Crystal structures and adsorption spectra of mono-dimensional hexanuclear heterometallic complexes with no bridge assisted rhodium–platinum bonds

As analogues to a previous compound [{Rh2(O2CCH3)4}{Pt2(piam)2(NH3)4}2]n(PF6)4n·6nH2O (1, where piam = pivalamidate), two hexanuclear complexes [{Rh2(O2CCH3)4}{Pt2(piam)2(NH2CH3)4}2](PF6)4 (2) and [{Rh2(O2CCH3)4}{Pt2(piam)2(bpy)2}2](PF6)4 (3, bpy = 2,2′-bipyridine) have been synthesized by following a simple procedure of mixing separately, a [Rh2(O2CCH3)4] complex (i.e., [Rh2]) with two pivalamidate-bridged platinum complexes containing different co-ligands (i.e., [Pt2]). Single-crystal X-ray analyses for 2 and 3 reveal that [Pt2] is linked by [Rh2] with metal–metal bonds to form a linear alignments of [Pt2]–[Rh2]–[Pt2]. Taking into account for the metal–metal distances, elemental analyses, and X-ray photoelectron spectra (XPS), the oxidation state of each metal in 2 and 3 can be considered as being [Pt2II,II]–[Rh2II,II]–[Pt2II,II], which is unchanged from that in the starting compounds. These hexanuclear backbones are attributed to easily formation of unbridged Rh–Pt bonds, which are caused not only by hydrogen bonds of ligands between [Rh2] and [Pt2], but also HOMO–LUMO interaction between vacant σ∗ in [Rh2II,II] and filled σ∗ in [Pt2II,II]. Electronic absorption spectra of 2 and 3 show three new peaks E1, E2, and E3 involved with σ-type orbitals, instead of original ones, π∗(Rh2) → σ∗(Rh–O) and π∗(Rh2) → σ∗(Rh2) transitions in the Rh2 core of [Rh2(O2CCH3)4], revealing the presence of metal–metal interactions between Rh and Pt atoms.

The Pt co-ligands in heterometallic 1D chains are changed to modulate the electronic structures of two novel hexanuclear complexes.Figure optionsDownload as PowerPoint slideHighlights
► Two heterometallic Pt–Pt–Rh–Rh–Pt–Pt complexes were synthesized.
► The Pt–Rh bonds were formed by the overlaps of filled and vacant σ∗ orbitals.
► The XPS measurements reveal that the oxidation state of each metal is +2.
► Electronic absorption spectra show three new peaks involved with σ-type orbitals.