Tetranuclear Lanthanide(III) Complexes in a Seesaw Geometry: Synthesis, Structure, and Magnetism

The reaction of 2-methoxy-6-(pyridin-2-ylhydrazonomethyl)­phenol (LH) with Ln­(III) (Ln = Gd, Tb, Dy, Ho) salts in the presence of an excess of triethylamine afforded [Gd₄(L)₄(μ₄-OH)­(μ₃-OH)₂(NO₃)₄]·(NO₃)·4CH₃CN·CH₃OH·2H₂O (<b>1</b>), [Tb₄(L)₄(μ₄-OH)­(μ₃-OH)₂(NO₃)₄]·(NO₃)·4CH₃CN·3H₂O (<b>2</b>), [Dy₄(L)₄(μ₄-OH)­(μ₃-OH)₂(NO₃)₄]·(NO₃)·6CH₃CN·H₂O (<b>3</b>), and [Ho₄(L)₄(μ₄-OH)­(μ-OH)₂(NO₃)₄]·(NO₃)·8CH₃CN·3CH₃OH·2H₂O (<b>4</b>). All four complexes contain a monocationic tetranuclear core with a unique <i>seesaw</i> topology. The tetranuclear assembly is formed through the coordination of four [L]⁻, one μ₄-OH, two μ₃-OH, and four chelating nitrate ligands, with a charge-balancing nitrate counteranion. Magnetic studies reveal a weak antiferromagnetic coupling throughout the series. Compound <b>1</b> can be modeled well with an isotropic exchange between all centers parametrized by <i>J</i> = −0.09 cm^–1. Compound <b>3</b> exhibits slow magnetic relaxation at low temperatures

Tetranuclear Lanthanide(III) Complexes in a Seesaw Geometry: Synthesis, Structure, and Magnetism

The reaction of 2-methoxy-6-(pyridin-2-ylhydrazonomethyl)­phenol (LH) with Ln­(III) (Ln = Gd, Tb, Dy, Ho) salts in the presence of an excess of triethylamine afforded [Gd₄(L)₄(μ₄-OH)­(μ₃-OH)₂(NO₃)₄]·(NO₃)·4CH₃CN·CH₃OH·2H₂O (<b>1</b>), [Tb₄(L)₄(μ₄-OH)­(μ₃-OH)₂(NO₃)₄]·(NO₃)·4CH₃CN·3H₂O (<b>2</b>), [Dy₄(L)₄(μ₄-OH)­(μ₃-OH)₂(NO₃)₄]·(NO₃)·6CH₃CN·H₂O (<b>3</b>), and [Ho₄(L)₄(μ₄-OH)­(μ-OH)₂(NO₃)₄]·(NO₃)·8CH₃CN·3CH₃OH·2H₂O (<b>4</b>). All four complexes contain a monocationic tetranuclear core with a unique <i>seesaw</i> topology. The tetranuclear assembly is formed through the coordination of four [L]⁻, one μ₄-OH, two μ₃-OH, and four chelating nitrate ligands, with a charge-balancing nitrate counteranion. Magnetic studies reveal a weak antiferromagnetic coupling throughout the series. Compound <b>1</b> can be modeled well with an isotropic exchange between all centers parametrized by <i>J</i> = −0.09 cm^–1. Compound <b>3</b> exhibits slow magnetic relaxation at low temperatures

Hypokinesia in adolescents

Title: Hypokinesia in adolescents Objectives: The main target is, to find out how frequent and extensive the hypokinesis appears in terms of the exploratory subject. We mainly search for the relationship of high school adolescents to the physical activities, how often it's being practicised and in which kind of environment. Methods: In order to prove my thesis, we decided to use a long version of international standardized IPAQ questionnaire translated to the czech language. The exploratory sample consisted of 46 high school adolescent students. The results were afterwards analysed according to the basic statistic principles. Subsequently we compared the quantity of physical activity between boys and girls during seven days of the research. Results: The results of research apparently meet the criteria of the sufficient count of teenager activities. In the average the sample was evaluated as moderately active individuals in both gender types. Despite the negative public image in terms of quantity of youth physical activities, the actual rate meets general requirements. Boys reached the rate of 1333,8 MET- min/week, girls reached the count of 2013,9 MET-min/week. Keywords: adolescence, physical activity, lack of exercise, lifestyl

In Situ Spectroelectrochemical Investigations of the Redox-Active Tris[4-(pyridin-4-yl)phenyl]amine Ligand and a Zn²⁺ Coordination Framework

An investigation of the redox-active tris­[4-(pyridin-4-yl)­phenyl]­amine (NPy₃) ligand in the solution state and upon its incorporation into the solid-state metal–organic framework (MOF) [Zn­(NPy₃)­(NO₂)₂·<i>x</i>MeOH·<i>x</i>DMF]_<i>n</i> (MeOH = methanol and DMF = <i>N</i>,<i>N</i>-dimethylformamide) was conducted using in situ UV/vis/near-IR, electron paramagentic resonance (EPR), and fluorescence spectroelectrochemical experiments. Through this multifaceted approach, the properties of the ligand and framework were elucidated and quantified as a function of the redox state of the triarylamine core, which can undergo a one-electron oxidation to its radical cation. The use of pulsed EPR experiments revealed that the radical generated was highly delocalized throughout the entire ligand backbone. This combination of techniques provides comprehensive insight into electronic delocalization in a framework system and demonstrates the utility of in situ spectroelectrochemical methods in assessing electroactive MOFs

In Situ Spectroelectrochemical Investigations of the Redox-Active Tris[4-(pyridin-4-yl)phenyl]amine Ligand and a Zn²⁺ Coordination Framework

An investigation of the redox-active tris­[4-(pyridin-4-yl)­phenyl]­amine (NPy₃) ligand in the solution state and upon its incorporation into the solid-state metal–organic framework (MOF) [Zn­(NPy₃)­(NO₂)₂·<i>x</i>MeOH·<i>x</i>DMF]_<i>n</i> (MeOH = methanol and DMF = <i>N</i>,<i>N</i>-dimethylformamide) was conducted using in situ UV/vis/near-IR, electron paramagentic resonance (EPR), and fluorescence spectroelectrochemical experiments. Through this multifaceted approach, the properties of the ligand and framework were elucidated and quantified as a function of the redox state of the triarylamine core, which can undergo a one-electron oxidation to its radical cation. The use of pulsed EPR experiments revealed that the radical generated was highly delocalized throughout the entire ligand backbone. This combination of techniques provides comprehensive insight into electronic delocalization in a framework system and demonstrates the utility of in situ spectroelectrochemical methods in assessing electroactive MOFs

In Situ Spectroelectrochemical Investigations of the Redox-Active Tris[4-(pyridin-4-yl)phenyl]amine Ligand and a Zn²⁺ Coordination Framework

An investigation of the redox-active tris­[4-(pyridin-4-yl)­phenyl]­amine (NPy₃) ligand in the solution state and upon its incorporation into the solid-state metal–organic framework (MOF) [Zn­(NPy₃)­(NO₂)₂·<i>x</i>MeOH·<i>x</i>DMF]_<i>n</i> (MeOH = methanol and DMF = <i>N</i>,<i>N</i>-dimethylformamide) was conducted using in situ UV/vis/near-IR, electron paramagentic resonance (EPR), and fluorescence spectroelectrochemical experiments. Through this multifaceted approach, the properties of the ligand and framework were elucidated and quantified as a function of the redox state of the triarylamine core, which can undergo a one-electron oxidation to its radical cation. The use of pulsed EPR experiments revealed that the radical generated was highly delocalized throughout the entire ligand backbone. This combination of techniques provides comprehensive insight into electronic delocalization in a framework system and demonstrates the utility of in situ spectroelectrochemical methods in assessing electroactive MOFs

Hexanuclear 3d–4f Neutral Co^II₂Ln^III₄ Clusters: Synthesis, Structure, and Magnetism

The sequential reaction of the multisite coordination ligand 6,6′-{(2-(dimethylamino)­ethyl azanediyl)­bis­(methylene)}­bis­(2-methoxy-4-methylphenol) (LH₂) with Ln^III salts (Ln = Gd, Tb, Dy) and Co­(ClO₄)₂·6H₂O in the presence of triethylamine and pivalic acid (pivH) in ambient conditions afforded a series of isostructural heterometallic hexanuclear Co^II/Ln^III complexes with the general formula [Co^II₂Ln₄­(μ₃-OH)₄­(L)₂(piv)₈­(μ-OH₂)]­·<i>w</i>CH₃C­·<i>x</i>CH₂Cl₂­·<i>y</i>CH₃OH­·<i>z</i>H₂O (<b>1</b>: Ln = Gd, <i>w</i> = 5, <i>x</i> = 2, <i>y</i> = 0, <i>z</i> = 2; <b>2</b>: Ln = Tb, <i>w</i> = 7, <i>x</i> = 4, <i>y</i> = 2, <i>z</i> = 0; <b>3</b>: Ln = Dy; <i>w</i> = 4, <i>x</i> = 2, <i>y</i> = 2, <i>z</i> = 0). Compounds <b>1</b> and <b>3</b> crystallize in the monoclinic system, space group <i>P</i>2₁/<i>n</i> (<i>Z</i> = 4), while compound <b>2</b> crystallizes in <i>P</i>2/<i>n</i> (<i>Z</i> = 2). The hexanuclear core of the complexes comprises of a nonplanar arrangement of lanthanide ions bridged by two μ₃-OH ligands. This tetranuclear motif is connected to the Co^II ions by two μ₃-OH ligands. The overall structure contains four interlinked incomplete cubic subunits (two Co^IILn^III₂O₄ and two Ln^III₃O₄) that are connected to each other by the sharing of two Ln^III ions. The lanthanide centers are eight-coordinate (distorted trigonal-dodecahedron) and nine-coordinate (distorted monocapped square-antiprism), while the cobalt centers are six-coordinate (distorted octahedral). Magnetic measurement of the dysprosium analogue shows a slow magnetic relaxation

Single-Molecule Magnetism in Tetrametallic Terbium and Dysprosium Thiolate Cages

Metalation of ethanethiol by [{(Me₃Si)₂N}₃Ln­(μ-Cl)­Li­(thf)₃] (Ln = Gd, Tb, Dy) in thf produces the thiolate-bridged tetralanthanide compounds [Li­(thf)₄]­[Ln₄{N­(SiMe₃)₂}₄(μ-SEt)₈(μ₄-SEt)], where Ln = Gd is [Li­(thf)₄]­[<b>1</b>], Ln = Tb is [Li­(thf)₄]­[<b>2</b>], and Ln = Dy is [Li­(thf)₄]­[<b>3</b>]. Crystallographic studies reveal that the monoanions <b>1</b>–<b>3</b> are essentially isostructural, consisting of tetrametallic Ln₄ units in which the lanthanides are bridged by μ-ethanethiolate ligands and the individual lanthanide centers occupy distorted six-coordinate {LnNS₅} coordination environments. The magnetic susceptibility properties of all three compounds were measured in a static (dc) field of 1000 G: the data for the gadolinium anion <b>1</b> were reproduced by a model that suggests weak antiferromagnetic and ferromagnetic exchange, with coupling constants of <i>J</i> = −0.09 and +0.04 cm^–1 (−2<i>J</i> formalism). Magnetic susceptibility measurements in a dynamic (ac) field at various frequencies on [Li­(thf)₄]­[<b>2</b>] and [Li­(thf)₄]­[<b>3</b>], in zero dc field, reveal properties characteristic of a single-molecule magnet (SMM). Analysis of the out-of-phase magnetic susceptibility for <b>2</b> in zero applied field yielded a small anisotropy barrier of <i>U</i>_eff = 4.6 cm^–1, and a similar analysis on <b>3</b> produced <i>U</i>_eff = 46 cm^–1. Compounds [Li­(thf)₄]­[<b>2</b>] and [Li­(thf)₄]­[<b>3</b>] are rare examples of sulfur-ligated SMMs

Single-Molecule Magnetism in Tetrametallic Terbium and Dysprosium Thiolate Cages

Metalation of ethanethiol by [{(Me₃Si)₂N}₃Ln­(μ-Cl)­Li­(thf)₃] (Ln = Gd, Tb, Dy) in thf produces the thiolate-bridged tetralanthanide compounds [Li­(thf)₄]­[Ln₄{N­(SiMe₃)₂}₄(μ-SEt)₈(μ₄-SEt)], where Ln = Gd is [Li­(thf)₄]­[<b>1</b>], Ln = Tb is [Li­(thf)₄]­[<b>2</b>], and Ln = Dy is [Li­(thf)₄]­[<b>3</b>]. Crystallographic studies reveal that the monoanions <b>1</b>–<b>3</b> are essentially isostructural, consisting of tetrametallic Ln₄ units in which the lanthanides are bridged by μ-ethanethiolate ligands and the individual lanthanide centers occupy distorted six-coordinate {LnNS₅} coordination environments. The magnetic susceptibility properties of all three compounds were measured in a static (dc) field of 1000 G: the data for the gadolinium anion <b>1</b> were reproduced by a model that suggests weak antiferromagnetic and ferromagnetic exchange, with coupling constants of <i>J</i> = −0.09 and +0.04 cm^–1 (−2<i>J</i> formalism). Magnetic susceptibility measurements in a dynamic (ac) field at various frequencies on [Li­(thf)₄]­[<b>2</b>] and [Li­(thf)₄]­[<b>3</b>], in zero dc field, reveal properties characteristic of a single-molecule magnet (SMM). Analysis of the out-of-phase magnetic susceptibility for <b>2</b> in zero applied field yielded a small anisotropy barrier of <i>U</i>_eff = 4.6 cm^–1, and a similar analysis on <b>3</b> produced <i>U</i>_eff = 46 cm^–1. Compounds [Li­(thf)₄]­[<b>2</b>] and [Li­(thf)₄]­[<b>3</b>] are rare examples of sulfur-ligated SMMs

Transmetalation of Chromocene by Lithium-Amide, -Phosphide, and -Arsenide Nucleophiles

The pnictogen-centered nucleophiles LiE­(SiMe₃)₂ (E = N, P, or As) substitute a cyclopentadienide ligand of chromocene (Cp₂Cr), with elimination of lithium cyclopentadienide, to give the series of pnictogen-bridged compounds [(μ:η²:η⁵-Cp)­Cr­{μ-N­(SiMe₃)₂}₂Li] (<b>1</b>) and [(η⁵-Cp)­Cr­{μ-E­(SiMe₃)₂}]₂, with E = P (<b>2</b>) or E = As (<b>3</b>). Whereas <b>1</b> is a heterobimetallic coordination polymer, <b>2</b> and <b>3</b> are homometallic dimers, with the differences being due to a structure-directing influence of the hard or soft character of the bridging group 15 atoms. For compound <b>1</b>, the experimental magnetic susceptibility data were accurately reproduced by a single-ion model based on high-spin chromium­(II) (<i>S</i> = 2), which gave a <i>g</i>-value of 1.93 and an axial zero-field splitting parameter of <i>D</i> = −1.83 cm^–1. Determinations of phosphorus- and arsenic-mediated magnetic exchange coupling constants, <i>J</i>, are rare: in the dimers <b>2</b> and <b>3</b>, variable-temperature magnetic susceptibility measurements identified strong antiferromagnetic exchange between the chromium­(II) centers, which was modeled using the spin Hamiltonian <i>H</i> = −2<i>J</i>(<i>S</i>_CrA·<i>S</i>_CrB), and produced large coupling constants of <i>J</i> = −166 cm^–1 for <b>2</b> and −77.5 cm^–1 for <b>3</b>