Electronic Coupling through Intramolecular π–π Interactions in Biscobaltocenes: A Structural, Spectroscopic, and Magnetic Study

Abstract

The paramagnetic dinuclear complexes 1,8-bis(cobaltocenyl)naphthalene (2) and 1,8-bis[(pentamethyl-η(5)-cyclopentadienyl)(η(5)-cyclopentadiendiyl)cobalt(II)]naphthalene (4) were synthesized. The molecular structures were characterized by X-ray structure analysis and consisted of two cobaltocenes linked through a distorted naphthalene clamp. Electronic interactions between the two cobalt atoms were observed by cyclic voltammetric studies. Superconducting quantum interference device (SQUID) measurements of the pure compounds and diluted in their diamagnetic iron derivatives, as well as variable-temperature NMR spectroscopy experiments in solution are presented. Magnetic measurements revealed an antiferromagnetic coupling of the electrons in complexes 2 and 4. From NMR spectroscopy experiments, Curie behavior in the temperature range from -60 to +60 °C can be deduced. The electronic structure and magnetic behavior is supported by results of broken-symmetry DFT and multireference calculations along with UV/Vis spectroscopic data, which revealed an intramolecular through space π-π interaction between the cobaltocene units.

Interconnected Cobaltocene Complexes on Metal Surfaces

“…In the present case, each cobaltocene unit of the NBC molecule should have one unpaired electron and hence a spin S = 1/2 (ref .). The singly occupied molecular orbitals consist of d yz cobalt orbitals which are strongly hybridized with the orbitals of the ligand rings.…”

“…37,38 The coupling between the magnetic centers may be realized through the linker or by the linker imposing a particular molecular arrangement where the π orbitals of one metallocene overlap with that of the other metallocene. 39,40 However, when the molecules are adsorbed on a surface, depending on the nature and size of the linker, it may enforce particular adsorption geometries of the molecule on the surface. In turn, different adsorption geometries can lead to different coupling to the substrate and subsequently affect the magnetic properties of the adsorbed molecules.…”

“…20,52,53 The model used in Figure 1a deviates from the structure inferred from X-ray diffraction data of bulk crystals. 40,42 The twist angle, i.e., the angle between the naphthalene and the Cp planes, goes from ≈47°(bulk molecule) to ≈90°(model). This renders the naphthalene plane parallel to the long axes through the two Co atoms.…”

“…A wide variety of metallocenes with distinct magnetic properties may be realized by exchanging the metal center . Furthermore, the Cp ring of the metallocene may be connected by organic groups in order to couple the magnetic centers. ,− Various classes of interconnection designs were reported, ranging from simple fused-ring ligands to complex molecular switches. , The coupling between the magnetic centers may be realized through the linker or by the linker imposing a particular molecular arrangement where the π orbitals of one metallocene overlap with that of the other metallocene. , However, when the molecules are adsorbed on a surface, depending on the nature and size of the linker, it may enforce particular adsorption geometries of the molecule on the surface. In turn, different adsorption geometries can lead to different coupling to the substrate and subsequently affect the magnetic properties of the adsorbed molecules.…”

Synthesis, characterization and magnetic properties of head-to-head stacked vanadocenes

“…The solvent was decanted and the crystals were washed with n-pentane (20 mL). The complex 2 was obtained as a violet, crystalline solid (0.95 g, 4.3 mmol, 54 % (69 %) [1] 5] , [CoCo] * 2 [5] and [NiNi] * 2 [6] obtained from X-ray structure analysis and from the structure optimization of the BS determinant with TPSSH / def2-TZVP; cent [4] : centroid of the corresponding Cp ligand; plane [4] : best-fit plane through corresponding atoms.…”