Magnetochemical complexity of hexa- and heptanuclear wheel complexes of late-3d ions supported by N,O-donor pyridyl-methanolate ligands

Abstract

The scaffold geometries, stability and magnetic features of the (pyridine-2-yl)methanolate (L) supported wheel-shaped transition-metal complexes with compositions [M6L12] (1), [Na⊂(ML2)6](+) (2), and [M'⊂(ML2)6](2+) (3), in which M=Co(II), Ni(II), Cu(II), and Zn(II) were investigated with density functional theory (DFT). The goals of this study are manifold: 1) To advance understanding of the magnetism in the synthesized compounds [Na⊂(ML2)6](+) and [M'⊂(ML2)6](2+) that were described in Angew. Chem. Int. Ed.- 2010, 49, 4443 (I-{Na⊂Ni6}, I-{Ni'⊂Ni6}) and Dalton Trans.- 2011, 40, 10526 (II-{Na⊂Co6}, II-{Co'⊂Co6}); 2) To disclose how the structural, electronic, and magnetic characteristics of 1, 2, and 3 change upon varying M(II) from d(7) (Co(2+)) to d(10) (Zn(2+)); 3) To estimate the influence of the Na(+) and M'(2+) ions (X(Q+)) occupying the central voids of 2 and 3 on the external and internal magnetic coupling interactions in these spin structures; 4) To assess the relative structural and electrochemical stabilities of 1, 2, and 3. In particular, we focus here on the net spin polarization, the determination of the strength and the sign of the exchange coupling energies, the rationalization of the nature of the magnetic coupling, and the ground-state structures of 1, 2, and 3. Our study combines the broken symmetry DFT approach and the model Hamiltonian methodology implemented in the computational framework CONDON 2.0 for the modeling of molecular spin structures, to interpret magnetic susceptibility measurements of I-{Na⊂Ni6} and I-{Ni'⊂Ni6}. We illustrate that whereas the structures, stability and magnetism of 1, 2, and 3 are indeed influenced by the nature of 3d transition-metals in the {M6} rims, the X(Q+) ions in the inner cavities of 2 and 3 impact these properties to an even larger degree. As exemplified by I-{Ni'⊂Ni6}, such heptanuclear complexes exhibit ground-state multiplets that cannot be described by simplistic model of spin-up and spin-down metal centers. Furthermore, we assess how future low-temperature susceptibility measurements at high magnetic fields can augment the investigation of compound 3 with M=Co, Ni.

Keywords: density functional calculations; electrochemistry; host-guest systems; magnetochemistry; transition metals.