Integration of Paramagnetic Diruthenium Complexes into an Extended Chain by Heterometallic Metal–Metal Bonds with Diplatinum Complexes

We
successfully obtained a paramagnetic one-dimensional (1D) chain complex
[{Ru2(O2CCH3)4}­{Pt2(piam)2(NH3)4}2]n(PF6)4n·4nH2O (2; piam
= pivalamidate) extended by metal–metal bonds. Compound 2 comprises two types of metal species, ruthenium and platinum,
where an acetate-bridged dinuclear ruthenium complex (i.e., [Ru2]) and a pivalamidate-bridged platinum complex (i.e., [Pt2]) are connected by axial metal–metal bonds, forming
an attractive quasi-1D infinite chain that can be expressed as −{[Pt2]–[Ru2]–[Pt2]}n–. Such axial metal–metal bonds are
attributed to the interaction between the highest occupied molecular
orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO)
along the z axis, where both the HOMO in [Pt2II,II] and the LUMO in [Ru2II,II] are σ* orbitals associated with metal cores. The crystal
structure and X-ray photoelectron spectrum for 2 reveal
that metal oxidation states are −{[Pt2II,II]–[Ru2II,II]–[Pt2II,II]}n–, where [Ru2II,II] can have an electronic configuration of
σ2π4δ2δ*2π*2 or σ2π4δ2π*4. The magnetic susceptibility
of 2 has a μeff [∝(χT)1/2] value of 2.77 μB per [Pt2II,II]–[Ru2II,II]–[Pt2II,II] unit at 300 K, showing that two unpaired
electrons lie on π*­(Ru2). Magnetic measurements performed
at temperatures of 2–300 K indicate that S = 1 Ru2II,II units are weakly antiferromagnetically
coupled (zJ = −1.4 cm–1)
with a large zero-field splitting (D = 221 cm–1).