Enhanced Magnetic Coupling of One-Dimensional Straight Backbone Chains Extended by −Pt···Pt– Bonds in Paramagnetic Trinuclear Complexes

The paramagnetic trinuclear complexes trans -[Pt 2 M(acam) 4 (NH 3 ) 4 ](ClO 4 ) 2 ( 1-M; acam = acetamidate, M = Co, Ni, and Cu), which comprise one-dimensional (1D) chains formed by the Pt–M–Pt moiety with each metal bridged in trans fashion, were rationally synthesized from an acetamidate-hanging Pt mononuclear complex and first-row transition metals (M). The Pt and M atoms exhibit planar coordination environments and are stacked in a face-to-face fashion, showing a straight-backbone structure. The 1D ···Pt–M–Pt···Pt–M–Pt··· chains are formed through interactions between the half-filled σ-type orbitals delocalized over the Pt–M–Pt moiety involving unbridged Pt···Pt bonds at a distance of approximately 3.5 Å. Physical measurements and calculations reveal that the M atoms in 1-M have high-spin states, indicating the presence of localized unpaired electrons on the M center, i.e., three unpaired electrons in the d x 2 –y 2, d z 2, and d yz orbitals of Co, two unpaired electrons in the d x 2 –y 2 and d z 2 orbitals of Ni, and one unpaired electron in the d x 2 –y 2 orbital of Cu. Magnetic susceptibility measurements show relatively strong antiferromagnetic interactions between the two M centers, which are separated by 8.7 Å through – Pt···Pt– bonds with exchange strengths of – 9.0 cm –1 ( 1-Co ) and – 27.9 cm –1 ( 1-Ni ). In contrast, 1-Cu does not exhibit magnetic interactions because the d x 2 –y 2 spin on Cu(II) is less overlapped with the neighboring d x 2 –y 2 orbitals.