Investigation of nitro-nitrito photoisomerization: crystal structures of trans-{2,2'-[ethane-1,2-diylbis(nitrilo-methyl-idyne)]diphenolato}(pyridine/4-methyl-pyridine)-nitro-cobalt(III).

The reaction cavities of the nitro groups in the title compounds, trans-{2,2'-[ethane-1,2-diylbis(nitrilo-methyl-idyne)]diphenolato-κ4 O,N,N',O'}(nitro-κN)(pyridine-κN)cobalt(III), [Co(C16H14N2O2)(NO2)(C5H5N)], (I), and trans-{2,2'-[ethane-1,2-diylbis(nitrilo-methyl-idyne)]diphenolato-κ4 O,N,N',O'}(4-methyl-pyridine-κN)(nitro-κN)cobalt(III), [Co(C16H14N2O2)(NO2)(C6H7N)], (II), have been investigated to reveal that the inter-molecular CMe-H⋯O(nitro) contacts in (II) are unfeasible for the nitro-nitrito photochemical linkage isomerization process. In (I), there are two independent complexes showing similar conformations, and the central five-membered chelate ring of the tetra-dentate salen ligand adopts the same absolute configuration. This is the result of pseudo-spontaneous resolution, since the configuration of the five-membered chelate ring may frequently be reversed in solution. In the crystals of (I) and (II), the mol-ecules are linked into three-dimensional networks by C-H⋯O hydrogen bonds.

Investigation of nitro-nitrito photoisomerization: crystal structure of trans-chlorido-nitro-(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N,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 mol-ecule. 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.

Investigation of nitro-nitrito photoisomerization: crystal structures of trans-bis-(acetyl-acetonato-O,O')(pyridine/4-methyl-pyridine/3-hy-droxy-pridine)nitro-cobalt(III).

The reaction cavities of the nitro groups in the title compounds, trans-bis-(acetyl-acetonato-κ2 O,O')(nitro)(pyridine-κN)cobalt(III), [Co(C5H7O2)2(NO2)(C5H5N)], (I), trans-bis-(acetyl-acetonato-κ2 O,O')(4-methyl-pyridine-κN)(nitro)cobalt(III), [Co(C5H7O2)2(NO2)(C6H7N)], (II), and trans-bis-(acetyl-acetonato-κ2 O,O')(3-hy-droxy-pyridine-κN)(nitro)cobalt(III) monohydrate, [Co(C5H7O2)2(NO2)(C5H5NO)]·H2O, (III), have been investigated to reveal that bifurcated inter-molecular 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 mol-ecule of crystallization is statistically disordered over two sites adjacent to the mirror plane. In the crystals of (I) and (II), the mol-ecules 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 solid-state photochemical nitro-nitrito linkage isomerization: crystal structures of trans-bis-(ethyl-enedi-amine)(iso-thio-cyanato)-nitritocobalt(III) salts: thio-cyanate, chloride monohydrate, and perchlorate-thio-cyanate-(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 inter-molecular 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 R 2 2(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 thio-cyanate anions and to higher precision.

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, 1; Ln = Dy, 2), 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 (4f(8), J = 6, S = 3, L = 3, g(J) = 3/2, (7)F6) and the Dy(III) ion (4f(9), J = 15/2, S = 5/2, L = 5, g(J) = 4/3, (6)H(15/2)). The Stark splittings of the ground states (7)F6 of the Tb(III) ion and (6)H(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 2. The solid-state emission spectra of both complexes displayed sharp bands corresponding to the f-f transitions, and the fine structures assignable to the (5)D4 → (7)F6 transition for 1 and the (6)F(9/2) → (6)H(15/2) transition for 2 were related to the energy diagram patterns from the magnetic analyses. 1 and 2 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.

Synthesis, structure, luminescence, and magnetic properties of a single-ion magnet "mer"-[tris(N-[(imidazol-4-yl)-methylidene]-DL-phenylalaninato)terbium(III) and related "fac"-DL-alaninato derivative.

Two Tb(III) complexes with the same N6O3 donor atoms but different coordination geometries, "fac"-[Tb(III)(HL(DL-ala))3]·7H2O (1) and "mer"-[Tb(III)(HL(DL-phe))3]·7H2O (2), were synthesized, where H2L(DL-ala) and H2L(DL-phe) are N-[(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 1 consists of enantiomers "fac"-[Tb(III)(HL(D-ala))3] and "fac"-[Tb(III)(HL(L-ala))3], while 2 consists of "mer"-[Tb(III)(HL(D-phe))2(HL(L-phe))] and "mer"-[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 (4f(8), J = 6, S = 3, L = 3, gJ = 3/2, (7)F6). The Stark splitting of the ground state (7)F6 was evaluated from magnetic analysis, and the energy diagram pattern indicated easy-plane and easy-axis (Ising type) magnetic anisotropies for 1 and 2, respectively. Highly efficient luminescences with Φ = 0.50 and 0.61 for 1 and 2, respectively, were observed, and the luminescence fine structure due to the (5)D4 → (7)F6 transition is in good accordance with the energy diagram determined from magnetic analysis. The energy diagram of 1 shows an approximate single-well potential curve, whereas that of 2 shows a double- or quadruple-well potential within the (7)F6 multiplets. Complex 2 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, 1 did not show any meaningful out-of-phase ac susceptibility. Pulsed-field magnetizations of 1 and 2 were measured below 1.6 K, and only 2 exhibited magnetic hysteresis. This finding agrees well with the energy diagram pattern from crystal field calculation on 1 and 2. DFT calculation allowed us to estimate the negative charge distribution around the Tb(III) ion, giving a rationale to the different magnetic anisotropies of 1 and 2.

Synthesis, structure, luminescent, and magnetic properties of carbonato-bridged Zn(II)2Ln(III)2 complexes [(µ4-CO3)2{Zn(II)L(n)Ln(III)(NO3)}2] (Ln(III) = Gd(III), Tb(III), Dy(III); L(1) = N,N'-bis(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato, L(2) = N,N'-bis(3-ethoxy-2-oxybenzylidene)-1,3-propanediaminato).

Carbonato-bridged Zn(II)2Ln(III)2 complexes [(µ4-CO3)2{Zn(II)L(n)Ln(III)(NO3)}2]·solvent were synthesized through atmospheric CO2 fixation reaction of [Zn(II)L(n)(H2O)2]·xH2O, Ln(III)(NO3)3·6H2O, and triethylamine, where Ln(III) = Gd(III), Tb(III), Dy(III); L(1) = N,N'-bis(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato, L(2) = N,N'-bis(3-ethoxy-2-oxybenzylidene)-1,3-propanediaminato. Each Zn(II)2Ln(III)2 structure possessing an inversion center can be described as two di-µ-phenoxo-bridged {Zn(II)L(n)Ln(III)(NO3)} binuclear units bridged by two carbonato CO3(2-) ions. The Zn(II) ion has square pyramidal coordination geometry with N2O2 donor atoms of L(n) and one oxygen atom of a bridging carbonato ion at the axial site. Ln(III) ion is coordinated by nine oxygen atoms consisting of four from the deprotonated Schiff-base L(n), two from a chelating nitrate, and three from two carbonate groups. The temperature-dependent magnetic susceptibilities in the range 1.9-300 K, field-dependent magnetization from 0 to 5 T at 1.9 K, and alternating current magnetic susceptibilities under the direct current bias fields of 0 and 1000 Oe were measured. The magnetic properties of the Zn(II)2Ln(III)2 complexes are analyzed on the basis of the dicarbonato-bridged binuclear Ln(III)-Ln(III) structure, as the Zn(II) ion with d(10) electronic configuration is diamagnetic. ZnGd1 (L(1)) and ZnGd2 (L(2)) show a ferromagnetic Gd(III)-Gd(III) interaction with J(Gd-Gd) = +0.042 and +0.028 cm(-1), respectively, on the basis of the Hamiltonian H = -2J(Gd-Gd)SGd1·SGd2. The magnetic data of the Zn(II)2Ln(III)2 complexes (Ln(III) = Tb(III), Dy(III)) were analyzed by a spin Hamiltonian including the crystal field effect on the Ln(III) ions and the Ln(III)-Ln(III) magnetic interaction. The Stark splitting of the ground state was so evaluated, and the energy pattern indicates a strong easy axis (Ising type) anisotropy. Luminescence spectra of Zn(II)2Tb(III)2 complexes were observed, while those of Zn(II)2Dy(III)2 were not detected. The fine structure assignable to the (5)D4 → (7)F6 transition of ZnTb1 and ZnTb2 is in good accord with the energy pattern from the magnetic analysis. The Zn(II)2Ln(III)2 complexes (Ln(III) = Tb(III), Dy(III)) showed an out-of-phase signal with frequency-dependence in alternating current susceptibility, indicative of single molecule magnet. Under a dc bias field of 1000 Oe, the signals become significantly more intense and the energy barrier, Δ/kB, for the magnetic relaxation was estimated from the Arrhenius plot to be 39(1) and 42(8) K for ZnTb1 and ZnTb2, and 52(2) and 67(2) K for ZnDy1 and ZnDy2, respectively.

Theoretical study of magnetic properties of oxovanadium(IV) complex self-assemblies with tetradentate Schiff base ligands.

The theoretical study of the magnetic properties of oxovanadium(IV) complex self-assemblies with tetradentate Schiff base ligands is discussed on the basis of DFT calculations. Large negative spin densities are found on the axial oxygens of the various oxovanadium(IV) complexes. The relationship between the effective exchange parameters J(ab) and the geometrical parameters for these complexes was studied by changing the position of the neighboring molecules for the purpose of clarifying the mechanism of the ferromagnetic coupling. The intermolecular ferromagnetic interaction of the oxovanadium(IV) complexes with tetradentate Schiff base ligands is significantly affected by the formation of polymeric octahedral structures in the solid state. The overlap between the 2p orbitals of the axial oxygen and the 3d orbitals of the adjacent vanadium is effective for the ferromagnetic coupling. On the other hand, the effect of overlap between the vanadium 3d(xy) orbitals is too small to lead to magnetic coupling. It was revealed that the intermolecular ferromagnetic interaction of the polynuclear oxovanadium(IV) complexes is significantly affected by the spin polarization on the axial oxygen.

Ferromagnetic NiII-GdIII interactions in complexes with NiGd, NiGdNi, and NiGdGdNi cores supported by tripodal ligands.

Dinuclear [(NiL)Gd(hfac)(2)(EtOH)](H(3)L = 1,1,1-tris(N-salicylideneaminomethyl)ethane, Hhfac = hexafluoroacetylacetone), trinuclear [(NiL)(2)Gd(NO(3))], and tetranuclear [(NiL)Gd(CH(3)CO(2))(2)(MeOH)](2) complexes, were prepared by treating [Ni(HL)] with [Gd(hfac)(3)(H(2)O)(2)], Gd(NO(3))(3).6H(2)O, and Gd(CH(3)CO(2))(3).4H(2)O, respectively, in the presence of Et(3)N. All the complexes show that ferromagnetic interactions occur between the Ni(II) and Gd(III) ions.