Magnetic properties of nickelocene. A reinvestigation using inelastic neutron scattering and magnetic susceptibility

Abstract

The magnetic properties of nickelocene, undiluted and doped into ruthenocene and ferrocene, have been determined by susceptibility measurements on powder samples and crystallites oriented in high magnetic fields, respectively, between 4.4 and about 200 K. The results reveal that there is a predominantly ferromagnetic coupling of a nickelocene molecule to its nearest neighbors in an undiluted sample, whereas the interaction with triplet-state molecules at greater distances in diluted samples seems to be antiferromagnetic. By introduction of two molecular fields, describing the intermolecular interactions and an intramolecular zero-field splitting, the magnetic susceptibility of nickelocene, undiluted and doped into isostructural diamagnetic hosts, can be interpreted by the same spin-Hamiltonian parameters: D0 = 33.6 ± 0.3 cm'1, = 0.63 cm'1, and Ts = 0.89 cm'1. Furthermore the singlet-triplet separation in polycrystalline Ni(C5D5)2 has been determined by inelastic neutron scattering (INS) spectroscopy. The observed magnetic transition at 31.6 ± 1.0 cm'1 in the INS spectra does not correspond directly to the zero-field splitting of the isolated molecule, D0, but shows some influence of the intermolecular coupling and the deuteriated ligands.

Solid-State NMR Spectroscopy of Paramagnetic Metallocenes

“…As for the effect of g-factor anisotropy, this would introduce errors via both the pseudocontact shift and the anisotropy of the contact shift (26,27). The axial and equatorial g-factor components, g || and g ⊥ , of solid nickelocene are 2.0023 and 2.11, respectively (29). This corresponds to a gfactor anisotropy of 5% and justifies the estimation of ρ p from the shift tensor anisotropy.…”

Synthesis, crystal structure, magnetic properties and reactivity of a Ni–Ru model of NiFe hydrogenases with a pentacoordinated triplet (S=1) NiII center

“…¼ 2:07. The D value is among the highest observed for discrete nickel(II) complexes [13][14][15][16]. Since g = is lower than g ?…”

Large isotropic exchange interactions from E.P.R. on doublet-triplet organometallic molecular pairs in diamagnetic host-lattices

“…ENDOR measurements on single-doped ruthenocene showed that it incorporates V(bz)2 isomorphically [32]. This was also found for Ni(cp) 2 guest molecules [6].…”

“…As we will demonstrate, DT pairs involving a nickelocene triplet are favourable systems to derive exchange parameters from E.P.R. : the triplet ground state of Ni(cp) 2 is split by 33"6cm -1 [6] due to spin-orbit and spin-spin interactions.…”

“…All J values were calculated by equations (6,8,9) and also checked by a numerical diagonalization of the full hamiltonian (4). Parameters: hv = 0.3 cm-1, I1 --1/2 for simplicity; g21 = 2-11(3), D 2 = 33'6(3) [6].…”