Paramagnetic one-dimensional chains containing high-spin manganese atoms showing antiferromagnetic interaction through –Pt–Rh–Rh–Pt– bonds

Abstract

To exploit the magnetic interactions of multiple metals, a heterometallic one-dimensional (1D) chain containing three kinds of metals, Rh, Pt, and Mn, where [Rh₂(O₂CCH₃)₄] and [Pt₂Mn(piam)₄(NH₃)₄]²⁺ (piam = pivalamidate) are connected through unbridged Rh–Pt bonds to form –Rh–Rh–Pt–Mn–Pt– alignments was successfully synthesized. The Mn atoms are tetrahedrally coordinated by four oxygen atoms of the piam ligands, where the coordination geometries form a zigzag 1D chain. Each Mn atom is linked by –Pt–Rh–Rh–Pt–, with a Mn–Mn separation of 13.9 Å. In parent [Pt₂Mn(piam)₄(NH₃)₄](PF₆)₂, Mn adopts two coordination environments, octahedral and tetrahedral, both of which are Mn(+2) high-spin states. In EtOH, [Rh₂(O₂CCH₃)₄] selectively binds tetrahedral Mn to afford a 1D chain. Physical analysis of the 1D chain using electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) revealed that all metals are divalent, indicating five unpaired spin-localized electrons on the Mn atoms. Magnetic susceptibility measurements indicated antiferromagnetic intra-chain interactions between the Mn atoms in the 1D chain, where χT at 300 K was 5.33 cm³ K mol⁻¹ and gradually decreased to 1.65 cm³ K mol⁻¹ at 2 K. Theoretical fitting of the magnetic behavior showed weak exchange coupling (zJ = −0.43 cm⁻¹) between two high-spin Mn(+2) ions through diamagnetic Pt–Rh–Rh–Pt.