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

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.