Light induced excited high spin-state trapping in [FeL2](BF4)2 (L = 2,6-di(pyrazol-1-yl)pyridine)

The spin-crossover complex [FeL2](BF4)2 undergoes a LIESST transition at 30 K on irradiation; the structures of the low-spin ground and high-spin metastable states at this temperature are presented.     

Phase transitions of polycrystalline [Fe(H2O)6](ClO4)3 and [Cr(H2O)6](ClO4)3 studied by DSC

The effects of heat treatment on soymilk protein denaturation were studied by differential scanning calorimetry (DSC) and electrophoresis. Transition behavior of soymilk was studied by DSC. Three endotherms were found in DSC heating curves; the transition observed at around 70°C is attributed to the denaturation of 7S (b-conglycinin) and the transition at around 90°C is to 11S (glycinin). The denaturation temperature increased with the increasing soymilk protein content. The change of electrophoretic patterns after heat treatments indicated that soy proteins were dissociated into subunits, some of which coalesced. When the heating temperature is below their denaturation temperature, the protein fractions cannot completely be denatured even after heat exposure for extended periods of time. This revised version was published online in August 2006 with corrections to the Cover Date.     

Anion doping as a probe of cooperativity in the molecular spin-crossover compound [FeL2][BF4]2 (L = 2,6-di{pyrazol-1-yl}pyridine)

The complex dications in the cooperative spin-crossover compound [FeL(2)][BF(4)](2) (2,6-di(pyrazol-1-yl)pyridine) pack through pi-pi interactions into a 2-D layered structure (a "terpyridine embrace" motif). The effects of doping the larger ClO(4)(-) ion into this lattice have been investigated. The bulk solids [FeL(2)][ClO(4)](x)[BF(4)](2-x) are isostructural with [FeL(2)][BF(4)](2) when x = 0.30 and 0.98, and isostructural with (structurally distinct) [FeL(2)][ClO(4)](2) when x = 1.89. When x = 1.68, powder samples are a mixture of both phases, but crystalline material adopts purely the ClO(4)(-) structure. Increasing the perchlorate content in the lattice for 0 < or =x< or = 1.68 causes a small decrease in T(1/2) and a narrowing of hysteresis in their spin-crossover, but with no significant reduction in cooperativity. It also leads to more pronounced decreases in DeltaH [by up to 3.2(5) kJ mol(-1)] and DeltaS [by up to 10(2) J mol(-1) K(-1)] for the transition by DSC. Single crystals of formula [FeL(2)][ClO(4)](y)[BF(4)](2-y) (y = 0.44 and 1.13) are isostructural with the pure BF(4)(-) salt. While their molecular structures are indistinguishable, the distances between cations in the lattice increase in the doped materials. Weakening of intermolecular pi-pi interactions between cations is the likely reason for the reduced enthalpy of spin-crossover as x increases. However, the biggest stuctural change is an increase in the spacing between the 2-D layers with increased ClO(4)(-). These results suggest that cooperativity in this material is transmitted within the terpyridine embrace layers.     

DSC study of the phase transitions in [Ni(D2O)6](ClO4)2 and [Ni(H2O)6](ClO4)2

DSC measurements were carried out for [Ni(H₂O)₆](ClO₄)₂ (sampleH) and [Ni(D₂O)₆](ClO₄)₂ (sampleD) in the temperature range 300–380 K. For both compounds two anomalies on the DSC curves were detected. The results for sampleH are compared to those previously obtained using adiabatic calorimetry method. For both compounds studied in this work the high-temperature transition appears at the same temperature while the low-temperature one is shifted towards higher temperatures in sampleD. Disorder connected with H₂O or D₂O groups is suggested in the intermediate phase between the low- and high-temperature transitions.     

A study of the thermal and light induced spin transition in [FeL2](BF4)2 and [FeL2](ClO4)2 L=2,6-di(3-methylpyrazol-1-yl)pyrazine

The spin crossover compounds [FeL2](BF4)2, L=2,6-di(3-methylpyrazol-1-yl)pyrazine and [FeL2](ClO4)2 have very unusual two stage spin transitions which are initially steep and then become more gradual. A detailed variable temperature single crystal X-ray diffraction study has shown that the course of the spin transition is controlled by an order-disorder transition in the counter anions. The high and low spin states both crystallise in the tetragonal space group I4, the structures of the high and low spin states are presented at 290 and 30 K, respectively. The title compounds are shown to undergo LIESST (Light Induced Excited Spin State Trapping) under irradiation with either red or green laser light with wavelengths of 632.8 and 532.06 nm, respectively, at 30 K. The cell parameters for the tetragonal photo-induced metastable high spin state at this temperature are a= 9.169(6), c= 17.77(1) A for [FeL2](ClO4)2 with an increase in unit cell volume of 21 A3, and a= 9.11(1), c= 17.75(2) A and an increase in volume of 42.8 A3 for [FeL2](BF4)2.     

Synthesis and Crystal Structure of [NiL_2(H_2O)_2](ClO_4)_2L=MBPT=4-P-methylphenyl-3,5-bis-(pyridin-2-yl)-1,2,4-triazole

The substituted l,2,4-triazoles are very useful ligands in coordination chemistry'-'. It isvery interesting that some complexes containing substituted l,2,4-triazoles ligands havethe spin-crossover phenomena, which could be used as magnetic materials4-5. However,complexes containing triaryltriazole ligands have been little known so far. We haverecently synthesized some triaryltriazole compounds'-', and we first report here thesynthesis and crystal structure of [Ni(MBPT),(H,O),](CIO.),.Expe…     

SPIN-CROSSOVER OF [Fe(Cl-BZIMPY)2](ClO4)2 INDUCED BY DEPROTONATION

Abstract

The ligand 4-Cl-2,6-bis(benzimidazol-2′-yl)-pyridine(Cl-bzimpy;H₂L) acts as a bidentate when coordinated with transition metal ions and the complex [Fe(Cl-bzimpy)₂](ClO₄)₂ was isolated as a solid. The protonation constants (logK). The free ligand and the complex were evaluated in 30:70 (v/v) H₂O:EtOH at room temperature and ionic strength of 0.13M (KCl). Coordination of the ligand to the metal ion leads to an increase of the acidity of the imino-hydrogen of the benzimidazole group. Deprotonation leads to a change in the spin-state (to the low-spin state; HS → LS transition) of the complex associated with a decrease in the spin-crossover equilibrium constant (K_sc). An opposite shift of spin-state is observed when HClO₄ is added to the complex solution, thus showing the reversibility of the process.     

A New Diiminopyridyl Cobalt Complex [CoCl2L] (L = 2,6-Bis(N,N'-bis(2,6-diisopropyl-4-(2,3-dimethyoxylbenzoylamide)phenylimino))pyridine)

The reaction of CoCl2·6H2O with 2,6-bis(N,N'-bis(2,6-diisopropyl-4-(2,3-dimethy-oxyl-benzoylamide)phenylimino))pyridine (L) afforded the complex [CoCl2L], which was fully characterized by elemental analysis, UV-vis, IR spectroscopy, fluorescence, and X-ray diffraction analysis. The compound is oftriclinie system, space group P1- with a = 13.058(3), b = 13.798(3), c =16.695(3) (A), α = 98.191(3),β = 102.792(3), γ = 101.820(3)°,V= 2815.0(9) (A)3, Z= 2, F(000) = 1122,μ = 0.45 mm-1, R = 0.061 and wR= 0.1349 for 9842 observed reflections (1 2σ(Ⅰ)). The Co(Ⅱ center adopts a distorted square-pyramidal coordination geometry. The extended structure shows a one-dimensional zigzag double chain linked by hydrogen bonds and π-π stacking interactions.     

[Fe(L)3](ClO4)3(L=bpy,phen)与Na2S2O3在室温下的固相氧化还原反应

本文研究室温下[Fe(bpy)3](ClO4)3.3H2O和[Fe(phen)3](ClO4)3.H2O分别与Na2S2O3.5H2O发生的固-固相氧化还原反应。用Mossbauer谱、XRD、IR、UV漫反射谱、元素分析、TG-DTA和磁化率测定等手段表征了反应24h后的固相产物,报道了[Fe(bpy)3](ClO4)2的结晶学数据。结果表明, 室温下反应速度快, 反应进行完全。     

Calorimetric study and thermal analysis of [ErY(Ala)4(H2O)8](ClO4)6 (Ala=ALANINE)

A solid complex of rare-earth compounds with alanine, [ErY(Ala)₄(H₂O)₈](ClO₄)₆ (Ala=alanine), was synthesized, and a calorimetric study and thermal analysis for it was performed through adiabatic calorimetry and thermogravimetry. The low-temperature heat capacity of [ErY(Ala)₄(H₂O)₈](ClO₄)₆ was measured with an automated adiabatic precision calorimeter over the temperature range from 78 to 377 K. A solid-solid phase transition was found between 99 and 121 K with a peak temperature at 115.78 k. The enthalpy and entropy of the phase transition was determined to be 1.957 Kj mol^-1, 16.90 j mol^-1 k^-1, respectively. Thermal decomposition of the complex was investigated in the temperature range of 40~550°C by use of the thermogravimetric and differential thermogravimetric (TG/DTG) analysis techniques. The TG/DTG curves showed that the decomposition started from 120 and ended at 430°C, completed in three steps. A possible mechanism of the thermal decomposition was elucidated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and Structure of [Cu2（μ—NO2）（aepy）4]（ClO4）3 （aepy=2—（2—Aminoethyl）pyridine）

1 INTRODUCTION There has been great and considerable interest in the study of copper nitrite complexes because they are relevant to the study of copper-containing enzymes involved in the denitrification process[1]; in particular, copper-nitrite complexes are potentially relevant to the nitrite reductases[2] (the enzyme from Achromobacter Cycloclastes) which convert NO2－ to NO and/or N2O. Many attempts have been made to synthesize a variety of copper-nitrite complexes, in which the n…     

Syntheses,crystal structures and spectroscopic properties of the novel complexes [M(MOBPT)*2 (H2O)2](ClO4)2 · 4H2O (M = CoII and NiII)

The novel cobalt(II) and nickel(II) complexes with 4-(p-methoxyphenyl)-3,5-bis(pyridin-2-yl)-1,2,4-triazole (MOBPT) have been synthesized and their molecular structures determined by X-ray analysis, i.r. and by ESI-MS spectroscopy. The metal atom is in a distorted octahedral environment. Two bidentate chelating ligands (MOBPT) coordinate to the metal center equatorially and two water molecules coordinate axially. Each MOBPT entity coordinates via one triazole nitrogen and one pyridine nitrogen atom. Magnetic measurements show that the complexes are high-spin species in the 75–300 K range.     

Water oxidation catalyzed by the tetranuclear Mn complex [Mn(IV)4O5(terpy)4(H2O)2](ClO4)6

The tetranuclear manganese complex [Mn(IV)(4)O(5)(terpy)(4)(H(2)O)(2)](ClO(4))(6) (1; terpy = 2,2':6',2″-terpyridine) gives catalytic water oxidation in aqueous solution, as determined by electrochemistry and GC-MS. Complex 1 also exhibits catalytic water oxidation when adsorbed on kaolin clay, with Ce(IV) as the primary oxidant. The redox intermediates of complex 1 adsorbed on kaolin clay upon addition of Ce(IV) have been characterized by using diffuse reflectance UV/visible and EPR spectroscopy. One of the products in the reaction on kaolin clay is Mn(III), as determined by parallel-mode EPR spectroscopic studies. When 1 is oxidized in aqueous solution with Ce(IV), the reaction intermediates are unstable and decompose to form Mn(II), detected by EPR spectroscopy, and MnO(2). DFT calculations show that the oxygen in the mono-μ-oxo bridge, rather than Mn(IV), is oxidized after an electron is removed from the Mn(IV,IV,IV,IV) tetramer. On the basis of the calculations, the formation of O(2) is proposed to occur by reaction of water with an electrophilic manganese-bound oxyl radical species, (?)O-Mn(2)(IV/IV), produced during the oxidation of the tetramer. This study demonstrates that [Mn(IV)(4)O(5)(terpy)(4)(H(2)O)(2)](ClO(4))(6) may be relevant for understanding the role of the Mn tetramer in photosystem II.     

Dopamine interaction in the absence and in the presence of Cu2+ ions with macrocyclic and macrobicyclic polyamines containing pyrazole units. Crystal structures of [Cu2(L1)(H2O)2](ClO4)4 and [Cu2(H-1L3)](ClO4)3*2H2O.

The interaction with Cu2+ and dopamine of three polyazacyclophanes containing pyrazole fragments as spacers is described. Formation of mixed complexes Cu2+-macrocycle-dopamine has been studied by potentiometric methods in aqueous solution. The crystal structures of the complexes [Cu2(L1)(H2O)2](ClO4)4*2H2O (4) (L1 = 13,26-dibenzyl-3,6,9,12,13,16,19,22,25,26-decaazatricyclo[22.2.1.1(11,14)]octacosa-1(27),11,14(28),24-tetraene) and [Cu2(H-1L3)](HClO4)(ClO4)2*2H2O (6) (L3 = 1,4,7,8,11,14,17,20,21,24,29,32,33,36-tetradecaazapentacyclo[12.12.12.1(6,9).1(19,22).1(31,34)]hentetraconta-6,9(41),19(40),21,31,34(39)-hexaene) are presented. In the first one (4), each Cu2+ coordination site is made up by the three nitrogens of the polyamine bridge, a sp2 pyrazole nitrogen and one water molecule that occupies the axial position of a square pyramid. The distance between the copper ions is 6.788(2) A. In the crystal structure of 6, the coordination geometry around each Cu2+ is square pyramidal with its base being formed by two secondary nitrogens of the bridge and two nitrogen atoms of two different pyrazolate units which act as exobidentate ligands. The axial positions are occupied by the bridgehead nitrogen atoms; the elongation is more pronounced in one of the two sites [Cu(1)-N(1), 2.29(2) A; Cu(2)-N(6), 2.40(1) A]. The Cu-N distances involving the deprotonated pyrazole moieties are significantly shorter than those of the secondary nitrogens. The Cu(1)...Cu(2) distance is 3.960(3) A. The pyrazole in the noncoordinating bridge does not deprotonate and lies to one side of the macrocyclic cavity. One of the aliphatic nitrogens of this bridge is protonated and hydrogen bonded to a water molecule, which is further connected to the sp2 nitrogen of the pyrazole moiety through a hydrogen bond. The solution studies reveal a ready deprotonation of the pyrazole units induced by coordination to Cu2+. In the case of L2 (L2 = 3,6,9,12,13,16,19,22,25,26-decaazatricyclo[22.2.1.1(11,14)]octacosa-1(27),11,14(28),24-tetraene), deprotonation of both pyrazole subunits is already observed at pH ca. 4 for 2:1 Cu2+:L2 molar ratios. All three free receptors interact with dopamine in aqueous solution. L3 is a receptor particularly interesting with respect to the values of the interaction constants over five logarithmic units at neutral pH, which might suggest an encapsulation of dopamine in the macrocyclic cage. All three receptors form mixed complexes Cu2+-L-dopamine. The affinity for the formation of ternary dopamine complexes is particularly high in the case of the binuclear Cu2+ complexes of the 1-benzyl derivative L1.     

高氯酸碳酰肼钴、高氯酸碳酰肼镍快速热分解反应动力学

利用温度跃升傅立叶变换红外原位分析技术(T-jump/FTIR)对高氯酸碳酰肼钴和高氯酸碳酰肼镍的快速热分解反应进行了研究. 研究表明, 目标化合物快速热分解逸出的主要气相产物是CO2, H2O, HCN, HNCO和HONO. 借助快速升温过程中Pt金属丝的控制电压变化曲线得到剧烈放热峰的诱导出现时间tx, 利用tx值计算了两种目标化合物的快速热分解动力学参数. 在0.1 MPa氩气气氛, 613～653 K的实验温度范围内, 高氯酸碳酰肼钴的活化能Ea=39.42 kJ•mol−1, lnA=5.93; 在0.1 MPa氩气气氛, 618～678 K的实验温度范围内, 高氯酸碳酰肼镍的活化能Ea=60.44 kJ•mol−1, lnA=9.40.