One-dimensional complexes extended by unbridged metal–metal bonds based on a HOMO–LUMO interaction at the dz2 orbital between platinum and heterometal atoms

Abstract

In this review, the crystal structures of seventeen heterometallic one-dimensional compounds 1–17 are shown, and their electronic structures are discussed based on the diffuse reflectance spectra and other physical measurements. Compounds 1–17 comprise two kinds of complexes with HOMO–LUMO interactions at σ-type (d_z²) orbitals between platinum and heterometal atoms, where two or three kinds of metal are regularly aligned through metal–metal bonds. In [{PtRh(piam)₂(NH₃)₂Cl_2.5}₂{Pt₂(piam)₂(NH₃)₄}₂]_n(PF₆)_6n·2nMeOH·2nH₂O (3, piam = pivalamidate), the platinum and rhodium atoms are aligned as –Pt–Rh–Pt–Pt–Pt–Pt–Rh–Pt–Cl– with a mixed valence, where an unpaired electron hops from one Rh atom to another. [{Rh₂(O₂CCF₃)₄}{Pt₂(piam)₂(NH₃)₄}₂]_n(CF₃CO₂)_4n·2nEtOH·2nH₂O (6) with –Pt–Pt–Rh–Rh–Pt–Pt– alignment has a conduction band (CB) and a valence band (VB) attributed to σ-type orbitals, exhibiting narrower gaps between CB and VB than other analogues. [{Ru₂(O₂CCH₃)₄}{Pt₂(piam)₂(NH₃)₄}₂]_n(PF₆)_4n·4nH₂O (14) with –Pt–Pt–Ru–Ru–Pt–Pt– and [{Rh₂(O₂CCH₃)₄}{Pt₂Cu(piam)₄(NH₃)₄}]_n(PF₆)_2n (15) with –Rh–Rh–Pt–Cu–Pt– are paramagnetic chains, where one or two unpaired electrons reside at each metal per repeating unit. Thus, this system is diverse in modulating the electronic structures, band structures and the expected physical properties based on the unique oxidation states and redox properties attributed to the metal–metal interaction.