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.