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

A family of single-chain magnets (SCMs), of which the SCM character originated from the spatial arrangement of high spin Fell ions with easy-plane anisotropy, was synthesized, and their magnetic properties were investigated. The chain complexes including alternating high-spin Fell ions and low-spin Fe" ions, catena-Fell(C104)2{Felll(bpca)2}1C104 3MeNO2 (1.3MeNO(7)), catena-[Fell(C104)(H20){Feu(MeL)2}(CI04)2 2MeN04 H20 (2- 2MeNO2. H20), catena-Fell(C104)(H20){(FeBu)-Bu-III ( L)2}i(uu 4)2.3.5MeNO2 (3- 3,5MeNO2), and catena-[{F ell (C104)(F120)F ell (H20)21 0.5{Fe"( L)211(C104)2.5.4EtNO2 (4.4EtNO2), were synthesized with the use of bridging ligand Hbpca (bis-(2-pyridylcarbonyl)amine)) and its derivatives of eel., HBI, and HPhL 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 A/kB values of 22.5(4), 21.8(18), and 28.8(3) K for 1.3MeNO2, 2- 2MeNO2" H20, and 3 -3.5MeNO2, of which the easy-axis anisotropy was originated from the orthogonal arrangement of easy-planes of Fen ions. In the crystal structures, cylindrical voids were formed along the chain axis being surrounded by four chains in 1 -3MeNO2, 2 -2MeNO(2)- H2O, and 4 4EtNO(2) and two chains in 3 "3.5MeNO2, and solvent molecules as well as coordination-free perchlorate anions occupied these voids in a slightly different fashion depending on the complexes. 2.2MeNO2-1-120 maintains its chemical composition in a dried condition, whereas 1 "3MeNO2, 3 -3.5MeNO2, and 4 " 4EtNO2 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 3MeNO2 and 3- 3.5MeNO2, 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.