Synthesis and structural characterisation of five copper(I) and silver(I) complexes with 2-aminopyridine (2-APy), [Cu(μ-Cl)(2-Apy)(PPh3)]2, [Ag(μ-X)(2-Apy)(PPh3)]2 (X = Cl,Br), [Ag(μ-ONO2)(2-Apy)(EPh3)]2 (E = P,As)

Five new copper(I)/silver(I) complexes containing 2-aminopyridine, [Cu(μ-Cl)(2-Apy)(PPh₃)]₂(1), [Ag(μ-Cl)(2-Apy)(PPh₃)]₂(2), [Ag(μ-Br)(2-Apy)PPh₃)]₂(3), [Ag(μ-ONO₂)(2-Apy)(PPh₃)]₂(4), [Ag(μ-ONO₂)(2-Apy)(AsPh₃)]₂(5) have been synthesised for the first time. Complexes 1–5 are obtained by the reactions of MX (MX = CuCl for 1; M = Ag for 2–5; X = Cl, Br for 2–3; X = NO₃ for 4–5) with the monodentate ligands EPh₃ (E = P for 1–4; E = As for 5) and 2-Apy in the molar ratio of 1:1:2 in the mixed solvent of CH₂Cl₂ and MeOH. Complexes 1–5 are characterised by IR and X-ray diffraction. In 1–5, chloride, bromide and nitrate ions bridge two metal atoms to form dinuclear complexes containing the parallelogram cores M₂X₂ (M = Cu, Ag).     

Synthesis and structure of sulfur and selenium capped dihydride triruthenium clusters [Ru3(CO)7(μ-H)2(μ-dppm)(μ3-E)] (E = S, Se)

Reaction of [Ru₃(CO)₁₀(μ-dppm)] (1) with H₂S at 66 °C affords high yields of the sulfur-capped dihydride [Ru₃(CO)₇(μ-H)₂(μ-dppm)(μ₃-S)] (2), formed by oxidative-addition of both hydrogen-sulfur bonds. Hydrogenation of [Ru₃(CO)₇(μ-dppm)(μ₃-CO)(μ₃-S)] (3) at 110 °C also gives 2 in similar yields, while hydrogenation of [Ru₃(CO)₇(μ-dppm)(μ₃-CO)(μ₃-Se)] (4) affords [Ru₃(CO)₇(μ-H)₂(μ-dppm)(μ₃-Se)] (5) in 85% yield. The molecular structures of 2 and 5 reveal that the diphosphine and one hydride simultaneously bridge the same ruthenium-ruthenium edge with the second hydride spanning one of the non-bridged edges. Both 2 and 5 are fluxional at room temperature being attributed to hydride migration between the non-bridged edges. Addition of HBF₄ to 2 affords the cationic trihydride [Ru₃(CO)₇(μ-H)₃(μ-dppm)(μ₃-S)][BF₄] (6) in which the hydrides are non-fluxional due to the blocking of the free ruthenium-ruthenium edge.     

Synthesis,crystal structure and magnetic properties of a new dinuclear copper(II) amino acid complex [Cu2(l-arg)2(μ-HPO4-O)(μ-HPO4-O,O′)(μ-OH)] · (H3O) · (H2O)6

A novel dinuclear copper(II) complex with the amino acid l-arginine (l-arg), with mono and bidentate HPO₄²⁻ oxoanions and an OH⁻ anion. [Cu₂(l-arg)₂(μ-HPO₄-O)(μ-HPO₄-O,O′)(μ-OH)]⁻ · (H₃O)⁺ · 6H₂O (1) was prepared and its structure was determined by X-ray diffraction methods. The two independent copper ions are in a distorted square pyramidal coordination, each bonded to one l-arginine molecule. These two Cu(l-arg) units are bridged by two monoatomic equatorial–apical oxygen ligands belonging to a monodentate hydrogenphosphate group, and to the hydroxyl group. The copper ions in the dinuclear unit at d = 3.1948(8) Å are also connected by two equatorial oxygen belonging to a bidentate hydrogenphosphate. This dinuclear character and bridging scheme, not common for metal–amino acid compounds, is a consequence of the properties of the phosphate anions. The magnetic susceptibility at temperatures between 2 and 300 K and the isothermal magnetization curves at T = 2.29(1) K with applied fields up to 9 T were measured. The magnetic data indicate an antiferromagnetic intradinuclear exchange coupling J/k_B = −3.7(1) K and using a molecular field approximation we estimated a weaker ferromagnetic interaction J′/k_B ∼ 0.3 K between neighbour dinuclear units.     

The orthopalladation dinuclear [Pd(L1)(μ-OAc)]2, [Pd(L2)(μ-OAc)]2 and mononuclear [Pd(L3)2] complexes with [N, C, O] or [N, O] containing ligands: Synthesis, spectral characterization, electrochemistry and catalytic properties

Treatment of the salicylaldimine ligands (L₁H, L₂H, L₃H, L₄H and L₅H) with palladium(II) acetate in absolute ethanol gave the orthopalladation dinuclear [Pd(L₁)(μ-OAc)]₂, [Pd(L₂)(μ-OAc)]₂ and mononuclear [Pd(L₃)₂] with the tetradentate ligands [N, C, O] or [N, O] moiety. The ligands L₁H and L₂H are coordinated through the imine nitrogen and aromatic ortho carbon atoms, whereas the ligand L₃H coordinated through the imine nitrogen and phenolic oxygens atoms. The Pd(II) complexes have a square-planar structure and were found to be effective catalysts for the hydrogenation of both nitrobenzene and cyclohexene. These metal complexes were also tested as catalysts in Suzuki-Miyaura coupling of aryl bromide in the presence of K₂CO₃. The catalytic studies showed that the introduction of different groups on the salicyl ring of the molecules effected the catalytic activity towards hydrogenation of nitrobenzene and cyclohexene in DMF at 25 and 45 °C. The Pd(II) complexes easily prepared from cheap materials could be used as versatile and efficient catalysts for different C-C coupling reactions (Suzuki-Miyaura reactions). The structure of ligands and their complexes was characterized by UV-Vis, FT-IR, ¹H and ¹³C NMR, elemental analysis, molar conductivity, as well as by electrochemical techniques.     

Di-μ-hydroxo bridge-cleavage reactions between [Co(nta)(μ-OH)]2 2− and different monodentate ligands

The cleavage of the di--hydroxo bridges of [Co(nta)(-OH)]₂ ^2– by dimethylaminopyridine (dmap) and pyridine (py) has been investigated. [Co(nta)(-OH)]₂ ^2– equilibrates rapidly in aqueous basic solutions with a mono--hydroxo bridged Co^III species [pK _OH = 3.26(2)] and both these species react with the incoming ligand to form different ion associated species which react in the subsequent rate-determining steps (k ₁ and k ₂) to form presumably a ligand-substituted, mono-bridged species, [(nta)(OH)Co--OH-Co(nta)(L)]^2–. Values for k ₂, the preferred mono--hydroxo bridged substitution pathway for these reactions, vary between 6.8(2) × 10^–4 s^–1 (py) and 8.5(4) × 10^–2 s^–1 (dmap).     

Synthesis and structures of CpFe(CO)2(κE-ECS2Ph) and [CpFe(CO)(κS,E-ECS2Ph)] (E = S,Se)

The iron trithiocarbonato complex CpFe(CO)₂(κS-SCS₂Ph) (1a) and its selenodithiocarbonato analogue CpFe(CO)₂(κSe-SeCS₂Ph) (1b) were generated by room temperature reactions of (μ-E_x)[CpFe(CO)₂]₂ (E = S; x = 2, 3. E = Se; x = 1) with PhSC(S)Cl. These compounds can be converted into the complexes CpFe(CO)(κ²S,E-ECS₂Ph) [E = S (2a), Se (2b)], in which the trithiocarbonato or the selenodithiocarbonato ligand is bonded to the iron in a chelate form, under photolytic conditions. The composition and structure of all products have been verified by elemental analyses, IR and ¹H NMR spectroscopies. The crystal structures for compounds 1a, 1b, and 2b show a three-legged piano-stool configuration at Fe in each complex. The spectroscopic and structural data in this work are commensurate with the electronic factor of the S- and Se-donor ligands.     

Generation of Ir-Sn and Rh-Sn bonds from the oxidative addition of tin(IV) halides to [Ir(μ-Cl)(1,5-COD)]2 and [Rh(μ-Cl)(1,5-COD)]2

Facile oxidative addition of SnCl₄, MeSnCl₃, and SnBr₄ across Ir(I) and Rh(I) cyclooctadiene complexes resulted in the formation of the corresponding Ir-Sn and Rh-Sn heterobimetallic complexes. Treatment of SnCl₄ with [Ir(COD)(μ-Cl)]₂ and [Rh(COD)(μ-Cl)]₂ afforded [Ir(COD)(μ-Cl)Cl(SnCl₃)]₂ (1) and [Rh(COD)(μ-Cl)Cl(SnCl₃)]₂ (2), respectively. Reaction of the organotin halide MeSnCl₃ with [Ir(COD)(μ-Cl)]₂ led to the formation of [Ir(COD)(μ-Cl)Cl(MeSnCl₂)]₂ (3). The reaction of SnBr₄ to Ir^I and Rh^I precursors gave [Ir(COD)(μ-Br)Br(SnBr₃)]₂ (4) and [Rh(COD)(μ-Br)Br(SnBr₃)]₂ (5) respectively, which indicates halide exchange at post-oxidative addition stage. The structures of complexes 1-5 were confirmed by X-ray crystallography. A cis-addition of Sn-X bond across Ir^I/Rh^I is proposed from the analysis of the geometrical features of “X-M-Sn” triangular units in 1-5.     

Syntheses,spectral, thermal and structural characterization of dinuclear and polynuclear copper(II) orotate complexes, [Cu2(HOr)2(H2O)4] and [Cu(μ-HOr)(ba)2]n

The novel catena-poly-μ-orotatobis(butylamine)copper(II), [Cu(μ-HOr)(ba)₂]_n (1), and diaqua(orotato)copper(II), [Cu₂(HOr)₂(H₂O)₄] (2), complexes have been prepared and characterized by elemental analysis, magnetic measurements, FT-IR spectroscopy, EPR spectroscopy, thermal analysis and X-ray diffraction. Both complexes crystallize in the monoclinic space group, C2/c in 1 and P2₁/n in 2. In the complexes, the copper(II) ion is chelated by a deprotonated pyrimidine nitrogen atom and a carboxylate oxygen atom of the orotate. While the coordination sphere around Cu(II) is completed by two N atoms from butylamine groups and a carboxylic O atom in the axial position from a neighboring molecule in 1, the square-planar environment of Cu(II) is completed by two water atoms and one axial position is occupied by the carbonyl oxygen atom from the symmetry related molecule in 2. The coordination sphere should be described as a square pyramid and (4+1)-geometry in 1 and 2, respectively. While complex 1 shows a polymeric arrangement, compound 2 has a dimeric arrangement. The non-covalent Cu(II)-π binding force is very important for stabilizing the crystal structure of 2. The thermal decomposition of the complexes has been predicted by the help of thermal analysis (TG, DTG and DTA).     

Synthesis of electronically and coordinatively unsaturated complexes [Ru2(CO)4(μ-H)(μ-PBu2)(μ-L2)] (L2 = biphosphanes)

A convenient synthesis and the characterization of six new electronically and coordinatively unsaturated complexes of the formula [Ru₂(CO)₄(μ-H)(μ-P^tBu₂)(μ-L₂)] (2b-g) (RuRu) is described exhibiting a close relation to the known [Ru₂(CO)₄(μ-H)(μ-P^tBu₂)(μ-dppm)] (2a). The complexes 2b-g were obtained in a kind of one-pot synthesis starting from [Ru₃(CO)₁₂] and P^tBu₂H in the first step followed by the reaction with the bidentate bridging ligand in the second step. The method was developed for the following bridging ligands (μ-L₂): dmpm (2b, dmpm = Me₂PCH₂PMe₂), dcypm (2c, dcypm = Cy₂PCH₂PCy₂), dppen (2d, dppen = Ph₂PC(=CH₂)PPh₂), dpppha (2e, dpppha = Ph₂PN(Ph)PPh₂), dpppra (2f, dpppra = Ph₂PN(Pr)PPh₂), and dppbza (2g, dppbza = Ph₂PN(CH₂Ph)PPh₂). The molecular structures of all new complexes 2b−g were determined by X-ray diffraction.     

Synthesis, Characterization and Crystal Structure of [Na2(APZC)2(μ-H2O)2(μ3-H2O)]n

The synthesis and spectroscopic properties of a Na^＋ complex with ligand 3-aminopyrazine-2-carboxylic acid were described. The resulting complex was characterized by elemental analysis, IR, UV-Vis, NMR spectroscopy and single crystal X-ray diffraction method. The title compound crystallizes in the triclinic system with space group . The crystalline structure of this compound consists of supramolecular architectures involving strong intramolecular N—H…O in pyrazine molecules and intermolecular O—H…N, O—H…O, and N—H…N hydrogen bonds between substituted pyrazine and water molecules.     

Hydrothermal synthesis,crystal structures,and properties of two 3-D network nickel nicotinate coordination polymers: [Ni4(μ-H2O)2(nicotinate)8 · 2H2O] and [Ni2(H2O)2(nicotinate)4(4,4′-bpy)]

The three-dimensional coordination polymers [Ni₄(μ-H₂O)₂(nic)₈ · 2H₂O] (nic = nicotinate, 3-pyridylcarboxylate) (1) and [Ni₂(H₂O)₂(nic)₄(4,4′-bpy)] (2) were prepared by the hydrothermal reaction of nickel(II) chloride, nicotinic acid, sodium hydroxide and an organoimine (several choices for 1, 4,4′-bipyridine for 2). The non-centrosymmetric crystal structure of 1 is constructed from binuclear [Ni₂(μ-H₂O)(μ₃-nic)₂]²⁺ subunits joined into 3-D via μ₂- and μ₃-nicotinate ligands, forming “bird”-shaped cavities that contain water molecule dimers. The crystal structure of 1 is compared and contrasted to two previously reported nickel(II) nicotinate phases. In contrast, the crystal structure of 2 is assembled from neutral [Ni(H₂O)(μ₂-nic)₂] layers, connected into 3-D via tethering 4,4′-bpy moieties. 1 exhibits weak antiferromagnetic coupling across its binuclear subunits (J = −1.61(2) cm⁻¹ for g = 2.233(2)), although anisotropy due to single-ion zero-field-splitting (D) cannot be excluded. The 3-D structures of 1 and 2 remain stable above 300 °C and 200 °C, respectively.     

Reactivity of [Os3(CO)10(NCMe)2] and [Os3(CO)10(μ-Cl)(μ-AuPPh3)] with 4-mercaptopyridine: X-ray structure of [Os3(CO)10(μ-H)(μ-SC5H4N)] and [Os3(CO)10(μ-AuPPh3)(μ-SC5H4N)]

The compound [Os₃(CO)₁₀(μ-Cl)(μ-AuPPh₃)] (2) was prepared from the reaction between [Os₃(CO)₁₀(NCMe)₂] (1) and [AuClPPh₃] under mild conditions. The reaction of 2 with 4-mercaptopyridine (4-pyS) ligand yielded compounds [Os₃(CO)₁₀(μ-H)(μ-SC₅H₄N)] (4), formed by isolobal replacement of the fragment [AuPPh₃]⁺ by H⁺ and [Os₃(CO)₁₀(μ-AuPPh₃)(μ-SC₅H₄N)] (5). [Os₃(CO)₁₀(μ-H)(μ-SC₅H₄N)] (4) was also obtained by substitution of two acetonitrile ligands in the activated cluster 1 by 4-pyS, at room temperature in dichloromethane. Compounds 2-5 were characterized spectroscopically and the molecular structures of 4 and 5 in the solid state were obtained by single crystal X-ray diffraction studies.     

Synthesis and Crystal Structure of [Cd(NBA)(μ_3-OH)(4,4′-bipy)_(1/2)]_n

A new cadmium polymer [Cd(NBA)(μ3-OH)(4,4′-bipy)1/2]n 1 (NBA = m-nitrobenzoic acid and 4,4′-bipy = 4,4-bipyridine) has been synthesized by hydrothermal reaction. Its structure was determined by single-crystal X-ray diffraction method, and characterized by elemental analysis and IR spectrum. The crystal is of monoclinic, space group C2/c, with a = 15.6912(9), b = 25.9394(15), c = 6.7332(4) ′, β = 114.7700(10)°, V = 2488.4(3) 3, C12H9CdN2O5, Mr = 373.61, Z = 8, Dc = 1.995 g/cm3, μ = 1.776 mm-1, F(000) = 1464, R = 0.0411 and wR = 0.1128 for 2130 observed reflections (I > 2σ(I)). X-ray diffraction studies reveal that the compound features a layered structure, in which 4,4′-bipy ligands bridge Z type of double chains [Cd(μ3-OH)]n and NBA ligands locate at the two sides of the layer. The π-π interactions between the benzene rings of NBA ligands of two adjacent layers lead to the 3D framework.     

Syntheses, structures, and dynamic properties of M(CO)2(η-C3H5)(en)(X) (M = Mo, W; X = Br, N3, CN) and [(en)(η-C3H5)(CO)2M(μ-CN)M(CO)2(η-C3H5)(en)]Br (M = Mo, W)

Mononuclear compounds M(CO)₂(η³-C₃H₅)(en)(X) (X = Br, M = Mo(1), W(2); X = N₃, M = Mo(3), W(4); X = CN, M = Mo(5), W(6)) and cyanide-bridged bimetallic compounds [(en)(η³-C₃H₅)(CO)₂M(μ-CN)M(CO)₂(η³-C₃H₅)(en)]Br (M = Mo (7), W(8)) were prepared and characterized. These compounds are fluxional and display broad unresolved proton NMR signals at room temperature. Compounds 1-6 were characterized by NMR spectroscopy at −60 °C, which revealed isomers in solution. The major isomers of 1-4 adopt an asymmetric endo-conformation, while those of 5 and 6 were both found to possess a symmetric endo-conformation. The single crystal X-ray structures of 1-6 are consistent with the structures of the major isomer in solution at low temperature. In contrast to mononuclear terminal cyanide compounds 5 and 6, cyanide-bridged compounds 7 and 8 were found to adopt the asymmetric endo-conformation in the solid state.     

Synthesis and characterization of mono and polymeric cyclopalladated compounds: Crystal and molecular structure of [{Pd(dmba)(ONO2)}2(μ-pz)] · H2O (pz = pyrazine)

In the treatment of cyclometallated dimer [Pd(dmba)(μ-Cl)]₂ (dmba = N,N-dimethylbenzylamine) with AgNO₃ and acetonitrile the result was the monomeric cationic precursor [Pd(dmba)(NCMe)₂](NO₃) (NCMe = acetonitrile) (1). Compound 1 reacted with m-nitroaniline (m-NAN) and pirazine (pz), originating [Pd(dmba)(ONO₂)(m-NAN)] (2) and [{Pd(dmba)(ONO₂)}₂(μ-pz)] · H₂O (3), respectively. These compounds were characterized by elemental analysis, IR and NMR spectroscopy. The IR spectra of (2–3) display typical bands of monodentade O-bonded nitrate groups, whereas the NMR data of 3 are consistent with the presence of bridging pyrazine ligands. The structure of compound 3 was determined by X-ray diffraction analysis. This packing consists of a supramolecular chain formed by hydrogen bonding between the water molecule and nitrato ligands of two consecutive [Pd₂(dmba)₂(ONO₂)₂(μ-pz)] units.     

A unique example of a co-crystal of [Ag(atr)2][Cr(dipic)2] (dipic = dipicolinate; atr = 3-amino-1H-1,2,4-triazole) and dinuclear [Cr(H2O)(dipic)(μ-OH)]2, with different coordination environment of Cr(III) ions

Treatment of a neutral aqueous solution of dipicolinic acid (dipicH₂), 3-amino-1H-1,2,4-triazole (atr) and CrCl₃·6H₂O in the presence of AgNO₃ (in molar ratio 1:1:1:3) under hydrothermal condition led to the formation of a co-crystal of {[Ag(atr)₂][Cr(dipic)₂]}₂·[Cr(H₂O)(dipic)(μ-OH)]₂·4H₂O (1). Compound 1 was characterized by elemental analyses, IR and UV-Vis spectroscopy as well as X-ray diffraction studies. The structure consists of two [Ag(atr)₂]⁺ cations, two [Cr(dipic)₂]⁻ anions, one co-crystallized neutral dinuclear chromium(III) complex, [Cr(H₂O)(dipic)(μ-OH)]₂, and four co-crystallized water molecules. Silver(I) ion in [Ag(atr)₂]⁺ is coordinated by two monodentate 3-amino-1H-1,2,4-triazole ligands, bound via endocyclic nitrogen atoms, in a linear fashion. Chromium(III) ion is octahedrally coordinated by two O,N,O-tridentate dipicolinate ligands in anionic complex. Each chromium(III) ion in neutral dinuclear complex, [Cr(H₂O)(dipic)(μ-OH)]₂, is octahedrally coordinated by one O,N,O-tridentate dipicolinate ligand, one water molecule and two bridging μ-OH ions in cis position. Thermal methods (TGA/DTA) confirm the number of co-crystallized water molecules in 1.     

[M(dipicH2)(H2O)3], M = Ni,Cu, Zn (dipicH2 = dipicolinic acid) – A combined crystallographic,spectroscopic and computational study

Cationic metal complexes of dipicolinic acid (dipicH₂) are stabilized by [Ce(dipic)₃]²⁻ ions in the three isomorphous crystals [M(dipicH₂)(OH₂)₃][Ce(dipic)₃] · 3H₂O (M = Ni, 1; Cu, 2; Zn, 3). Magnetic dilution provided by the bulky anions leads to well-resolved EPR spectra in polycrystalline samples of 2. The cations have 4+2 coordination, the carbonyl atom of the carboxylic acid groups coordinating weakly from trans positions. In the case of 2 this steric distortion is augmented by Jahn–Teller distortion. All the three structures are satisfactorily modelled by calculations based on density functional theory (DFT). The switch of the Jahn–Teller axis upon deprotonation of the complex, leading to the neutral species Cu(dipic)(H₂O)₃, is also reproduced by DFT. Electronic transition energies as well as the g-tensor component of the d⁹ complex obtained are in good agreement with experiment. However, the calculated hyperfine coupling constants are in error. DFT also fails to satisfactorily account for the electronic transition in the d⁸ ion in 1.     

Synthesis and characterization of binuclear μ-oxo and μ-telluro molybdenum(V) complexes, [CpMo(O)(μ-Te)]2

Pyrolysis of an in-situ generated intermediate, produced in the reaction of [Cp^∗MoCl₄], 1, (Cp^∗ = η⁵-C₅Me₅) with [LiBH₄·THF], with an excess of difuryl ditelluride in toluene at 90 °C yielded syn and anti isomers of [Cp^∗Mo(O)(μ-Te)]₂ (2, 3) and [Cp^∗₂Mo₂O₂(μ-O)(μ-Te)] (4, 5). In a similar fashion, dibenzyl diselenide yielded syn and anti isomers of [Cp^∗Mo(O)(μ-Se)]₂ (6, 7), along with the known nido-[(Cp^∗Mo)₂B₄H₈Se₂]. Note that in parallel with 2-7, [(Cp^∗Mo)₂B₅H₉] was isolated as the major product in both cases. Compounds 2-7 have been isolated in modest yield as orange to brown crystalline solids. All the new compounds have been characterized in solution by mass, IR, ¹H, ¹³C, ⁷⁷Se and ¹²⁵Te NMR spectroscopy, and the structural types were unequivocally established by crystallographic analysis of 2-4 and 7.