Substituent effect of the coordinated pyridine in a series of pyrazolato bridged dinuclear diiron(II) complexes on the spin-crossover behavior

Two series of pyrazolato bridged dinuclear NCS and NCBH3 diiron(II) complexes with various types of 3- or 4-substituted pyridines, [{Fe(NCS or NCBH3)(X-py)}2(mu-bpypz)2], were prepared and their variable-temperature magnetic susceptibilities were measured. There were found linear correlations of the spin-crossover temperatures Tc not only between the NCS and NCBH3 complexes with the corresponding substituted pyridines, but also between the Tc and the Hammett constants, supporting the electronic substituent effect of the coordinated pyridine rather than a steric effect. The ligand field and the interelectronic repulsion parameters together with the thermodynamic data and/or cooperativity factor were discussed in relation with their spin-crossover behavior.     

New oxalate-bridged CrIII-MnII polymeric network incorporating a spin-crossover [Co(terpy)2]2+ cation

The reaction of Mn2+ with [Cr(ox)3]3- in the presence of the spin-crossover [Co(terpy)2]2+ cation gives rise to a 1D [Co(terpy)2][Mn(H2O)ClCr(ox)3].H2O.0.5MeOH (1) or a 2D [Co(terpy)2][Mn(H2O)Cr(ox)3]2.5H2O.0.5MeOH (2). The trimetallic complexes display dominant ferromagnetic behavior, and spin-crossover of [Co(terpy)2]2+ is suppressed by the chemical pressure of the polymeric oxalate-bridged network.     

高价钼络合物化学:(I)五价钼半胱氨酸体系,Na_2Mo_2(μ_2-O)_(2-m)(μ_2-S)_m~-O_2Cys_2的化学稳定性和磁性

钼酸根或硫代钼酸根与半胱氨酸盐酸盐及次硫酸钠作用生成氧桥或硫桥二钼(V)丰胱氦酸络合物。本文剖析反应过程和合成产物在酸碱溶液中的核磁共振谱,顺磁共振谱,电子谱,磁化率以及晶体结构的数据;推导化合物的合成机理;讨论化合物在酸碱溶液中的化学稳定性以及不同桥原子对化学稳定性的影响。本文还对可能的磁结构作了探讨。     

Towards the Molecular Design of Spin-Crossover Complexes of 2,6-Bis(pyrazol-3-yl)pyridines

The molecular design of spin-crossover complexes relies on controlling the spin state of a transition metal ion by proper chemical modifications of the ligands. Herein, the first N,N’-disubstituted 2,6-bis(pyrazol-3-yl)pyridines (3-bpp) are reported that, against the common wisdom, induce a spin-crossover in otherwise high-spin iron(II) complexes by increasing the steric demand of a bulky substituent, an ortho-functionalized phenyl group. As N,N’-disubstituted 3-bpp complexes have no pendant NH groups that make their spin state extremely sensitive to the environment, the proposed ligand design, which may be applicable to isomeric 1-bpp or other families of popular bi-, tri- and higher denticity ligands, opens the way for their molecular design as spin-crossover compounds for future breakthrough applications.     

2-甲基喹 淋与Cu(ClO~4)~2和Cu(BF~4)~2生成配合物的结构研究

以2-甲基喹 啉为配体合成了五种含有阴离子ClO~4^-或BF~4^-的铜(II)配合物, 利用元素分析、红外光谱、电子光谱、电导、热重谱、ESR谱及变温磁化率的测定推测了配合物的结构, 提出双核铜配合物中含有直线型单氧桥Cu(II)-O-Cu(II)键的可能构型。     

Positron annihilation and1H NMR study of [Zn(1-propyltetrzole)6](BF4)2 and [Fe(Methyltetrazole)6](BF4)2 complexes

The complexes [Zn(1-propyltetraole)₆](BF₄)₂ (Zn-ptz) and [Fe(methyltetrazole)₆](BF₄)₂ (Fe-mtz) were investigated by positron annihilation and solid-state NMR spectroscopy. For Zn-ptz signs of structural rearrangements were found between 70 and 145 K. For the spin-crossover complex Fe-mtz a transition affecting the high-spin stat Fe²⁺ ions at lattice site B occurs below 15 K.     

The spin-states and spin-transitions of mononuclear iron(II) complexes of nitrogen-donor ligands

A survey of mononuclear iron(II) complexes with heterocyclic N-donor ligation is presented. A brief introduction to spin-crossover chemistry and low-temperature spin-trapping is provided, since many of these compounds undergo thermal spin-transitions upon cooling or heating. These are highlighted, and the structural changes underlying spin-crossover are discussed where this is known. Materials showing spin-trapping behaviour following thermal quenching or irradiation at very low temperatures are also described.     

Iron(III) spin-crossover compounds with a wide apparent thermal hysteresis around room temperature.

The magnetic properties of the spin-crossover compounds, [Fe(qsal)2]NCSe-MeOH (1) and [Fe(qsal)2]NCSe-CH2Cl2 (2), have been measured. We have discovered that both compounds 1 and 2 exhibit a wide thermal hysteresis loop of 140 K (T(1/2) upward arrow = 352 K and T(1/2) downward arrow = 212 K) and 180 K (T(1/2) upward arrow = 392 K and T(1/2) downward arrow = 212 K), respectively, in the first cycle. Thermogravimetric analysis shows that solvent molecules escape from compounds 1 and 2 around 340 and 395 K, respectively. This means that the hysteresis loops observed for the first cycle are only apparent ones. Following the first loop, they show a two-step spin-crossover in warming mode. The so-called "step 1" and "step 2" are centered around T(1/2(S1)) upward arrow = 215 K and T(1/2(S2)) upward arrow = 282 K, respectively. On the other hand, a one-step spin-crossover occurs at T(1/2) downward arrow = 212 K in cooling mode. The hysteresis widths can be estimated to be 3 K (step 1) and 70 K (step 2), assuming that the widths in steps 1 and 2 are defined as the differences between T(1/2(S1)) upward arrow and T(1/2) downward arrow, and T(1/2(S2)) upward arrow and T(1/2) downward arrow, respectively. The hysteresis width of 70 K in step 2 is one of the widest values reported so far for spin-crossover complexes. It is thought that the cooperativity operating in the complexes arises mainly from the intermolecular pi interactions between quinoline and phenyl rings. Using a previously reported model, we are able to simulate the hysteresis loop with a two-step spin-crossover in warming mode and a one-step transition in cooling mode.     

Synthesis of bromine- or aryl-substituted ditopic Schiff base ligands and their bimetallic iron(II) complexes: electronic and magnetic properties

Syntheses of three new ditopic Schiff base ligands bearing bromine, phenyl or 2-thienyl substituents are described. Bimetallic iron(II) complexes were prepared from these ligands and were characterized. Electrochemical measurements suggest no measurable electronic coupling between the metal ions in each complex. Variable temperature magnetic susceptibility measurements indicate gradual spin-crossover is operative in the complexes studied, with the low-spin state as the ground state in all cases. Density functional theory calculations corroborate these experimental observations. Attempts to electropolymerize the 2-thienyl-substituted complexes were not successful.     

桥连双(酮亚胺)和双(二酮亚胺)及其铝配合物的合成与催化活性

通过桥连双β-二酮类化合物与取代苯胺反应, 合成了5个新的桥连双(β-单酮亚胺)化合物(1~5)和2个新的桥连双(β-二酮亚胺)化合物(6,7), 它们与三甲基铝反应, 得到了相应的3个双(β-酮亚胺基)二铝配合物(8~10)和2个双(β-二酮亚胺基)二铝配合物(11,12). 采用核磁共振、 红外光谱和质谱等对这些化合物进行了表征, 通过X射线单晶衍射分析证实了铝配合物的结构, 并考察了这些铝配合物在ε-己内酯开环聚合反应中的催化活性.     

Evidence of the chemical uniaxial strain effect on electrical conductivity in the spin-crossover conducting molecular system: [Fe(III)(qnal)2][Pd(dmit)2]5.acetone

A novel spin-crossover molecular conductor, [Fe(qnal)2][Pd(dmit)2]5.acetone, was prepared and characterized. The crystal structural analyses of both the low- and high-temperature phases revealed that the supramolecular pi-pi interactions between the spin-crossover Fe(qnal)2 cations as well as the cation contraction play an important role in the uniaxial lattice deformation which will modulate the electrical conductivity of the conducting Pd(dmit)2 layer.     

An unprecedented trinuclear structure involving two high-spin and one spin-crossover iron(II) centers

Anaerobic reaction of ferrous thiocyanate with the deprotonated form of the pentadentate dinucleating Schiff base 1,3-bis[(2-pyridylmethyl)imino]propan-2-ol (LH) yields the novel trinuclear [Fe3L2(NCS)4(H2O)] species 1. LH results from the bis-condensation of 2-acetyl-pyridine with 1,3-diaminopropan-2-ol and includes an N4O donor set. The X-ray crystal structure of 1 [C38H40N12O3S4Fe3, triclinic, space group P-1; a = 10.7730(10) angstroms, b = 12.2048(14) angstroms, c = 19.0559(19) angstroms, alpha = 76.908(12) degrees, beta = 89.106(12) degrees, gamma = 79.637(12) degrees, V = 2399.8(4) angstroms3] can be described either as a bent linear arrangement of ferrous centers pairwise bridged through the alkoxo oxygen atom of L- or as a triangular FeII3 core with an Fe2-SCN-Fe3 bridge as the longer side of the Fe1-Fe2-Fe3 triangle. The metric parameters characterizing the ligand environments of the three ferrous centers in 1 and its M?ssbauer spectra show that this unprecedented trinuclear structure involves two high-spin (Fe2 and Fe3) and one spin-crossover (Fe1) FeII centers. The donor set to the spin-crossover center (Fe1) is unprecedented: two Npyridine, two Nimine, and two Oalkoxo. Weak antiferromagnetic interactions transmitted through the end-to-end NCS bridge and/or through the O1-Fe1-O2 bridge operate between Fe2 and Fe3.     

Photoluminescent properties and molecular structures of [NaphAu(PPh(3))] and [mu-Naph {Au(PPh(3))}(2)] ClO(4) (Naph = 2-naphthyl)

The complexes [NaphAu(PPh(3))], and [mu-Naph{Au(PPh(3))}(2)]ClO(4), having the Au-C (aromatic) bond have been synthesized and characterized. The unique structure of with two gold atoms bridged by a naphthyl group has been determined by X-ray crystallography. The intramolecular Au-Au separation in is 2.7731(4) A. Upon excitation at 266 nm, both complexes display intraligand phosphorescence at room temperature in solution and in solid state.     

Molecular Structure of the Bis[tris(2-aminoethyl)aminecyano]dicobalt(III) Ion and its UV/VIS Spectrum

Formation of μ-peroxodicobalt(III) complexes has been studied in solutions containing tris(2-aminoethyl)aminecobalt(II) and additional monodentate ligands X. Depending n the nature and the concentration of X and on pH, singly bridged [(tren)XCoOOCoX(tren)]⁴⁺ and/or doubly bridged [(tren)Co(C₂OH)Co(tren)]³⁺ are formed. The UV/VIS spectra of these complexes are discussed on the basis of a theoretical model which stresses the importance of the dihedral angle of the CoOOCo-group. [(tren)(CN)CoOOCo(CN)(tren)](ClO₄)₂ has been synthesized and its structure determined by single crystal X-ray diffraction. The CoOOCo-group of the cation is planar. Solutions of the complex as well as the solid show two CT bands in the 300–400 nm region.     

Spanning pairs of Rh2(acetate)4 units with Ru(II) complexes

A synthetic route to linear pairs of Rh2 "paddlewheel" dimers bridged by Ru(II) complexes is presented. A bis(4'-(4-carboxyphenyl)-terpyridine)Ru(II) complex spans two Rh2 dimers and displays a 26 A separation between the dimers. Increased electronic interaction is found for the dimer of dimers without the phenyl groups using bis(4'-(4-carboxy)-terpyridine)Ru(II) as the bridging complex.     

Preparation and Radical Oligomerization of anFe(II) Complex without Loss of Spin-Crossover Properties

 11-(4H-1,2,4-Triazol-4-yl)-undecylmethacrylate (1), a new ligand for Fe(II) spin-crossover (SCO) complexes containing a polymerizable group, was synthesized and characterized. The complex [Fe·1 ₃](BF₄)₂ (2) was obtained by reaction of 1 with Fe(BF₄)₂·6H₂O (molar ratio 1/Fe(II) = 3/1) in THF. Complex 2 showed a gradual spin-crossover between 80 and 230 K. The methacrylate units in the ligands of complex 2 could be oligomerized radically in solution (initiator: azoisobutyronitrile) without loss of the spin-crossover behaviour.     

Chelating and bridging diphosphinoamine (PPh2)2N(iPr) complexes of copper(I)

The ligand bis(diphenylphosphino)isopropylamine (dppipa) has been shown to be a versatile ligand sporting different coordination modes and geometries dictated by copper(I). Most of the molecular structures were confirmed by X-ray crystallography. It is found in a chelating mode, in a monomeric complex when the ligand to copper ratio is 2:1. A tetrameric complex is formed when low ratios of ligand to metal (1:2) were used. But with increasing ratios of ligand to metal (1:1 and 2:1), a trimer or a dimer was obtained depending on the crystallization conditions. Variable temperature ³¹P{¹H} NMR spectra of these complexes in solution showed that the Cu–P bond was labile and the highly strained 4-membered structure chelate found in the solid state readily converted to a bridged structures. On the other hand, complexes with the ligand in a bridging mode in the solid state did not form chelated structures in solution. The effect of adding tetra-alkylammonium salts to solutions of various complexes of dppipa were probed by ³¹P{¹H} NMR and revealed the effect of counter ions on the stability of complexes in solution.     

E.s.r., magnetic, optical and biological (SOD and antimicrobial) studies of imidazolate bridged Cu(II)-Zn(II) and Cu(II)-Ni(II) complexes with tris(2-amino ethyl)amine as capping ligand: a plausible model for superoxide dismutase

X-band e.s.r. and optical absorption spectra of the imidazolate bridged heterobimetallic complexes [(tren)Cu-E-Im-Zn-(tren)](ClO(4))(3) and [(tren)Cu-E-Im-Ni-(tren)](ClO(4))(3), where trentris(2-aminoethyl)amine, E-Im=2-ethylimidazolate ion and the related mononuclear complexes [Cu(tren)](ClO(4))(2) and [(tren)Cu-E-ImH)](ClO(4))(2) have been described. Biological activities (superoxide dismutase and antimicrobial) have also been measured and compared with reported complexes.     

Family of carboxylate- and nitrate-diphenoxo triply bridged dinuclear Ni(II)Ln(III) complexes (Ln = Eu, Gd, Tb, Ho, Er, Y): synthesis, experimental and theoretical magneto-structural studies, and single-molecule magnet behavior

Seven acetate-diphenoxo triply bridged M(II)-Ln(III) complexes (M(II) = Ni(II) and Ln(III) = Gd, Tb, Ho, Er, and Y; M(II) = Zn(II) and Ln(III) = Ho(III) and Er(III)) of formula [M(μ-L)(μ-OAc)Ln(NO(3))(2)], one nitrate-diphenoxo triply bridged Ni(II)-Tb(III) complex, [Ni(μ-L)(μ-NO(3))Tb(NO(3))(2)]·2CH(3)OH, and two diphenoxo doubly bridged Ni(II)-Ln(III) complexes (Ln(III) = Eu, Gd) of formula [Ni(H(2)O)(μ-L)Ln(NO(3))(3)]·2CH(3)OH have been prepared in one pot reaction from the compartmental ligand N,N',N"-trimethyl-N,N"-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H(2)L). Moreover, Ni(II)-Ln(III) complexes bearing benzoate or 9-anthracenecarboxylate bridging groups of formula [Ni(μ-L)(μ-BzO)Dy(NO(3))(2)] and [Ni(μ-L)(μ-9-An)Dy(9-An)(NO(3))(2)]·3CH(3)CN have also been successfully synthesized. In acetate-diphenoxo triply bridged complexes, the acetate bridging group forces the structure to be folded with an average hinge angle in the M(μ-O(2))Ln bridging fragment of ~22°, whereas nitrate-diphenoxo doubly bridged complexes and diphenoxo-doubly bridged complexes exhibit more planar structures with hinge angles of ~13° and ~2°, respectively. All Ni(II)-Ln(III) complexes exhibit ferromagnetic interactions between Ni(II) and Ln(III) ions and, in the case of the Gd(III) complexes, the J(NiGd) coupling increases weakly but significantly with the planarity of the M-(O)(2)-Gd bridging fragment and with the increase of the Ni-O-Gd angle. Density functional theory (DFT) theoretical calculations on the Ni(II)Gd(III) complexes and model compounds support these magneto-structural correlations as well as the experimental J(NiGd) values, which were found to be ~1.38 and ~2.1 cm(-1) for the folded [Ni(μ-L)(μ-OAc)Gd(NO(3))(2)] and planar [Ni(H(2)O)(μ-L)Gd(NO(3))(3)]·2CH(3)OH complexes, respectively. The Ni(II)Dy(III) complexes exhibit slow relaxation of the magnetization with Δ/k(B) energy barriers under 1000 Oe applied magnetic fields of 9.2 and 10.1 K for [Ni(μ-L)(μ-BzO)Dy(NO(3))(2)] and [Ni(μ-L)(μ-9-An)Dy(9-An)(NO(3))(2)]·3CH(3)CN, respectively.     

Preparation and Radical Oligomerization of anFe(II) Complex without Loss of Spin-Crossover Properties

Summary.  11-(4H-1,2,4-Triazol-4-yl)-undecylmethacrylate (1), a new ligand for Fe(II) spin-crossover (SCO) complexes containing a polymerizable group, was synthesized and characterized. The complex [Fe·1 ₃](BF₄)₂ (2) was obtained by reaction of 1 with Fe(BF₄)₂·6H₂O (molar ratio 1/Fe(II) = 3/1) in THF. Complex 2 showed a gradual spin-crossover between 80 and 230 K. The methacrylate units in the ligands of complex 2 could be oligomerized radically in solution (initiator: azoisobutyronitrile) without loss of the spin-crossover behaviour. Received May 30, 2000. Accepted December 10, 2000