Coordination-Tuned Single-Molecule-Magnet Behavior of Tb^III−Cu^II Dinuclear Systems

TbIII−CuII-based single-molecule magnet (SMM) and non-SMM were synthesized to investigate the relationship between magnetic anisotropy and the symmetry of the ligand field by the reaction of [TbCu(o-vanilate)2(NO3)3] with methoxypropylamine (MeOC3H6NH2, 1) or ethoxyethylamine (EtOC2H4NH2, 2). In both complexes, TbIII ions have a bicapped square-antiprism coordination geometry. When the TbIII ion is in a less symmetrical ligand field, it has an easy-axis anisotropy and shows SMM behavior, whereas when it is in a more symmetrical environment, it has an easy-plane anisotropy and exhibits non-SMM behavior

Coordination-Tuned Single-Molecule-Magnet Behavior of Tb^III−Cu^II Dinuclear Systems

TbIII−CuII-based single-molecule magnet (SMM) and non-SMM were synthesized to investigate the relationship between magnetic anisotropy and the symmetry of the ligand field by the reaction of [TbCu(o-vanilate)2(NO3)3] with methoxypropylamine (MeOC3H6NH2, 1) or ethoxyethylamine (EtOC2H4NH2, 2). In both complexes, TbIII ions have a bicapped square-antiprism coordination geometry. When the TbIII ion is in a less symmetrical ligand field, it has an easy-axis anisotropy and shows SMM behavior, whereas when it is in a more symmetrical environment, it has an easy-plane anisotropy and exhibits non-SMM behavior

Solid-State Electrochemistry of a Semiconducting MMX-Type Diplatinum Iodide Chain Complex

Electron-transfer-facilitated dissolution, ion insertion, and desorption associated with an MMX-type quasi-one-dimensional iodide-bridged dinuclear Pt complex (MMX chain) have been investigated for the first time. K₂(NC₃N)­[Pt₂(pop)₄I]·4H₂O (<b>1</b>) (NC₃N²⁺ = (H₃NC₃H₆NH₃)²⁺; pop = P₂H₂O₅^2–) is a semiconductor with a three-dimensional coordination-bond and hydrogen-bond network included in the chain. The cyclic voltammetry of <b>1</b> was studied by using <b>1</b>-modified electrodes in contact with acetonitrile solutions containing electrolyte. The chemical reversibility for oxidation of <b>1</b> depended on the electrolyte cation size, with large cations such as tetrabutylammonium (Bu₄N⁺) being too large to penetrate the pores formed by the loss of K⁺ and NC₃N²⁺ upon oxidation. The potential for reduction of <b>1</b> decreased as the cation size increased. The presence of the acid induced additional well-defined processes but with gradual solid dissolution, attributed to the breaking of the coordination-bond networks

Direct Observation of the Disorder of the Methyl Group of (<i>R</i>)-1,2-Diaminopropane Ligand in the Quasi-1D Bromo-Bridged Ni(III) Complex by STM

Scanning tunneling microscopy (STM) has been measured in quasi-one-dimensional (Quasi-ID) bromo-bridged Ni(III) complexes. In the STM image of [Ni(pn)2Br]Br2 (pn = (R)-1,2-diaminopropane), the bright spots are fluctuated zigzags. Such a result indicates that the methyl groups of the pn ligands are not arranged on the right- and left-hand alternatively along the chains, but in the domain structures or fluctuated structures. This is the first direct observation of the disorder of the methyl group of pn ligands in real space

Reversible Magnetism between an Antiferromagnet and a Ferromagnet Related to Solvation/Desolvation in a Robust Layered [Ru₂]₂TCNQ Charge-Transfer System

The charge-transfer compound [{Ru2(O2CPh-o-Cl)4}2TCNQ(MeO)2]·CH2Cl2 (1; o-ClPhCO2− = o-chlorobenzoate; TCNQ(MeO)2 = 2,5-dimethoxy-7,7,8,8-tetracyanoquinodimethane) was synthesized from the reaction of the neutral precursors [Ru2II,II(O2CPh-o-Cl)4] (abbreviated as [Ru2II,II] or [Ru24+]) and TCNQ(MeO)2 in a CH2Cl2/nitrobenzene solution. The structure consists of two-dimensional layers consisting of an infinite array in which [Ru2II,II] units are involved in charge transfer to TCNQ(MeO)2 to give a formal charge of [{Ru24.5+}-TCNQ(MeO)2• −-{Ru24.5+}]. Interstitial CH2Cl2 molecules are located in the void spaces between the layers. Strong intralayer magnetic coupling between the units [Ru2II,II] with S = 1 or [Ru2II,III] with S = 3/2 and TCNQ(MeO)2• − with S = 1/2, as well as long-range ordering due to antiferromagnetic interlayer interactions, was observed. An antiferromagnetic ground state exists below TN = 75 K, which undergoes a metamagnetic transition under applied fields less than 2 T to a field-induced canted antiferromagnetic state with large coercivities up to Hc = 1.6 T at 1.8 K. Compound 1 gradually loses the interstitial CH2Cl2 molecule at room temperature to form a dried sample (1-dry) without loss of crystallinity and converts nearly reversibly back to 1 after being exposed to CH2Cl2 vapor for 72 h (distinguished as 1′). Interestingly, during this process there is no significant change in lattice dimensions and bond distances or angles with a volume change of only 1.2 vol %. The only discernible difference is ordering/disordering of a pendant ligand orientation, but the magnetism is dramatically altered to a ferromagnetic state with Tc ≈ 56 K for 1-dry. The magnetic property changes are gradual and depend on the degree of interstitial CH2Cl2 molecule loss with reversibility in the process of going between 1 and 1-dry. In addition, in the case of partially desolvated crystals that have mixed domains of ferromagnetically and antiferromagnetically ordered domains for desolvated and solvated segments, respectively, the complete change to ferromagnet can also be triggered by magnetic fields even if the desolvated segments are comparatively minor compared to the solvated segments in a crystal. Surprisingly, the information of the existence of ferromagnetically ordered domains is dynamically recorded in the entire crystal after applying significant magnetic fields as if the majority of the antiferromagnetically ordered domains for solvated segments were never present

Direct Observation of the Disorder of the Methyl Group of (<i>R</i>)-1,2-Diaminopropane Ligand in the Quasi-1D Bromo-Bridged Ni(III) Complex by STM

Scanning tunneling microscopy (STM) has been measured in quasi-one-dimensional (Quasi-ID) bromo-bridged Ni(III) complexes. In the STM image of [Ni(pn)2Br]Br2 (pn = (R)-1,2-diaminopropane), the bright spots are fluctuated zigzags. Such a result indicates that the methyl groups of the pn ligands are not arranged on the right- and left-hand alternatively along the chains, but in the domain structures or fluctuated structures. This is the first direct observation of the disorder of the methyl group of pn ligands in real space

Direct Observation of the Disorder of the Methyl Group of (<i>R</i>)-1,2-Diaminopropane Ligand in the Quasi-1D Bromo-Bridged Ni(III) Complex by STM

Scanning tunneling microscopy (STM) has been measured in quasi-one-dimensional (Quasi-ID) bromo-bridged Ni(III) complexes. In the STM image of [Ni(pn)2Br]Br2 (pn = (R)-1,2-diaminopropane), the bright spots are fluctuated zigzags. Such a result indicates that the methyl groups of the pn ligands are not arranged on the right- and left-hand alternatively along the chains, but in the domain structures or fluctuated structures. This is the first direct observation of the disorder of the methyl group of pn ligands in real space

Reversible Magnetism between an Antiferromagnet and a Ferromagnet Related to Solvation/Desolvation in a Robust Layered [Ru₂]₂TCNQ Charge-Transfer System

The charge-transfer compound [{Ru2(O2CPh-o-Cl)4}2TCNQ(MeO)2]·CH2Cl2 (1; o-ClPhCO2− = o-chlorobenzoate; TCNQ(MeO)2 = 2,5-dimethoxy-7,7,8,8-tetracyanoquinodimethane) was synthesized from the reaction of the neutral precursors [Ru2II,II(O2CPh-o-Cl)4] (abbreviated as [Ru2II,II] or [Ru24+]) and TCNQ(MeO)2 in a CH2Cl2/nitrobenzene solution. The structure consists of two-dimensional layers consisting of an infinite array in which [Ru2II,II] units are involved in charge transfer to TCNQ(MeO)2 to give a formal charge of [{Ru24.5+}-TCNQ(MeO)2• −-{Ru24.5+}]. Interstitial CH2Cl2 molecules are located in the void spaces between the layers. Strong intralayer magnetic coupling between the units [Ru2II,II] with S = 1 or [Ru2II,III] with S = 3/2 and TCNQ(MeO)2• − with S = 1/2, as well as long-range ordering due to antiferromagnetic interlayer interactions, was observed. An antiferromagnetic ground state exists below TN = 75 K, which undergoes a metamagnetic transition under applied fields less than 2 T to a field-induced canted antiferromagnetic state with large coercivities up to Hc = 1.6 T at 1.8 K. Compound 1 gradually loses the interstitial CH2Cl2 molecule at room temperature to form a dried sample (1-dry) without loss of crystallinity and converts nearly reversibly back to 1 after being exposed to CH2Cl2 vapor for 72 h (distinguished as 1′). Interestingly, during this process there is no significant change in lattice dimensions and bond distances or angles with a volume change of only 1.2 vol %. The only discernible difference is ordering/disordering of a pendant ligand orientation, but the magnetism is dramatically altered to a ferromagnetic state with Tc ≈ 56 K for 1-dry. The magnetic property changes are gradual and depend on the degree of interstitial CH2Cl2 molecule loss with reversibility in the process of going between 1 and 1-dry. In addition, in the case of partially desolvated crystals that have mixed domains of ferromagnetically and antiferromagnetically ordered domains for desolvated and solvated segments, respectively, the complete change to ferromagnet can also be triggered by magnetic fields even if the desolvated segments are comparatively minor compared to the solvated segments in a crystal. Surprisingly, the information of the existence of ferromagnetically ordered domains is dynamically recorded in the entire crystal after applying significant magnetic fields as if the majority of the antiferromagnetically ordered domains for solvated segments were never present

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 FeII ions with easy-plane anisotropy, was synthesized, and their magnetic properties were investigated. The chain complexes including alternating high-spin FeII ions and low-spin FeIII ions, catena-[FeII(ClO4)2{FeIII(bpca)2}]ClO4·3MeNO2 (1·3MeNO2), catena-[FeII(ClO4)(H2O){FeIII(MeL)2}](ClO4)2·2MeNO2·H2O (2·2MeNO2·H2O), catena-[FeII(ClO4)(H2O){FeIII(BuL)2}](ClO4)2·3.5MeNO2 (3·3.5MeNO2), and catena-[{FeII(ClO4)(H2O)FeII(H2O)2}0.5{FeIII(PhL)2}](ClO4)2.5·4EtNO2 (4·4EtNO2), were synthesized with the use of bridging ligand Hbpca (bis-(2-pyridylcarbonyl)amine)) and its derivatives of HMeL, HBuL, 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 Δ/kB values of 22.5(4), 21.8(18), and 28.8(3) K for 1·3MeNO2, 2·2MeNO2·H2O, and 3·3.5MeNO2, of which the easy-axis anisotropy was originated from the orthogonal arrangement of easy-planes of FeII ions. In the crystal structures, cylindrical voids were formed along the chain axis being surrounded by four chains in 1·3MeNO2, 2·2MeNO2·H2O, and 4·4EtNO2 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·H2O 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

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 FeII ions with easy-plane anisotropy, was synthesized, and their magnetic properties were investigated. The chain complexes including alternating high-spin FeII ions and low-spin FeIII ions, catena-[FeII(ClO4)2{FeIII(bpca)2}]ClO4·3MeNO2 (1·3MeNO2), catena-[FeII(ClO4)(H2O){FeIII(MeL)2}](ClO4)2·2MeNO2·H2O (2·2MeNO2·H2O), catena-[FeII(ClO4)(H2O){FeIII(BuL)2}](ClO4)2·3.5MeNO2 (3·3.5MeNO2), and catena-[{FeII(ClO4)(H2O)FeII(H2O)2}0.5{FeIII(PhL)2}](ClO4)2.5·4EtNO2 (4·4EtNO2), were synthesized with the use of bridging ligand Hbpca (bis-(2-pyridylcarbonyl)amine)) and its derivatives of HMeL, HBuL, 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 Δ/kB values of 22.5(4), 21.8(18), and 28.8(3) K for 1·3MeNO2, 2·2MeNO2·H2O, and 3·3.5MeNO2, of which the easy-axis anisotropy was originated from the orthogonal arrangement of easy-planes of FeII ions. In the crystal structures, cylindrical voids were formed along the chain axis being surrounded by four chains in 1·3MeNO2, 2·2MeNO2·H2O, and 4·4EtNO2 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·H2O 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