Paramagnetic one-dimensional chains comprised of trinuclear Pt-Cu-Pt and paddlewheel dirhodium complexes with metal-metal bonds

Abstract

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, [Rh 2(O2CCH3)4] (i.e., [Rh 2]), has a vacant σ* orbital which accepts the electrons from the filled dz2 orbital of cis-[Pt(piam)2(NH 3)2]·2H2O (1, i.e. [Pt], where piam = pivalamidate) to afford a tetranuclear complex, [{Rh2(O 2CCH3)4}{Pt(piam)2(NH 3)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 [Pt 2Cu(piam)4(NH3)4](PF 6)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), [{Rh 2(O2CCH3)4}{Pt2Cu(piam) 4(NH3)4}]n(PF6) 2n (5), or [{Rh2(O2CCH3) 4}{Pt2Cu(piam)4(NH3) 4}]n(PF6)2n·6nMe 2CO (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 CF 3CO2-, ClO4-, and water molecules influence the crystal packing to form an octanuclear complex of [{Rh2(O2CCH3)4}{Pt 2Cu(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-Pt II]}n- or [PtII-CuII-Pt II]-[Rh2II,II]-[PtII-Cu II-PtII], which are unchanged from those in the starting compounds. Electron paramagnetic resonance spectra of 4-7 show axially symmetric spectra with g∥ > gτ, 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. © 2013 American Chemical Society.