Dinuclear complexes with a μ-cyano ligand. Part X. Synthesis and characterization of several derivatives of cis-diaquaamminecobalt(III) complexes. Influence of pH

Six new dinuclear complexes, derived from cis-[Co(H₂O)₂(NH₃)₄]³⁺, cis-[Co(H₂O)₂(en)₂]³⁺ and [M(CN)₄^2? (M = Ni, Pd, Pt) were prepared and characterized by means of chemical analysis, electronic and IR measurements. The influence of the pH on the rate of the reaction was studied for the two derivatives of [Pd(CN)₄]^2?, showing that the best conditions to obtain the dinuclear compounds are at pH near 6, where the predominant species are cis-[Co(OH)(H₂O)(amine)₂]²⁺. The [Pt(CN)₄]^2? derivatives show PtPt interactions both in the solid state and in solution.     

Steric effects, solvent effects, and turnover in hydrolytic cleavage of peptides promoted by palladium(II) aqua complexes

 Dipeptides and tripeptides AcMet-aaH containing N-acetyl methionine, in which the group aaH is GlyH, AlaH, ValH, or Gly-GlyH, undergo hydrolytic cleavage of the Met-aaH peptide bond in the presence of the following complexes of palladium(II): cis-[Pd(en)(H₂O)₂]²⁺, cis-[Pd(tn)(H₂O)₂]²⁺, cis-[Pd(en)(CH₃OH)₂]²⁺, cis-[Pd(S,N-MetH)(H₂O)₂]²⁺, cis-[Pd(S,N-Met-GlyH)(H₂O)₂]²⁺, and cis-[Pd(S,N-Met-AlaH)(H₂O)₂]²⁺. These mononuclear complexes are precursors of binuclear palladium(II) complexes containing the substrates AcMet-aaH as bridging thioether ligands. The rate constant for cleavage is higher when the bidentate ligand in the precursor complex is ethylenediamine (which is completely displaced) than S,N-methionine (of which only the amino group is displaced), because the number of aqua ligands available for cleavage is greater in the former than in the latter case. The demonstrated dependence of the rate constant on the steric bulk (volume) of the leaving group, aaH, points the way toward achieving a degree of sequence selectivity in cleavage of peptide bonds by palladium(II) aqua complexes. One equivalent of cis-[Pd(en)(H₂O)₂]²⁺ cleaves as many as ten equivalents of AcMet-GlyH, but the rate constant decreases as the molar excess of the dipeptide over the catalyst increases. This demonstration of catalytic turnover points the way to our ultimate goal – artificial metallopeptidases. Received: 13 June 1997 / Accepted: 24 September 1997     

Reaction of platinum(II) diamine and triamine complexes with selenomethionine

We have reacted [Pt(dien)Cl]Cl, [Pt(en)(D₂O)₂]²⁺, and [Pt(Me₄en)(D₂O)₂]²⁺ [Me₄en = N,N,N′,N′-tetramethylethylenediamine] with selenomethionine (SeMet). When [Pt(dien)Cl]Cl is reacted with SeMet, [Pt(dien)(SeMet-Se)]²⁺ is formed; two Se-CH₃ resonances are observed due to the different chiralities at the Se atom upon platination. In a reaction of [Pt(dien)Cl]Cl with an equimolar mixture of SeMet and Met, the SeMet product forms more quickly though a slow equilibrium with approximately equal amounts of both products is reached. [Pt(Me₄en)(D₂O)₂]²⁺ reacts with SeMet to form [Pt(Me₄en)(SeMet-Se)(D₂O)]²⁺ initially but forms [Pt(Me₄en)(SeMet-Se,N)]⁺ ultimately. One stereoisomer of the chelate, assigned to the R chirality at the Se atom, dominates within the first few minutes of reaction. [Pt(en)(D₂O)₂]²⁺ forms a variety of products depending on reaction stoichiometry; when one equivalent or less of SeMet is added, the dominant product is [Pt(en)(SeMet-Se,N)]⁺. In the presence of excess SeMet, [Pt(en)(SeMet-Se)₂]²⁺ is the dominant initially, but displacement of the en ligand occurs leading to [Pt(SeMet-Se,N)₂] as the eventual product. Displacement of the en ligand from [Pt(en)(SeMet-Se,N)]⁺ does not occur. In reactions of K₂PtCl₄ with two equivalents of SeMet, [Pt(SeMet-Se,N)₂] is formed, and three sets of resonances are observed due to different chiralities at the Se atoms. Only the cis geometric isomers are observed by ¹H and ¹⁹⁵Pt NMR spectroscopy.     

Hydrolysis of the amide bond in methionine-containing peptides catalyzed by various palladium(II) complexes: Dependence of the hydrolysis rate on the steric bulk of the catalyst

¹H NMR spectroscopy was applied to study the reactions of cis-[Pd(L)(H₂O)₂]²⁺ complexes (L is en, pic and dpa) with the N-acetylated tripeptides L-methionylglycylglycine, MeCOMet–Gly–Gly, and glycyl–L-methionyl–glycine, MeCOGly–Met–Gly. All reactions were performed in the pH range 2.0–2.5 with equimolar amounts of the cis-[Pd(L)(H₂O)₂]²⁺ complex and the tripeptide at 60 °C. The hydrolytic reactions of the cis-[Pd(en)(H₂O)₂]²⁺, cis-[Pd(pic)(H₂O)₂]²⁺ and cis-[Pd(dpa)(H₂O)₂]²⁺ complexes with MeCOMet–Gly–Gly were regioselective and only the amide bond involving the carboxylic group of methionine was cleaved. However, in the reactions of these three Pd(II) complexes with MeCOGly–Met–Gly, two amide bonds, Met–Gly and MeCO–Gly, were cleaved. From UV–Vis spectrophotometry studies, it was found that the rate-determining step of these hydrolytic reactions is the monodentate coordination of the corresponding Pd(II) complex to the sulfur atom of the methionine side chain. The rate of the cleavage of these amide bonds is dependent on the nature of the bidentate coordinated diamine ligand L (en > pic > dpa). The hydrolytic reaction of cis-[Pd(L)(H₂O)₂]²⁺-type complexes with MeCOMet–Gly–Gly, containing the methionine side chain in the terminal position of the peptide, is regioselective while in the reaction of these Pd(II) complexes with MeCOGly–Met–Gly, none selective cleavage of the peptide occurs. This study contributes to a better understanding of the selective cleavage of methionine-containing peptides employing palladium(II) complexes as catalysts.     

Copper(II) PMDTA and copper(II) TMEDA complexes: precursors for the synthesis of dinuclear dicationic copper(II) complexes

Copper(II) cations coordinated with PMDTA (pentamethyldiethylenetriamine) and TMEDA (tetramethylethylenediamine) possess a high synthetic potential. The synthesis of these cations was carried out by metathesis reactions with silver salts. The cationic copper(II) complexes, [Cu(PMDTA)(Me₂CO)Cl]⁺, [Cu(PMDTA)(H₂O)Cl]⁺, [Cu(PMDTA)(DMF)]⁺, [Cu(PMDTA)Cl]⁺, [Cu(PMDTA)OAc]⁺, [Cu(PMDTA)(MeCN)₂]²⁺, [Cu₂(TMEDA)₂Cl₃]⁺ and [Cu(TMEDA)(MeCN)₃]²⁺ were synthesised as PF₆ salts, crystallised and characterised by single-crystal X-ray diffraction.     

Metal(II) complexes of 1-formylisoquinoline thiosemicarbazone: their preparation,characterization and antitumour activity

Complexes of Co(II), Ni(lI), Cu(II), Zn(II) and Pt(II) with 1-formylisoquinoline thiosemicarbazone (1-iqtsc-H) were prepared and characterized by elemental analyses, conductance measurement and spectral studies. On the basis of these studies a distorted octahedral structure for [Co(1-iqtsc)₂]·2H₂O, a distorted trigonal-bipyramidal structure for [Ni- (1-iqtsc-H)Cl₂], [Cu(1-iqtsc-H)Cl₂] and [Zn(1-iqtsc- H)(OAc)₂]·H₂O and a square-planar structure for [Pt(1-iqtsc)Cl] are suggested. All these metal(II) complexes were screened for their antitumour activity in the P388 lymphocytic leukaemia test system in mice. Except for Pt(Il), the complexes were found to possess significant activity; the Ni(II) complex showed a T/C value of 161 at the optimum dosage.     

Synthesis and spectral investigation of manganese(II), cadmium(II) and oxovanadium(IV) complexes with 2,6-diacetylpyridine bis(2-aminobenzoylhydrazone): Crystal structure of manganese(II) and cadmium(II) complexes

The chelating behavior of 2,6-diacetylpyridine bis(2-aminobenzoylhydrazone) (H₂dapa) towards manganese(II), cadmium(II) and oxovanadium(IV) ions has been studied by elemental analyses, conductance measurements, magnetic properties and spectral (IR, ¹H NMR, UV-Vis and EPR) studies. The IR spectral studies suggest the pentadentate nature of the ligand with pyridine nitrogen, two azomethine nitrogens and two carbonyl oxygen atoms as the ligating sites. Six coordinate structure for [VO(H₂dapa)]SO₄ · H₂O and seven coordinate structures for [Mn(H₂dapa)(Cl)(H₂O)]Cl · 2H₂O and [Cd(H₂dapa)Cl₂] · H₂O complexes have been proposed. Pentagonal bipyramidal geometry for [Mn(H₂dapa)(Cl)(H₂O)]Cl · 2H₂O and [Cd(H₂dapa)(Cl₂)] · H₂O complexes was confirmed by single crystal analysis. The X-band EPR spectra of the oxovanadium(IV) and manganese(II) complexes in the polycrystalline state at room (300 K) and also at liquid nitrogen temperature (77 K) were recorded and their salient features are reported.     

Theoretical Studies on α-Helix—DNA Interactions

Abstract

The ¹H NMR relaxation effects produced by paramagnetic Cr(III) complexes on nucleoside 5′-mono- and -triphosphates in D₂O solution at Ph′=3 were measured. The paramagnetic probes were [Cr(III)(H₂O) ₆]³⁺, [Cr(III)(H₂O)₃ (HATP)], [Cr(III)(H₂O)₃(HCTP)] and [Cr(III) (H₂O)₃(UTP)^?, while the matrix nucleotides (0.1 M) were H₂AMP, HIMP^?, and H₂ATP^2-. For the aromatic base protons, the ratios of the transverse to longitudinal paramagnetic relaxation rates (R_2p/R_1p) for the [Cr(III)(H₂O)₆]³⁺/H₂ATP^2-, [Cr(III)(H₂O)₃(HATP)]/H₂ATP^2-, [Cr(III)(H₂O)₃(HCTP)]/H₂ATP² and [Cr(III)(H₂O)₃(UTP)]^?/H₂ATP² systems were below 2.33 so the dipolar term predominates. For a given nucleotide, R_1p for the purine H(8) signal was larger than for the H(2) signal with the [Cr(III)(H₂O)₆]³⁺ probe, while R_1p for the H(2) signal was larger with all the other Cr(III) probes. Molecular mechanics computations on the [Cr(III)(H₂O)₄(HPP)(α,β)], [Cr(III)(NH₃)₄(HPP)(α,β)], [Co(III)(NH₃)₃(H₂PPP)(α,βγ)] and [Co(III)(NH₃)₄(HPP)(α,β)] complexes gave calculated energy-minimized geometries in good agreement with those reported in crystal structures. The molecular mechanics force constants found were then used to calculate the geometry of the inner sphere [Cr(III)(H₂O)₆]³⁺ and [Cr(III)(H₂O)₃(HATP)(α,βγ)] complexes as well as the structures of the outer sphere [Cr(III) (H₂O)₆]³⁺-(H₂AMP) and [Cr(III)(H₂O)₆]-(HIMP)^? species. The gas-phase structure of the [Cr(III)(H₂O)₃(HATP)(α,βγ)] complex shows the existence of a hydrogen bond interaction between a water ligand and the adenine N(7) (O…N = 2.82 Å). The structure is also stabilized by intramolecular hydrogen bonds involving the -O(2′)H group and the adenine N(3) (O…N = 2.80 Å) as well as phosphate oxygen atoms and a water molecule (O…O = 2.47 Å). The metal center has an almost regular octahedral coordination geometry.

The structures of the two outer-sphere species reveal that the phosphate group interacts strongly with the hexa-aquochromium probe. In both complexes, the nucleotides have a similar “anti” conformation around the N(9)-C(l′) glycosidic bond. However, a very important difference characterizes the two structures. For the (HIMP)^? complex, strong hydrogen bond interactions exist between one and two water ligands and the inosine N(7) and O(6) atoms, respectively (O…O = 2.63 Å O…N = 2.72, 2.70 Å). For the H₂AMP complex, the [Cr(III) (H₂O)c]³⁺ cation does not interact with N(7) since it is far from the purine system. Hydrogen bonds occur between water ligands and phosphate oxygens. The Cr-H(8) and Cr-H(2) distances revealed by the energy-minimized geometries for the two outer sphere species were used to calculate the R_1p values for the H(8) and H(2) signals for comparison with the observed R_1p values: 0.92(c), 1.04(ob) (H(8)) and 0.06(c), 0.35(ob) (H(2)) for H₂AMP; and 3.76(c), 4.53(ob) (H(8)) and 0.16(c), 0.77(ob) s^?1 (H(2)) for HIMP^?. These results suggest that the dynamic relaxation effects can be only partially understood with molecular mechanics computations, although the success of the geometry calculations suggests that future efforts in the development of computational methods are justified.     

A Study of the Interaction of Cr(III) Complexes and Their Selective Binding with B-DNA: A Molecular Modeling Approach

Abstract

Molecular modeling and energy minimisation calculations have been used to investigate the interaction of chromium(III) complexes in different ligand environments with various sequences of B-DNA. The complexes are [Cr(salen)(H₂O)₂]⁺; salen denotes 1, 2 bis-salicylideneaminoethane, [Cr(salprn)(H₂O)₂]⁺; salprn denotes 1, 3 bis- salicylideneamino-propane, [Cr(phen)₃]³⁺; phen denotes 1, 10 phenanthroline and [Cr(en)₃]³⁺; en denotes eth- ylenediamine. All the chromium(III) complexes are interacted with the minor groove and major groove of d(AT)₁₂, d(CGCGAATTCGCG)₂ and d(GC)₁₂ sequences of DNA. The binding energy and hydrogen bond parameters of DNA-Cr complex adduct in both the groove have been determined using molecular mechanics approach. The binding energy and formation of hydrogen bonds between chromium(III) complex and DNA has shown that all complexes of chromium(III) prefer minor groove interaction as the favourable binding mode.     

Theoretical Study of the Water Exchange Reaction on Divalent Zinc Ion using Density Functional Theory

Recent ab initio studies reported in the literature have challenged the mechanistic assignments made on the basis of volume of activation data [1,2]. In addition to that ab initio molecular orbital calculations on hydrated zinc(II)-ions were used to elucidate the general role of this ion in metalloproteins [3]. Due to our interest in both inorganic reaction mechanisms and enzymatic catalysis we started a systematic investigation of solvent exchange processes on divalent zinc-ion using density functional calculations. Our investigations cover aqua complexes of the general form [Zn(H₂O)_n]²⁺·mH₂0 with n=3-6 and m=0-2, where n and m represent the number of water molecules in the coordination and solvation sphere, respectively.The complexes [Zn(H₂O)₅]²⁺·2H₂O and [Zn(H₂O)₄]²⁺·2H₂O turnend out to be the most stable zinc complexes with seven and six water molecules, respectively. This implies that a heptacoordinated zinc(II) complex, where all water molecules are located in the co-ordination sphere, should be energetically highly unfavorable and that [Zn(H₂O)₆]²⁺ can quite readily push two coordinated water molecules into the solvation sphere. For the pentaqua complex [Zn(H₂O)₅]²⁺ only one water molecule is easily lost to the solvation sphere, which makes the [Zn(H2O)₄]²⁺·H₂O complex the most favorable in order to consider the limiting dissociative and associative water exchange process of hexacoordinated zinc(II). The dehydration and hydration energies using the most stable zinc(II) complexes [Zn(H₂O)₄]²⁺·2H₂O, [Zn(H₂O)₅]²⁺·2H₂O and [Zn(H₂O)₄]²⁺·H₂O were calculated to be 24.1 and -21.0 kcal/mol, respectively.     

Different coordination modes of Hdipic and dipic ligands to nickel(II) ions in a same environment (dipic = 2,6-pyridinedicarboxylate, dipicolinate)

Two new nickel(II) complexes of the composition [Ni(cyclam)(Hdipic)₂] · 2H₂O (1) and [Ni(cyclam)(H₂O)₂][Ni(dipic)₂] · 2.5H₂O (2) (cyclam = 1,4,8,11-tetraazacyclotetradecane) have been prepared and structurally characterized by a combination of analytical, spectroscopic, thermogravimetric, and crystallographic methods. The structure of 1 shows that the central nickel(II) ion is coordinated axially by two monodentate Hdipic ligands. The discrete neutral complex 1 further extends its structure by hydrogen bonding interactions to form a one-dimensional supramolecule. The structure of 2 consists of two independent nickel(II) centers. Water molecules instead of dipic ligands prefer to coordinate to the Ni1 ion forming a divalent cation [Ni(cyclam)(H₂O)₂]²⁺. Two dipic ligands coordinate to the second Ni2 ion forming a divalent anion [Ni(dipic)₂]²⁻. The divalent cations and anions are charge-balanced, resulting in a molecular salt. The divalent cations and anions are interconnected by multiple types of hydrogen bonding interactions.     

Study of Pt(II)-cyclic amines complexes of the types cis- and trans-Pt(amine)2I2 and cis- and trans-Pt(amine)2(NO3)2 and their aqueous products by

Complexes of the types cis- and trans-Pt(amine)₂I₂ containing cyclic amines were synthesized and studied mainly by IR and multinuclear NMR spectroscopies. The compounds were converted to cis- and trans-Pt(amine)₂(NO₃)₂, which were also investigated. The hydrolysis and the aquation reactions of the latter compounds were then studied in D₂O in different conditions of pH. In acidic medium, the aqueous product is [Pt(amine)₂(D₂O)₂]²⁺ and for a few amines, [Pt(amine)₂(D₂O)(NO₃)]⁺ was detected. In basic pH, the main product is Pt(amine)₂(OD)₂ and Pt(amine)₂(OD)(NO₃) was detected for several compounds. In neutral pH, the cis isomers form between two and four species in fresh solutions. The most shielded species in ¹⁹⁵Pt NMR is the monoaqua-monohydroxo complex cis-[Pt(amine)₂(D₂O)(OD)]⁺ and the less shielded compound is the dihydroxo-bridged dimer [Pt(amine)₂(μ-OD)₂Pt(amine)₂]²⁺, which were observed for all the compounds. For a few amines, the monohydroxo-bridged dimer [Pt(D₂O)(amine)₂(μ-OD)Pt(OD)(amine)₂]²⁺ was detected and for cyclohexylamine, a fourth signal was assigned to a cyclic hydroxo-bridged trimer [(Pt(amine)₂(μ-OD))₃]³⁺. ¹⁹⁵Pt NMR spectroscopy has shown that the concentration of the monomer decreases with time, while the concentration of the dimers increases. Only one product was observed for the trans isomers in neutral pH. The signal was assigned to the monoaqua-monohydroxo species trans-[Pt(amine)₂(D₂O)(OD)]⁺. The ¹³C and ¹H NMR spectra of most of the complexes were measured. All the coupling constants ^2,3J(¹⁹⁵Pt-¹H) and ^2,3J(¹⁹⁵Pt-¹³C) are larger in the cis compounds than in the trans isomers.     

Reduction of pentaamminenitrocobalt(III) by hexaaquachromium(II) ion. Reinvestigation of the mechanism

Products of the reduction of [CoNO₂(NH₃)₅]²⁺ by Cr²⁺ were separated and identified under the conditions of [Cr²⁺]₀/[Co(IlI)]₀⩽3 and 0.02 M ⩽[H⁺] ⩽ 0.75 M. The product distribution was dependent on both [Cr²⁺]_o and [H⁺]. The following mechanism is proposed: [CoNO₂(NH₃)₅]²⁺ + Cr²⁺→Co²⁺ + [CrONO(H₂O)₅]²⁺ (i) [CrONO(H₂O)₅]²⁺ + H⁺→[Cr(H₂O)₆]³⁺ + HNO₂ (ii) [CrONO(H₂O)₅]²⁺ + Cr²⁺→Cr(IV) + [CrNO(H₂O)₅]²⁺ (iii) Cr(IV) + Cr²⁺→[(H₂O)₄Cr(OH)₂Cr(H₂O)₄]⁴⁺ (iv) HNO₂ + 2Cr²⁺→[Cr(H₂O)₆]³⁺ + [CrNO(H₂O)₅]²⁺ (v)     

Binding of palladium(II) complexes to guanine, guanosine or guanosine 5-monophosphate in aqueous solution: potentiometric and NMR studies

The interaction of guanine, guanosine or 5^′-GMP (guanosine 5^′-monophosphate) with [Pd(en)(H₂O)₂](NO₃)₂ and [Pd(dapol)(H₂O)₂](NO₃)₂, where en is ethylenediamine and dapol is 2-hydroxy-1,3-propanediamine, were studied by UV-Vis, pH titration and ¹H NMR. The pH titration data show that both N1 and N7 can coordinate to [Pd(en)(H₂O)₂]²⁺ or [Pd(dapol)(H₂O)₂]²⁺. The pK_a of N1-H decreased to 3.7 upon coordination in guanosine and 5^′-GMP complexes, which is significantly lower than that of ∼9.3 in the free ligand. In strongly acidic solution where N1-H is still protonated, only N7 coordinates to the metal ion, but as the pH increases to pH ∼3, ¹H NMR shows that both N7-only and N1-only coordinated species exist. At pH 4-5, both N1-only and N1,N7-bridged coordination to Pd(II) complexes are found for guanosine and 5^′-GMP. The latter form cyclic tetrameric complexes, [Pd(diamine)(μ-N1,N7-Guo]₄⁴⁺ and [Pd(diamine)(μ-N1,N7-5^′-GMP)]₄H_x^(4−x)−, (x=2,1, or 0) with either [Pd(en)(H₂O)₂](NO₃)₂ or [Pd(dapol)(H₂O)₂](NO₃)₂. The pH titration data and ¹H NMR data agree well with the exception that the species distribution diagrams show the initial formation of the N1-only and N1,N7-bridged complexes to occur at somewhat higher pH than do the NMR data. This is due to a concentration difference in the two sets of data.     

Cobalt(III)-promoted hydrolysis of atp

The rate of phosphate hydrolysis of ATP in the substitution-inert complex Co(NH₃)₄ATP-has been examined in the presence and absence of [Co(cyclen)(H₂O)₂]³⁺. The rate of hydrolysis of Co(NH₃)₄ATP- in the absence of [Co(cyclen)(H₂O)₂]³⁺ is essentially independent of pH in the range 6.0 to 9.0, and the rate constant is 2.6 × 10^?5 sec ^?1 at pH 9.0, 40°C, and 1.0 M ionic strength Rate constants for the hydrolysis of Co(NH₃)₄ATP- in the presence of [Co(cyclen)(H₂O)₂]³⁺ are sharply dependent upon pH in the same range. The rate constants at pH 8.0, 8.6, and 9.0 are 8, 63, and 95 times larger than the rate constant at pH 7.0. At pH 9 the rate constant is 1.2 × 10^?3 sec^?1 for 16 mM Co(NH₃)₄ATP- in the presence of 10 mM [Co(cyclen)(H₂O)₂]³⁺. The proposed mechanism for hydrolysis involves the coordination of a phosphate group of Co(NH₃)₄ATP- by [Co(cyclen)(H₂O)₂]³⁺ to form a dinuclear species, followed by internal attack of coordinated hydroxide on the phosphate chain.     

A new synthetic route towards heterotrimetallic complexes. Synthesis, crystal structure and magnetic properties of a [CuMnCr] trinuclear complex

The heterotrimetallic complex, [{LCuMn(H₂O)}{Cr(phen)(C₂O₄)₂}](ClO₄) · H₂O (1), has been obtained by assembling heterobinuclear cations, [LCuMn]²⁺, with [Cr(phen)(C₂O₄)₂]⁻ ions (H₂L is the compartmental Schiff-base resulting from the stepwise condensation of 2,6-diformyl-p-cresol with ethylenediamine and diethylenetriamine). The copper(II) and manganese(II) ions are hosted into the compartments of the macrocyclic ligand. [Cr(phen)(C₂O₄)₂]⁻ acts as a ligand, being coordinated through one oxalato oxygen atom to the apical position of the square pyramidal copper(II) ion. The cryomagnetic investigation of 1 reveals an antiferromagnetic interaction between Cu^II and Mn^II within the compartmental ligand (J = −39 cm⁻¹). The interaction between Cu^II and Cr^III across the oxalato bridge is negligible. The crystal structure of [LCuPb](ClO₄)₂ · H₂O, a useful precursor in obtaining 3d-3d′ complexes, is also reported.     

Four coordination polymers constructed from a multicarboxylate ligand and metal centers various from Ba, Cu, Zn to Gd: Syntheses, crystal structures and properties

Hydrothermal reactions between H₄ODPA (2,2′,3,3′-oxydiphthalic acid) and metal ion salts of Ba²⁺, Cu²⁺, Zn²⁺ and Gd³⁺ afford four novel coordination polymers [Ba(H₂ODPA)(H₂O)₄] · H₂O (1), [Cu₂(ODPA)(H₂O)₃] · H₂O (2), Zn₂(ODPA)(H₂O)₂ (3) and [Gd(HODPA)(H₂O)_3.5] · H₂O (4), accordingly. These polymers show great differences in regard to their structures and properties originated from the variation of size and coordination geometry of the metal ions. Compound 1 presents puckered achiral layer structure with (4.8²) topology with helices, 2 has a 6³ topology with copper tetramer as SBUs, 3 has chiral layer with two kinds of helices built up from Zn-binuclear “paddle-wheel” like SBUs, and 4 features a simple 1D helix with opposite chirality. Compound 3 shows obvious fluorescent emissions upon excitation. Compound 2 shows ferromagnetic interactions between Cu^II centers bridged by carboxylate groups, whereas compound 4 presents weak ferromagnetic interaction between Gd^III ions.     

Four novel polytungstate compounds built up of paradodecatungstate clusters and transition-metal complexes/transition metal: Synthesis, structure, and electrochemical properties

A series of novel polytungstates, [{Cu(bim)(H₂O)₂}₄(H₄W₁₂O₄₂)]·14H₂O 1, (Himi)₆[{Mn(imi)(H₂O)}(H₄W₁₂O₄₂)]·2H₂O 2, [{Cu_0.5(H₂O)}₂{Cu_0.5(H₂O)₂}₂{Cu (bim)(H₂O)₂}₂(H₄W₁₂O₄₂)]·10H₂O 3 and [{Na(H₂O)₄}₂{Cu_0.5(H₂O)}₄{Cu_0.5 (H₂O)_1.5}₂(H₄W₁₂O₄₂)]·3H₂O 4 (imi = imidazole; bim = 2,2′-biimidazole), have been obtained by the routine synthetic reactions in aqueous solution and characterized by IR, X-ray powder diffraction, UV, elemental analysis, TG and X-ray single-crystal diffraction. All the compounds contain the [H₄W₁₂O₄₂]⁸⁻ polyanions as building units. Compound 1 is isolated structure, which is modified with four {Cu(bim)(H₂O)₂}²⁺ fragments. The compound 2 exhibits an infinite 1D “wave-like” chain based on the interaction between the [H₄W₁₂O₄₂]⁸⁻ polyanion and [Mn(imi)(H₂O)]²⁺ complex. The 2D layered structure of the compound 3 is formed by the interconnection 1D [{Cu_0.5(H₂O)}₂(H₄W₁₂O₄₂)]⁶⁻ and [{Cu_0.5(H₂O)₂}₂(H₄W₁₂O₄₂)]⁶⁻ chains. While compound 4 can be abstracted of structural topology with (6,2)-connected 3D network. In addition, the electrochemical properties of these compounds are investigated.     

Coordination chemistry of higher oxidation states. Part 21. Platinum-195 NMR studies of platinum(II) and platinum(IV) complexes of bi- and multi-dentate phosphorus,arsenic and sulphur ligands

195-Platinum NMR spectra are reported for a series of complexes of bidentate ligands [Pt(LL)X₄] (X=Cl, Br; LL=diphosphine, diarsine, dithioether, diselenoether), [Pt(Me₂PCH₂CH₂PMe₂)₂X₂]X₂, [Pt(o-C₆H₄(AsMe₂)₂)₂X₂]X₂, and for the Pt(II) analogues. The trends in chemical shifts δ(Pt) and ¹J(PtP), ¹J(PtSe) coupling constants are discussed, and used to establish the nature of the solution species obtained by oxidation of Pt(II) complexes of some multidentate phosphorus and arsenic ligands. The [Pt(LL)I₄] materials are shown to exist as [Pt^II(LL)I₂] in dimethylsulphoxide solution, but [Pt(o-C₆H₄(AsMe₂)₂)₂I₂]²⁺ is a genuine Pt(IV) iodo-complex.