Inorganic Approach to Stabilizing Nanoscale Toroidicity in a Tetraicosanuclear Fe18_{18}Dy6_{6} Single Molecule Magnet

Cyclic coordination clusters (CCCs) are proving to provide an extra dimension in terms of exotic magnetic behavior as a result of their finite but cyclized chain structures. The Fe$_{18}$Dy$_{6}$ CCC is a Single Molecule Magnet with the highest nuclearity among Ln containing clusters. The three isostructural compounds [Fe$_{18}$Ln$_{6}$(μ-OH)$_{6}$(ampd)$_{12}$(Hampd)$_{12}$(PhCO$_{2}$)$_{24}$](NO$_{3}$)$_{6}$·38MeCN for Ln = Dy$^{III}$ (1), Lu$^{III}$ (2), or Y$^{III}$ (3), where H$_{2}^{-}$ampd = 2-amino-2-methyl-1,3-propanediol, are reported. These can be described in terms of the cyclization of six {Fe$_{3}$Ln(μOH)(ampd)$_{2}$(Hampd)$_{2}$(PhCO$_{2}$)$_{4}$}$^{+}$ units with six nitrate counterions to give the neutral cluster. The overall structure consists of two giant Dy$_{3}$ triangles sandwiching a strongly antiferromagnetically coupled Fe$_{18}$ ring, leading to a toroidal arrangement of the anisotropy axis of the Dy ions, making this the biggest toroidal arrangement on a molecular level known so far

Assembly of high nuclearity clusters from a family of tripodal tris-carboxylate ligands

A family of four tris-carboxylic acid ligands 1,3,5-tris(4′-carboxybiphenyl-2-yl)benzene (H3L1), 1,3,5-tris-2-carboxyphenylbenzene (H3L2), 1,3,5-tris(4″-carboxy-para-terphenyl-2-yl)benzene (H3L3) and 1,3,5-tris(3′-carboxybiphenyl-2-yl)benzene (H3L4) have been synthesised and reacted with first row transition metal cations to give nine complexes which have been structurally characterised by X-ray crystallography. The ligands share a common design motif having three arms connected to a benzene core via three ortho-disubstituted phenyl linkers. The ligands vary in length and direction of the carboxylic acid functionalised arms and are all able to adopt tripodal conformations in which the three arms are directed facially. The structures of [Zn8(μ4-O)(L1)4(HCO2)2(H2O)0.33(DMF)2] (1a-Zn), [Co14(L2)6((μ3-OH)8(HCO2)2(DMF)4(H2O)6] (2-Co), [Ni14(L2)6(μ3-OH)8(HCO2)2(DMF)4(H2O)6] (2-Ni), [Zn8(μ4-O)(L3)4(DMF)(H2O)4(NO3)2] (3-Zn), [Ni5(μ-OH)4(L2)2(H2O)6(DMF)4] (5-Ni), [Co8(μ4-O)4(L4)4(DMF)3(H2O)] (6-Co) and Fe3(μ3-O)(L4)2(H2O)(DMF)2)] (7-Fe) contain polynuclear clusters surrounded by ligands (L1–4)3− in tripodal conformations. The structure of [Zn2(HL1)2(DMF)4] (1b-Zn) shows it to be a binuclear complex in which the two ligands (HL2)2− are partially deprotonated whilst {[Zn3(L2)2(DMF)(H2O)(C5H5N)]·6(DMF)}n (4-Zn) is a 2D coordination network containing {Zn2(RCO2)4(solv)2} paddlewheel units. The conformations of the ligand arms in the complexes have been analysed, confirming that the shared ortho-disubstituted phenyl ring motif is a powerful and versatile tool for designing ligands able to form high-nuclearity coordination clusters when reacted with transition metal cations

Unraveling the influence of lanthanide ions on intra- and inter-molecular electronic processes in Fe 10 Ln 10 nano-toruses

We investigated the electronic properties of the molecular magnetic nanoto-ruses [Fe III10LnIII10(Me-tea)10(Me-teaH)10(NO3)10], examining the dependence on the lanthanide (Ln) of both the intra and intermolecular electronic channels. Using femtosecond absorption spectroscopy we show that the intramolecular electronic channels follow a three-step process, which involves vibrational cooling and crossing to shallow states, followed by recombination. A comparison with the energy gaps showed a relationship between trap efficiency and gaps, indicating that lanthanide ions create trap states to form excitons after photo-excitation. Using high-resistance transport measurements and scaling techniques, we investigated the intermolecular transport, demonstrating the dominant role of surface-limited transport channels and the presence of different types of charge traps. The intermolecular transport properties can be rationalized in terms of a hopping model, and a connection is provided to the far-IR spectroscopic properties. Comparison between intra and intermolecular processes highlights the role of the excited electronic states and the recombination processes, showing the influence of Kramers parity on the overall mobility

Unraveling the influence of lanthanide ions on intra- and inter-molecular electronic processes in Fe 10 Ln 10 nano-toruses

We investigated the electronic properties of the molecular magnetic nanoto-ruses [Fe III10LnIII10(Me-tea)10(Me-teaH)10(NO3)10], examining the dependence on the lanthanide (Ln) of both the intra and intermolecular electronic channels. Using femtosecond absorption spectroscopy we show that the intramolecular electronic channels follow a three-step process, which involves vibrational cooling and crossing to shallow states, followed by recombination. A comparison with the energy gaps showed a relationship between trap efficiency and gaps, indicating that lanthanide ions create trap states to form excitons after photo-excitation. Using high-resistance transport measurements and scaling techniques, we investigated the intermolecular transport, demonstrating the dominant role of surface-limited transport channels and the presence of different types of charge traps. The intermolecular transport properties can be rationalized in terms of a hopping model, and a connection is provided to the far-IR spectroscopic properties. Comparison between intra and intermolecular processes highlights the role of the excited electronic states and the recombination processes, showing the influence of Kramers parity on the overall mobility

Unraveling the influence of lanthanide ions on intra- and inter-molecular electronic processes in Fe 10 Ln 10 nano-toruses

We investigated the electronic properties of the molecular magnetic nanoto-ruses [Fe III10LnIII10(Me-tea)10(Me-teaH)10(NO3)10], examining the dependence on the lanthanide (Ln) of both the intra and intermolecular electronic channels. Using femtosecond absorption spectroscopy we show that the intramolecular electronic channels follow a three-step process, which involves vibrational cooling and crossing to shallow states, followed by recombination. A comparison with the energy gaps showed a relationship between trap efficiency and gaps, indicating that lanthanide ions create trap states to form excitons after photo-excitation. Using high-resistance transport measurements and scaling techniques, we investigated the intermolecular transport, demonstrating the dominant role of surface-limited transport channels and the presence of different types of charge traps. The intermolecular transport properties can be rationalized in terms of a hopping model, and a connection is provided to the far-IR spectroscopic properties. Comparison between intra and intermolecular processes highlights the role of the excited electronic states and the recombination processes, showing the influence of Kramers parity on the overall mobility