Preparation and structural characterization of [RuCl2(CO)2{Te(CH2SiMe3)2}2] and [RuCl2(CO){Te(CH2SiMe3)2}3]

The objective of the present work was to synthesize mononuclear ruthenium complex [RuCl₂(CO)₂{Te(CH₂SiMe₃)₂}₂] (1) by the reaction of Te(CH₂SiMe₃)₂ and [RuCl₂(CO)₃]₂. However, the stoichiometric reaction affords a mixture of 1 and [RuCl₂(CO){Te(CH₂SiMe₃)₂}₃] (2). The X-ray structures show the formation of the cis(Cl), cis(C), trans(Te) isomer of 1 and the cis(Cl), mer(Te) isomer of 2. The ¹²⁵Te NMR spectra of the complexes are reported. The complex distribution depends on the initial molar ratio of the reactants. With an excess of [RuCl₂(CO)₃]₂ only 1 is formed. In addition to the stoichiometric reaction, a mixture of 1 and 2 is observed even when using an excess of Te(CH₂SiMe₃)₂. Complex 1 is, however, always the main product. In these cases the ¹²⁵Te NMR spectra of the reaction solution also indicates the presence of unreacted ligand.     

Metal(II)-promoted hydrolysis of pyridine-2-carbonitrile to pyridine-2-carboxylic acid. The structure of [Cu(pyridine-2-carboxylate)2] · 2H2O

Pyridine-2-carbonitrile (2-CNpy) undergoes Cu(II) or Co(II)-promoted hydrolysis to pyridine-2-carboxamide (piaH) and/or pyridine-2-carboxylic acid (pycH). The pathway of pycH formation depends on the presence of 2-amino-2-hydroxymethyl-1,3-propanediol (AL¹) and on the central atom. In the absence of AL¹, Co(II) or Cu(II) ions mediate piaH formation under mild reaction conditions in the first hydrolytic step. Cu(II) ions assist in piaH transformation to pycH by subsequent reflux. In the presence of AL¹ and Co(II), a Co(II) complex containing pyoxaL¹ (2-(2-pyridinyl)-4,4-bis(hydroxymethyl)-2-oxazoline) is formed in the first stage; subsequent decomposition of pyoxaL¹ under the reflux yields pycH. Under similar conditions, no solid Cu(II) complex with pyoxaL¹ can be isolated, but a Cu(II) complex with coordinated pyc⁻ anions precipitates from the reaction mixture. The synthesis, spectral and magnetic properties of the complexes [Co(H₂O)₂ (piaH)₂]Cl₂, [Co(H₂O)₂(pyc)₂] · 2H₂O, [Cu(H₂O)₂(piaH)₂]Cl₂, [Cu(pyc)₂] and [Cu(pyc)₂] · 2H₂O, including the structure determination of the latter one, are described.     

The first non-acetato members of the bis(anion)octacarboxylatotetrakis{di-2-pyridyl-methanediolate(−2)}enneametal(II) family of complexes: Synthesis, X-ray structures and magnetism of [M9(N3)2(O2CCMe3)8{(py)2CO2}4] (M = Co, Ni)

The combined use of di-2-pyridyl ketone [(py)₂CO] and azides (N₃⁻) in nickel(II) and cobalt(II) pivalate chemistry has afforded complexes [Ni₉(N₃)₂(O₂CCMe₃)₈{(py)₂CO₂}₄] (1) and [Co₉(N₃)₂(O₂CCMe₃)₈{(py)₂CO₂}₄] (2), where (py)₂CO₂²⁻ is the gem-diolate(−2) form of (py)₂CO. The complexes are isostructural and crystallize in the monoclinic P2₁/c space group. Their molecular structures consist of nine metal(II) ions, eight of which are arranged as two parallel squares flanking the ninth. DC magnetic susceptometry on powdered samples of 1 (1-p) reveal an overall antiferromagnetic behavior, leading to an S = 0 ground state. AC susceptometry reveals out-of-phase signals between 10 and 27 K, and ZFC and FC experiments show a divergence of the two curves below ∼27 K. Magnetization-decay and field-sweep experiments verify the relaxation behavior of the sample. Samples of the complex arising from carefully washed single crystals (1-cr) reveal a similar DC behavior, without however the appearance of cusps in the χ_ΜΤ versus T curves, and no relaxation. The relaxation behavior has been assigned to NiO impurities. The results illustrate the extreme care that should be taken when examining the magnetic properties of apparently analytically pure materials obtained under heating. Complex 2 exhibits an overall antiferromagnetic behavior, without observation of any relaxation phenomena.     

Synthesis and structural aspects of M-allyl (M = Ir, Rh) complexes

The synthesis, characterization and chemistry of novel η³-allyl metal complexes (M = Ir, Rh) are described. The structures of compounds (C₅Me₄H)Ir(PPh₃)Cl₂ (1), (C₅Me₄H)Ir(PPh₃)(η³-1-methylallyl)Br (3a), (C₅Me₄H)Ir(η⁴-1,3,5-hexatriene) (8), and (C₅Me₅)Rh(η³-1-ethylallyl)Br (5d) have been determined by X-ray crystallography. Structural comparisons among these complexes are discussed. It is found that the neutral metal allylic complex [Cp^∗IrCl(η³-methylallyl)] (5) ionizes in polar solvents to give [Cp^∗Ir(η³-methylallyl)]⁺Cl⁻ (6) and reaches equilibrium (5 ? 6) at room temperature. Addition of tertiary phosphine ligands to neutral complexes such as [Cp^∗Ir(η³-methylallyl)Cl], results in the formation of stable ionic phosphine adducts. Factors such as solvent, length of carbon chain, temperature and light are discussed with respect to the formation, stability and structure of the allyl complexes.     

Crystal structure and spectral characterization of hexanuclear oxo titanium(IV) clusters: [Ti6O6(OSi(CH3)3)6(OOCR)6] (R = Bu,CH2Bu,C(CH3)2Et)

Hexanuclear oxo titanium(IV) siloxo carboxylate complexes with the general formula [Ti₆O₆(OSi(CH₃)₃)₆(OOCR)₆] (R = Bu^t (1), CH₂Bu^t (2), C(CH₃)₂Et (3)) were synthesized in quantitative yield, by the reaction of Ti(OSiMe₃)₄ with the appropriate organic acid. Crystal structure determination revealed that molecules of 1–3 are composed of [Ti₆-(μ₃-O)₆] cores stabilized by six syn–syn carboxylato bridges and six terminal siloxide ligands. Each metal atom is surrounded by six oxo atoms, capping the triangular faces of the distorted octahedron. Spectral characterization (IR, NMR) of 1–3 revealed a significant non-equivalence of the carboxylate group interactions, resulting from the asymmetry of the Ti-μ-OOC bonds of the syn–syn bridges. The thermal stability of the studied compounds was determined from TGA/DTA analysis.     

Synthesis and structural characterization of cobalt(II) and zinc(II) complexes with 2-(indazol-1-yl)-2-thiazoline (TnInA). X-ray characterization of [CoCl2(TnInA)2] · C2H6O and [(M)(TnInA)2(H2O)2](NO3)2 (M = Co, Zn)

Several complexes of 2-(indazol-1-yl)-2-thiazoline (TnInA) with the divalent ions Co and Zn have been synthesized by the direct combination of the ligand and the metal chloride or nitrate hydrated salts in ethanol. These complexes have been characterized by a variety of physical–chemical techniques. Moreover, the structures of [CoCl₂(TnInA)₂] · C₂H₆O (1) and [(M)(TnInA)₂(H₂O)₂](NO₃)₂ (M = Co, 3; Zn, 4) were determined by single-crystal X-ray diffraction. In all the complexes, the ligand TnInA bonds to the metal ion through the indazole and thiazoline nitrogen atoms. In complex 1 the environment around the cobalt ion may be described as a distorted octahedron with two TnInA ligands and two chlorine ligands. Compounds 3 and 4 are isostructural with a distorted octahedral geometry around the metal center, being linked to two water molecules and two TnInA ligands. However, in complex [ZnCl₂(TnInA)] (2) the zinc atom is four-coordinated with a probable tetrahedral environment with two chloro ligands and one TnInA ligand bonded to the metal ion.     

Synthesis and characterization of some novel cadmium(II) complexes with 3-hydroxypicolinic acid (3-OHpicH): Crystal and molecular structures of [CdI(3-OHpic)(3-OHpicH)(H2O)]2, [Cd(3-OHpic)2(H2O)2] and [Cd(3-OHpic)2]n

Cadmium(II) complexes of 3-hydroxypicolinic acid, namely [CdI(3-OHpic)(3-OHpicH)(H₂O)]₂ (1), [Cd(3-OHpic)₂(H₂O)₂] (2) and [Cd(3-OHpic)₂]_n (3) were prepared and characterized by spectroscopic methods (IR, NMR) and their molecular and crystal structures were determined by X-ray crystal structure analysis. Complexes 1 and 2 were prepared in similar reaction conditions using different cadmium(II) salts: cadmium(II) iodide and cadmium(II) acetate dihydrate, respectively, while 3 was prepared by recrystallization of 2 from N,N-dimethylformamide solution. Various coordination modes of 3-OHpicH in 1–3 were established in the solid state: bidentate N,O-chelated mode in 1 and 2, monodentate mode through the carboxylate O atom from zwitterionic ligand in 1 and bidentate N,O-chelated and bridging mode in 3. In the DMF solution of all prepared complexes, only monodentate mode of 3-OHpicH binding to cadmium(II) through the carboxylate O atom was established by ¹H, ¹³C, ¹⁵N and ¹¹³Cd NMR spectroscopy.     

Synthesis, characterization and structural studies of dithiocarbamate derivatives of 2,2,6,6-tetramethyl-1-oxa-4,4-diiodo-4-tellura-2,6-disilacyclohexane,O[Si(CH3)2CH2]2TeI(dtc)

Five new hetero-organotellurium (IV) dithiocarbamates O[Si(CH₃)₂CH₂]₂TeIS₂CN(CH₂CH₂)₂ (1), O[Si(CH₃)₂CH₂]₂TeIS₂CN(CH₂CH)₂ (2), O[Si(CH₃)₂CH₂]₂TeIS₂CN(CH₂CH₂)₂O (3), O[Si(CH₃)₂CH₂]₂-TeIS₂CN(CH₂CH₂)₂S (4) and O[Si(CH₃)₂CH₂]₂TeIS₂CN(CH₂CH₂)₂CH₂ (5) were prepared from the 2,2,6,6-tetramethyl-1-oxa-4,4-diiodo-4-tellura-2,6-disilacyclohexane and the corresponding dithiocarbamate (dtc) sodium salts in ethanol. The compounds were characterized by means of Elemental Analyses, FAB MS, IR, ¹H, ¹³C, ¹²⁵Te NMR spectroscopy. The crystal structures of 1, 3 and 4 were determined. Dithiocarbamate ligands display an anisobidentate chelating coordination mode on interacting with the tellurium center in all compounds. The Te(IV) immediate environment can be described as that of a sawhorse structure in which the lone pair is apparently stereochemically active and occupying an equatorial position in a distorted trigonal bipyramid. The two methylene groups occupy the other equatorial positions with a sulfur atom of the dithiocarbamate group and the iodine atom occupying the axial positions. The solid state structures of 3 and 4 exhibit important intermolecular interaction Te?S(2B). This interaction results in the formation of a dimer, which is better described as a distorted octahedron with an apparently inactive lone pair.     

Synthetic studies for the preparation of phosphorus carbonyl rhenacycles with the selenoimidodiphosphinate ligand [N(SePPh2)2]

The synthesis of the rhenacycles [Re(CO)₃(PR₃){Ph₂P(Se)NP(Se)Ph₂-κ²Se}], PR₃ = PPh₃ (1), PMePh₂ (2), and PMe₂Ph (3) by a straightforward high yield procedure is described. Attempts at the preparation of the spiro [Re(CO)₂(Ph₂PCH₂CH₂PPh₂-κ²P){Ph₂P(Se)NP(Se)Ph₂-κ²Se}] resulted in the formation of complexes [Re₂(CO)₆{Ph₂P(Se)NP(Se)Ph₂-κ²Se}₂(μ-Ph₂PCH₂CH₂PPh₂)] (4) and [Re(CO)₃(Ph₂PCH₂CH₂PPh₂-κ²P){Ph₂P(Se)NP(Se)Ph₂-κSe}] (5). All new inorganic rhenacycles 1-5 were characterized in solution and in solid state. The X-ray diffraction analysis of [Re(CO)₃PPh₃{Ph₂P(Se)NP(Se)Ph₂-κ²Se}] showed that its MnSePNPSe ring conformation is sensitive to temperature.     

The decomposition kinetics of [Et4N]2[M(dmit)2] (M = Ni, Pd) in a nitrogen atmosphere using thermogravimetry

Thermal properties and thermal decompositions of [NEt₄]₂[M(dmit)₂] (M = Ni(II), Pd(II), dmit = 1,3-dithiole-2-thione-4,5-dithiolate) have been studied by thermogravimetry (TG). The TG analysis has shown that the complexes are thermally stable up to 460 K and the decomposition of the complexes occurs in three consecutive stages up to 873 K. A thermal stability scale for [M(dmit)₂]ⁿ⁻ anions was based on the thermal properties. Kinetics parameters, such as activation energy, E_a, and kinetic apparent pre-exponential factor, ln A_app, have been calculated from the thermogravimetric data at heating rates of 10, 15, 20 and 25 K/min involving differential (Friedman's equation) and integral (Flynn-Wall-Ozawa's equation) methods.     

Synthesis,structure and properties of [ML(NO3)2]: M = Co,Ni, Cu; L = N-(2-pyridylethyl)pyridine-2-carbaldimine

Syntheses of complexes of the type [ML(NO₃)₂], where M = Co(II), Ni(II), and Cu(II), L = N-(2-pyridylethyl)pyridine-2-carbaldimine, a tridentate ligand, are described. They were characterized by elemental analysis, spectral, magnetic, thermal studies, and X-ray crystallography. In the cobalt (1), nickel (2), and copper (3) complexes, the bivalent metal ion is coordinated by the three nitrogen atoms of the tridentate L with two pyridine-N groups occupying trans positions. Amongst the two nitrates one coordinates in a bidentate fashion while the other adopts a monodentate fashion. The X-band EPR spectra of 1, 2, and 3 in the polycrystalline state and in acetonitrile solution at 77 K are reported. Room temperature vibrating sample magnetometer data of 1, 2, and 3 afforded μ_eff values respectively of 3.928, 3.897, and 1.952 BM. The thermal stability order is 1 > 2 > 3, showing a reverse Irving-Williams trend.     

Diorganotin(IV) complexes of dideprotonated pyridoxine (PN, vitamin B6). The crystal structures of [SnEt2(PN-2H)] · CH3OH, [SnEt2(PN-2H)(DMSO)] and [SnBu2(PN-2H)]

The reactions of dimethyl-, diethyl- and dibutyltin(IV) oxides with pyridoxine (PN) in toluene/ethanol led to the formation of compounds [SnR₂(PN-2H)] which were characterized by EI and FAB mass spectrometry and by IR, Raman, Mössbauer and ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy. The structures of [SnEt₂(PN-2H)] · CH₃OH, [SnBu₂(PN-2H)] and [SnEt₂(PN-2H)(DMSO)] were determined by X-ray diffractometry. The first two contain dimeric [SnR₂(PN-2H)]₂ units in which two bridging-chelating pyridoxinate anions link the Sn atoms, while in [SnEt₂(PN-2H)(DMSO)] the DMSO coordinates to the tin atom via its O atom in a similar dimeric unit.     

Synthesis, characterization and reactivity of the molybdenum(VI) complex [MoCl(NAr)2(CH2CMe2Ph)] (Ar=2,6-Pr2C6H3)

The compounds [MoCl(NAr)₂R] (R=CH₂CMe₂Ph (1) or CH₂CMe₃(2); Ar=2,6-Prⁱ₂C₆H₃) have been prepared from [MoCl₂(NAr)₂(dme)] (dme=1,2-dimethoxyethane) and one equivalent of the respective Grignard reagent RMgCl in diethyl ether. Similarly, the mixed-imido complex [MoCl₂(NAr)(NBu^t)(dme)] affords [MoCl(NAr)(NBu^t)(CH₂CMe₂Ph)] (3). Chloride substitution reactions of 1 with the appropriate lithium reagents afford the compounds [MoCp(NAr)₂(CH₂CMe₂Ph)] (4) (Cp=cyclopentadienyl), [MoInd(NAr)₂(CH₂CMe₂Ph)] (5) (Ind=Indenyl), [Mo(OBu^t)(NAr)₂(CH₂CMe ₂Ph)] (6), [MoMe(NAr)₂(CH₂CMe₂Ph)] (7), [MoMe(PMe₃)(NAr)₂(CH₂CMe ₂Ph)] (8) (formed in the presence of PMe₃) and [Mo(NHAr)(NAr)₂(CH₂CMe₂P h)](9). In the latter case, a by-product {[Mo(NAr)₂(CH₂CMe₂Ph) ]₂(μ-O)}(10) has also been isolated. The crystal structures of 1, 4, 5 and 10 have been determined. All possess distorted tetrahedral metal centres with cis near-linear arylimido ligands; in each case (except 5, for which the evidence is unclear) there are α-agostic interactions present.     

Synthesis, crystal structure and bioactivity of a novel 18-metallacrown-6 [Mn6(H2O)6 (anshz)6] · 10DMF

A novel macrocyclic hexanuclear manganese(III) 18-metallacrown-6 compound, [Mn₆(H₂O)₆ (anshz)₆] · 10DMF, has been prepared using a trianionic pentadentate ligand N-acetyl-5-nitrosalicylhydrazide (anshz³⁻) and characterized by X-ray diffraction (DMF = N,N-dimethylformamide). The crystal structure contains a neutral 18-membered metallacrown ring consisting of six Mn(III) and six anshz³⁻ ligands. The 18-membered metallacrown ring is formed by the succession of six structural moieties of the type [Mn(III)NN]. Due to the meridional coordination of the ligand to the Mn³⁺ ion, the ligand enforces the stereochemistry of the Mn³⁺ ions as a propeller configuration with alternating Δ/Λ forms. The disc-shaped hexanuclear ring shows at its largest diameter about 7.14 Å at entrance, about 9.76 Å at the center of the cavity, respectively. Antibacterial screening data showed that the manganese metallacrown has strong antimicrobial activity against Bacillus subtilis.     

X-Ray, FTIR and quantum chemical studies of short and asymmetric hydrogen bonds in bis(2,6-dimethylpyridine-N-oxide) sulphate [2,6-(CH3)2C5H3N---OH]2[SO4]

Crystals of bis(2,6-dimethylpyridine-N-oxide) sulphate are monoclinic, space group P2₁/c, a = 14.098(2) Å, b = 7.855(1) Å, c = 15.203(3) Å, β = 104.84(1)°. The crystal structure has been refined to R = 0.0373 (2052 reflections). The disordered SO²⁻₄ anion accepts hydrogen bonds from two protonated 2,6-dimethylpyridine-N-oxides and two alternative conformations of the SO²⁻₄ group are distinguished. The occupancy factor of the predominant orientation is 0.63 and the O...O distances are 2.445(2) and 2.453(4) Å; in the second form (fraction, 0.37), these distances are 2.445(2) and 2.544(9) Å.

The PM3 and AM1 methods predict three minima for the title complex, whereas the SAM1 and BLYP/6-31G methods predict only one. All methods predict that molecular complex 3 is the most stable. The SAM1 geometry is very close to that of BLYP/6-31G.

The Fourier transform IR (FTIR) spectrum shows a very intense and broad (continuum) absorption within the 1600-400 cm⁻¹ region, typical of short hydrogen bonds. There is no absorption in the 3000-2000 cm⁻¹ region expected for the longer hydrogen bond (2.544(9) Å) in the less populated orientation. Isotope and solvent effects are discussed.     

Novel bicyclic hexanuclear copper(I) aggregate: Structure and solid state P CPMAS NMR spectra of [(Cu3L3)2] and [Cu(PPh3)2L] complexes of N-(diisopropoxythiophosphinyl)-N′-phenylthiourea (HL)

A new complex of N-thiophosphorylthiourea PhNHC(S)NHP(S)(OiPr)₂ (HL) of formula [(Cu₃L₃)₂] has been synthesized and characterized by single crystal X-ray diffraction, FT-IR, ¹H, ³¹P NMR in solution and by ³¹P CPMAS NMR spectroscopy in the solid state. A comparison of the structure and the spectral parameters of [(Cu₃L₃)₂] with those of the mononuclear analogue [Cu(PPh₃)₂L] was performed. In the solid state the aggregate [(Cu₃L₃)₂] represents the first example of a spontaneous “side-by-side” association of two neutral cyclic [Cu₃L₃] moieties using two Cu-S-Cu bridges formed by the sulfur atoms of the PS-groups. The values of the ¹J(³¹P-^63,65Cu) and ²J(³¹P-³¹P) coupling constants of the [Cu(PPh₃)₂]⁺ moiety in the solid state spectra are reported.