Series of Single-Ion and 1D Chain Complexes Based on Quinolinic Derivative: Synthesis, Crystal Structures, HF-EPR, and Magnetic Properties

Abstract

By utilizing the quinolinic derivative, 8-carboxymethoxy-2-carboxylicquinoline (L), five transition metal coordination complexes, [M(L)(HO)]·HO] (M = Mn (1), Co (2)), [Ni(L)(HO)] (3), and {[M(L)](HO)} (M = Ni (4), Cu (5)), were synthesized by hydrothermal methods employing similar synthetic strategies. The crystal structures, magnetism and high-field EPR were characterized for the obtained compounds. 1-3 are mononuclear compounds. 1 and 2 have pentagonal bipyramidal geometry, while 4 and 5 exhibit one-dimensional zig-zag chain. Direct current magnetic and EPR studies demonstrate that compound 2 has large and positive D value (∼70.4 cm), indicating the easy plane magnetic anisotropies of 2. This D value is the largest one in the reported Co(II) complexes with pentagonal bipyramidal geometry. Field-induced slow magnetic relaxation behavior was observed for 2 by the dynamic ac magnetic susceptibility measurements. The dc magnetic susceptibility studies of 4 and 5 give similar weak M-M antiferromagnetic interactions ( J = -1.50 and -3.55 K for 4 and 5, respectively). High-field EPR results show that 4 can be considered as a quantum antiferromagnet.

Water Molecule-Induced Reversible Magnetic Switching in a Bis-Terpyridine Cobalt(II) Complex Exhibiting Coexistence of Spin Crossover and Orbital Transition Behaviors

“…In these ln­(τ) vs T –1 plots, linear data corresponding to the Arrhenius law τ = τ 0 exp­( U eff / k B T ) were obtained, with an effective energy barrier of U eff = 4.2 K (τ 0 = 1.1 × 10 –5 s) and 3.6 K (τ 0 = 1.1 × 10 –2 s) for the fast and slow relaxation processes, respectively. These values are similar to those obtained for other reported Co­(II) complexes. , The relaxation mechanisms for a mononuclear single-molecule magnet system are usually very complex and involve multiple relaxation pathways. Although up to four possible relaxation mechanisms (QTM, direct, Raman, and Orbach processes) may usually occur, the QTM should, in principle, be suppressed in the case of measurements under an applied dc field.…”

“…These values are similar to those obtained for other reported Co(II) complexes. 50,51 The relaxation mechanisms for a mononuclear single-molecule magnet system are usually very complex and involve multiple relaxation pathways. Although up to four possible relaxation mechanisms (QTM, direct, Raman, and Orbach processes) may usually occur, the QTM should, in principle, be suppressed in the case of measurements under an applied dc field.…”

Probing the Influence of Structural Distortion and Axial Ligands on Magnetic Anisotropy in a Series of Chiral Pentagonal Bipyramidal Co(II) and Ni(II) Complexes

“…The axial Ni–O­(H 2 O) bond distances in compounds 1 , 2 , and 4 are found to be in the range 2.009–2.082 Å (Table S4), while the axial Co–O­(H 2 O) bond distances in compounds 6 , 8 , and 9 are found to be in the range 2.090–2.157 Å (Table S5). These bond distances are comparable with those of the reported nonchiral Ni–O­(H 2 O) and Co–O­(H 2 O) bond distances. − ,− , In compounds 3 and 5 , one of the axial Ni–N­(thiocyanato) bond distances is slightly longer than the other (2.009 and 2.030 Å for 3 and 2.015 and 2.048 Å for 5 , respectively), and these observations are in good agreement with the Ni–N bond distances observed in earlier reported mononuclear PBP Ni­(II) complexes bearing thiocyanato groups in axial positions. , In compounds 7 and 10 , the axial Co–N­(thiocyanato) bond distances are in the range 2.044–2.121 Å, which are in good agreement with the Co–N bond distances observed for related nonchiral mononuclear PBP Co­(II) complexes bearing thiocyanato groups in axial positions . In compounds 1 – 10 , the five donor atoms from the chiral ligand form an nearly an ideal planar structure as the sum of the chelate angles and the bite angle O(1)–M(1)–O(2) [where M = Ni, Co] measures between 360.0 and 360.4°.…”

“…Observation of giant uniaxial magnetic anisotropy in trigonal bipyramidal Co­(II) and Ni­(II) complexes can be attributed to the presence of low-lying excited electronic states with orbital degeneracy. − Apart from that, seven-coordinate Fe­(II), Co­(II), and Ni­(II) complexes with a pentagonal-bipyramid-shaped (PBP) coordination sphere have also emerged as attractive options for achieving large magnetic anisotropy in a molecular unit. ,− In a PBP coordination environment, Fe­(II) and Ni­(II) typically show uniaxial magnetic anisotropy (characterized by a negative zero field splitting parameter, D ) while Co­(II) shows an easy plane of magnetic anisotropy (positive D ). The origins of magnetic anisotropy in PBP Co­(II) and Ni­(II) complexes have been recently probed by using wave function based theoretical studies, and these results suggested the possibility of enhancing magnetic anisotropy by manipulation of the ligand field environment around the metal ion.…”

Structure and Magnetic Properties of Two Discrete 3d‐4f Heterometallic Complexes

“…[6][7][8][9] A large number of 3d complexes were reported. [10][11][12] However, it is very difficult to enhance their ground state spin and easy-axis anisotropy parameter simultaneously, [13][14][15] which limits the breakthrough of 3d complex in relaxation time and effective energy barrier. A long relaxation time is usually associated with a large anisotropic barrier.…”