Low Dimensional Magnetism in Cu(tn)Cl2 Mediated by Hydrogen Bonds

[Ni(HF2)(3-Clpy)4]BF4 (py = pyridine): Evidence for Spin Exchange Along Strongly Distorted F···H···F– Bridges in a One-Dimensional Polymeric Chain

“…The magnetic contribution can be approximated by a / T 2 in a high-temperature series expansion whereas C latt can be estimated by bT 3 + cT 5 . By plotting C p T 2 vs T (Figure b), we found a sublinear dependence of the data over a certain interval . A fit of those data gave a = 267(15) J·K/mol, b = 0.0106(2) J·K 4 /mol, and c = −1.33(4) × 10 –5 J·K 6 /mol.…”

Structural, Electronic, and Magnetic Properties of Quasi-1D Quantum Magnets [Ni(HF2)(pyz)2]X (pyz = pyrazine; X = PF6–, SbF6–) Exhibiting Ni-FHF-Ni and Ni-pyz-Ni Spin Interactions

“…In the various, albeit few, examples of quasi-1D and 2D Ni-pyz coordination polymers that have been reported, the Ni-pyz-Ni exchange interactions ( J ⊥ ) are relatively weak as can be seen in Table . − Upon close inspection of these data, there is no apparent correlation between the type of ligand donor atoms, Ni–N bond lengths, pyrazine tilt angle, or dimensionality of the spin system. Another important aspect worthy of consideration may lie in the donor/acceptor properties of the coordinated ligands themselves and perhaps a correlation among Racah B parameters or other ligand field parameters may arise.…”

“…For 1 and 2 , the difference in computed J ⊥ values may be linked to the rhombic distortion of the NiN 4 F 2 center and bent Ni···N···N paths in 1 which reduces the effective σ-overlap between Ni d x 2 – y 2 and pyz lone-pair orbitals. However, J 1D for Ni(Pr i xa) 2 (pyz) (Pr i xa = propylxanthate = i -C 3 H 7 OCS 2 – ) is comparatively large even though its Ni(II) center is substantially more distorted than that of 1 …”

“…However, the model employed above assumed that the two unique Ni-pyz-Ni pathways gave the same exchange constant which may be an oversimplification. Because of the differing values of S for Cu(II) and Ni(II) we cannot directly compare their J ⊥ values (i.e., Ni-pyz-Ni) but we can compare the net effective exchange integral 4 S 2 J for the various compounds including [ M (HF 2 )(pyz) 2 ]X ( M = Ni, Cu; X = PF 6 – , SbF 6 – ). , From Table it can be seen that 1 , 2 , and Ni(Pr i xa) 2 (pyz) exhibit relatively large J and 4 S 2 J values while the other compounds are significantly lower. More definitive comparisons cannot be made because of the lack of structural and magnetic data for many of the listed Ni(II) compounds.…”

Antiferromagnetism in a Family of S = 1 Square Lattice Coordination Polymers NiX2(pyz)2 (X = Cl, Br, I, NCS; pyz = Pyrazine)

“…Since Haldane , predicted that an antiferromagnetic Heisenberg chain has a singlet ground state and a finite gap to the lowest excited state for integer spins, this conjecture has inspired numerous studies of S = 1 antiferromagnets in low dimensions. While most of the work done so far is related to one-dimensional (1D) models or quasi-one-dimensional (Q1D) compounds, − less work has been performed on two-dimensional models (2D) or quasi-two-dimensional (Q2D) compounds − partially due to the difficulty in applying theoretical/numerical techniques to these models. In low-dimensional S = 1 antiferromagnets, the nature of the ground state can be strongly modified by the spatial dimensionality as well as the zero-field splitting (ZFS) of 3d 8 Ni­(II), both of which can be tuned by chemical synthesis.…”