Stepwise synthesis of the heterotrimetallic chains [MRu2(dpa)4X2]0/1+ using group 7 to group 12 transition metal ions and [Ru2(dpa)4Cl]

Abstract

The CoRu₂(dpa)₄Cl₂ (1) (dpa: 2,2′-dipyridylamide) is synthesized by the reaction of Ru₂(OAc)₄Cl and Co₃(dpa)₄Cl₂. By mixing 1 with NH₃, Co²⁺ can be removed and result in the formation of unique binuclear complex 4,0-Ru₂(dpa)₄Cl (2) featuring one coordination pocket supported by free pyridine groups. Hence, this complex can act as an outstanding precursor for the formation of heterotrimetallic chains with MRu₂ cores. A series of M–Ru₂⁵⁺ complexes (M = Co²⁺ (3), Ag⁺ (4), Mn²⁺ (5), Fe²⁺ (6), Zn²⁺ (7), Cd²⁺ (8), Pd²⁺ (9), Rh²⁺ (10), and Ir²⁺ (11)) were prepared and isolated, representing the most complete series of heterotrimetallic chains to date. All these metal string complexes are in a linear trimetallic framework helically wrapped by four dpa⁻ ligands, characterized by X-ray diffraction measurements. The bending of the trinuclear metal cores in RhRu₂ (10) and IrRu₂ (11) (∠Ru–Ru–Rh: 167.58° and ∠Ru–Ru–Ir: 167.61°) indicates that a heterometallic metal–metal bonds (Ru–Rh; Ru–Ir) are generated. The studies from DFT calculation of 10 and 11 coincide with the experimental results. Furthermore, the M⋯Ru₂⁵⁺ distances are regulated by the factors including the bonding force of M–pyridyl and the static repulsion between M and Ru₂⁵⁺ unit. Interestingly, the trend for these distances is in line with that observed in trans-M(py)₄Cl₂ complexes.