The kinetics of substitution reactions of mixed platinum(II)-bis(nucleoside) complexes in aqueous solution in the presence of thiourea; X-ray crystal structure determination of cis-

In aqueous solution, bis(nucleoside) complexes formed by the reaction of cis-[Pt(NH3)2(H2O)2]2+ with an excess of either adenosine (ado) or a mixture of adenosine and guanosine (guo) undergo a slow N7--> N1 linkage isomerisation in the adenine moiety. The isomerisation probably involves the breaking and reformation of Pt-nucleoside bonds, thus favouring the more stable N1 binding mode of the adenine base. Dynamic processes due to the presence of adenosine in the platinum coordination sphere are slow on the NMR time scale. The N7 binding mode of PtII in cis-[Pt(NH3)2(ado-N7)2](ClO4)2. 3.5H2O was confirmed by X-ray crystal structure analysis. In both of the crystallographically independent cations, the PtII coordination sphere is almost ideally square planar, with typical Pt-N bond lengths and angles. The most significant difference between the two cations lies in the sugar conformation of the coordinated nucleosides. In one cation, both have an anti (-ap) conformation, whilst in the other cation one has an anti (-ap) conformation and the other a syn (+sc) conformation stabilised by a relatively strong H-bond. Substitution of the nucleoside(s) by thiourea follows an associative mechanism with only a negligible contribution by the solvent path. For symmetric complexes, the order of lability of different binding modes is ado-N1 相似文献   

Four-component relativistic calculations of NMR shielding constants of the transition metal complexes. Part 1: Pentaammines of cobalt,rhodium, and iridium

The nonrelativistic and four-component fully relativistic calculations of ¹H, ¹⁵N, ⁵⁹Co, ¹⁰³Rh, and ¹⁹³Ir shielding constants of pentaammineaquacomplexes of cobalt(III), rhodium(III), and iridium(III) were carried out at the density functional theory (DFT) level of theory. The noticeable deshielding relativistic corrections were observed for nitrogen shielding constants (chemical shifts), whereas those corrections were found to be negligible for protons. For the transition metals cobalt, rhodium, and iridium, relativistic corrections to their nuclear magnetic resonance (NMR) shielding constants were found to be rather small for cobalt and rhodium (some 5–10%), whereas they are essentially larger for iridium (up to 70%).     

Complexes of palladium (II) with L-proline. Mixed L-prolinato nucleoside complexes of Palladium (II)

The reaction of Palladium (II) chloride and L-proline (ProH) in aqueous solution gave the dimeric complex, Pd(Pro)Cl₂, which was characterized by elemental analysis, molecular weight, conductivity measurements and IR and NMR spectra. The complex, reacted further with the purine nucleosides inosine or guanosine (Nucl) and the complexes Pd(Pro)(Nucl-H⁺) were isolated from aqueous solution. The insolubility of these complexes suggested a rather polymeric structure in which the nucleoside bridges two adjacent palladium atoms through its N(7) and the exocyclic O(6) atoms. Reaction in dmso gave the complex Pd(Pro)(Nucl)Cl in which the nucleoside act as monodentate ligands with their N(7) atom as ligation site. In aqueous solutions these complexes are quantitatively transformed to the polymeric analogues with the liberation of HCl. The nucleoside adenosine (Ado) reacted in a different way giving only the dimeric complex [Cl(Pro)PdAdoPd(Pro)Cl] in which adenosine bridges two palladium atoms through its N(1) and N(7) atoms. Finally with the pyrimidine nucleoside cytidine (Cyd) the monomer Pd(Pro)(Cyd)Cl was isolated.     

1H, 13C and 15N NMR studies on adducts formation of rhodium(II) tetraacylates with some azoles in CDCl3 solution

Adduct formations of rhodium(II) tetraacetate and tetratrifluoroacetate with some 1H-imidazoles, oxazoles, thiazoles, 1H-pyrazoles and isoxazole have been investigated by the use of 1H, 13C, 15N NMR and electronic absorption spectroscopy (VIS) in the visible range. Azoles tend to form axial adducts containing rhodium(II) tetraacylates bonded via nitrogen atom. Bulky substituents close to the nitrogen atom prevent the Rh--N bond formation, and in several cases switch over the binding site to the oxygen or sulphur atoms. The (15)N adduct formation shift Deltadelta(15N) (Deltadelta = delta(adduct) - delta(ligand)) varied from ca - 40 to - 70 ppm for the nitrogen atom involved in complexation, and of a few parts per million only, from ca - 6 to 3 ppm, for the non-bonded nitrogen atom within the same molecule. The Deltadelta(1H) values do not exceed one ppm; Deltadelta(13C) ranges from - 1 to 6 ppm. Various complexation modes have been proved by electronic absorption spectroscopy in the visible region (VIS). For comparison purposes, some adducts of pyridine, thiophene and furan derivatives have been measured as well. The experimental findings were compared with calculated chemical shifts, obtained by means of DFT B3LYP method, using 6-311 + G(2d,p), 6-31(d)/LanL2DZ and 6-311G(d,p) basis set.     

Nitric oxide adsorption and reduction reaction mechanism on the Rh7(+) cluster: a density functional theory study

The transition metal rhodium has been proved the effective catalyst to convert from NO(x) to N(2.) In the present work, we are mainly focused on the NO adsorption and decomposition reaction mechanism on the surface of the Rh(7)(+) cluster, and the calculated results suggest that the reaction can proceed via three steps. First, the NO can adsorb on the surface of the Rh(7)(+) cluster; second, the NO decomposes to N and O atoms; finally, the N atom reacts with the second adsorbed NO and reduces to a N(2) molecule. The N-O bond breaks to yield N and O atoms in the second step, which is the rate-limiting step of the whole catalytic cycle. This step goes over a relatively high barrier (TS(12)) of 39.6 kcal/mol and is strongly driven by a large exothermicity of 55.1 kcal/mol during the formation of stable compound 3, accompanied by the N and O atoms dispersed on the different Rh atoms of the Rh(7)(+) cluster. In addition, the last step is very complex due to the different possibilities of reaction mechanism. On the basis of the calculations, in contrast to the reaction path II that generates N(2) from two nitrogen atoms coupling, the reaction path I for the formation of intermediate N(2)O is found to be energetically more favorable. Present work would provide some valuable fundamental insights into the behavior of the nitric oxide adsorption and reduction reaction mechanism on the Rh(7)(+) cluster.     

Interaction of Rh(I) with meso-arylsapphyrins and -rubyrins: first structural characterization of bimetallic hetero-rubyrin complex

The ligational behavior of meso-arylsapphyrins and rubyrins toward Rh(I) is investigated. Sapphyrins form monometallic complexes with coordination of one imine and amine type nitrogens of the bipyrrole unit in an eta2 fashion. The Rh(I) coordination is completed by the presence of two ancillary carbon monoxide ligands. Rubyrins form both monometallic and bimetallic complexes. Two types of bimetallic complexes have been isolated. In the first type, both rhodium atoms are projected above the mean rubyrin plane, while in the second type, one rhodium atom is projected above and the other below the mean plane. Detailed 1H and 2D NMR spectral analyses along with IR and UV-visible spectra of the complexes confirm the proposed binding modes for the rhodium complexes. Furthermore, the single-crystal X-ray analysis of one of the bimetallic complexes of rubyrin shows a bowl-shaped symmetric structure where both Rh(I) atoms are projected above the mean rubyrin plane at an angle of 71.73 degrees. The geometry around each rhodium center is approximately square planar [N1-Rh1-N2, 80.38(9) degrees; C15-Rh1-C16, 86.95(14) degrees; N1-Rh1-C15, 97.13(12) degrees; and N2-RH1-C16, 94.97(12) degrees ]. The omicronbserved distance of 4.313 A between the two rhodium centers reveals very little interaction between the two rhodium atoms. This type of metal binding is accompanied by a 180 degrees ring flip of the heterocyclic ring connecting the two bipyrrole units. In dioxarubyrin, where one of the pyrrole rings of the bipyrrole unit is inverted, Rh(I) binds at the periphery to the pyrrole nitrogen, leaving the rubyrin cavity empty. The absence of one amino and one imino nitrogen on the dipyrromethene subunits in the sapphyrins and rubyrins described here forces Rh(I) to bind to bipyrrole nitrogens.     

Equilibrium and NMR Studies of Noncovalent Interactions in Binary Systems: Uridine,Adenosine, Cytidine and Thymidine,and Adenosine (or Cytidine) 5′-Monophosphate in Aqueous Solution

The molecular complex formation reactions of uridine (Urd) with adenosine (Ado), cytidine (Cyd), thymidine (Thd), adenosine 5-monophosphate (AMP) and cytidine 5-monophosphate (CMP) have been studied at 20°C. It was found that the main positive noncovalent centers of ion–dipole and dipole–dipole type interactions are the protonated N(3) atoms of Urd, whereas the negative centers are the endocyclic atoms of the bases characterized by high electron density from the second molecule involved in the reaction. Moreover, NMR results indicate the occurrence of stacking in the complex (Urd)H(Cyd), whereas in the complex, (Urd)H₂(Thd), it is the only type of interaction. Deprotonation of the latter species brings about a change in the character of the reaction and ion–dipole interactions have been detected in the adduct, (Urd)H(Thd). Interestingly, no involvement of the phosphate groups in the formation of AMP and CMP adducts has been evidenced and the main centers of the reactions were found to be the N(7)and N(1) atoms of AMP, or the N(3) atoms of CMP and Urd. Moreover, in the Urd/CMP system the NMR results suggest stacking-type interactions.     

The RhX n (X = S,Se, Te) Coordination Polyhedra in Crystal Structures

The Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres were applied to crystal-chemical analysis of all known compounds whose structures contain rhodium atoms surrounded by chalcogen atoms. The influence of the rhodium valence state and the nature of the chalcogen on the main features of Rh stereochemistry are discussed. Rhodium atoms exhibit coordination numbers of 6, 5, or 4 with respect to S, Se, or Te atoms; in addition to the bonds with chalcogens, rhodium can form 1 to 4 bonds with metal atoms. The VDP volume for Rh(III), Rh(2.67), and Rh(II) atoms in selenides and tellurides very weakly depends on the valence state, whereas in the case of sulfides, the volume increases rather regularly with a decrease in the metal oxidation number from Rh(III) to Rh(I).     

Complexes of Oxygenated trans-Azoalkanes and Tetracyanoethylene. The Interaction of pi Oxygen Dipoles with an Electron Poor Alkene

The N-oxide and N,N'-dioxide (1ao and 1ado) of trans-1,1'-azonorbornane (1) associate with TCNE in solution and in the solid state. The solution complexes are characterized by charge-transfer optical absorptions at lambda(m) 364 and 540 nm in CH(2)Cl(2) for 1ao/TCNE and 1ado/TCNE, respectively. These complexes are weakly bound, with K(f) values of 0.5-3.0 M(-)(1). Crystals of (1ao)(2)/TCNE and 1ado/TCNE are isolable, and their structures have been determined by X-ray diffraction. Local donor-acceptor (DA) interactions between the pi dipolar donors and the electron poor TCNE are found. Crystals of (1ao)(2)/TCNE are composed of discrete D-A-D triads in which the 1ao oxygen approaches one of the olefinic C atoms (C(1), 2.86 ?) of TCNE more closely than the other (C(2), 3.07 ?). The O-C(1)-C(2) angle is 87 degrees, and the azooxide molecular plane lies perpendicular to the molecular plane of TCNE. 1ado/TCNE crystals are composed of extended -D-A-D-A- strands in which both oxygen poles of the azodioxide simultaneously interact with alternate TCNE acceptors. The D-A geometry here is structurally analogous to that in the (1ao)(2)/TCNE crystal. PM3 calculations of 1:1 and 1:2 trans HN(O)NH(O)/TCNE complexes constrained to have D-A (O-C) distances of 2.88 ?, but which are otherwise geometry optimized, reproduce the DA topology observed in the crystalline samples.     

Understanding the acid-base properties of adenosine: the intrinsic basicities of N1, N3 and N7

Adenosine (Ado) can accept three protons, at N1, N3, and N7, to give H(3) (Ado)(3+) , and thus has three macro acidity constants. Unfortunately, these constants do not reflect the real basicity of the N sites due to internal repulsions, for example, between (N1)H(+) and (N7)H(+). However, these macroconstants are still needed for the evaluations and the first two are taken from our own earlier work, that is, pK(H)(H(3))((Ado)) = -4.02 and pK(H)(H(2))((Ado)) = -1.53; the third one was re-measured as pK(H)(H)((Ado)) = 3.64 ± 0.02 (25 °C; I=0.5 M, NaNO(3)), because it is the main basis for evaluating the intrinsic basicities of N7 and N3. Previously, contradicting results had been published for the micro acidity constant of the (N7)H(+) site; this constant has now been determined in an unequivocal manner, and that of the (N3)H(+) site was obtained for the first time. The micro acidity constants, which describe the release of a proton from an (N)H(+) site under conditions for which the other nitrogen atoms are free and do not carry a proton, decrease in the order pk(N7-N1)(N7(Ado)N1·H)) = 3.63 ± 0.02 > pk(N7-N1)(H·N7(Ado)N1) = 2.15 ± 0.15 > pk(N3-N1,N7)(H·N3(Ado)N1,N7) =1.5 ± 0.3, reflecting the decreasing basicity of the various nitrogen atoms, that is, N1>N7>N3. Application of the above-mentioned microconstants allows one to calculate the percentages (formation degrees) of the tautomers formed for monoprotonated adenosine, H(Ado)(+) , in aqueous solution; the results are 96.1, 3.2, and 0.7% for N7(Ado)N1·H(+), (+)H·N7(Ado)N1, and (+)H·N3(Ado)N1,N7, respectively. These results are in excellent agreement with theoretical DFT calculations. Evidently, H(Ado)(+) exists to the largest part as N7(Ado)N1·H(+) having the proton located at N1; the two other tautomers are minority species, but they still form. These results are not only meaningful for adenosine itself, but are also of relevance for nucleic acids and adenine nucleotides, as they help to understand their metal ion-binding properties; these aspects are briefly discussed.     

Effectiveness of Phosphate Groups in Noncovalent Interactions in Binary Adenosine Nucleotides/Phosphoserine Aqueous Systems

Adduct formation in binary systems of O-phospho-L-serine (Ser-P) with adenosine 5′-monophosphate (AMP), adenosine 5′-diphosphate (ADP) and adenosine 5′-triphosphate (ATP), has been investigated. This study was performed in aqueous solutions using a potentiometric method with computer analysis of the data, together with ¹³C and ³¹P NMR spectroscopic measurements. The overall stability constants of the adducts and the equilibrium constants for their formation have been determined. Ion-dipole and ion-ion interactions have been established to occur in the identified noncovalent complexes. An analysis of the equilibrium constants of the reaction has allowed the determination of the effectiveness of the phosphate groups and donor atoms of heterocyclic rings for molecular complex formation. The potential reaction centers are the atoms N(1) and N(7) from the purine base, the phosphate group of the nucleotides, and the phosphate, carboxyl and amine groups from phosphorylated serine. Sites for the interactions in the bioligands have been found on the basis of an equilibrium constant study and an analysis of the changes in the signal positions of their NMR spectra.     

Synthesis,spectroscopy and structure of cis,cis,trans:N,N;P,P;S,S-[bis(triphenylphosphine)] [bis(pyrimidine-2-thiolato)]ruthenium(II)

Reaction of RuCl₂(PPh₃)₃with pyrimidine-2-thione (HpymS) in a 1:2?mol ratio in dry benzene in the presence of triethylamine as base yielded a complex of stoichiometry [Ru(pymS)₂(PPh₃)₂] (1). This has been characterized using analytical data and IR, ¹H, ¹³C and ³¹P NMR spectroscopy. ¹H NMR confirmed the deprotonation of HpymS. ³¹P NMR spectra showed a single peak confirming equivalent P atoms. Complex 1 crystallizes in space group Pī and HpymS acts as a η²-N,S-deprotonated bidentate anionic ligand. The coordination geometry around the Ru center is distorted octahedral with cis dispositions of P atoms, as well as two N atoms of pymS^– and trans S atoms of pymS^–. Important bond distances and angles are: Ru–N, 2.119(2), 2.106(2); Ru–S, 2.4256(8), 2.4413(8); and Ru–P, 2.3266(7), 2.3167(7)?Å; P(2)–Ru(1)–P(1), 96.07(3); N(21)–Ru(1)–N(11), 83.46(9); and S(1)–Ru(1)–S(2), 153.02(3)°.     

Exploring the Reactivity of Rh<Subscript>2</Subscript> (OAc)<Subscript>4</Subscript> with 2, 2′ -Dipyridylamine

A series of three new compounds obtained from the reaction of Rh₂(OAc)₄ and 2, 2 -dipyridylamine (Hdpa) under various conditions have been characterized. All are diamagnetic and have a Rh–Rh single bond. In Rh₂(dpa)₄, 1, there are four bridging dpa anions which bind the two Rh atoms through one pyridyl N atom and one amido N atom though two of these ligands interact further with a rhodium atom through the third N atom. In the other two compounds the Hdpa ligand is neutral. Thus Rh₂(OAc)₄(Hdpa)₂, 2, is an adduct of the well known complex dirhodium tetraacetate in which the two Hdpa ligands occupy axial positions. In the third compound, Rh₂(Hdpa)₂(OAc)₂Cl₂, 3, only two acetate bridges are present. One Hdpa molecule chelates equatorially each rhodium atom and the chloride ions are axially coordinated. The Rh–Rh distances are 2. 4005(6) and 2. 4042(8) Å for 1 and 2, respectively. For 3, the Rh–Rh distance of 2. 593(1) Å is significantly longer than those in 1 and 2 because of the presence of fewer bridging ligands.     

Structure, magnetic properties and Sn Mössbauer spectroscopy of PrRhSn

PrRhSn was synthesized in polycrystalline form by a reaction of praseodymium, rhodium, and tin in an arc-melting furnace. The sample was investigated by powder and single crystal X-ray diffraction: ZrNiAl type, space group a=742.49(7), c=415.05(5) pm, wR₂=0.0737, 353F² values and 14 variables. The PrRhSn structure has two crystallographically independent rhodium sites with a tricapped trigonal prismatic coordination, i.e. [Rh1Sn₃Pr₆] and [Rh2Sn₆Pr₃]. The rhodium and tin atoms build up a three-dimensional [RhSn] network with short Rh-Sn contacts (278 and 285 pm), in which the praseodymium atoms fill distorted hexagonal channels. The magnetic and electronic properties of PrRhSn have been studied by means of AC and DC magnetic susceptibility measurements as well as ¹¹⁹Sn Mössbauer spectroscopy. A transition from a paramagnetic to a ferromagnetic state was found at .     

Studies of the hydrated complexes of NiBr2 with adenosine

Summary Hydrated complexes of NiBr₂ with adenosine have been obtained and the thermal dehydration process thereof investigated. Changes in the coordination sphere have been studied. In a majority of the salts, Ni^II ions are six-coordinate, and adenosine molecules are bonded to Ni^II through the N(7) atom. In only one salt does the adenosine molecule formed a bridge: through the N(7) and N(3) atoms. Water molecules are bonded directly to Ni^II andvia hydrogen bonds. Anions are bonded to the metal ion in terminal positions.     

Chemical conversions of rhodium selenochloride Rh<Subscript>2</Subscript>Se<Subscript>9</Subscript>Cl<Subscript>6</Subscript>

Rhodium selenochloride Rh₂Se₉Cl₆ (1) reacts with aqueous solutions of KCN and CsCl and 4-cyanopyridine (4-CNPy) to give complexes KCs₂Rh(CN)₆ (2) and RhCl₃(4-CNPy)₃ (3). According to X-ray diffraction data, 2 and 3 have mononuclear structures in which the rhodium atoms are in the oxidation state III and six-coordinate environment. Reactions 1 with CN-containing ligands lead to complete displacement of selenium-containing ligands from the rhodium coordination sphere.     

4-硝基邻苯二硫酚金属镍配合物的合成、结构和性质

合成了4-硝基邻苯二硫酚配体及相应金属镍配合物，(Bu₄N)₂[Ni(nbdt)₂] (1)和(Bu₄N)[Ni(nbdt)₂] (2)(nbdt=4-硝基邻苯二硫酚阴离子), 并通过X-射线单晶结构测定、循环伏安、ESR谱、紫外可见吸收光谱和变温磁化率实验对其结构和性质进行了表征。这两个化合物均为略有变形的平面四方型配合物。配合物2是由配合物1通过I₂氧化制备。配合物2含有一个未成对电子，磁性研究表明由于分子间的自旋耦合使它表现为反铁磁性。     

Use of 13C as an indirect tag in 15N specifically labeled nucleosides. Syntheses of [8-13C-1,7,NH2-15N3]adenosine, -guanosine, and their deoxy analogues

We have previously reported the use of a 13C tag at the C2 of 15N-multilabeled purine nucleosides to distinguish the adjacent-labeled 15N atoms from those in an untagged nucleoside. We now introduce the use of an indirect tag at the C8 of 15N7-labeled purine nucleosides. This tag allows unambiguous differentiation between a pair of 15N7-labeled purines in which only one is 13C8 labeled. Although the very small C8-N7 coupling (<1 Hz) precludes its direct detection in 1D 15N spectra, 2D 1H-15N NMR experiments display the large C8-H8 coupling (>200 Hz) because H8 is coupled to both N7 and C8. The 13C8 atom is introduced by means of a ring closure of the exocyclic amino groups of a pyrimidinone using [13C]sodium ethyl xanthate. Here, we present methods for the syntheses of [8-13C-1,7,NH2-15N3]adenosine, -guanosine, and their deoxy analogues.     

Sur la non-equivalence des liaisons CH du groupement methyle dans les complexes cristallises de trans-bromotetracarbonyle methyle carbyne de chrome

The syntheses, ³¹P{¹H} NMR spectra, and a structure of “mixed” 1,5-cyclo-octadienebis(tertiary phosphine)dirhodium complexes possess a rhodiumrhodium bond, briding diphenylphosphido and two different stereochemistries around the rhodium atoms. One rhodium is tetrahedral and surrounded by four phosphorus atoms and the other rhodium (bonded to COD) is nearly planar.     

由氢键连接的三个金属-有机网状化合物的合成、结构及半导体性质

以2,4,6-三(1-吡唑基)-1,3,5-三嗪(TPTz)与不同金属离子进行溶剂热反应,得到了3个氢键连接的金属-有机网状化合物。实验发现TPTz的水解产物6-(1-吡唑基)-1,3,5-三嗪-2,4-二酚(H₂L)在反应中起到了实际的配位作用。单晶结构分析表明,它们是同构化合物,分子式为[M(HL)₂]·2H₂O(M=Zn,1;Co,2;Mn,3)。每个中心金属原子分别与2个吡唑基上的N、2个吡嗪环上的N和2个水分子中的O形成六配位的结构。2个HL-与1个中心金属配位形成一个零维的金属-有机配合物小分子,这些小分子通过氢键连接进一步拓展为二维层状结构。紫外-可见漫反射(UV-VisDRS)分析结果表明,这3种化合物都是宽系半导体材料,其带隙宽度分别为3.80(Zn),3.30(Co),3.27(Mn)eV,其半导体性质同中心金属原子表现出明显的相关性。