Dinuclear and Mononuclear Rhenium Coordination Compounds upon Employment of a Schiff-Base Triol Ligand: Structural, Magnetic, and Computational Studies.

Abstract

The 1:1 reaction of trans-[ReIIICl3(PPh3)2(MeCN)] with 2-(β-naphthalideneamino)-2-hydroxymethyl-1-propanol, H3L, in toluene gave the dinuclear complex [ReIII2Cl4(HL)(PPh3)]·2C7H8 (1·2C7H8), while the 1:2 reaction led to the formation of complex [ReIVCl2(HL)(PPh3)] (2). In both species, the Schiff-base ligand exists in its doubly deprotonated form, HL2-, forming chelate rings around the metallic centers. In addition, 1·2C7H8 displays a unique triple metal-to-metal bond between the two trivalent rhenium ions separated at a 2.229(1) Å bond distance, while in complex [ReIVCl2(HL)(PPh3)] (2) the two aromatic ligands, HL2- and PPh3, occupy axial positions, with the terminal Cl- ions in the trans position. Investigation of the magnetic properties revealed a Curie paramagnetic behavior ( S = 1/2) with a pronounced temperature independent paramagnetism (TIP) for 1·2C7H8 and 2. Both the geometry and the electronic structure of both compounds have been studied by means of density functional theory (DFT) calculations, confirming the triplet and doublet spin ground state of the complexes and furthermore establishing an electron-rich σ2π4δ1δ*1 bond order of 3 for 1·2C7H8. In addition, the absorption spectrum of 1·2C7H8 in CH2Cl2 was simulated by means of DFT calculations and is in excellent agreement with both the crystallographic and theoretical studies. Complex 1·2C7H8 is the first dinuclear rhenium complex with a triple metal-metal bond between trivalent rhenium centers.