Exchange interactions and spin dynamics in a [CuNd2(C4O4)4(H2O)16]·2H2O crystal

Crystalline [CuNd₂(C₄O₄)₄(H₂O)₁₆]·2H₂O constructed of complexes of trivalent neodymium and divalent copper, has been synthesized and studied by EPR. The square anion groups (C₄O₄) enter as bridge ligands, forming chains of neodymium ions interconnected by (C₄O₄)Cu(C₄O₄) fragments. It is found that the relaxation rate of the neodymium subsystem at room temperature significantly exceeds the exchange interaction rate between copper and neodymium ions. Under these conditions the magnetic properties of the crystal are determined by two magnetically nonequivalent chains of copper ions, which do not interact. The intrachain exchange interaction via hydrogen bonds is estimated to be ∼0.1 cm⁻¹. As one proceeds from the high-temperature (250<T<300 K) to the low-temperature region (T<40 K), a substantial change in the nature of the interaction is revealed. An unusual magnetic structure given in a crystal is observed at low temperatures, which is determined by the presence of two magnetically nonequivalent “ribbons,” formed by the interacting copper and neodymium ions: chains of copper ions are framed on two sides by chains of neodymium ions. The magnitude of the parameter of the exchange interaction between the copper and neodymium ions is estimated as J ^Cu-Nd⩾0.2 cm⁻¹. An exchange interaction between magnetically nonequivalent neodymium ions is not revealed in the EPR spectra. Fiz. Tverd. Tela (St. Petersburg) 39, 2057–2061 (November 1997)     

Thermochromic Phase Transition in [NH2(C2H5)2]2CuCl4 Crystals

The absorption spectra of [NH₂(C₂H₅)₂]₂CuCl₄ crystals in the visible spectral region in the vicinity of the thermochromic phase transition at T ₁ = 311 K are investigated. It is shown that in these crystalline compounds the phenomenon of thermochromism is primarily associated with the change of the plane-quadratic geometry of the coordination environment of Cu²⁺ to the tetrahedral form. The influence of ionizing irradiation on the phase-transition temperature and on the thermochromic properties of this crystal is studied.     

NQR, NMR and Crystal Structure Studies of [C(NH2)3]3Sb2Br9

The crystal structure of [C(NH₂)₃]₃Sb₂Br₉ was determined at 143 K: monoclinic, space group C2/c, Z = 4, a = 15.695 (3), b = 9.039(2), c = 18.364(3) Å, β = 96.94(1)°. The structure consists of two crystallographically independent guanidinium ions and two-dimensional corrugated sheets of (Sb₂Br₉ ^3?) _n , in which SbBr₆ octahedra are connected through three bridging Br atoms each other. One of the cations situates in a cavity of the (Sb₂Br₉ ^3?) _n layer with statistical disorder, while the other situates between the layers without disorder. Three ⁸¹Br NQR resonance lines were assignable to terminal Br atoms, while only one line was found for two inequivalent bridging Br atoms. All the ⁸¹Br NQR resonance lines were subjected to fade-out at low temperatures. The temperature dependence curve of ¹H NMR T ₁ showed well defined two minima, which were explained by postulating the C₃ reorientations of two types of cations with very different activation energies. The DTA (DSC) measurement revealed a phase transition of a first-order type at 444 K.     

NQR, NMR and Crystal Structure Studies of [C(NH2)3]2HgX4 (X = Br, I)

The crystal structure of [C(NH₂)₃]₂HgBr₄ has been determined at room temperature: monoclinic, space group C2/c, with a = 10.035(2), b = 11.164(2), c = 13.358(3) Å, β = 111.67(3)°, and Z = 4. The crystal consists of planar [C(NH₂)₃]⁺ and distorted tetrahedral [HgBr₄]^2? ions. The Hg atom is located on a two-fold axis such that two sets of inequivalent Br atoms exist in an [HgBr₄]^2? ion. In accordance with the crystal structure, two ⁸¹Br NQR lines widely separated in frequency were observed between 77 and ca. 380 K. [C(NH₂)₃]₂HgI₄ yielded four ¹²⁷I NQR lines ascribable to m = ±1/2 ? ±3/2 transitions, indicating that its crystal structure is different from the bromide complex. The ¹H NMR T ₁ measurements showed a single minimum for the bromide but two minima for the iodide. The analyses based on the C₃ reorientations of the planar [C(NH₂)₃]⁺ ions gave the activation energies of 29.8 kJ mol^?1 for the bromide, and 30.2 and 40.0 kJ mol^?1 for the iodide.     

Thermal contact between Na3[Ce(C7H3NO4)3] · 15H2O and liquid 3He at millikelvin temperatures

Very short thermal equilibrium times have been observed at millikelvin temperatures between powdered Na₃[Ce(C₇H₃NO₄)₃] · 15 H₂O, and pure ³He. Both a large increase in these times and a change in their temperature dependence occurs when 1% ⁴He. Both a large increase in these times and a change in their temperature dependence occurs when 1% ⁴He is added.     

Vibrational Spectra of [Zn(15NH3)4] (ReO4)2 and [Cd(NH3)4] (ReO4)2 With 110Cd/116Cd and H/D Isotopic Substitution

The infrared spectra of the zinc tetraammine with ¹⁵N, and cadmium tetraammine perrhenates with ¹¹⁰Cd/¹¹⁶Cd and H/D isotopic substitution, provides useful data in determining skeletal pseudo - exact force constants. An approximate set of force constants in the F₂ symmetry class for the whole complexes were obtained.     

Eu（C8H7O3）3·C12N2·H2O配合物的合成与表征

合成了新的Eu(C8H7O3)3·C12H8N2·H2O配合物.并经元素分析、摩尔电导、IR、UV、1H NMR等表征,初步确定配体3-甲氧基苯甲酸以桥式双齿形式和Eu(Ⅲ)配位.     

Study of Phase Transformations in (Cs,NH4)4(HSO4)3(H2PO4) Crystals

Physics of the Solid State - Phase transitions in crystals of (Cs,NH4)4(HSO4)3(H2PO4) solid solutions have been investigated by synchronous thermal analysis and polarization microscopy at different...     

81Br NQR Study of [NH3(CH2) n NH3]CdBr4 (n = 4 and 5) and [NH3(CH2) n NH3]ZnBr4 (n = 5 and 6)

⁸¹Br NQR frequencies and differential scanning calorimetry (DSC) were measured as a function of temperature. [NH₃(CH₂)₄ NH₃]CdBr₄ (1) and [NH₃(CH₂)₅NH₃]CdBr₄ (2) showed a doublet and quartet ⁸¹Br NQR spectrum, respectively. [NH₃(CH₂)₅NH₃]ZnBr₄ (3) and [NH₃(CH₂)₆NH₃]ZnBr₄ (4) exhibited a four-line ⁸¹Br NQR spectrum. From the NQR results, it is inferred that (1) and (2) consist of infinite two-dimensional sheets of corner-sharing CdBr₆ octahedra, whereas (3) and (4) have isolated [ZnBr₄]²⁻ tetrahedra. All of the crystals except (1) showed at least one structural phase transition above 380 K.     

[Fe3O（Ala）6（H2O）3]（ClO4）7和[Fe3O（Gly）6（H2O）3]（NO3）7·3H2O的顺原共振谱及变温磁化率研究

本文通过对[Fe 3O(Ala) 6(H 2O) 3](ClO 4) 7和[Fe 3O(Gly) 6(H 2O) 3](NO 3) 7·3H 2O的ESR谱的解析及变温磁化率的研究,得出它们的ESR谱具有各向同性的特点;朗德因子分别为2.019和1.997;两种配合物中铁离子间有反铁磁相互作用.     

Magnetic studies on synthetic phosphoferrite Fe 3 2+ (H2O)3(PO4)2

Synthetic crystals of phosphoferrite were studied by Mössbauer spectroscopy for temperatures ranging from 4.2 to 17.5 K. The analysis of the behaviour of the hyperfine fields for the two unequivalent sites near the Néel temperature (17.4 K) allowed the determination of the critical exponent for each site as ₁=0.171 and ₂=0.314.     

Neutron diffraction study of ammonium tartrate (NH4)2C4H4O6

A neutron diffraction study of ammonium tartrate has been carried out. Using the diffractometer in symmetrical setting, intensities of 750 reflections have been measured. The positions of all the hydrogen atoms have been determined. A good agreement is noticed between the present neutron and the earlier x-ray heavy atom parameters. The tartrate ion consists of two nearly identical planar halves, with an interplanar angle of 62°. Tre structure is stabilized by a net-work of hydrogen bonds. Details of hydrogen bonding and the ammonium ions environment are discussed.     

2,3-二羟基萘钼多酸有机衍生物的合成及1H NMR和IR谱学研究

本文对二种新合成的2,3－二羟基萘二钼和四钼多酸有机衍生物[n-Bu)4N]2[Mo2O5(OC10H6O)2](Ⅰ）和[n-Bu)4N]2[Mo4O10(OC10H6O)2(OCH3)2](Ⅱ)进行了红外光谱与核磁共振波谱研究,发现[Mo2O5]^2 中钼氧多桥键的红外振动频率较[Mo4O10(OCH3)2]^2 中钼氧多桥键的红外振动频率红移,而在配合物Ⅱ中2,3－二羟基中芳环的^1H化学位移较配合物Ⅰ中向低场移动。同时还发现含二钼配位中心[Mo2O5]^2 的[Mo2O5(OC10H6O)2]^2-与含四钼配位中心[Mo4O10(OCH3)2]^2 的[Mo4O10(OC10H6O)2(OCH3)2]^2-生成条件的差异仅仅只在反应体系的pH值的微小变化,说明钼多酸有机衍生物阴离子是对体系酸碱度极为敏感的物质。     

Mn5(PO3(OH))2(PO4)2(H2O)4的水热合成和光谱研究

在水热反应条件下合成出具有红磷锰矿结构的Mn5(PO3(OH) ) 2 (PO4 ) 2 (H2 O) 4单晶 ,在X ray单晶结构分析的基础上 ,对其固体紫外可见漫反射光谱、红外光谱、荧光光谱和热重光谱进行了研究。结果表明 ,构成该化合物的PO4 四面体及MnO6 八面体通过共顶点或共棱方式相连接 ,与P ,Mn配位的氧分为 3类 :即端基氧 (Od)、二桥氧 (Ob)和三桥氧 (Oc)。因而在 2 10和 2 5 0nm左右出现了Od→Mn和Ob ,c→Mn的荷移跃迁吸收谱带 ;在 10 0 0～ 110 0cm- 1 处 ,P—O的伸缩振动峰分裂为 3个 ;70 0～ 980cm- 1 处存在 3类Mn—O的伸缩振动。对标题化合物分别采用 2 18和 310nm的光激发 ,分别在 35 4和 4 13nm产生强而尖锐的荧光光谱发射峰 ,表现了很强的光学效应。热重分析表明该化合物在 2 70℃以下结构保持稳定 ,在 2 70～36 0℃范围内失去配位水。量化计算得单点能为 - 4 5 5 8 6 5 95 5 5 1a u ;前线轨道能量HOMO(Alpha) =- 0 2 80 80a u ,LOMO(Alpha) =0 0 15 2 7a u ,能隙为 0 2 96 0 7a u ;HOMO(Beta) =- 0 2 5 919a u ,LOMO(Beta)=0 0 0 10 8a u ,能隙为 0 2 6 0 72a u ;偶极矩为 4 2 0 82Debye。     

配合物[Zn(PSA)2(H2O)2]的合成及其晶体结构研究

合成了配合物单晶[Zn(PSA)2(H2O)2],其中PSA-为4-苯基丁酸根.配合物为单斜晶系,Cc空间群,a=3.8340(11)nm,b=0.51865(15)nm,c=1.0734(3)nm.a=90°,β=103.064(4).,r=90°,C20H26O6Zn.Mr=427.79,Z=4,V=2.0791(10)nm3,D=1.212g/cm3,F(000)=900,-46≤h≤43,-4≤k≤6,-13≤l≤13,R1=0.0780,wR2=0.2029.PSA-以两个氧原子与中心离子Zn(Ⅱ)离子形成四元螯合环,PSA与PSA反式构型.配合物分子之间存在氢键弱相互作用.     

Transient optical absorption of hole polarons in ADP (NH4H2PO4) and KDP (KH2PO4) crystals

A study of transient optical absorption of the ADP (NH₄H₂PO₄) and KDP (KH₂PO₄) nonlinear crystals in the visible and UV spectral regions is reported. Measurements made by absorption optical spectroscopy with nanosecond-time resolution established that the transient optical absorption (TOA) of these crystals originates from optical transitions in the hole A and B radicals and the optical-density relaxation kinetics is rate-controlled by interdefect tunneling recombination, which involves these hole centers and the electronic H⁰ centers representing neutral hydrogen atoms. At 290 K, hole polarons and the H⁰ centers undergo thermally stimulated migration, which is not accompanied by carrier ejection into the conduction or valence band. The slow components of the TOA kinetics with characteristic times from a few tens of milliseconds to a few seconds can be assigned to diffusion-controlled annihilation of hydrogen vacancies associated with impurity or structural defects.     

The Mössbauer spectrum of synthetic hureaulite: Fe5 2+(H2O)4(PO4H)2(PO4)2

The crystal structure of synthetic ferrous hureaulite, Fe₅ ²⁺ (H₂O)₄(PO₄H)₂(PO₄)₂, was refined from single-crystal X-ray data. It is monoclinic, space group C2/c, with a=17.487(4), b=9.017(2), c=9.338(2) Å, β=96.27(3)°, V=1463.6(6) Å³, Z=4 and D _calc=3.327 g/cm³. This end member of the hureaulite series was crystallized under distinctly acidic conditions, by a method that gives perfect crystals, large enough for X-ray single crystal studies. The main feature of the hureaulite structure is that it has an equal number of normal (PO₄)³⁺ and acid (PO₄H)²⁺ tetradentate groups. These are centered on Fe²⁺ atoms and share corners with edge-linked octahedra, forming pentamer units. The five Fe²⁺ atoms are distributed on three distinct sites in these units. This can be directly observed in the Mössbauer spectrum at 295 K, which contains three doublets whose relative intensities correspond to the 1:2:2 distributions of crystallographic sites.     

Elastic properties of monoclinic telluric acid ammonium phosphate,Te(OH)6·2NH4H2PO4·(NH4)2HPO4, near the paraelectric-ferroelectric transition

The elastic constants of Te(OH)₆·2NH₄H₂PO₄·(NH₄)₂HPO₄, TAAP, point symmetrym, have been measured by ultrasonic resonance methods passing through the paraelectric-ferroelectric transition at ca. 320 K. In the range between 273 and 340 K the elasticity tensor exhibits only a slight anisotropy. No discontinuity of the elastic constants is observed. However, some temperature derivatives of the elastic constants show slight anomalies within the range 310 to 325 K. The strongest effect occurs with the longitudinal elastic resistancec ₂₂. The thermal expansion which varies only slightly between 263 and 340 K, is highly anisotropic in contrast to the thermoelastic behaviour. A strong negative thermal expansion is observed in a direction within the mirror plane, ca. 45° apart from the direction of spontaneous polarization.This effect is not accompanied by a corresponding thermoelastic anomaly. The interactions connected with the transition are of the totally symmetric type. Like many other properties the elastic and thermoelastic behaviour of TAAP resembles that of triglycine sulphate (TGS). Larger differences between TAAP and TGS are found in the pressure dependence of various properties. For example the pressure dependence of the transition temperatureT is negative for TAAP (–3.8 K/kbar) and positive for TGS (3.9 K/kbar).Dedicated to Prof. Dr. H.E. Müser on the occasion of his 60th birthday