Investigation of solid-state photochemical nitro–nitrito linkage isomerization: crystal structures of trans-bis(ethylenediamine)(isothiocyanato)nitritocobalt(III) salts: thiocyanate, chloride monohydrate, and perchlorate–thiocyanate(0.75/0.25)

The reaction cavities of the nitro groups in the crystals of the title compounds, trans-[Co(NO2)(NCS)(C2H8N2)2]·X, X = SCN− (I), Cl−·H2O (II), and (ClO4−)0.75(SCN−)0.25 (III), have been investigated, revealing that the geometry of the intermolecular N—H...O hydrogen bonds in (I) is unsuitable for nitro–nitrito photo-isomerization. The common main building block of these crystal structures is a centrosymmetric pair of complex cations connected by pairwise N—H...O(nitro) hydrogen bonds forming an R22(4) ring, which is a narrow diamond shape in (I) but is approximately square in (II) and (III). The structure of (I) was reported earlier [Börtin (1976). Acta Chem. Scand. A, 30, 503–506] but is described here with an improved disorder model for the thiocyanate anions and to higher precision

Investigation of nitro–nitrito photoisomerization: crystal structures of trans-bis(acetylacetonato-O,O′)(pyridine/4-methylpyridine/3-hydroxypridine)nitrocobalt(III)

The reaction cavities of the nitro groups in the title compounds, trans-bis(acetylacetonato-κ2O,O′)(nitro)(pyridine-κN)cobalt(III), [Co(C5H7O2)2(NO2)(C5H5N)], (I), trans-bis(acetylacetonato-κ2O,O′)(4-methylpyridine-κN)(nitro)cobalt(III), [Co(C5H7O2)2(NO2)(C6H7N)], (II), and trans-bis(acetylacetonato-κ2O,O′)(3-hydroxypyridine-κN)(nitro)cobalt(III) monohydrate, [Co(C5H7O2)2(NO2)(C5H5NO)]·H2O, (III), have been investigated to reveal that bifurcated intermolecular C(py)—H...O,O contacts in (III) are unfeasible for the nitro–nitrito photochemical linkage isomerization process. In each structure, the pyridine ring and the Co atom lie on a crystallographic mirror plane; in (I) and (II) the nitro group lies in the same plane, whereas in (III), which crystallizes as a monohydrate, the nitro group is disordered over three orientations in a 0.672 (16):0.164 (8):0.164 (8) ratio; the water molecule of crystallization is statistically disordered over two sites adjacent to the mirror plane. In the crystals of (I) and (II), the molecules are linked into [100] chains by C—H...O hydrogen bonds, whereas the extended structure of (III) features (010) layers linked by O—H...O and C—H...O hydrogen bonds. Compounds (I) and (II) were refined as inversion twins

Investigation of nitro–nitrito photoisomerization: crystal structure of trans-chloridonitro(1,4,8,11-tetraazacyclotetradecane-κ4N,N′,N′′,N′′′)cobalt(III) chloride

The reaction cavity of the nitro group in the crystal of the title compound, [CoCl(NO2)(C10H24N4)]Cl, (I), was investigated to confirm that it offers sufficient free space for linkage isomerization to occur in accordance with the observed photochemical reactivity. The complex cation has crystallographic 2/m symmetry and the nitro and chloro ligands at the trans positions are statistically disordered. The complete cyclam ligand is generated by symmetry from a quarter of the molecule. In the crystal of (I), the complex cations and Cl− ions are linked into a three-dimensional network by N—H...Cl(counter-ion) hydrogen bonds

Synthesis, Structure, Luminescence, and Magnetic Properties of a Single-Ion Magnet “<i>mer</i>”‑[Tris(<i>N</i>‑[(imidazol-4-yl)-methylidene]-dl-phenylalaninato)terbium(III) and Related “<i>fac</i>”-dl-Alaninato Derivative

Two Tb^III complexes with the same N₆O₃ donor atoms but different coordination geometries, “<i>fac</i>”-[Tb^III(HL^dl‑ala)₃]·7H₂O (<b>1</b>) and “<i>mer</i>”-[Tb^III(HL^dl‑phe)₃]·7H₂O (<b>2</b>), were synthesized, where H₂L^dl‑ala and H₂L^dl‑phe are <i>N</i>-[(imidazol-4-yl)­methylidene]-dl-alanine and -dl-phenylalanine, respectively. Each Tb^III ion is coordinated by three electronically mononegative NNO tridentate ligands to form a coordination geometry of a tricapped trigonal prism. Compound <b>1</b> consists of enantiomers “<i>fac</i>”-[Tb^III(HL^d‑ala)₃] and “<i>fac</i>”-[Tb^III(HL^l‑ala)₃], while <b>2</b> consists of “<i>mer</i>”-[Tb^III(HL^d‑phe)₂(HL^l‑phe)] and “<i>mer</i>”-[Tb^III(HL^d‑phe)­(HL^l‑phe)₂]. Magnetic data were analyzed by a spin Hamiltonian including the crystal field effect on the Tb^III ion (4f⁸, <i>J</i> = 6, <i>S</i> = 3, <i>L</i> = 3, <i>g</i>_<i>J</i> = 3/2, ⁷F₆). The Stark splitting of the ground state ⁷F₆ was evaluated from magnetic analysis, and the energy diagram pattern indicated easy-plane and easy-axis (Ising type) magnetic anisotropies for <b>1</b> and <b>2</b>, respectively. Highly efficient luminescences with Φ = 0.50 and 0.61 for <b>1</b> and <b>2</b>, respectively, were observed, and the luminescence fine structure due to the ⁵D₄ → ⁷F₆ transition is in good accordance with the energy diagram determined from magnetic analysis. The energy diagram of <b>1</b> shows an approximate single-well potential curve, whereas that of <b>2</b> shows a double- or quadruple-well potential within the ⁷F₆ multiplets. Complex <b>2</b> displayed an onset of the out-of-phase signal in alternating current (ac) susceptibility at a direct current bias field of 1000 Oe on cooling down to 1.9 K. A slight frequency dependence was recorded around 2 K. On the other hand, <b>1</b> did not show any meaningful out-of-phase ac susceptibility. Pulsed-field magnetizations of <b>1</b> and <b>2</b> were measured below 1.6 K, and only <b>2</b> exhibited magnetic hysteresis. This finding agrees well with the energy diagram pattern from crystal field calculation on <b>1</b> and <b>2</b>. DFT calculation allowed us to estimate the negative charge distribution around the Tb^III ion, giving a rationale to the different magnetic anisotropies of <b>1</b> and <b>2</b>

Synthesis, Structure, Luminescence, and Magnetic Properties of a Single-Ion Magnet “<i>mer</i>”‑[Tris(<i>N</i>‑[(imidazol-4-yl)-methylidene]-dl-phenylalaninato)terbium(III) and Related “<i>fac</i>”-dl-Alaninato Derivative

Two Tb^III complexes with the same N₆O₃ donor atoms but different coordination geometries, “<i>fac</i>”-[Tb^III(HL^dl‑ala)₃]·7H₂O (<b>1</b>) and “<i>mer</i>”-[Tb^III(HL^dl‑phe)₃]·7H₂O (<b>2</b>), were synthesized, where H₂L^dl‑ala and H₂L^dl‑phe are <i>N</i>-[(imidazol-4-yl)­methylidene]-dl-alanine and -dl-phenylalanine, respectively. Each Tb^III ion is coordinated by three electronically mononegative NNO tridentate ligands to form a coordination geometry of a tricapped trigonal prism. Compound <b>1</b> consists of enantiomers “<i>fac</i>”-[Tb^III(HL^d‑ala)₃] and “<i>fac</i>”-[Tb^III(HL^l‑ala)₃], while <b>2</b> consists of “<i>mer</i>”-[Tb^III(HL^d‑phe)₂(HL^l‑phe)] and “<i>mer</i>”-[Tb^III(HL^d‑phe)­(HL^l‑phe)₂]. Magnetic data were analyzed by a spin Hamiltonian including the crystal field effect on the Tb^III ion (4f⁸, <i>J</i> = 6, <i>S</i> = 3, <i>L</i> = 3, <i>g</i>_<i>J</i> = 3/2, ⁷F₆). The Stark splitting of the ground state ⁷F₆ was evaluated from magnetic analysis, and the energy diagram pattern indicated easy-plane and easy-axis (Ising type) magnetic anisotropies for <b>1</b> and <b>2</b>, respectively. Highly efficient luminescences with Φ = 0.50 and 0.61 for <b>1</b> and <b>2</b>, respectively, were observed, and the luminescence fine structure due to the ⁵D₄ → ⁷F₆ transition is in good accordance with the energy diagram determined from magnetic analysis. The energy diagram of <b>1</b> shows an approximate single-well potential curve, whereas that of <b>2</b> shows a double- or quadruple-well potential within the ⁷F₆ multiplets. Complex <b>2</b> displayed an onset of the out-of-phase signal in alternating current (ac) susceptibility at a direct current bias field of 1000 Oe on cooling down to 1.9 K. A slight frequency dependence was recorded around 2 K. On the other hand, <b>1</b> did not show any meaningful out-of-phase ac susceptibility. Pulsed-field magnetizations of <b>1</b> and <b>2</b> were measured below 1.6 K, and only <b>2</b> exhibited magnetic hysteresis. This finding agrees well with the energy diagram pattern from crystal field calculation on <b>1</b> and <b>2</b>. DFT calculation allowed us to estimate the negative charge distribution around the Tb^III ion, giving a rationale to the different magnetic anisotropies of <b>1</b> and <b>2</b>

Crystal Field Splitting of the Ground State of Terbium(III) and Dysprosium(III) Complexes with a Triimidazolyl Tripod Ligand and an Acetate Determined by Magnetic Analysis and Luminescence

Terbium­(III) and dysprosium­(III) complexes with a tripodal N₇ ligand containing three imidazoles (H₃L) and a bidentate acetate ion (OAc^–), [Ln^III(H₃L)­(OAc)]­(ClO₄)₂·MeOH·H₂O (Ln = Tb, <b>1</b>; Ln = Dy, <b>2</b>), were synthesized and studied, where H₃L = tris­[2-(((imidazol-4-yl)­methylidene)­amino)­ethyl]­amine. The Tb^III and Dy^III complexes have an isomorphous structure, and each Tb^III or Dy^III ion is coordinated by the tripodal N₇ and the bidentate acetate ligands, resulting in a nonacoordinated capped-square-antiprismatic geometry. The magnetic data, including temperature dependence of the magnetic susceptibilities and field dependence of the magnetization, were analyzed by a spin Hamiltonian, including the crystal field effect on the Tb^III ion (4f⁸, <i>J</i> = 6, <i>S</i> = 3, <i>L</i> = 3, <i>g</i>_<i>J</i> = 3/2, ⁷F₆) and the Dy^III ion (4f⁹, <i>J</i> = 15/2, <i>S</i> = 5/2, <i>L</i> = 5, <i>g</i>_<i>J</i> = 4/3, ⁶H_15/2). The Stark splittings of the ground states ⁷F₆ of the Tb^III ion and ⁶H_15/2 of the Dy^III ion were evaluated from the magnetic analyses, and the energy diagram patterns indicated an easy axis (Ising type) anisotropy for both complexes, which is more pronounced for <b>2</b>. The solid-state emission spectra of both complexes displayed sharp bands corresponding to the f–f transitions, and the fine structures assignable to the ⁵D₄ → ⁷F₆ transition for <b>1</b> and the ⁶F_9/2 → ⁶H_15/2 transition for <b>2</b> were related to the energy diagram patterns from the magnetic analyses. <b>1</b> and <b>2</b> showed an out-of-phase signal with frequency dependence in alternating current (ac) susceptibility under a dc bias field of 1000 Oe, indicative of a field-induced SIM