Metalloligand‐Directed Stepwise Assembly of Heteropentanuclear Metal String Complexes From a Modular Ni 2 Ru 2 Platform

ABSTRACT A modular stepwise strategy for the controlled synthesis of heteronuclear metal string complexes (HMSCs) remains highly desirable but is challenging because of the similar coordination preferences of transition‐metal ions. Herein, we demonstrate that a metalloligand‐based assembly strategy can be extended from trinuclear to pentanuclear metal strings through the synthesis of a family of heteropentanuclear Ni 2 Ru 2 M (M = Ru, Rh, and Ir) HMSCs. The key intermediate, ClNi 2 Ru 2 (tpda) 4 ( 1 ), contains a mixed‐valent [Ru 2 ] 5+ core and four terminal pyridyl donors that serve as a preorganized coordination pocket for the sequential installation of a third metal center. Subsequent coordination with Ru, Rh, or Ir precursors afforded the corresponding pentanuclear complexes [ClNi 2 Ru 2 (tpda) 4 MCl](PF 6 ), which were fully characterized by high‐resolution MALDI‐TOF mass spectrometry, UV–vis–NIR spectroscopy, NMR spectroscopy, single‐crystal X‐ray diffraction, SQUID magnetometry, and electrochemistry. Structural analyses reveal that all complexes retain a linear Ni 2 Ru 2 M metal framework featuring a terminal high‐spin Ni 2+ center coupled to a delocalized [Ru 2 –M] 7+ fragment through significant metal–metal bonding. While the Ru and Rh derivatives exhibit bent Ru–Ru–M units consistent with second‐order Jahn–Teller distortion, the Ir analogue adopts an essentially linear geometry, highlighting the influence of the terminal 5d metal on the electronic structure of the metal chain. Magnetic studies reveal ferromagnetic exchange coupling between the terminal Ni 2+ ion and the trinuclear [Ru 2 –M] 7+ unit, arising from the orthogonality of their frontier magnetic orbitals. Cyclic voltammetry further demonstrates that substitution of the terminal metal effectively modulates the redox properties of the heterometallic chain. This work establishes metalloligand‐directed stepwise assembly as a general strategy for the construction of higher‐nuclearity HMSCs, providing a modular platform for the rational design of metal string architectures with tunable structural, magnetic, and electronic properties.