ L(OAc)](I₃ ) (9) were synthesized and fully characterized. A common feature of the CT adducts is a polyiodide matrix, which surrounds the individual complex molecules, stabilized by secondary I⋅⋅⋅I interactions with the CT linkages. The scatter in both the RS-I (2.6 to 3.0 Å) and the I-I bond lengths (2.7 to 3.0 Å) is indicative of both a variable strength of the RS^- →I₂ bond and a varying degree of charge transfer. An analysis of the structural parameters was undertaken accompanied by DFT calculations to quantify the donating ability of the bridging thiolate functions and to shed more light on the bonding in this rare sort of charge-transfer complexes. The stability of the CT complexes and the results of preliminary transport measurements are also reported.

Keywords: charge transfer; crystal structures; density functional calculations; iodine; nickel thiophenolate complexes.