Synthesis, Structure, and Magnetic Properties of Linear Trinuclear Cu^II and Ni^II Complexes of Porphyrin Analogues Embedded with Binaphthol Units

Abstract

A porphyrin analogue embedded with (S)-1,1′-bi-2-naphthol units was synthesized without reducing optical purity of the original binaphthol unit. This new macrocyclic ligand provides the hexaanionic N4O4 coordination environment that enables a linear array of three metal ions. That is, it provides the square planar O4 donor set for the central metal site and the distorted square planar N2O2 donor set for the terminal metal sites. In fact, a CuII3 complex with a Cu(1)–Cu(2) distance of 2.910 Å, a Cu(1)–Cu(2)–Cu(1′) angle of 174.7°, and a very planar Cu2O2 diamond core was obtained. The variable-temperature 1H-NMR study of the CuII3 complex showed increasing paramagnetic shifts for the naphthyl protons as temperature increased, which suggests strong antiferromagnetic coupling of CuII ions. The temperature dependence of the magnetic susceptibility indicated antiferromagnetic coupling both for the CuII3 complex (J = −434 cm−1) and for the NiII3 complex (J = −49 cm−1). The linear (L)M(µ-OR)2M(µ-OR)2M(L) core in a rigid macrocycle cavity made of aromatic components provides robust metal complexes that undergo reversible ligation at the apical sites of the central metal.

Keywords

• porphyrinoids
• multinuclear complexes
• chiral ligands
• circular dichroism
• paramagnetic NMR
• magnetochemistry