Despite the significance of nickel compounds, NMR spectroscopy of the active nickel isotope 61Ni remains a largely unexplored field. While nickel(0) compounds have been studied by 61Ni NMR in solution, solid-state experiments have been limited to Knight shift studies of nickel metal and nickel intermetallics. In conjunction with an NMR study of their ligands and 61Ni relativistic computations, the first 61Ni solid-state NMR (SSNMR) spectra of diamagnetic compounds are reported here. Specifically, bis(1,5-cyclooctadiene)nickel(0) [Ni(cod)2], tetrakis(triphenylphosphite)nickel(0) [Ni[P(OPh)3]4], and tetrakis(triphenylphosphine)nickel(0) [Ni(PPh3)4] were studied. 61Ni SSNMR spectra of Ni(cod)2 were used to determine its isotropic chemical shift (δiso = 965 ± 10 ppm), span (Ω = 1700 ± 50 ppm), skew (κ = -0.15 ± 0.05), quadrupolar coupling constant (CQ = 2.0 ± 0.3 MHz), quadrupolar asymmetry parameter (η = 0.5 ± 0.2), and the relative orientation of the chemical shift and electric field gradient tensors. A solution study of Ni(cod)2 in C6D6 yielded a narrow 61Ni signal, and the temperature dependence of δiso(61Ni) was assessed (δiso being 936.5 ppm at 295 K). The solution is proposed as a secondary chemical shift reference for 61Ni NMR in lieu of the extremely toxic Ni(CO)4 primary reference. For Ni[P(OPh)3]4, 61Ni SSNMR was used to infer the presence of two distinct crystallographic sites and establish ranges for δiso in the solid state, as well as an upper bound for CQ (3.5 MHz for both sites). For Ni(PPh3)4, line shape fitting provided a δiso value of 515 ± 10 ppm, Ω of 50 ± 50 ppm, κ of 0.5 ± 0.5, CQ of 0.05 ± 0.01 MHz, and η of 0.0 ± 0.2. The study of Ni(PPh3)4, in particular, demonstrates the utility of 61Ni SSNMR given the lack of a previously reported crystal structure and transient nature of Ni(PPh3)4 in solution.

Structural and Crystallographic Information from 61Ni Solid-State NMR Spectroscopy: Diamagnetic Nickel Compounds.

NMR and μ-SR study on competing Heisenberg chain Cs2Cu2Mo3O12

The high-field ground state of the competing-spin-chain compound Cs2Cu2Mo3O12 with the ferromagnetic first-nearest-neighbor J1=-93 K and the antiferromagnetic second-nearest-neighbor J2 = +33 K was investigated by 133Cs-NMR. A divergence of T1-1 and a peak-splitting in spectra were observed at TN = 1.85 K, indicating the existence of a field-induced long range magnetic order. In the paramagnetic region above 4 K, T1-1 showed a power-law temperature dependence T2K-1. The exponent K was strongly field-dependent, suggesting the possibility of the spin-nematic Tomonaga Luttinger Liquid state.

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Ground state of the competing spin chain Cs2Cu2Mo3O12

133Cs/7Li-NMR study was performed on a quasi-two-dimensional spin system Cs2Mn3LiF12, in which S = 2 Mn atoms form undistorted Kagome lattice. We have observed a clear splitting in the Li-NMR resonance line for a single crystal at low temperatures below TN = 3.6 K. The longitudinal nuclear spin relaxation rate T−11 of both Cs and Li-NMR showed a critical divergence at the same temperature. These observations are considered to be a microscopic evidence for an occurrence of long range magnetic order due to a weak inter-plane spin interactions.

https://iopscience.iop.org/article/10.1088/1742-6596/568/4/042008/pdf

NMR study on kagome-lattice antiferromagnet Cs2Mn3LiF12

The heavy fermion compound Ce7Ni3 is an antiferromagnet with TN∼1.7 K. According to the high pressure experiment, this compound has undergone a transition to a non-Fermi liquid state at ∼0.32 GPa and has recovered a Fermi liquid state at ∼0.62 GPa again. Before the high pressure nuclear magnetic resonance (NMR) study through two transitions, we have performed NMR experiments of 61Ni, 59Co and 63Cu in order to clarify the electronic states at ambient pressure. Two kinds of partially overlapping Ni NMR spectra were observed in Ce7Ni3 containing an enriched 61Ni. This result may be ascribed to two intrinsic local fields presumably due to the lattice distortion, etc. All the relaxation rates studied here are proportional to temperature above 1.4 K in the paramagnetic state, which indicates that the systems are in the Fermi liquid state at ambient pressure. The increase of (1/T1T) with increasing Co concentration, CCo, tells us that the partial density of states on Ni-3d states at Fermi level, N(EF)Ni, increas...

S. Mishina

Papers

Nuclear magnetic resonance and nuclear quadrupole resonance studies of 61Ni in heavy fermion compounds Ce7Ni3