Novel folding of N,N′-naphthalenebis(o-mercaptobenzamide) in nickel(II) complexes: monomeric and trimeric species with unexpected ‘butterfly’ and ‘slant chair’ structure

In order to determine the role of carboxamido nitrogen and thiolato sulfur donors on the structure and properties of metal complexes, we have synthesized the designed ligand N,N′-napthalenebis(o-mercaptobenzamide) (NpPepSH4) with an N2S2 donor set. In the deprotonated form, NpPepS4− binds nickel(II) to afford the diamagnetic complex (Et4N)2[Ni(NpPepS)] (1) with square-planar geometry. The ligand frame of NpPepS4− wraps around the Ni(II) center in an unexpected butterfly fashion presumably due to steric interactions. The [Ni(NpPepS)]2− unit further coordinates to Ni(II) and Pd(II) to give trimeric thiolato-bridged complexes (Et4N)2[Ni(Ni{NpPepS})2] (2) and (Et4N)2[Pd(Ni{NpPepS})2] (3). The structure of the [Ni(CH3OH)6]2+ salt of 3 namely, [Ni(CH3OH)6][Pd(Ni{NpPepS})2] (3′) reveals a novel slant chair structure. Unlike the previously reported similar trimeric complexes, the N2NiS2PdS2NiN2 moiety in 3′ is planar with slant naphthalene rings attached on both ends.