Uranyl nitrate complexes of some Schiff bases of 4-aminoantipyrine and certain carbonyl compounds

A series of nine complexes of uranyl nitrate with some Schiff bases derived from 4-aminoantipyrine and certain carbonyl compounds, such as benzaldehyde, 2-nitrobenzaldehyde, 3-nitrobenzaldehyde, 4- methylbenzaldehyde, 4-N,N-dimethylaminobenzaldehyde, 2-hydroxybenzaldehyde, 2-hydroxy-1-naphthaldehyde, acetylacetone and benzoylacetone have been synthesized. These complexes have been characterized by elemental analysis, molecular weight determination and IR spectral, conductance and magnetic studies. From these studies they can be formulated as [UO₂L₂(NO₃)₂], in which the first five ligands (in the order given above) and nitrate ions are coordinated bidentately, while the last four ligands (which have either a phenolic hydroxyl group or a side-chain carbonyl group as an additional site) act as terdentate ligands, and nitrate ions are coordinated monodentately. Hence the proposed general formula for the complexes suggests that the uranyl ion has a coordination number of eight in addition to the two oxygen atoms which have already been bonded to the U(VI) species.     

Formation of coordination polymer and molecular complex of 4,4′-bipyridyl-N,N′-dioxide of manganese and zinc

A 1D-coordination polymer [{Mn₃(C₆H₅COO)₆(BPNO)₂(MeOH)₂}(MeOH)₂]_n (1) having benzoate as the anionic ligand and 4,4′-bipyridyl-N,N′-dioxide (BPNO) as bridging ligand is synthesized by reacting benzoic acid with manganese(II) acetate tetrahydrate followed by reaction with 4,4′-bipyridyl-N N′-dioxide. The bridging bidentate BPNO ligands in this coordination polymer along with the benzoate bridges hold the repeated units. The chain like structure in one dimension by benzoate bridges are connected to each other through the μ³-η²:η¹ bridges of BPNO ligands. This coordination polymer can be transformed to a molecular complex [Mn(H₂O)₆](C₆H₅COO)_2.4BPNO (2). In this complex the BPNO remains outside the coordination sphere but they are hydrogen bonded to water molecules to form self assembled structure. The reaction of 3,5-pyrazoledicarboxylic acid (L₁H2) and BPNO with manganese(II) acetate or zinc(II) acetate led to molecular complexes with composition [M₂(L₁)₂(H₂O)₆].BPNO·xH₂O {where M = Mn(II) (3), Zn(II)(4)}. These molecular complexes of BPNO are characterised by X-ray crystallography. The complexes 3-4 are binuclear carboxylate complexes having M₂O₂ core formed from carboxylate ligands with two metal ions.     

Mononuclear and dinuclear peroxotungsten complexes with co-ordinated dipeptides as potent inhibitors of alkaline phosphatase activity

New molecular peroxotungstate(VI) complexes with dipeptides as ancillary ligands of the type, [WO(O₂)₂(dipeptide)(H₂O)].3H₂O, dipeptide = glycyl-glycine or glycyl-leucine, have been synthesized and characterized by elemental analysis, spectral and physico-chemical methods including thermal analysis. The complexes contain side-on bound peroxo groups and a peptide zwitterion bonded to the metal centre unidentately through an O(carboxylate) atom. Investigations on certain biologically important key properties of these compounds and a set of dimeric compounds in analogous co-ligand environment, Na₂[W₂O₃(O₂)₄(dipeptide)₂].3H₂O, dipeptide = glycyl-glycine and glycyl-leucine, reported previously by us revealed interesting features of the compounds. Each of the compounds despite having a 7 co-ordinated metal centre exerts a strong inhibitory effect on alkaline phosphatase activity with a potency higher than that of the free dipeptide, tungstate or peroxotungstate. The compounds exhibit remarkable stability in solutions of acidic as well as physiological pH and are weaker as substrate to the enzyme catalase, compared to H₂O₂. The mononuclear and dinuclear peroxotungsten compounds are efficient oxidants of reduced glutathione (GSH), a reaction in which only one of the peroxo groups of a diperoxotungsten moiety of the complexes was found to be active.     

Synthesis and structures of aryl-substituted tetramethylcyclopentadienyl dinuclear metal carbonyl complexes

A series of 14 aryl-substituted tetramethylcyclopentadienyl dinuclear metal carbonyl complexes have been synthesized by treating the corresponding ligands (C₅Me₄C₆H₄X-4) (X = H, Me, Cl, OMe) with Ru₃(CO)₁₂, Fe(CO)₅, or Mo(CO)₃(MeCN)₃, respectively in refluxing xylene. It showed that the electronic effects of the substituents had influence on the molecular structures and reactions of the complexes, especially for the ruthenium and molybdenum complexes. In the reactions of aryl-substituted tetramethylcyclopentadiene with Mo(CO)₃(MeCN)₃, the electron-withdrawing effect of the substituent in the para position of benzene ring is favorable to produce the Mo-Mo triple bonded complexes, but the electron-donor effect of the substituent in the para position of benzene ring is favorable to produce the Mo-Mo single bonded complexes. In a given condition, the Mo-Mo single bonded complex could be transformed into the corresponding Mo-Mo triple bonded complex. The structures of nine complexes were determined by single crystal X-ray diffraction.     

Crystal structures of Pt(II) and Pd(II) complexes with the free radical 4-aminoTEMPO

Pt(II) and Pd(II) compounds containing the free radical 4-aminoTEMPO (4amTEMPO) were synthesized and characterised by X-ray diffraction methods. The disubstituted complexes cis- and trans-Pt(4amTEMPO)₂I₂ were studied. The trans isomer was prepared from the isomerisation of the cis analogue. The two Pd(II) compounds trans-Pd(4amTEMPO)₂X₂ (X = Cl and I) were also characterised by crystallographic methods. A mixed-ligand complex cis-Pt(DMSO)(4amTEMPO)Cl₂ was synthesized from the isomerisation of the trans isomer in hot water. Its crystal structure was also determined. In all the complexes, the 4amTEMPO ligand is bonded to the metal through the -NH₂ group, since the nitroxide O atom is not a good donor atom for the soft Pt(II) and Pd(II) metals. The conformation of the 4-aminoTEMPO ligand was compared to those of the few reported structures in the literature.     

Synthesis and characterisation of the carboxylate linked osmium clusters [{Os3H(CO)10}2(CO2CH2CO2)], [{Os3H(CO)10}2(CO2C2H4CO2)], [{Os3H(CO)10}2(C4O4)] and [{Os3H(CO)10}2(C4O4){Co2(CO)6}]

Reactions between the activated cluster [Os₃(CO)₁₀(NCMe)₂] and malonic acid, succinic acid and dicarboxylic acetylene, respectively, lead to the formation of the linked cluster complexes [{Os₃H(CO)₁₀}₂(CO₂CH₂CO₂)] (1), [{Os₃H(CO)₁₀}₂(CO₂C₂H₄CO₂)] (2), and [{Os₃H(CO)₁₀}₂(C₄O₄)] (3) in good yield. Cluster 3 was subsequently treated with [Co₂(CO)₈] and this results in the addition of a “Co₂(CO)₆” group giving [{Os₃H(CO)₁₀}₂(C₂O₄){Co₂(CO)₆}] (4). The X-ray crystal structures are reported for 2–4. In each structure the two triangular triosmium units are linked by the carboxylate groups and within each complex the carboxylate groups are chelating and bridge two osmium atoms.     

The X-ray crystal structures of [Hg(C6F4OH-p)2OH2] and [Hg(C6H4OMe-p)(O2CC6F4OMe-p)] - Factors influencing supramolecular Hg-O interactions

An X-ray crystal structure has shown that the previously reported bis(p-hydroxytetrafluorophenyl)mercury crystallises as a monohydrate [Hg(C₆F₄OH-p)₂(OH₂)] exhibiting rare coordination of water to a diorganomercurial. The stereochemistry of the three-coordinate mercury is T-shaped with the water coordinated perpendicular to the near linear C-Hg-C unit. The molecules are linked in chains by hydrogen bonding between the hydroxy groups, and the chains into layers by hydrogen bonding between the water oxygen and an OH group. Thermogravimetric analysis shows two water molecules are eliminated together, both the coordinated water and one formed through condensation of the linked -OH groups. In [Hg(p-MeOC₆H₄)(O₂CC₆F₄OMe-p)], molecules with a near linear strongly bonded C-Hg-O arrangement are observed. These are linked into a linear polymer through Hg-O (carboxylate) bridges giving alternate four-membered and eight-membered rings giving mercury overall square planar stereochemistry.     

Complexation of Al(III) with reduced glutathione in acidic aqueous solutions

The complexation of reduced glutathione (GSH) in its free and Al(III)-bound species in acidic aqueous solutions was characterized by means of multi-analytical techniques: pH-potentiometry, multinuclear (¹H, ¹³C and ²⁷Al) and two-dimensional nuclear Overhauser enhancement NMR spectroscopy (¹H, ¹H-NOESY), electrospray mass spectroscopy (ESI-MS), and ab initio electronic structure calculations. The following results were found. In the 25 °C 0.1 M KCl and 37 °C 0.15 M NaCl ionic medium systems, Al³⁺ coordinates with the important biomolecule GSH through carboxylate groups to form various mononuclear 1:1 (AlHL, AlH₂L and AlH₋₁L), 1:2 (AlL₂) complexes, and dinuclear (Al₂H₅L₂) species, where H₄L⁺ denotes totally protonated GSH. Besides the monodentate complexes through carboxylate groups, the amino groups and the peptide bond imino and carbonyl groups may also be involved in binding with Al³⁺ in the bidentate and tridentate complexes. The present data reinforce that the glycine carboxylate group of GSH has a higher microscopic complex formation constant than γ-glutamyl carboxylate. Compared with simple amino acids, the tripeptide GSH displays a greater affinity for the Al³⁺ ion and thus may interfere with aluminum’s biological role more significantly.     

Mercury complexes with the ligand benzaldehyde-N(4),N(4)-dimethylthiosemicarbazone

The Schiff base benzaldehyde-N(4),N(4)-dimethylthiosemicarbazone (LH) and its complexes [Hg(NO₃)(LH)₂]NO₃ (1), [Hg(L)₂] (2), [Hg(LH)₂(μ-X)₂HgX₂] [X = Cl (3), Br (4)], [HgI(LH)(μ-I)₂HgI(LH)] (5) and [HgI₂(LH)] (6) have been synthesized and characterized by IR, mass spectrometry, ¹H and ¹³C NMR and by single crystal X-ray diffraction. All the complexes were obtained in ethanol and complex 2, in which the ligand is deprotonated, in addition needs the presence of basic medium. From mercury(II) iodide two complexes with the same molar ratio but with different structures were isolated. In all the complexes the ligand acts as a NS chelate, except in complex 5 in which is only S-donor. The coordination number of the mercury ion and the structures of the complexes depend on the counterion. Complexes 1, 2 and 6 are monomeric species but with different coordination spheres: N₂S₂O₂ with a distorted octahedral arrangement in complex 1, and N₂S₂ or NSI₂ in a pseudo-tetrahedral geometry in complexes 2 and 6, respectively. However, 3, 4 and 5 are binuclear complexes with two halido bridges, but they show two different structures. In 3 and 4, each mercury ion has a different environment giving an asymmetric structure, one is bonded to two NS-ligands and two halido bridges in a distorted octahedral geometry, and the other one has a tetrahedral environment formed by four halido ligands. In complex 5 both mercury ions are equivalent with a SI₃ distorted tetrahedral coordination sphere, formed by one S-bonded ligand, one terminal iodido and two iodido bridges.     

Ethanol catalyzed synthesis of titanocene aryl carboxylate complexes and crystal structure of (η-C5H5)2Ti(2-OH-5-S-O2CC6H3)2

A method for the synthesis of titanocene (IV) aryl carboxylate complexes is presented in this paper. It is based on the fact that alcohol can catalyze the reaction between Cp₂TiCl₂ and aryl carboxylate ligands in the presence of sodium hydroxide (NaOH). The effects of the catalyst on the reaction system were studied and the possible reaction mechanism was proposed. This method was used to prepare a series of titanocene (IV) aryl carboxylate complexes and a macrocyclic titanocene (5,5′-dithiodisalicylato titanocene), whose structure was determined by X-ray diffraction analysis.     

Synthesis, characterization, and reactivity of zinc carboxylate complexes of 2,3-pyridine dicarboxylic acid and (3-oxo-2,3-dihydro-benzo[1,4]oxazin-4-yl)acetic acid

Ethylenediammonium tris-2,3-pyridine dicarboxylato zinc(II) trihydrate (enH₂)₂[ZnL₃]·2H₂O (1) (where H₂L = 2,3-pyridine dicarboxylic acid, en = ethylenediamine) and a mixed metal coordination polymer with composition [Na₂ZnL′₃(OAc)(H₂O)₃]_n (2) {where L′ = anion of (3-oxo-2,3-dihydro-benzo[1,4]oxazin-4-yl)acetic acid} are synthesized and characterized. The complex 1 is mono nuclear complex with three coordinating carboxylate anion along with nitrogen chelating zinc ion and there is three uncoordinated carboxylate group one each from three ligand molecules making a complex anion of zinc(II). The zinc(II) ion are in distorted octahedral coordination geometry. In this complex diprotonated ethylenediamines serve as cations. The complex 2 has a polymeric structure with one acetate and three carboxylate of L′ binding to zinc ion provides a tetrahedral environment and these ligands further hold dinuclear units of tri-aquated sodium ions; each dinuclear sodium units are bridged by one water molecule make the coordination polymer. The catalytic ability of these two complexes 1 and 2 towards carbon-carbon bond formation reaction between 3,4-dimethoxy benzaldehyde and acetone are studied. Both the complexes as well as sodium salt of L′ are found to be catalyst for such reactions.     

Three-dimensional 3d-4f heterometallic polymers containing both azide and carboxylate as co-ligands

The hydrothermal reaction of Ln(NO₃)₃, Ni(NO₃)₂, NaN₃, and isonicotinic acid (L) yielded two novel 3-D coordination frameworks (1 and 2) of general formula [Ni₂Ln(L)₅(N₃)₂ (H₂O)₃] · 2H₂O (Ln = Pr(III) for 1 and Nd(III) for 2), containing Ni-Pr or Ni-Nd hybrid extended three-dimensional networks containing both azido and carboxylate as co-ligands. Both the compounds are found to be isostructural and crystallize in monoclinic system having P2₁/n space group. Here the lanthanide ions are found to be nonacoordinated. Both bidentate and monodentate modes of binding of the carboxylate with the lanthanides have been observed in the above complexes. Variable temperature magnetic studies of the above two complexes have been investigated in the temperature range 2-300 K which showed dominant antiferromagnetic interaction in both the cases and these experimental results are analyzed with the theoretical models.     

EPR study of the oxidation reaction of nickel(0) phosphine complexes with Lewis and Brønsted acids

The oxidation of Ni(PPh₃)₄ with BF₃ · OEt₂, H₃CCOOH, and F₃CCOOH, and that of (PPh₃)₂Ni(C₂H₄) with BF₃ · OEt₂ is studied by EPR spectroscopy. The reaction of the Ni(0) complexes with BF₃ · OEt₂ gives Ni(II) complexes with which they react to form Ni(I) compounds with covalent Ni-F and Ni-B bonds that transform with excess BF₃ · OEt₂ into cationic paramagnetic Ni(I) complexes. Acetic acid also adds oxidatively to Ni(PPh₃)₄ to form a Ni(II) complex that reacts further to give Ni(I) hydride and carboxylate complexes. The Ni(I) hydride is transformed by the acid into the Ni(I) carboxylate with release of hydrogen, the amount of which depends on the rate of acid addition. The following Ni(I) complexes are identified in the reaction medium: [Ni(PPh₃)₃]BF₄, [(PPh₃)₂Ni(OEt₂)]BF₄, [(PPh₃)Ni(OEt₂)_n]BF₄, (PPh₃)₂NiBF₂, (PPh₃)₃NiOOCCH₃, and [(PPh₃)₂Ni(OEt₂)P(OEt)₃]BF₄. Oxidation schemes of Ni(0) complexes by Lewis and Brønsted acids are given.     

Rhodium paddlewheel dimers containing the π···π stacking, 1,8-naphthalimide supramolecular synthon

The bifunctional ligand 3-(1,8-naphthalimido)propanoate (L_C2⁻), which contains a carboxylate group linked to the robust π···π stacking 1,8-naphthalimide supramolecular synthon, has been used to prepare two new rhodium carboxylate dimer complexes, [Rh₂(L_C2)₄(DMF)₂] (1) and [Rh₂(L_C2)₄(py)₂]·3DMF (2). Both complexes have been structurally characterized and contain the Rh₂(O₂CR)₄ paddlewheel core, but have different axial ligands. The four naphthalimide side arms in the carboxylate ligands are arranged in the square shape imposed by the SBU in complex 1, but are bent in 2. In both cases, the supramolecular structure is organized into one-dimensional chains by strong π···π stacking interactions between only two of the 1,8-naphthalimide moieties on each dimeric unit. In 1, the other naphthalimide units do not interact strongly and in 2 they intramolecularly π···π stack with the adjacent axial pyridine molecules.     

Cobaltocene reductions of multiply bonded dirhenium complexes. II. The isolation of the paramagnetic species [(η5-C5H5)2Co][Re2(hp)4X2] (hp = anion of 2-hydroxypyridine; X = Cl,Br, or I)

Reaction of the quadruply bonded dirhenium(III) complexes (n-Bu₄N)₂Re₂X₈ (X = Cl, Br, or I) with 2-hydroxypyridine (Hhp) in refluxing n-pentanol gives Re₂(hp)₄X₂ in high yield (>;90%). These complexes are reduced by cobaltocene to yield the paramagnetic salts [(η⁵-C₅H₅)₂Co][Re₂(hp)₄X₂]. The spectroscopic (electronic absorption and infrared) and electrochemical properties of these sets of complexes are in accord with them possessing σ²π⁴δ²(Re₂⁶⁺) or σ²π⁴δ²δ*¹(Re₂⁵⁺ ground state electronic configurations.     

95Mo NMR studies of complexes containing the Mo2O52+ core and crystal structure of Mo2O5[SC6H4NHCH2C5H4N]2(C3H7NO)3

The crystal structure of Mo₂O₅[SC₆H₄NHCH₂C₅H₄N]₂(C₃N₇NO)₃ is reported and seen to consist of a single oxo-bridged species with each Mo atom bonded to cis dioxo groups and the nitrogen atoms and thiolate group of the tridentate ligand. ⁹⁵Mo NMR spectra of this and three related complexes are presented and attempts made to interpret them in terms of their crystal structures.     

Protonation and Zn(II) complexation with versatile valine and glycylglycine N-pyrimidines derivatives: crystal structures of layered {[Zn(HL1)2] · 2H2O}n and [Zn(HL2)2(H2O)4]

Protonation and Zn(II) complexation of N-substituted amino acids, valine (H₂L1) and glycylglycine (H₂L2), with 4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxopyrimidin-2-yl as substituent, were studied by potentiometric and UV-Vis measurements. Bianions L1 and L2 suffer three protonation steps in aqueous medium corresponding to the amide and carboxylate groups of the amino acidic moiety, and the nitrogen atom of the nitroso group of the pyrimidine fragment. Both ligands form mononuclear Zn(II) complexes in aqueous solutions. The binding donor groups are the nitroso and/or the oxo groups of the pyrimidinic moiety or the carboxylate group, depending on whether the ligands are neutral or anionic, respectively. Weak metal-to-ligand interactions were observed independently of the functionality used by the corresponding ligand on bonding to Zn(II). The reaction of ZnCl₂ with the monodeprotonated ligands (1:1) yields a polynuclear 2D {[Zn(HL1)₂] · 2H₂O}_n and a mononuclear [Zn(HL2)₂(H₂O)₄] complexes, showing the influence of the susbtituent on the amino acids fragment as well as the versatility of this class of compounds when acting as ligands.     

Synthesis and structure of a zinc(II)-carboxylate trimer containing the π···π stacking, 1,8-naphthalimide synthon: A supramolecular metal-organic framework

The reaction of the bifunctional ligand 3-(1,8-naphthalimido)propanoate (L_C2⁻), which combines a 1,8-naphthalimide strong π···π stacking synthon and a carboxylate donor group, with Zn(O₂CCH₃)₂(H₂O)₂ in methanol yields trimetallic Zn₃(L_C2)₆(MeOH)₄. The solid state structure has a central zinc(II) linked to two equivalent outer zinc(II) by both μ-κ¹ and μ-κ² carboxylate ligands. The two equivalent five-coordinate terminal zinc centers are also bonded to a third nonbridging κ²-carboxylate and to the oxygen atom of a methanol molecule. The central zinc(II) is six-coordinate with the four bridging carboxylate oxygen atoms forming a square planar arrangement and two trans oriented methanol molecules completing the coordination sphere. These trimers are organized into an extended structure exclusively by noncovalent interactions. Two types of strong π···π stacking interactions between sets of three stacked naphthalimide rings from three different trinuclear molecules organize the structure into two-dimensional thick sheets. The third dimension is organized by intermolecular hydrogen bonding interactions between the methanol molecules bonded to the terminal zinc(II) and the free oxygen of the μ-κ¹-carboxylates from adjacent trimeric units. This interaction is supported by weak π···π stacking. Overall the structure is a highly organized supramolecular metal-organic framework (SMOF) solid.     

Cobalt(III) promoted ligand fusion reactions of thiobarbituric acid and 4,6-diamino-2-thiouracil (or 4-amino-2-thiouracil)

Novel cobalt(III) complexes containing three kinds of assembled ligands, L₁L₂=dapymt-tbba(2-), tbba-dapymt(1-) and apymt-tbba(1-) (H₃tbba=thiobarbituric acid; Hdapymt=4,6-diamino-2-thiouracil; Hapymt=4-amino-2-thiouracil), were prepared from the mixed ligand systems, where L₂ indicates the coordinated ligand to the Co(III) ion and L₁ is a pendant ligand bonded to L₂. These complexes were characterized by UV-Vis absorption spectra and NMR spectroscopy. The crystal structures of [Co(Htbba)(en)₂]ClO₄·2H₂O (2) (en=ethane-1,2-diamine), [Co{dapymt-tbba(2-)}(en)₂]ClO₄·3H₂O (3) and [Co{apymt-tbba(1-)}(en)₂](ClO₄)Cl·3H₂O (5′) revealed that coordination occurs through the S(1) and N(1) donors of tbba and the latter complexes 3 and 5′ have an assembled ligand; a new bond is formed between the C(5) atom of tbba and the S(2) atom of dapymt or apymt. An intramolecular hydrogen bond between O(1) of tbba and NH of en was found in all crystals. An interesting intermolecular π-π stacking interaction was found in 5′.     

Magnetostructural correlations in μ-pyrazolato-μ-acetato dinickel(II) complexes: Subtle effects of acetate tilting

A series of dinickel acetato complexes [LNi₂(OAc)(solvent)_x](ClO₄)₂ (1-3, 5) as well as related complexes [LNi₂(OAc)₂](OAc) (4) and [LNi₂(OAc)(NO₃)₂] (6), all derived from three pyrazolate-based binucleating ligands, have been prepared and characterized by X-ray crystallography. The solid state structures reveal different acetate binding modes (μ_1,3-bridging and bidentate chelating) plus severe twisting and tilting of the μ_1,3-acetate bridges with respect to their bimetallic scaffolds, reflecting the great flexibility of carboxylate coordination. Magnetic properties of all six complexes have been investigated, and the strength of antiferromagnetic coupling is discussed in the light of the structural differences, suggesting a magnetostructural correlation for acetato-bridged complexes.