Single-Chain Magnets Constructed by Using the Strict Orthogonality of Easy-Planes: Use of Structural Flexibility to Control the Magnetic Properties

Abstract

A family of single-chain magnets (SCMs), of which the SCM character originated from the spatial arrangement of high spin Fe(II) ions with easy-plane anisotropy, was synthesized, and their magnetic properties were investigated. The chain complexes including alternating high-spin Fe(II) ions and low-spin Fe(III) ions, catena-[Fe(II)(ClO(4))(2){Fe(III)(bpca)(2)}]ClO(4)·3MeNO(2) (1·3MeNO(2)), catena-[Fe(II)(ClO(4))(H(2)O){Fe(III)((Me)L)(2)}](ClO(4))(2)·2MeNO(2)·H(2)O (2·2MeNO(2)·H(2)O), catena-[Fe(II)(ClO(4))(H(2)O){Fe(III)((Bu)L)(2)}](ClO(4))(2)·3.5MeNO(2) (3·3.5MeNO(2)), and catena-[{Fe(II)(ClO(4))(H(2)O)Fe(II)(H(2)O)(2)}(0.5){Fe(III)((Ph)L)(2)}](ClO(4))(2.5)·4EtNO(2) (4·4EtNO(2)), were synthesized with the use of bridging ligand Hbpca (bis-(2-pyridylcarbonyl)amine)) and its derivatives of H(Me)L, H(Bu)L, and H(Ph)L each incorporating methyl, tert-butyl, or phenyl group on the 4-position of pyridyl ring. These complexes showed a typical ferrimagnetic behavior on direct current (dc) susceptibility data, and from an alternating current (ac) susceptibility measurements, SCM or superparamagnetic behaviors were confirmed with the Δ/k(B) values of 22.5(4), 21.8(18), and 28.8(3) K for 1·3MeNO(2), 2·2MeNO(2)·H(2)O, and 3·3.5MeNO(2), of which the easy-axis anisotropy was originated from the orthogonal arrangement of easy-planes of Fe(II) ions. In the crystal structures, cylindrical voids were formed along the chain axis being surrounded by four chains in 1·3MeNO(2), 2·2MeNO(2)·H(2)O, and 4·4EtNO(2) and two chains in 3·3.5MeNO(2), and solvent molecules as well as coordination-free perchlorate anions occupied these voids in a slightly different fashion depending on the complexes. 2·2MeNO(2)·H(2)O maintains its chemical composition in a dried condition, whereas 1·3MeNO(2), 3·3.5MeNO(2), and 4·4EtNO(2) easily release solvent molecules to give 1, 3, and 4, respectively. 1 and 3 maintain the crystalline character showing slightly different X-ray diffraction (XRD) patterns from those of 1·3MeNO(2) and 3·3.5MeNO(2), and an enhancement of SCM character after release of the solvent molecules was observed for both. 4 lost crystalline character to become amorphous, and it lost the SCM character at the same time.

A toolbox of building blocks, linkers and crystallisation methods used to generate single-chain magnets

“…[130]) based around a bis(pyridylcarbonyl)amine core (Fig. 28) [23,43], and presenting an interesting double-sided pocket. These ligands are deprotonated and hence anionic when bridging the building blocks using the pair of 'spare' imide oxygen donors (Fig.…”

Crystal structures of three N-(pyridine-2-carbonyl)pyridine-2-carboxamides as potential ligands for supramolecular chemistry

“…N-(Pyridine-2-carbonyl)pyridine-2-carboxamide systems and their derivatives have been shown to be very useful intermediates for the construction of molecular building blocks, able to self-assemble into a wide range of super-architectures taking advantage of acceptor-donor-donor-acceptor (ADDA) arrays of hydrogen-bonding sites (Corbin et al, 2001). Further interest in this family of compounds has involved the investigation of their metal coordination complexes, which possess strong luminescence characteristics (Das et al, 2018), as well as their electrochemical (Gasser et al, 2012), magnetic (Kajiwara et al, 2010) and catalytic properties (Chowdhury et al, 2007). Consequently, the synthesis of N-(pyridine-2-carbonyl)pyridine-2-carboxamide, containing different functional groups, at a large scale and in a high yield is of great importance in the field of supramolecular chemistry.…”

Effective easy-axis anisotropy of the two-sublattice single-chain magnet with twisted easy planes

“…From the prospects for spintronics, compounds supporting radiation-induced long-lived magnetic excitations are of considerable interest [1,5,6]. Such compounds include the four-sublattice SCM catena − [Fe II (ClO 4 ) 2 Fe III (bpca) 2 ](ClO 4 ) [7][8][9] with twisting and mutually ortoghonal easy planes. Due to the different orientations of the above easy planes, the effective easy-axis anisotropy is induced and microscopic magnetic domains with sharp domain walls are created [7,9].…”

“…Such compounds include the four-sublattice SCM catena − [Fe II (ClO 4 ) 2 Fe III (bpca) 2 ](ClO 4 ) [7][8][9] with twisting and mutually ortoghonal easy planes. Due to the different orientations of the above easy planes, the effective easy-axis anisotropy is induced and microscopic magnetic domains with sharp domain walls are created [7,9]. On the other hand, the presence of the easy-plane single-ion anisotropy induces strong spin fluctuations [10,11] which have to be taken into account for consecutive analysis of experimental data [8,12].…”