Molecular Dynamics Simulation of the Interaction between Common Metal Ions and Humic Acids

Humic acids (HAs) have important environmental and geochemical effects on soil, water environments and sediment. HAs strongly complex some metal ions, which affects the migration of metal ions and the colloidal aggregation of HA. Here, the complexation of Ca2+ and Mg2+ with HA in aqueous solution under neutral conditions has been systematically studied by molecular dynamics (MD) simulation. The results show that the aggregation of HA is caused by the complexation of HA and metal ions, mainly due to the intermolecular bridging between Ca2+, Mg2+ and COO− groups. Monodentate and bidentate coordinations have been found between Ca2+ and COO− groups of different HA molecules in the same simulation system. Mg2+ only has a monodentate coordination with COO− group.

Synthesis, Structures, and Water Adsorption of Two Coordination Polymers Constructed by M(II) (M = Ni (1) and Zn (2)) with 1,3-Bis(4-Pyridyl)Propane (bpp) and 1,2,4,5-Benzenetetracarboxylate (BT4−) Ligands

Two coordination polymers (CPs), with chemical formulas {[Ni2(bpp)2(BT)(H2O)6] 1.5(EtOH) 1.5H2O}n (1) and [Zn(bpp)(BT)0.5]·5H2O (2) (bpp = 1,3-bis(4-pyridyl)propane, and BT4− = tetraanion of 1,2,4,5-Benzenetetracarboxylic acid), have been synthesized and structurally characterized by single-crystal X-ray diffraction methods. In compound 1, the coordination environments of two crystallographically independent Ni(II) ions are both distorted octahedral bonded to two nitrogen donors from two bpp ligands and four oxygen donors from one BT4- ligand and three water molecules. Both bpp and BT4− act as bridging ligands with bis-monodentate and 1,4-bis-monodentate coordination modes, respectively, connecting the Ni(II) ions to form a 2D layered metal-organic framework (MOF). Adjacent 2D layers are then arranged orderly in an ABAB manner to complete their 3D supramolecular architecture. In 2, the coordination environment of Zn(II) ion is distorted tetrahedral bonded to two nitrogen donors from two bpp ligands and two oxygen donors from two BT4− ligands. Both bpp and BT4- act as bridging ligands with bis-monodentate and 1,2,4,5-tetrakis-monodentate coordination modes, respectively, connecting the Zn(II) ions to form a 3D MOF. The reversible water de-/adsorption behavior of 1 between dehydrated and rehydrated forms has been verified by cyclic Thermogravimetric (TG) analyses through de-/rehydration processes. Compound 1 also exhibits significant water vapor hysteresis isotherms.

SYNTHESIS AND SPECTRAL CHARACTERISTICS OF THE Ru(III,ІІ), Rh(III) AND Pd(II) COMPLEXES BASED ON N-ALLYLTHIOAMIDES AND PRODUCTS THEIR PROTON- AND IODOCYCLIZATION

The paper shows the possibility of using N-allylthioamides H2L1-H2L3 and products of their proton / iodine cyclization HL4, HL5 as chelating agents in the complexation reactions with Ru(III,II), Rh(III) and Pd(II) ions. As a result, a series of new chelating complexes of [M(HL1-3)Cl2(H2O)2], [M(HL1-3)2(H2O)2]Cl (2), [М(HL1-3)2(H2O)Cl] (3), [Ru(HL1-3)(PPh3)2]Cl (4), K[Pd(HL1-3)Cl2] (5), [Pd(HL1-3)2] (6), [M(L4,5)2(H2O)2]Cl (7), K[Pd(L4,5)Cl2] (8), [Pd(L4,5)2] (9) in which the ligands are coordinated to the metal ions by O,S- or O,N-bidentate chelate manner in a monodeprotonated form, where synthesis, isolated in solid state and characterized by the methods of elemental chemical analysis, 1H NMR, IR and UV-Vis spectroscopy. It was found that HL4,5, when complexed, is converted to the corresponding tautomeric form with O,N-coordination through the oxygen atoms of the deprotonated hydroxyl group and the nitrogen atoms of the dihydrothiazolyl ring. It has been established that the allyl moiety does not participate in the formation of a coordination bond with the Ru (III,II), Rh(III) and Pd(II) ions, which is probably due to the presence in the molecules of ligands of other donor nucleophilic centers located in advantageous position for the formation of six-membered chelated metal cycles. In contrast to complexes 1-9, the compounds of [M(HL6)2(H2O)2Cl2]Cl (10), [Pd(HL6)2Cl2] (11) based on 2-(5-(iodomethyl)-1,3-thiazolidin-2-ylidene) malononitrile (HL6) were obtained with monodentate coordination of the ligand in molecular form, which is caused by the presence of two nitrile groups in the HL6 molecule with sp-hybridization of the nitrogen atomic orbitals, which provides almost linear overlap with the d-orbitals of the metal atom upon formation of CN→M bond. The study of the complex formation of metal chlorides with H2L1-H2L3 by the method of isomolar series and UV-Vis spectra showed that there is interaction in the M: L = 1:1, 1:2, 1:3 molar ratio (in the case of Ru3+, Rh3+ ions) and 1:1, 1:2 (in the case of Pd2+ and Ru2+ ions) which is related to the coordination capacity of metals and their ability to form octahedral (for Ru3+, Rh3+ ions) or square-planar (for Pd2+ ions) coordination unit. The reaction of Ru3+, Rh3+ and Pd2+ ions with HL4, HL5 in the isopropanol solution also occurs in the ratio M:L = 1:1, 1:2, 1:3, however, the titration curves are much less pronounced compared to complexes based on H2L1-H2L3. In the interaction of HL6 with the ions of the above metals, the curve has the appearance of an almost straight line, indicating the so-called "state of unsaturation" of the system in the corresponding concentration range due to the monodentate coordination of HL6. The solubility study of the obtained complexes showed that ionic type compounds 2, 4, 5, 7, 8, 10 were dissolved in methanol, partially (or completely) in ethanol, and at low concentrations (10-3-10-5 mol/l) - in water, while molecular type compounds 1, 3, 6, 11 are soluble in DMSO and DMF only.

Structural Diversity of Nickel and Manganese Chloride Complexes with Pyridin-2-One

Reactions of NiCl2·6H2O and pyridin-2-one (C5H5NO = Hhp) afforded novel molecular complexes, i.e., mononuclear [NiCl2(Hhp)4] (1), dinuclear [NiCl2(Hhp)(H2O)2]2.2Hhp (3) and [Ni2Cl4(Hhp)5]·2MeCN (4), and an ionic complex [Ni(Hhp)6]Cl2 (2). Single-crystal X-ray analyses revealed two modes of Hhp ligation in these complexes: a monodentate coordination of carbonyl oxygen in all of them and an additional µ2-oxygen bridging coordination in the dinuclear complex 4. Three bridging molecules of Hhp span two nickel(II) ions in 4 with a 2.9802 (5) Å separation of the metal ions. Complex 3 is a chlorido-bridged nickel dimer with a planar Ni2(µ-Cl)2 framework. Hydrogen bonds and parallel stacking arrangements of the Hhp molecules govern the connectivity patterns in the crystals, resulting in 1D structures in 1 and 5 or 2D in 3. A single manganese compound [MnCl2(Hhp)4] (5), isostructural to 1, was isolated under the similar conditions. This is in contrast to four nickel(II) chloride complexes with Hhp. Thermal analyses proved the stability of complexes 1 and 3 in argon up to 145 °C and 100 °C, respectively. The decomposition of 1 and 3 yielded nickel in argon and nickel(II) oxide in air at 800 °C.

Bis(3-methylsalicylato)bis(picolinamide)copper(II) complex — preparation, spectral properties and supposed structure

Blue methylsalicylatocopper(II) complex with picolinamide Cu(3-Mesal)2(pnia)2 has been prepared and characterized by elemental analysis and spectral methods. Based on the infrared spectra, monodentate coordination of 3-methylsalicylate anion has been assumed and the coordination variability of the anion has been shown. By determination and refinement of the unit cell from powder diffraction data, the existence of a monomeric Cu(II) complex can be anticipated. EPR spectrum of the complex is in good agreement with these results. The g-factors fulfil the relation g|| > g┴ > 2.0023, which is consistent with the dx2 – y2 ground electronic state and indicates coordination sphere of distorted tetragonal symmetry {CuN2O2O2´} for the central copper(II) ions.

2,2′:6′,2′′-Terpyridine switches from tridentate to monodentate coordination in a gold(iii) terpy complex upon reaction with sodium azide

The X-ray structure of a gold(iii) azido complex with a terpyridine coligand in a very rare monodentate coordination mode is reported.

Mechanism of fatty acid decarboxylation catalyzed by a non-heme iron oxidase (UndA): a QM/MM study

QM/MM calculations reveal that the fatty acid decarboxylase UndA employs the FeIII–OO˙− complex to initiate the β-H abstraction with the monodentate coordination mode. The iron center accepts the extra electron of the substrate radical.