One-dimensional chain structures constructed from tetra(acetamidato)dirhodium(II,III) complexes and square planar platinum and palladium complexes

The reaction of [Rh₂(acam)₄(H₂O)₂]ClO₄ (1) (Hacam = acetamide) with K₂PtCl₄ in aqueous solution gave crystals of [Rh₂(acam)₄(H₂O)₂][Rh₂(acam)₄{(μ-Cl)₂PtCl₂}] · 2H₂O (2). The reaction of 1 with K₂PdCl₄ produced the palladium analog [Rh₂(acam)₄(H₂O)₂][Rh₂(acam)₄{(μ-Cl)₂PdCl₂}] · 2H₂O (3) and a small amount of an aquated palladium complex [Rh₂(acam)₄{(μ-Cl)₂PdCl(H₂O)}] · H₂O (4). Complexes 2 and 3 have anionic chains of [Rh₂(acam)₄{(μ-Cl)₂MCl₂}]⁻ (M = Pt, Pd), while 4 includes neutral chains of [Rh₂(acam)₄{(μ-Cl)₂PdCl(H₂O)}]. Although all of the structures include infinite chains of (-Rh-Rh-Cl-M-Cl-)_n (M = Pt, Pd), the chain structures are different; zigzag for 2 and 3 and helical for 4. In the structures of 2 and 3, the counter cation [Rh₂(acam)₄(H₂O)₂]⁺ made a hydrogen-bonded chain with the crystallization water molecules. The cationic chains and the anionic chains are connected with hydrogen bonds. In the structure of 4, the chains are also linked together by direct hydrogen bonds between the chains and those with the crystallization water molecules. ESR spectra of the powdered samples of 2 and 3 at 77 K were consistent with a rhombic structure: for 2, g₁ = 2.111, g₂ = 2.054, g₃ = 2.004; for 3, g₁ = 2.115, g₂ = 2.057, g₃ = 2.007. These results indicate that there is a spin flip-flop exchange between the cations, [Rh₂(acam)₄(H₂O)₂]⁺, and the units in the anionic chains. The electrical conductivities of 2 and 3 were in the order of 10⁻⁷ S cm⁻¹ at room temperature.