Synthesis and characterization of a new quasi-one-dimensional antiferromagnet CoF2(H2O)2(pyrazine)

Abstract

A new one-dimensional (1D) antiferromagnetic transition metal hybrid fluoride CoF 2 (H 2 O) 2 (pyz) (pyz = pyrazine) together with two new isostructural MF 2 (H 2 O) 2 (pyz) (M = Ni 2+ , Zn 2+ ) have been successfully synthesized by the hydrothermal method. Their structures were determined by single crystal X-ray diffraction and they all crystallize in the same space group of C2/m. The magnetic property of CoF 2 (H 2 O) 2 (pyz) 1 was measured and discussed. The Weiss constant of −20.6 K indicates dominant antiferromagnetic interaction and the effective magnetic moment of about 5.66 μ B suggests large unquenched orbital contribution and anisotropy in 1. The quantum fluctuations in the quasi-1D antiferromagnet of 1 prevent the appearance of long range magnetic order until 2.9 K, suggesting good 1D magnetism.

CoMOF5(pyrazine)(H2O)2 (M = Nb, Ta): Two-Layered Cobalt Oxyfluoride Antiferromagnets with Spin Flop Transitions

“…The bond distance of four equatorial Nb–F 2 /O 2 is 1.910(3) Å and the two bridging Nb–F 1 ( trans ) bond lengths are both 1.925(4) Å. These bond lengths are all in agreement with other reported Co-based, Nb-based, and Ta-based oxyfluorides. ,− The pyrazine molecules are all parallelly aligned in the crystal structures of 1 and 2 , different with those in CoF 2 (H 2 O) 2 (pyrazine) and other reported pyrazine-contained hybrids. , The oxidation state of cobalt in +2, niobium in +5, tantalum in +5 are confirmed by bond valence sum (BVS) calculations using values reported by Brese and O’Keefe (Table ). …”

“…The value of P eff is slighhtly larger than the theoretical spin-only value of 3.87 μ B for free Co 2+ in a high spin state ( S = 3/2), suggesting a non-negligible unquenched orbital contribution. But interestingly, it is smaller than 5.00 μ B in HgCo­(SeO 3 ) 2 (H 2 O) 2 , 5.66 μ B in CoF 2 (pyz)­(H 2 O) 2 , and the values in other Co 2+ compounds. − For the low-temperature range, between 10 K and 20 K, Curie–Weiss fitting could yield P eff1 ′ = 3.82 μ B and θ 1 ′ = −8.2 K. The reduction of effective magnetic moment may suggest a spin crossover from a high spin state of 3/2 to a pseudospin state of 1/2, which is typical for Co 2+ in the octahedral environment, as also observed in Ba 3 CoSb 2 O 9 , Ba 8 CoNb 6 O 24 , and ACoX 3 (A = Cs, Rb; X = Cl, Br) . The negative value of Weiss constant indicates that the dominant magnetic interaction between Co 2+ spins in 1 is antiferromagnetic.…”

“…The bridging angle of ∠Co–F–Nb is 147.9° (∠Co–F–Ta = 146.2° for 2 ). Magnetic CoN 2 F 2 O 2 octahedra are slightly distorted with δ = ( d max – d min )/ d min = 2.9% for 1 and 1.9% for 2 , respectively, as shown in Figure , which are much smaller than 9.2% in the same heteroleptic CoO 2 N 2 F 2 octahedra in CoF 2 (pyz)­(H 2 O) 2 . Each [CoN 2 F 2 O 2 ] octahedron contains two bridging Co–N bonds with d Co–N = 2.111(4) Å and two bridging Co–F bonds with d Co–F = 2.050(4) Å in 1 .…”

“…Niobium or tantalum oxyfluoride anions [MO x F y ] n − (M = Nb, Ta) have been widely used to design and explore novel functional materials due to their rich chemical structure diversity, particularly for nonlinear optical materials attributed to the second-order Jahn–Teller distortion of Nb 5+ /Ta 5+ with d 0 electron configuration. As well, niobium or tantalum oxyfluoride anions [MO x F y ] n − (M = Nb, Ta) have been acted as basic building units for constructing low dimensional magnetic systems, such as triangular lattice systems of A 3 M’Nb 2 O 9 (A = Ca, Sr, Ba; M’ = Co, Ni, Mn), − Ba 8 CoNb 6 O 24 , and Ba 3 M”Ta 2 O 9 (M” = Co, Ni, Mn). , Meanwhile, organic molecule pyrazine (pyz) are also used to design and form low-dimensional magnets, including CuF 2 (pyz)­(H 2 O) 2 , [Cu 2 F­(HF)­(HF 2 )­(pyrazine) 4 ]­(SbF 6 ) 2 , CoF 2 (pyz)­(H 2 O) 2 and so on.…”

Synthesis of Sr1+2xLa1‐2xFe1‐xNbxO4 (x=0, 0.1, 0.3, and 0.5) by Sol‐gel Method: Structural, Magnetic, and Dielectric Properties

“…The result indicates that both samples are antiferromagnetic. [35] However, the value of θ increases for the doped sample, implying that the antiferromagnetic interaction decreases. [19] The effective magnetic moment (μ eff )a tx=0a nd 0.3 calculated from Currie-Weiss law are found to have the values 5.2 μBa nd 4.6 μB, respectively.…”