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1.
Dalton Trans ; 2020 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-32608445

RESUMO

A Hofmann-type two-step spin-crossover (SCO) complex with a pyrimidine derivative ligand, Fe(4-methylpyrimidine)2[Au(CN)2]2, was synthesized, and this complex shows a two-step SCO phenomenon in the intermediate state. Symmetry breaking also occurs in the intermediate state. These results reveal three spin states within the complex for high-spin (HS), HS0.5LS0.5, and low-spin (LS).

2.
Chemistry ; 22(44): 15725-15732, 2016 Oct 24.
Artigo em Inglês | MEDLINE | ID: mdl-27651203

RESUMO

Sandwich compounds often exhibit various phase transitions, including those to plastic phases. To elucidate the general features of the phase transitions in metallocenium salts, the thermal properties and crystal structures of [Fe(C5 Me5 )2 ]X ([1]X), [Co(C5 Me5 )2 ]X ([2]X), and [Fe(C5 Me4 H)2 ]X ([3]X) have been investigated, where the counter anions (X) are Tf2 N (=(CF3 SO2 )2 N- ), OTf (=CF3 SO3- ), PF6 , and BF4 . The Tf2 N salts commonly undergo phase transitions from an ordered phase at low temperatures to an anion-disordered phase, followed by a plastic phase and finally melt at high temperatures. All these salts exhibit a phase transition to a plastic phase, and the transition temperature generally decreases with decreasing cation size and increasing anion size. The crystal structures of these salts comprise an alternating arrangement of cations and anions. About half of these salts exhibit phase transitions at low temperatures, which are mostly correlated with the order-disorder of the anion.

3.
Dalton Trans ; 45(18): 7823-8, 2016 05 04.
Artigo em Inglês | MEDLINE | ID: mdl-27063188

RESUMO

A series of bimetallic coordination polymers with the elemental composition of [Cd(II)L2][Au(CN)2]2, (L = 3-methylpyridine, 4-ethylpyridine, 3,5-lutidine and 3-fluoropyridine) were synthesized and their crystal structures were determined. In all of the investigated compounds, there existed a pair of Au-Au atoms whose interatomic distance was shorter than the sum of van der Waals radii (0.36 nm) as an indication of the aurophilic interaction. The compounds were emissive under the irradiation at 370 nm. The emission spectra recorded in the temperature range of 183-363 K were characterized by the vibronic structures with a peak spacing (Δν) of ca. 2000 cm(-1). The value of Δν was close to the stretching vibration of the coordinated C[triple bond, length as m-dash]N (2150-2170 cm(-1)). It was postulated that C[triple bond, length as m-dash]N groups participated in the emission processes through their vibronic coupling. In the case of L = 4-ethylpyridine, the lifetime of emission was measured in the same temperature range, leading to the conclusion that the activation energy of the non-radiative processes (ΔEa) was estimated to be 20 kJ mol(-1).

4.
Phys Chem Chem Phys ; 17(28): 18288-93, 2015 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-26107642

RESUMO

Energy transfer was investigated between two types of iridium(III) complexes, [Ir(dfppy)2(Cn-bpy)](+) (dfppyH = 2-(2',4'-difluorophenyl)pyridine; Cn-bpy = 4,4'-dialkyl-2,2'-bipyridine; dialkyl = dimethyl (C1), didodecyl (C12), and dinonyldecyl (C19)) and [Ir(piq)2(Cn-bpy)](+) (piqH = 1-phenylisoquinoline) as a donor and an acceptor, respectively. The complexes were co-adsorbed by colloidally dispersed synthetic saponite. The efficiency of energy transfer (η(ET)) was obtained from emission spectra at various donor-to-acceptor ratios (D/A) on the basis of the Förster-type energy transfer mechanism. For C1-bpy, η(ET) was as high as 0.5 with a D/A of ca. 20. The results implied that the photon energy captured by several donor molecules was collected by a single acceptor molecule (i.e. the harvesting of light energy). Enantioselectivity was observed, which indicates the participation of a contact pair of donor and acceptor molecules. For C12-bpy and C19-bpy, η(ET) was low and exhibited no enantioselectivity, because their long alkyl chains inhibited close contact between the donor and acceptor molecules.

5.
Acta Crystallogr E Crystallogr Commun ; 71(Pt 5): m122-3, 2015 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-25995895

RESUMO

In the title dimeric complex, [{UO2(NO3)(C15H11N3)}2O2], a peroxide ion bridges the two uran-yl(VI) [O=U=O](2+) ions. The O-O bond length of the peroxide is 1.485 (6) Šand the mid-point of this bond is located at the inversion centre of the dimer. The U atom exhibits a distorted hexa-gonal-bipyramidal coordination geometry with two uran-yl(VI) O atoms occupying the axial positions and one O atom of the monodentate nitrate ion, both O atoms of the peroxide ion and the three N atoms of the chelating tridentate 2,2':6',2''-terpyridine (terpy) ligand in the equatorial positions. Two of the N atoms of the terpy ligand lie above and below the mean plane containing the equatorial ligand atoms and the U atom [deviations from the mean plane: maximum 0.500 (2), minimum -0.472 (2) and r.m.s. = 0.2910 Å]. The dihedral angle between the terpy ligand and the mean plane is 35.61 (7)°. The bond lengths around the U atom decrease in the order U-N > U-Onitrate > U-Operoxo > U=O. The dimeric complexes pack in a three-dimensional network held together by weak π-π inter-actions [centroid-centroid distance = 3.659 (3) Å] between pyridyl rings of the terpy ligands in neighbouring dimers, together with inter-molecular C-H⋯O and C-H⋯π inter-actions. Weak intra-molecular C-H⋯O inter-actions are also observed.

6.
Acta Crystallogr E Crystallogr Commun ; 71(Pt 1): 42-4, 2015 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-25705446

RESUMO

In the title compound, [UO2(C5H7O2)2(C14H15N)], the uran-yl(VI) unit ([O=U=O](2+)) is coordinated to two acetyl-acetonate (acac) anions and one 1-phenyl-3-(pyridin-4-yl)propane (ppp) mol-ecule. The geometry around the U atom is UNO6 penta-gonal-bipyramidal; two uran-yl(VI) O atoms are located at the axial positions, whereas four O atoms from two chelating bidentate acac ligands and one N atom of a ppp ligand form the equatorial plane.

7.
Dalton Trans ; 44(7): 3209-15, 2015 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-25594884

RESUMO

Dinuclear square planar palladium(ii) complexes, [{Pd(ii)La}2(baet)] (La(-) = ß-diketonato and baet(2-) = 1,2-diacetyl-1,2-bis(3-methylbutanoyl)ethanato), were prepared and used as chiral dopants to induce chiral nematic phases. The following ß-diketones were used as LaH: pentane-2,4-dione (acacH), dibenzoylmethane (dbmH), di-4-nonyloxybenzoylmethane (C9-dbmH) and 3-[4'-(4''-(octyloxy)phenylazo)phenyl]-2,4-dione (C8-azoacacH). When the enantiomers were doped in a nematic liquid crystal, they induced a chiral nematic phase with a helical twisting power (HTP) of 5-50 µm(-1). In particular, the sample doped with [{Pd(ii)(C8-azoacac)}2(baet)] exhibited a reversible change of the circular dichroism spectrum under alternate irradiation at 350 nm and 460 nm. It implied that the HTP changed reversibly in response to the cis-trans isomerization of the coordinated C8-azoacac ligand.

8.
Dalton Trans ; 42(48): 16680-2, 2013 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-24146024

RESUMO

A newly synthesized Hofmann-type bimetallic coordination polymer, [Cd(II)(3-methylpyridine)2][Au(CN)2]2, was luminescent with emission peaks at 400 nm, 440 nm, 490 nm and 550 nm (shoulder) under irradiation at 360 nm, whose multiple peak character in the emission spectrum was rationalized in terms of the vibrational structures in the interactions between the Au atoms in adjacent layers.

9.
Dalton Trans ; 42(21): 7579-85, 2013 Jun 07.
Artigo em Inglês | MEDLINE | ID: mdl-23536142

RESUMO

Mononuclear and dinuclear square planar palladium(II) complexes (denoted by [(hfac)Pd(II)(L-LH)] and [(hfac)Pd(II)(L-L)Pd(II)(hfac)], respectively) were synthesized. Here hfac(-), HL-L(-) and L-L(2-) denote hexafluoroacetylacetonato, monoprotonated and non-protonated bis-ß-diketonato ligands, respectively. Three bis-ß-diketones were used as HL-LH: 1,2-diacetyl-1,2-dibenzoylethane (denoted by dabeH2), 1,2-diacetyl-1,2-bis(3-methylbutanoyl)ethane (baetH2) and 1,2-diacetyl-1,2-propanoylethane (dpeH2). Both the monomeric and dimeric Pd(II) complexes were chiral due to the orthogonal twisting of the two non-symmetric diketonato moieties in HL-L(-) and L-L(2-), respectively. Optical resolution of [(hfac)Pd(II)(dabe)Pd(II)(hfac)] was achieved chromatographically on a chiral column to obtain a pair of optical antipodes which were stable against racemization. As for the other complexes, resolution was possible only after replacing hfac(-) with a bulky ligand such as dibenzoylmethanato (dbm(-)). Although a dinuclear complex with a symmetric bis-ß-diketonato ligand, [(hfac)Pd(II)(taet)Pd(II)(hfac)] (taet(2-) = 1,1,2,2-tetraacetylethanato), was achiral, the replacement of the terminal ligands with non-symmetric ß-diketonates yielded an axially chiral complex such as [(phacac)Pd(II)(taet)Pd(II)(phacac)], wherein phacac(-) denotes 1-phenyl-1,3-butanedionato. The UV and CD spectra of the Pd(II) complexes were analyzed with the help of the TDDFT calculations. The chiral monomeric species, [(dbm)Pd(II)(R- or S-baetH)], formed a heterometallic tetranuclear complex, [Fe(III){(dbm)Pd(II)(R- or S-baet)}3], in methanol solution.

10.
Dalton Trans ; 42(1): 232-7, 2013 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-23037769

RESUMO

Mononuclear and dinuclear ruthenium(III) complexes with bis-ß-diketonato ligands (denoted by [Ru(acac)(2)(L-LH)] and [Ru(acac)(2)(L-L)Ru(acac)(2)], respectively) were synthesized, where acac, L-LH(-) and L-L(2-) denote acetylacetonato, monoprotonated and unprotonated bis-ß-diketonato ligands, respectively. The following three ligands were used as the bis-ß-diketonato ligand (L-L(2-)): 1,2-diacetyl-1,2-dibenzoylethanato (denoted by dabe(2-)), 1,2-diacetyl-1,2-bis(3-methylbutanoyl)ethanato (baet(2-)) and 1,2-diacetyl-1,2-dipropanoylethanato (dpe(2-)). For the mononuclear and the meso-type dinuclear complexes, a pair of diastereomeric species were identified as Δ- (or Λ-) [Ru(acac)(2)(R- or S-L-LH)] and [Δ-Ru(acac)(2)(R- or S-L-L)Λ-Ru(acac)(2)], respectively. The possibility of thermal inversion in coordinated L-LH(-) (mononuclear) or L-L(2-) (dinuclear) was pursued by monitoring the changes in the electronic circular dichroism or the (1)H NMR spectra. No inversion occurred for the dinuclear complexes, when their chloroform solutions were kept at 50 °C for ca. 100 h. In contrast, some of the mononuclear complexes underwent the inversion of axial chirality to give an equilibrium mixture under the same conditions. The reaction followed the first-order rate law and the overall first-order rate constants (k) of [Ru(acac)(2)(L-LH)] were determined to be k = 0.13, 0.0048 and less than 0.001 h(-1) for L-LH(-) = dabeH(-), baetH(-) and dpeH(-), respectively. The results suggest that the main factor determining the barrier height of the internal rotation is not the steric but the electronic properties of the carbon-carbon bond connecting the two ß-diketonato moieties.

11.
Dalton Trans ; 40(10): 2249-56, 2011 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-21246130

RESUMO

To tune the lanthanide luminescence in related molecular structures, we synthesized and characterized a series of lanthanide complexes with imidazole-based ligands: two tripodal ligands, tris{[2-{(1-methylimidazol-2-yl)methylidene}amino]ethyl}amine (Me(3)L), and tris{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H(3)L), and the dipodal ligand bis{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H(2)L). The general formulas are [Ln(Me(3)L)(H(2)O)(2)](NO(3))(3)·3H(2)O (Ln = 3+ lanthanide ion: Sm (1), Eu (2), Gd (3), Tb (4), and Dy (5)), [Ln(H(3)L)(NO(3))](NO(3))(2)·MeOH (Ln(3+) = Sm (6), Eu (7), Gd (8), Tb (9), and Dy (10)), and [Ln(H(2)L)(NO(3))(2)(MeOH)](NO(3))·MeOH (Ln(3+) = Sm (11), Eu (12), Gd (13), Tb (14), and Dy (15)). Each lanthanide ion is 9-coordinate in the complexes with the Me(3)L and H(3)L ligands and 10-coordinate in the complexes with the H(2)L ligand, in which counter anion and solvent molecules are also coordinated. The complexes show a screw arrangement of ligands around the lanthanide ions, and their enantiomorphs form racemate crystals. Luminescence studies have been carried out on the solid and solution-state samples. The triplet energy levels of Me(3)L, H(3)L, and H(2)L are 21 000, 22 700, and 23 000 cm(-1), respectively, which were determined from the phosphorescence spectra of their Gd(3+) complexes. The Me(3)L ligand is an effective sensitizer for Sm(3+) and Eu(3+) ions. Efficient luminescence of Sm(3+), Eu(3+), Tb(3+), and Dy(3+) ions was observed in complexes with the H(3)L and H(2)L ligands. Ligand modification by changing imidazole groups alters their triplet energy, and results in different sensitizing ability towards lanthanide ions.

12.
Chemistry ; 16(29): 8785-96, 2010 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-20583049

RESUMO

In the series of polymeric spin-crossover compounds Fe(X-py)(2)[Ag(CN)(2))](2) (py=pyridine, X=H, 3-Cl, 3-methyl, 4-methyl, 3,4-dimethyl), magnetic and calorimetric measurements have revealed that the conversion from the high-spin (HS) to the low-spin (LS) state occurs by two-step transitions for three out of five members of the family (X=H, 4-methyl, and X=3,4-dimethyl). The two other compounds (X=3-Cl and 3-methyl) show respectively an incomplete spin transition and no transition at all, the latter remaining in the HS state in the whole temperature range. The spin-crossover behaviour of the compound undergoing two-step transitions is well described by a thermodynamic model that considers both steps. Calculations with this model show low cooperativity in this type of systems. Reflectivity and photomagnetic experiments reveal that all of the compounds except that with X=3-methyl undergo light-induced excited spin state trapping (LIESST) at low temperatures. Isothermal HS-to-LS relaxation curves at different temperatures support the low-cooperativity character by following an exponential decay law, although in the thermally activated regime and for aX=H and X=3,4-dimethyl the behaviour is well described by a double exponential function in accordance with the two-step thermal spin transition. The thermodynamic parameters determined from this isothermal analysis were used for simulation of thermal relaxation curves, which nicely reproduce the experimental data.

13.
Dalton Trans ; 39(7): 1719-21, 2010 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-20449412

RESUMO

A new spin crossover (SCO) coordination polymer, {[Fe(II)(4-methylpyridine)(2)][Au(I)(CN)(2)](2)}(n) () has been synthesized. The complex () has been observed to have a thermal induced three-step SCO transition, which is unprecedented behavior as compared with existing SCO complexes. In the complex, about 18%, 41% and 41% high spin states are changed to low spin states in the first-step, second-step and third-step, respectively.


Assuntos
Ouro/química , Ferro/química , Compostos Organometálicos/química , Polímeros/síntese química , Modelos Moleculares , Polímeros/química
14.
Dalton Trans ; 39(7): 1786-90, 2010 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-20449423

RESUMO

The novel bimetallic Fe(II)Ag(I) thermal-induced spin crossover coordination polymer {Fe(II)(3,5-dimethylpyridine)(2)[Ag(I)(2)(CN)(3)][Ag(I)(CN)(2)]}(n) was synthesized by one-pot reactions between 3,5-dimethylpyridine and K[Ag(I)(CN)(2)] in the presence of Fe(II) salt (FeSO(4).(NH(4))(2)SO(4).6H(2)O). Magnetic studies demonstrate the occurrence of a spin transition. The crystal structure has been studied at 293 K and 80 K. The compound is made up of unprecedented three-dimensional networks topology of Fe(II) ions bridged by binuclear [Ag(I)(2)(CN)(3)](-) and mononuclear [Ag(I)(CN)(2)](-) units; [Ag(I)(2)(CN)(3)](-) anion is very rare. In this complex, the presence of the Ag(I) ions plays a significant role in increasing the dimensionality and cooperatively due to the triangular argentophilic interactions.


Assuntos
Cianetos/química , Ferro/química , Magnetismo , Compostos Organometálicos/síntese química , Polímeros/química , Prata/química , Cristalografia por Raios X , Modelos Moleculares , Compostos Organometálicos/química
15.
Acta Crystallogr Sect E Struct Rep Online ; 64(Pt 5): m673-4, 2008 Apr 16.
Artigo em Inglês | MEDLINE | ID: mdl-21202213

RESUMO

The asymmetric unit of the title compound, [U(C(5)H(7)O(2))(2)O(2)(H(2)O)]·C(4)H(4)N(2), contains one [UO(2)(acac)(2)(H(2)O)] (where acac is acetyl-acetonate) and two half-mol-ecules of pyrazine. It exhibits a UO(7) penta-gonal-bipyramidal coordination geometry about the U(VI) atom, involving two bidentate acetyl-acetonate ions and one water mol-ecule. The N atoms of the pyrazine mol-ecules are not coordinated to the U(VI) atom, and are connected with the aqua O atom by hydrogen bonds. This results in a zigzag chain arrangement along the [10] direction.

16.
Acta Crystallogr Sect E Struct Rep Online ; 64(Pt 6): m788, 2008 May 10.
Artigo em Inglês | MEDLINE | ID: mdl-21202477

RESUMO

The title compound, [U(C(5)H(7)O(2))(2)O(2)(C(6)H(6)N(2)O)], exhibits a penta-gonal-bipyramidal coordination geometry around the U(VI) atom, involving two bidentate acetyl-acetonate ions and the pyridine ring of the pyridine-4-carbaldehyde oxime ligand. Hydrogen bonds exist between the OH group of the pyridine-4-carbaldehyde oxime ligand and the two O atoms of the acetyl-acetonate ions.

17.
J Phys Chem B ; 111(6): 1256-61, 2007 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-17253737

RESUMO

The two-dimensional (2D) polymeric spin crossover (SCO) compound Fe(py)2[Ag(CN)2]2 has been synthesized. The compound shows a two-step spin transition detected by magnetic, heat capacity, and X-ray diffraction measurements. The magnetic moment shows a high-temperature step (step 1) occurring at 146.3 K without hysteresis, while the low-temperature step (step 2) happens at 84 K on cooling and 98.2 K on heating. These measurements reveal a large amount of residual high spin (HS) species (23%) and that HS state trapping occurs at cooling rates of around 1 K min(-1) or higher. The two-step behavior has been confirmed by heat capacity, which gives, for steps 1 and 2, respectively, DeltaH1 = 3.33 kJ mol(-1), DeltaS1 = 22.6 J mol(-1) K(-1), and DeltaH2 = 1.51 kJ mol(-1), DeltaS2 = 15.7 J mol(-1) K(-1). For step 2 a hysteresis of 10 K has been determined with dynamic measurements. Powder X-ray diffraction at room temperature shows that the compound is isostructural to Cd(py)2[Ag(CN)2]2 previously reported. Powder X-ray diffraction indicates that there is only one crystallographic site for iron(II) in the whole temperature range, confirmed by Mössbauer spectroscopy. The X-ray diffraction study at different temperatures do not show any superstructure in the region between the transitions, discarding a crystallographic phase transition as the origin of the two-step behavior. However, an unexpected increase of the thermal factor is detected on lowering the temperature and considered as a manifestation of a disordered state between the two steps, consisting of a mixing of HS and LS species without long-range order.

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