A Single‐Ion Magnet Tape with Five‐Coordinate Cobalt(II) Centers

Abstract

A one-dimensional (1D) coordination polymer [Co(btca) 1/ 2 (mbpy)] n (1, mbpy = 4,4'-Dimethyl-2,2'-bipyridyl, H 4 btca = 1,2,4,5-Benzenetetracarboxylic acid) constructed by a mixed tetracarboxylic-dipyridyl ligand strategy with a ribbon topology was synthesized and magnetically characterized. Magnetic studies combined with theoretical calculations reveal large easy-axis magnetic anisotropy of the central Co(II) ions in a highly distorted five-coordination geometry. Interestingly, fieldinduced single-ion magnet (SIM) behavior was evidenced in the chain compound, making the cobalt(II) coordination ribbon to be the first five-coordinate SIM chain.

Incorporating Highly Anisotropic Four-Coordinate Co(II) Ions within One-Dimensional Coordination Chains

“…Magnetically, though 1 and 2 are coordination polymers with distinct 1D topologies, the Co II centers are bridged by various long organic ligands, giving rise to two magnetically noninteracting Co II centers in 1 and 2 . These coordination polymers with negligible magnetic interactions between the metal centers can still be treated as single-ion systems. − To estimate the zero-field splitting (ZFS) parameters ( D , E , g tensors) of 1 and 2 , the susceptibility and magnetization data in the measured temperature range were simultaneously fitted by the PHI program considering the following spin Hamiltonian: Ĥ = D [ Ŝ z − Ŝ false( Ŝ + 1 false) 3 ] + E ( Ŝ x 2 − Ŝ y 2 ) + μ normalB g · Ŝ · B where D , E , S , μ B , and B represent the axial and rhombic ZFS parameters, the spin operator, Bohr magneton, and magnetic field vectors, respectively. The best fits afford D = −21.1 cm –1 , | E/D | = 0.12, g = 2.457 for 1 , and D = −35.3 cm –1 , | E/D | = −0.16, g = 2.621 for 2 .…”

“…Besides the mononuclear complexes, a series of coordination polymers (CPs) or metal–organic frameworks (MOFs), which are built with metal nodes (a single metal ion or a cluster) and organic linking ligands were reported to display slow relaxation of the magnetization under zero filed or applied dc fields. − Such 3d or 4f complexes can be considered as SIM-CPs or SMM-CPs because magnetically they exhibit the nature of their metal nodes due to negligible internode interactions. − In fact, they have provided a new platform for manipulating the magnetic dynamics. As an illustrative example, Cano et al reported the guest-dependent SIM behavior in a family of cobalt­(II) MOFs .…”

“…As an illustrative example, Cano et al reported the guest-dependent SIM behavior in a family of cobalt­(II) MOFs . Our recent studies on some 1D or 2D SIM-MOFs also showed that the magnetic dynamics of such complexes can be tuned by switching the guest molecules, or varying the axial coordination atoms. − To date, however, the majority of such complexes, including discrete polynuclear complexes, are built with the six-coordinate and octahedral metal centers (Table S1, Table S2, SI) rather than the well-recognized highly anisotropic metal ions, including the low-coordinate ones. − One major reason lies in the synthetic challenge for preserving/realizing the selected particular geometries within a framework. , …”

A porous cobalt(ii)–organic framework exhibiting high room temperature proton conductivity and field-induced slow magnetic relaxation

“…The Co–N/O bond lengths are in the range of 2.054–2.230 Å, indicating the high spin Co 2+ ions in 1 . 20,21 Each H bic links the Co 2+ ion using its deprotonated carboxylic O and imidazole N, thereby forming 2D metal–organic layers with a simple (4, 4) topology (Fig. 1b).…”

“…With the above aspects in mind and following our long-term interests in SIMs and coordination polymers, 20,21 we aim to develop new multifunctional SIM framework materials. Herein, we report the synthesis, structural characterization, magnetic properties, proton conductivity, and computational studies of a porous 2D cobalt( ii ) coordination polymer, namely {[Co(Hbic)(H 2 O)]·4H 2 O} n ( 1 ), constructed by employing H 2 bic ligand and cobalt( ii ) salt (Fig.…”