Paramagnetic One-Dimensional Chains Comprised of Trinuclear Pt–Cu–Pt and Paddlewheel Dirhodium Complexes with Metal–Metal Bonds

One-dimensional
(1-D) chain complexes constructed by metal–metal bonds containing
three types of metal speciesplatinum, rhodium, and copperhave
been rationally synthesized and characterized by single-crystal X-ray
analyses and physical measurements. The paddlewheel or lantern type
complex, [Rh2(O2CCH3)4] (i.e., [Rh2]), has a vacant σ* orbital which accepts
the electrons from the filled dz2 orbital of cis-[Pt­(piam)2(NH3)2]·2H2O (1, i.e.
[Pt], where piam = pivalamidate) to afford a tetranuclear complex,
[{Rh2(O2CCH3)4}­{Pt­(piam)2(NH3)2}2]·2H2O (2). Compound 2 forms a linear alignment
as [Pt]–[Rh2]–[Pt] with unbridged Rh–Pt
bonds, where the oxygen atoms of the piam ligands in the [Pt] are
noncoordinated, showing the capability of binding another metal ion.
Simply mixing [Rh2] and the heterometallic trinuclear complex
[Pt2Cu­(piam)4(NH3)4]­(PF6)2 (3, i.e. [Pt–Cu–Pt])
in a ratio of 1:1 in MeOH, EtOH, or Me2CO affords [{Rh2(O2CCH3)4}­{Pt2Cu­(piam)4(NH3)4}]n(PF6)2n (4), [{Rh2(O2CCH3)4}­{Pt2Cu­(piam)4(NH3)4}]n(PF6)2n (5), or [{Rh2(O2CCH3)4}­{Pt2Cu­(piam)4(NH3)4}]n(PF6)2n·6nMe2CO (6),
respectively. Compounds 4–6 form
infinite chains with the repetition of −{[Rh2]–[Pt–Cu–Pt]}n–, which to our knowledge, are the
first examples of heterometallic 1-D chains comprised of three types
of metal species with direct metal–metal bonds. The CF3CO2–, ClO4–, and water molecules influence the crystal packing to form an octanuclear
complex of [{Rh2(O2CCH3)4}­{Pt2Cu­(piam)4(NH3)4}2]­(CF3CO2)2(ClO4)2·2H2O (7) with [Pt–Cu–Pt]–[Rh2]–[Pt–Cu–Pt] alignment. Considering the
crystal structures and X-ray photoelectron spectra (XPS) measurements
in 4–7, the oxidation states of the
metal atoms are −{[Rh2II,II]–[PtII–CuII–PtII]}n– or [PtII–CuII–PtII]–[Rh2II,II]–[PtII–CuII–PtII], which are
unchanged from those in the starting compounds. Electron paramagnetic
resonance spectra of 4–7 show axially
symmetric spectra with g∥ > g⊥, indicating that the HOMO (SOMO) is
a Cu dx2–y2 orbital. In 7, the hyperfine coupling
in the spectrum indicates that the unpaired spin on Cu is perturbed
by the Pt atoms.