Synthesis, Electronic Structure, and Magnetism of [Ni(6-Mes)₂]⁺: A Two-Coordinate Nickel(I) Complex Stabilized by Bulky N-Heterocyclic Carbenes

Abstract

The two-coordinate cationic Ni(I) bis-N-heterocyclic carbene complex [Ni(6-Mes)2]Br (1) [6-Mes =1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene] has been structurally characterized and displays a highly linear geometry with a C-Ni-C angle of 179.27(13)°. Density functional theory calculations revealed that the five occupied metal-based orbitals are split in an approximate 2:1:2 pattern. Significant magnetic anisotropy results from this orbital degeneracy, leading to single-ion magnet (SIM) behavior.

Magnetic anisotropy in two- to eight-coordinated transition–metal complexes: Recent developments in molecular magnetism

“…In 2013, Poulten et al described a two-coordinated Ni I complex, [Ni(6-Mes) 2 ] + (13), which was stabilized by bulky N-heterocyclic carbenes [37]. An orbital contribution (L = 2) to the magnetic moment was used to explain why the  M T value (1.12 cm 3 K mol -1 ) at 300 K was greatly above the spin-only Curie constant for an S = ½ spin state.…”

“…Their magnetic behavior exhibited distinct features, which were attributed to the effect of geometrical influences on orbital magnetism [38]. [K(18-crown-6)] (12) slightly bent nr [36] [Ni(6-Mes)2]Br (13) linear Yes 600 4.6  10 -6 11.8 [37] a Maximal temperature at which magnetic hysteresis was observed; b too small to be measured; nr = not reported.…”

One‐Electron Oxidation of [M(PtBu3)2] (M=Pd, Pt): Isolation of Monomeric [Pd(PtBu3)2]+ and Redox‐Promoted C−H Bond Cyclometalation

“…As imilar bond length elongation has been noted in closely related NHC complexes of Ni 0 /Ni (2) ). [10] Isolated 2a is air-sensitive in solution, but shows good stability under an argon atmosphere. Fori nstance,u nder argon the EPR spectrum intensity was essentially unchanged after 24 hat293 K(15 mm).…”

Slow Magnetic Relaxation in Mononuclear Octahedral Manganese(III) Complexes with Dibenzoylmethanide Ligands

“…The τ o values obtained here are comparable to those found in SIMs based on transition metal ions. [7][8][9][10][11] For 1, the energy barrier (4|D| = 18.2 cm -1 ) calculated from HFEPR data is considerably larger than the effective energy barrier (11.5 cm -1 ), and this may be explained by the existence of non-negligible QTM. However, in 2, the value of the energy barrier (4|D| = 13.7 cm -1 ) calculated from the dc magnetization measurements is smaller than the effective energy barrier 16.8 cm -1 .…”

“…[6] More recently, mononuclear complexes based on transition-metal ions have exhibited SMM behavior as well. [7][8][9][10][11] Mononuclear Mn III complexes are of particular interest, because the largest family of polynuclear SMMs contains the Mn III ion. The d 4 Mn III ion has an 5 E g ground state in an octahedral environment, such that the first-order orbital contribution is quenched.…”