Synthesis and solution studies of Cu(II) complexes with pyridine derivatives of iminobisphosphonic acids

New 2-pyridyl, 3-pyridyl and 4-pyridyl derivatives of iminobisphosphonic acid were prepared by addition of tris(trimethylsilyl)phosphite to the corresponding derivatives of pyridineimine-methylphosphonates 3 and subsequent methanolysis of the silylated products 4. Solution studies on the coordination abilities of the ligands have shown that these compounds bind copper(II) ion through the tridentate {N,O,O} mode, where Cu(II) is stabilized by two five-membered chelate rings. The complexes obtained are very stable, with the pCu(II) value above 12, and therefore the ligands can be used as powerful chelating agents for copper ion.     

Synthesis, characterization and antiproliferative behavior of tricarbonyl complexes of rhenium(I) with some 6-amino-5-nitrosouracil derivatives: crystal structure of fac-[ReCl(CO)3(DANU-N5,O4)] (DANU=6-amino-1,3-dimethyl-5-nitrosouracil)

New complexes of rhenium(I) with some 5-nitrosopyrimidines with general formula [ReCl(CO)3L] have been prepared and characterized by elemental analysis, conductivity measurements, IR and 1H, 13C and 15N NMR spectroscopic methods. The complexes appear to be monomeric and the pyrimidine ligands act in a neutral form. The structure of [ReCl(CO)3(DANU)].CH3CN has been solved by X-ray diffraction. The coordination environment around the Re(I) may be described as a distorted octahedron in which the ligand behaves in a bidentate fashion through N5 and O4 atoms, making a five-membered chelate ring. The coordination sphere is completed with three carbonyl groups in fac-arrangement and one chlorine atom. The evaluation of the antiproliferative behavior against five human tumor cell lines (human breast cancer MCF-7 and EVSA-T, human neuroblastoma NB69, human glioma H4 and human bladder carcinoma cell line ECV) suggested a modulator behavior of cell growth at low concentrations due to their estrogenic-like characteristics.     

Synthesis, characterization and supramolecular structures of two Ni(II) complexes with potentially heptadentate ligand N,N-bis(2-hydroxybenzyl)-1,3-bis[(2-aminoethyl)amino]-2-propanol

A potentially heptadentate ligand H₃L (N,N^′-bis(2-hydroxybenzyl)-1,3-bis[(2-aminoethyl)amino]-2-propanol) and its two Ni(II) complexes, [Ni(H₂L)H₂O](H₂O)₃ClO₄ (1) and [Ni(H₂L)(H₂O)](H₂O)Cl (2) were prepared and characterized. X-ray structural analyses indicate that complex 1 has a distorted octahedral coordination geometry, with four amine N atoms of H₂L⁻ defining the equatorial plane, one aqua O atom and one phenoxo O atom of the ligand occupying two axial positions, respectively. The Ni(II) center of 2 has coordination geometry similar to that of 1. IR and electronic spectra of 1 and 2 are in agreement with their crystal structural features. Approximately along the ab plane, 2D supramolecular structure of 1 is assembled through multiple hydrogen bonds between hydroxy groups of the ligands, coordinated and crystal lattice H₂O and π-π stacking interactions between adjacent phenyl rings of the ligands, while for that of 2, probably along the a axis, 1D chain structure is also formed by multiple hydrogen bonds, but lack of π-π stacking interactions.     

Complexes with 6-amino-5-nitroso-2-thiouracil and violuric acid derivatives containing the fac-Re(CO)3 core: Synthesis, XRD structural and photoluminescence characterization

The fac-tricarbonylrhenium(I) complexes of the 6-amino-1,3-dimethyl-5-nitroso-2-thiouracil (DANTU) and violuric acid (VIO) and its mono- (MVIO) and dimethyl (DVIO) derivatives have been prepared. The complexes have been characterized by elemental analysis, IR, ¹H and ¹³C NMR spectral methods and luminescence spectroscopy. The structures of [ReCl(CO)₃(DANTU)], [Re(H₂O)(CO)₃(VIOH₋₁)] and [Re(H₂O)(CO)₃(DVIOH₋₁)] complexes were solved from single-crystal X-ray diffraction experiments. The coordination environment around the Re(I) may be described as a distorted octahedron in which the ligand behaves in a bidentate fashion through the nitrogen atom of the nitroso group and an adjacent carbonylic oxygen, making a five-membered chelate ring. The coordination sphere is completed with three carbonyl groups in fac-arrangement and one chlorine atom (DANTU complex) or water molecule (VIO complexes). The higher acidity of violuric acids, if compared with DANTU one, may explain both synergic deprotonation and chloride substitution in the [ReCl(CO)₃]⁺ moiety to form the Re-violurato complexes.     

Intramolecular ether oxygen coordination in the zinc complexes with dipicolylamine (DPA)-derived ligands

The ether oxygen coordination to the zinc center in the complexes with dipicolylamine (DPA)-derived ligands, N-(2-methoxyethyl)-N,N-bis(2-pyridylmethyl)amine (L), N-(3-methoxypropyl)-N,N-bis(2-pyridylmethyl)amine (L′), and N-{3-(2-pyridylmethyloxy)propyl}-N,N-bis(2-pyridylmethyl)amine (L^Py) has been discussed. Upon chelation of the oxygen atom, L forms a five-membered chelate ring with respect to the 2-aminoethyl ether moiety whereas L′ forms a six-membered chelate in 3-aminopropyl ether unit. This difference was highlighted by the crystal structures of ZnCl₂ complexes, in which [Zn(L)Cl₂] (1) exhibited ether oxygen coordination but [Zn(L′)Cl₂] (2) had the ether oxygen non-coordinated. The terminal pyridyl group of L^Py facilitates the ether oxygen atom coordination via a metal binding from the basal plane trans to the aliphatic nitrogen.     

Steric influence on platinum(II) ascorbate complexes

From the reaction between dihydroxoplatinum(II) and l-ascorbic acid, two types of platinum(II) ascorbate complexes were obtained and structurally characterized with ethylenediamine (en), N,N-dimethylethylenediamine (dmen) and N,N,N′-trimethylethylenediamine (trimen) as stabilizing ligands. In [Pt(en)(asc-C,O)] (1), [Pt(dmen)(asc-C,O)] (2) and [Pt(trimen)(asc-C,O)] (4), the ascorbate dianion forms a five-membered chelate ring, coordinating to the Pt(II) ion at the 2-carbon and the 5-oxygen atoms (C,O-chelate). From the same mother solution, crystals of [Pt(trimen)(asc-O,O′)] (3) were obtained during the precipitation of 4; in 3 the ascorbate is bound to the Pt at the 2- and 3-oxygen atoms (O,O′-chelate). Compounds 3 and 4 are the first well-characterized linkage isomers among the transition-metal ascorbate complexes. The O,O′-chelated 3 slowly changes to the C,O-chelated 4 in an aqueous solution. Bulkiness of the stabilizing ligand, i.e. en, dmen and trimen has an influence on the formation of the C,O-chelated species, 1, 2 and 4.     

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′.     

A tridentate bis(pyrazolyl) ligand binds to Cu(II), without using the pyrazole group: a very unusual coordination mode of the ligand Hbdmpb, 1,3-bis(3,5-dimethylpyrazol-1-yl)-2-butanoic acid

A new pyrazole-based ligand, namely 1,3-bis(3,5-dimethylpyrazol-1-yl)-2-butanoic acid (Hbdmpb) was synthesised together with its copper complex Na[Cu(bdmpb)₂(OOCCH₃)H₂O] · 4H₂O. Both the free ligand and its Cu compound were fully characterised and their crystal structures were determined by X-ray analysis. The free-ligand molecular structure is uneventful. The Cu compound is highly unusual, as the pyrazole nitrogen atoms do not bind to the Cu ion. The copper(II) ion is coordinated by four nearly coplanar oxygen atoms from two dehydronated ligands bdmpb (CuO(1a) 1.942(4), CuO(1b) 1.933(4) Å), a monodentate acetate group (CuO(1) 1.927(3) Å) and a water molecule (CuO(1w) 1.937(4) Å). The nitrogen atoms of the pyrazole rings do not coordinate to the metal center, but instead are involved in strong intramolecular hydrogen bonds. The coordinated water molecule is strongly H-bonded to two pyrazole N atoms from two bdmpb ligands (N(12a) ? HO(1w) 2.762(7), N(12b) ? HO(1w) 2.774(7) Å). The other two pyrazole N atoms with a lone pair are hydrogen-bonded to water molecules in the lattice (N(22a) ? HO(2w) 2.763(7), N(22b) ? HO(6w) 2.892(7) Å). The sodium ion is six-coordinated by the oxygen atom O(2) of the acetato ligand and by five water molecules. The EPR spectrum recorded in the solid state shows a characteristic signal for an axial anisotropic S = 1/2 species. The spectrum recorded in methanol glass confirms the absence of the coordination of pyrazole nitrogen atoms to the copper centers.     

A fluorescent ligand rationally designed to be selective for zinc(II) over larger metal ions. The structures of the zinc(II) and cadmium(II) complexes of N,N-bis(2-methylquinoline)-2-(2-aminoethyl)pyridine

The metal ion coordinating properties of the ligands N,N-bis(2-methylquinoline)-2-(2-aminoethyl)pyridine (DQPEA) and N,N-bis(2-methylquinoline)-2-(2-aminomethyl)pyridine (DQPMA) are presented. DQPEA and DQPMA differ only in that DQPEA forms six-membered chelate rings that involve the pyridyl group, whereas DQPMA forms analogous five-membered chelate rings.These two ligands illustrate the application of a ligand design principle, which states that increase of chelate ring size in a ligand will result in increase in selectivity for smaller relative to larger metal ions. The formation constants (log K₁) of DQPEA and DQPMA with Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) are reported. As expected from the applied ligand design principle, small metal ions such as Ni(II) and Zn(II) show increases in log K₁ with DQPEA (six-membered chelate ring) relative to DQPMA (five-membered chelate ring), while large metal ions such as Cd(II) and Pb(II) show decreases in log K₁ when the chelate ring increases in size. In order to further understand the steric origin of the destabilization of complexes of metal ions of differing sizes by the six-membered chelate ring of DQPEA, the structures of [Zn(DQPEA)H₂O](ClO₄)₂ (1) [triclinic, , a = 9.2906(10), b = 10.3943(10), c = 17.3880(18) Å, α = 82.748(7)°, β = 88.519(7)°, γ = 66.957(6)°, Z = 4, R = 0.073] and [Cd(DQPEA)(NO₃)₂] (2) [monoclinic, C2/c, a = 22.160(3), b = 15.9444(18), c = 16.6962(18) Å, β = 119.780(3)°, Z = 8, R = 0.0425] are reported. The Zn in (1) is five-coordinate, with a water molecule completing the coordination sphere. The Cd(II) in (2) is six-coordinate, with two unidentate nitrates coordinated to the Cd. It is found that the bonds to the quinaldine nitrogens in the DQPEA complexes are considerably stretched as compared to those of analogous TPyA (tri(pyridylmethyl)amine) complexes, which effect is attributed to the greater steric crowding in the DQPEA complexes. The structures are analyzed for indications of the origins of the destabilization of the complex of the large Cd(II) ion relative to the smaller Zn(II) ion. A possible cause is the greater distortion of the six-membered chelate ring in (2) than in (1), as evidenced by torsion angles that are further away from the ideal values in (2) than in (1). Fluorescence properties of the DQPMA and DQPEA complexes of Zn(II) and Cd(II) are reported. It is found that the DQPEA complex of Zn(II) has increased fluorescence intensity compared to the DQPMA complex, while for the Cd(II) complex the opposite is found. This is related to the greater strain in the six-membered chelate ring of the Cd(II) DQPEA complex as compared to the Zn(II) complex, with resulting poorer overlap in the Cd-N bond, and hence greater ability to quench the fluorescence in the Cd(II) complex.     

Study of complex formation with 2-hydroxyiminocarboxylates: specific metal binding ability of 2-(4-methylthiazol-2-yl)-2-(hydroxyimino)acetic acid

Complex formation properties of a novel water soluble thiazolyloxime 2-(4-methylthiazol-2-yl)-2-(hydroxyimino)acetic acid (H₃L¹) with Cu²⁺ and Ni²⁺ were investigated in solution by potentiometrical and spectral (UV-Vis, EPR, NMR) methods. All Cu²⁺ and most of Ni²⁺ complex species detected in solution were found to have square-planar MN₄ core with oxime and heterocyclic nitrogen atoms which was rationalized in terms of destabilizing effect of repulsive interaction between oxygen atom of carboxylic group and nitrogen atom of thiazole ring in N,O-coordinated ligand conformation. It has been found that stability of metal complexes in a series of oxime ligands is dependent upon basicity of nitrogen atom of oxime group. The thiazolyloxime forms less stable complexes with Cu²⁺ but stronger ones with Ni²⁺ ions when compared to parent 2-(hydroxyimino)propanoic acid. The lower stability obtained for Cu²⁺ complexes was elucidated in terms of negative inductive effect of the thiazole and nitrile substituents as well as an effect of intramolecular attractive interaction between thiazolyl sulfur and oxime oxygen atoms in thiazolyloxime. In the case of Ni²⁺ the complexes formed are square-planar and it is why thiazolyl ligand is more effective in metal ion binding than simple 2-(hydroxyimino)propanoic acid forming only octahedral species. The solid state structure of the Co³⁺ complex K₃[Co(HL¹)₃]·5.5H₂O (1) was studied by X-ray analysis. The thiazolyloxime ligand is coordinated to Co³⁺ via oxime nitrogen and carboxylate oxygen atoms forming five-membered chelate rings.     

Sodium ions directed self-assembly with 3,5-pyridinedicarboxylate (3,5-pdc) and 4-pyridinecarboxylate (4-pc)

A 3D sodium(I) complex driven by the coordination bonds and a 3D hydrogen-bond-sustained network, with empirical formulae [Na₂(3,5-pdc)(H₂O)₄]_n (1) and [Na₂(4-pc)₂(H₂O)₈]_n (2), respectively, have been synthesized and characterized. X-ray single crystal determination of 1 reveals that two types of hexa-coordinate sodium(I) ions are alternately arranged through three double μ₂-OH₂ bridges and one double μ₂ oxygen bridge coming from one carboxylic oxygen atom of a 3,5-pdc ligand. In comparison to 1, only one kind of six-coordinate sodium ions in octahedral coordination configurations is bridged by double μ₂ aqua bridges in 2 forming a straight line via the similar Na-Na separations. In addition, the fixation of coordinating bonds around the sodium centers in 1 makes pyridine rings parallel to each other and the centroid-centroid separation of 3.539 Å, while in complex 2 pyridine rings are arranged more flexibly merely by the hydrogen bonding interactions associated with its nitrogen atom and a carboxylic group. To the best of our knowledge, 1 is the first 3D framework sustained only by coordination interactions between alkali metals and carboxylates. It is also noted that two types of hexa-coordinate sodium(I) centers are present in complex 1 at the same time and two kinds of topologies (zig-zag and ring) are produced. Complex 2 is an unprecedented 3D sodium(I) network sustained by the hydrogen bonding and the π-π interactions in the absence of coordination forces.     

Coordination behavior of three geometric isomers of indole-based S-benzyldithiocarbazone ligands towards nickel, zinc and cadmium divalent ions

Three indolyl-imine ligands have been synthesized through the condensation of S-benzyldithiocarbazate with indole-2-carbaldehyde, indole-3-carbaldehyde and indole-7-carbaldehyde. Treatment of these Schiff bases with acetate salts of Ni(II), Zn(II) and Cd(II) in ethanol yielded a series of complexes of 2:1 type (ligand/metal ratio) in which the ligands coordinated to the metal ions as monoanionic NS bidentate chelates. While the 2-imineindole and 3-imineindole formed the expected five-membered chelate rings, the X-ray crystal structure of [Cd(HL³)(py)₂], (HL³ = the mono-deprotonated 7-imineindole), revealed an unusual mode of coordination, namely formation of four-membered rings with the metal atom. Reaction of the 7-imineindole with the metal ions in the presence of potassium hydroxide produced complexes of the type [M(L³)(H₂O)] in which the Schiff base acts as a dianionic NNS tridentate ligand.     

Preparation, separation and characterisation of two regioisomers of a N-hydroxyalkylpyridylpyrazole ligand: A structural investigation of their coordination to Pd(II), Pt(II) and Zn(II) centres

The reaction of the β-diketone 1-phenyl-3-(pyridyn-2-yl)propane-1,3-dione, and the monosubstituted hydrazine 2-hydroxyethylhydrazine has been investigated. Two regioisomers were identified, 2-(3-phenyl-5-(pyridyn-2-yl)-1H-pyrazol-1-yl)ethanol (pzol.1) and 2-(5-phenyl-3-(pyridyn-2-yl)-1H-pyrazol-1-yl)ethanol (pzol.2) in 57:43 ratio. The separation of the regioisomers was done by silica column chromatography using ethyl acetate as eluent.Palladium(II) and platinum(II), [MCl₂(pzol.1)₂], [MCl₂(pzol.2)], and zinc(II), [ZnCl₂(pzol.1)], [ZnCl₂(pzol.2)] complexes were synthesised and characterised. The crystals and molecular structures of [PdCl₂(pzol.2)]·H₂O and [ZnCl₂(pzol.2)] were solved by X-ray diffraction, and consist of mononuclear complexes. In complex [PdCl₂(pzol.2)]·H₂O, the Pd(II) centre has a typical square planar geometry, with a slight tetrahedral distortion. The tetra-coordinated atom is bonded to one pyridinic nitrogen, one pyrazolic nitrogen and two chlorine atoms in cis disposition. The pzol.2 ligand acts as a bidentate chelate forming a five-membered metallocycle ring. In complex [ZnCl₂(pzol.2)], the Zn(II) is five-coordinated with two Zn-N bonds (Zn-N_pz and Zn-N_py), one Zn-OH bond and two Zn-Cl bonds. The coordination geometry is intermediate between a trigonal bipyramid and a square pyramid. In this complex, the ligand pzol.2 is tridentated and forms two metallocycle rings.     

Manganese(II) coordination polymers with bis(5-tetrazolyl)methane: Synthesis, structure and magnetic properties

Two new Mn(II) coordination polymers with bis(5-tetrazolyl)methane (H₂btm), [Mn(btm)(phen)(H₂O)] · H₂O (1) and [Mn(btm)(2,2′-bpy)] · 1.5H₂O (2), have been synthesized and their structures determined by X-ray diffraction. In complex 1, the btm ligands assume the μ₂-1,1′:4 coordination mode and interlink Mn(II) ions into infinite one-dimensional chains. The chains are assembled into a three-dimensional architecture via hydrogen bonds and π-π interactions. For 2, Mn(II) ions are connected by btm ligands in the μ₃-1,1′:2:3′ mode to produce two-dimensional (6,3) coordination network. Magnetic investigations revealed that interactions through the btm bridges in both 1 and 2 are antiferromagnetic.     

Dinuclear and mononuclear copper(II) carboxylate complexes with cis-chelating diacids

The synthesis and crystal structures of two new copper complexes with chelating dicarboxylic acids are described. Reaction of copper(II) acetate with diacid H₂L2 (HO₂CC(Me)₂OArOC(Me)₂CO₂H, Ar=1,3-substituted phenyl) gave a bischelate complex (L2)₂Cu₂ · 2MeOH with the normal paddlewheel structure and tilted, trans-oriented chelate rings with skewed conformations. The overall structure was reasonably well reproduced by density functional calculations on (L2)₂Cu₂. Treatment of the product from reaction of Cu₂(OAc)₄ and diacid H₂L3 (Ar=1,3-substituted 2,4-dibromophenyl) with pyridine gave a six-coordinate mononuclear chelate (L3)Py₂Cu · H₂O in which one chelate carboxylate is monodentate, the other is unsymmetrically bidentate, and the pyridines are cis-coordinated.     

Synthesis of dimethylcobalt(III) complexes containing trimethylphosphine and 2-formyl-phenolato- or 2-formyl-enolato(O:O) ligands

Substituted salicylaldehydes [C₆HR¹R²R³(CHO)(OH)] react with CoMe₃(PMe₃)₃ to afford 6-coordinate (cis-dimethyl)(2-formyl-phenolato)trans-bis(trimethylphosphine)cobalt(III) compounds Co[C₆HR¹R²R³(CHO)(O)Me₂](PMe₃)₂ (1: R¹ = H; R² = Me; R³ = tert-Bu; 2: R¹, R² = C₆H₄; R³ = H). Accordingly, substituted enolated malonic dialdehydes (CHO-CR⁴CR⁵-OH) react with CoMe₃(PMe₃)₃ to afford 6-coordinate (cis-dimethyl)(2-formyl-enolato)trans-bis(trimethylphosphine)cobalt(III) compounds Co[(CHO-CR⁴CR⁵-O)(Me)₂](PMe₃)₂ (3: R⁴, R⁵ = (CH₂)₂C₆H₄; 4: R⁴ = R⁵ = C₆H₅). In the molecular structure of 4, the cobalt atom is centred in an octahedral coordination geometry brought about by a six-membered chelate ring (O:O-ligand), cis-dimethyl and trans-trimethylphosphine groups. A reaction mechanism is suggested.     

Synthesis and characterization of two isomers of Os3(CO)10(C5H4N-2-C(H)NR) and the conversion to ortho-metallated HOs3(C5H3N-2-C(H)NR)(CO)9. Part III. X-ray Structure of HOs3(C5H3N-2-C(H)Ni-Pr)(CO)9

Os₃(CO)₁₀(MeCN)₂ reacts at room temperature in MeCN or toluene with R-Pyca2 to yield two isomers of Os₃(CO)₁₀(R-Pyca) that differ in the bonding of the R-Pyca ligand to the Os₃(CO)₁₀ unit. In all cases Os₃(CO)₁₀(R-Pyca(4e)) (isomer A; 4a: R = c-Pr, 4b: R = i-Pr, 4c: R = neo-Pent, 4d: R = t-Bu), containing a chelating 4e donating R-Pyca ligand and three OsS bonds, could be isolated. In the case of R = c-Pr and R = i-Pr Os₃(CO)₁₀(R-Pyca(6e)) (isomer B; 5a: R = c-Pr, 5b: R = i-Pr), in which only two OsS bonds are present and the R-Pyca ligand is bonded as a 6e donating ligand bridging two non-bonded Os atoms, could be isolated as a minor product.At 70 °C Os₃(CO)₁₀(R-Pyca(4e)) (4b and 4d) loses one carbonyl and the pyridine moiety of the R-Pyca ligand is ortho-metallated to form HOs₃(C₅H₃N-2-C(H)NR)(CO)₉ (6b: R = i-Pr and 6d: R = t-Bu). Under the same conditions Os₃(CO)₁₀(i-Pr-Pyca(6e)) (5b) reacts to Os₂(CO)₆(6e)) (7b) containing a bridging 6e donating ligands. The latter two reactions were followed with FT-IR spectroscopy in a high temperature IR cell.The structure of the complexes in solution have been studied by ¹H and ¹C NMR and IR spectroscopy. The stoichiometries of 4a and 5a were determined by FAB-mass spectrometry while an exact mass determination was carried out for 4a.The crystal structure of 6b has been determined. Crystal of 6b are monoclinic, space group P2₁/n, with a = 7.808(2),b = 17.613(3),c = 16.400(8)Å, β = 94.09(3)° and Z = 4. The structure was refined to R = 0.039. The molecule contains a triangular array of osmium atoms [Os(1)Os(2) = 2.898(2)Å, Os(1)Os(3) = 2.886(2)Åand Os(2)O(3) = 2.911(2)Å] and nine terminally bonded carbonyl ligands. The C₅H₃N-2-C(H)N-i-Pr ligand is chelate bonded to Os(2) with the pyridine and imine nitrogens atoms axially and equatorially coordinated respectively [Os(2)N(1) = 2.00(2)Åand Os(2)N(2) = 2.11(2)Å]. The i-Pr-Pyca ligand is ortho-metallated at C(1) and forms a four membered ring containing Os(2), Os(3), C(1) and N(1), the Os(3)C(1) distance being 2.12(2)Å. The hydride, which could not be located unequivocally from a difference Fourier map is proposed to bridge the Os(2)(3) bond on the basis of stereochemical considerations.     

Coordination polymers of manganese(II) and cobalt(II) of a flexible tetradentate pyridine amide ligand: 1D zigzag network and non-covalent interactions

Synthesis and crystal structure of two coordination polymers of composition [Mn^II(H₂bpbn)_1.5][ClO₄]₂ · 2MeOH · 2H₂O (1) and [Co^II(H₂bpbn)(H₂O)₂]Cl₂ · H₂O (2) [H₂bpbn = N,N′-bis(2-pyridinecarboxamido)-1,4-butane], formed from the reaction between [Mn(H₂O)₆][ClO₄]₂/CoCl₂ · 4H₂O with H₂bpbn in MeCN, are described. In 1 each Mn^II ion is surrounded by three pyridine amide units, providing three pyridine nitrogen and three amide oxygen donors. Each Mn^II center in 1 has distorted MnN₃O₃ coordination. In 2 each Co^II ion is coordinated by two pyridine amide moieties in the equatorial plane and two water molecules provide coordination in the axial positions. Thus, the metal center in 2 has trans-octahedral geometry. In both 1 and 2, the existence of 1D zigzag network structure has been revealed. Owing to π-π stacking of pyridine rings from adjacent layers 1 forms 2D network; 2 forms 2D and 3D network assemblies via N-H?Cl and O-H?Cl secondary interactions. Both the metal centers are high-spin.     

Spectroscopic and structural studies of 6-(1-methylbenzimidazol-2-yl)-1H-pyridin-2-one and of an unusual T4(2)7(2)6(2)7(2) water tape stabilized by the copper(II) coordination polymer

The solid-state structures of 6-(1-methylbenzimidazol-2-yl)-1H-pyridin-2-one (HL) and the copper(II) complex [Cu(L⁻)₂(OH₂)]·2H₂O (1) are established by X-ray crystallography and also by means of physicochemical and spectroscopic methods. The molecules of HL form a self-complementary head-to-tail hydrogen-bonded dimer through C-H?N and C-H?O contacts to give an infinite 1D chain. The copper(II) complex (1) is five-coordinate with distorted trigonal-bipyramidal (TBP) geometry of the N₄O donor atoms. The electronic and EPR data are in agreement with the X-ray structure of 1, showing that HL coordinates to copper(II) centre as a mono-anionic ligand through deprotonated pyridone N atom and the tertiary benzimidazole nitrogen atom to form a neutral complex in which the water molecule occupies the fifth position. The 1D water tape, T4(2)7(2)6(2)7(2) is anchored to the host through hydrogen bonds between coordinated water molecule [O(3w)] as acting double H-donor, pyridone carbonyl groups [O(2) and O(1)] as double H-acceptor and the lattice water molecules [O(4w) and O(5w)] as double H-donor and single H-acceptor).     

Microsolvation effect and hydrogen-bonding pattern of taurine-water TA-(H2O)n (n = 1-3) complexes

The microsolvation of taurine (TA) with one, two or three water molecules was investigated by a density functional theory (DFT) approach. Quantum theory of atoms in molecules (QTAIM) analyses were employed to elucidate the hydrogen bond (H-bond) interaction characteristics in TA-(H₂O)_n (n = 1–3) complexes. The results showed that the intramolecular H-bond formed between the hydroxyl and the N atom of TA are retained in most TA-(H₂O)_n (n = 1–3) complexes, and are strengthened via cooperative effects among multiple H-bonds from n = 1–3. A trend of proton transformation exists from the hydroxyl to the N atom, which finally results in the cleavage of the origin intramolecular H-bond and the formation of a new intramolecular H-bond between the amino and the O atom of TA. Therefore, the most stable TA-(H₂O)₃ complex becomes a zwitterionic complex rather than a neutral type. A many-body interaction analysis showed that the major contributors to the binding energies for complexes are the two-body energies, while three-body energies and relaxation energies make significant contributions to the binding energies for some complexes, whereas the four-body energies are too small to be significant.