Titan—sticksoff-verbindungen XXIX. Kristall- und molekülstruktur spicocyclischer amide von titan und zirkonium mit dem liganden meSi(N-t-Bu)2

The compounds M[(N-t-Bu)₂SiMe₂]₂ (I M = Ti; II, M = Zr) were prepared by treatment of dilithiated Me₂Si(NH-t-Bu)₂ with TiCl₄ and ZrCl₄, respectively. Crystals of I and II belong to the space groups P2₁2₁2₁ and C2/c, respectively. The spirocyclic molecules possess approximate D_2d symmetry with planar MN₂Si rings. Important ring dimensions are d(MN) 1.890(4)/2.053(2) » (I/II). d(SiN) 1.742(10)/1.753(2) », angle NMN 83.4(2)/77.9(1)° and angle NSiN 92.4(2)/94.8(1)°.     

Photophysical, electrochemical and electrochromic properties of copper-bis(4,4′-dimethyl-6,6′-diphenyl-2,2′-bipyridine) complexes

The synthesis, solution and solid state structural characterization, photophysical and electrochemical properties of two redox forms of an electrochromic copper-bis(4,4′-dimethyl-6,6′-diphenyl-2,2′-bipyridine) complex, [Cu(3)₂]ⁿ (n=+1, +2), are presented. Both complexes were characterized in the solid state by X-ray diffraction methods on single-crystals showing that both forms exist in a pseudo-tetrahedral coordination, and a comparison with other structures was made. Like most copper(I) complexes, the red [Cu(3)₂]⁺ complex shows a rather weak emission (Φ_em=2.7×10⁻⁴, dichloromethane). The lifetime of the emitting MLCT state is 34±1 ns, as observed with time resolved emission, and transient absorption (in deoxygenated dichloromethane). Typical emission and transient absorption spectra are presented. The transient absorption spectra indicate that the MLCT state absorbs stronger than the ground state, which is relatively uncommon for metal bipyridine complexes, i.e. no ground state bleaching is observed. The green [(3)₂Cu]²⁺ complex does not show any observable emission or transient absorption, which is a common feature for Cu(II) complexes of this type. The electronic absorption spectra of the chemically and electrochemically produced copper(I/II) complexes are identical. The repeated electrochemical conversion of the Cu(I) center into Cu(II) and vice versa does not cause any decomposition. This is consistent with a fully reversible Cu(I)/Cu(II) redox couple in the corresponding cyclic voltammogram, (E_1/2 (Cu(I)/Cu(II))=+0.68 V vs. SCE=+0.23 V vs. Fc/Fc⁺). These observations indicate that no large structural reorganization occurs upon electrochemical timescales (sub second), and that the different ways of generating the complexes does not effect their final structure, apart from the small differences observed in the X-ray structures of both forms. These characteristics make these complexes rather well suited for their incorporation into an electrochromic display configuration.     

Synthesis, X-ray structure and properties of a new nitrite-bound copper(II) complex with 2-(3,5- dimethylpyrazol-1-ylmethyl)pyridine in a CuN4(O) coordination

Synthesis and characterization of a nitrite-bound copper(II) compound [CuL⁴)₂(ONO)]ClO₄ have been achieved (L⁴ = 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine]. The bidentate ligand L⁴ provides a pyridine and a pyrazole donor site; however, they are separated by a methylene spacer. The complex has been structurally characterized and it belongs to only a handful of complexes having nitrito-bound mononuclear copper(II) centre. The metal atom has a distorted square pyramidal geometry with the copper atom displaced from the equatorial plane by 0.25 Å. In MeCN solution the green complex exhibits a broad ligand-field transition at 655 nm with a shoulder at 675 nm and in dichloromethane-toluene glass (80 K) it exhibits an EPR spectral feature characteristic of the unpaired electron in the d_x²−y² orbital. Variable-temperature (80–300 K) magnetic susceptibility measurements in the solid state as well as room temperature measurement in MeCN solution reveal mononuclear magnetically dilute copper(II) centre. When examined by cyclic voltammetry (MeCN solution) it displays electrochemically irreversible Cu^II---Cu^I response [cathodic peak potential, E_pc (V vs saturated calomel electrode (SCE)): −0.32]. An oxidative response is observed at 1.14 V, probably due to bound-nitrite oxidation and is partially removed to generate a solvated complex at the electrode surface. The latter species gives rise to reversible Cu^II---Cu^I redox response [ ].     

Characterization and crystal structures of copper(II), cobalt(II), and nickel(II) complexes with two kinds of piperidine carboxylic acids

Copper(II) complex with -piperidine-3-carboxylic acid ( -Hpipe-3):[Cu( -pipe-3)₂(H₂O)] and cobalt(II) and nickel(II) complexes with piperidine-4-carboxylic acid (Hpipe-4):[M(Hpipe-4)₂(H₂O)₄]Cl₂ (M: Co, Ni) have been prepared and characterized by means of IR and powder diffuse reflection spectra, thermal analysis, and magnetic susceptibility. The crystal structures of these complexes have been determined by X-ray diffraction. The crystal of [Cu( -pipe-3)₂(H₂O)] is orthorhombic with the space group Pbcn. The copper atom is in a square pyramidal geometry, ligated by two carboxylato oxygen atoms, two nitrogen atoms, and a water molecule. One molecule of this complex consists of either -piperidine-3-carboxylic acid or -piperidine-3-carboxylic acid. The crystals of [M(Hpipe-4)₂(H₂O)₄]Cl₂ are monoclinic with space group P2₁/n. In these complexes the metal atom is in an octahedral geometry ligated by two carboxylato oxygen atoms and four water molecules.     

NMR study of nickel(II) Schiff base complexes with benzoyl groups and long alkyl chains

The nickel(II) Schiff base complexes with 2-methylbutyl or 2-methylpentyl groups and their benzoyl derivatives have been prepared and characterized by ¹H and ¹³C NMR spectroscopy. The structure of the benzoyl derivatives in chloroform solution can be estimated as follows: the donor set of N₂O₂ has a square planar coordination, the benzoyl substituents are perpendicular to the chelate plane and the long alkyl chains (2-methylbutyl or 2-methylpentyl groups) move segmentally to aproach the benzoyl substituents.     

Cyano-bridged bimetallic complexes of copper(II) with tetracyanonickelate(II). Crystal structure of [Cu(dpt)Ni(CN)4]

Five new complexes of composition [Cu(dpt)Ni(CN)₄] (1) (dpt=dipropylenetriamine), [Cu(dien)Ni(CN)₄]·2H₂O (2) (dien=diethylenetriamine), [Cu(N,N′-dimeen)Ni(CN)₄]·H₂O (3) (N,N′-dimeen=N,N′-dimethylethylenediamine), [Cu(N,N-dimeen)Ni(CN)₄]·H₂O (4) (N,N-dimeen=N,N-dimethylethylenediamine) and [Cu(trimeen)Ni(CN)₄] (5) (trimeen=N,N,N′-trimethylethylenediamine) have been obtained by the reactions of the mixture of Cu(ClO₄)₂·6H₂O, appropriate amine and K₂[Ni(CN)₄] in water and have been characterized by IR and UV–Vis spectroscopies and magnetic measurements. The crystal structure of [Cu(dpt)Ni(CN)₄] (1) has been determined by single-crystal X-ray analysis. The structure of 1 consists of a one-dimensional polymeric chain ---Cu(dpt)---NC---Ni(CN)₂---CN---Cu(dpt)--- in which the Cu(II) and Ni(II) atoms are linked by CN groups. The nickel atom is four coordinate with four cyanide-carbon atoms (two cyano groups are terminal and two cyano groups (in cis fashion) are bridged) in a square-planar arrangement and the copper atom is five coordinate with two cyanide-nitrogen and three dpt-nitrogen atoms, in a distorted square-pyramidal arrangement. The temperature dependence of magnetic susceptibility (2–300 K) was measured for compound 1. The magnetic investigation showed the presence of a very weak antiferromagnetic interaction (J=−0.16 cm⁻¹) between the copper atoms within each chain through the diamagnetic Ni(CN)₄ ²⁻ ions.     

Synthesis, spectral properties, crystal structures and antimicrobial effects of copper(II) pyridinecarboxylate adducts with chelating ligands

The reaction of an ethanolic solution of copper(II) pyridinecarboxylates CuX₂·nH₂O (where X is nicotinate (nic) (n=0) or isonicotinate (isonic) (n=4)) with ethylenediamine (en) in a molar ratio of 1:2 lead to the isolation of solid tetragonally distorted octahedral complexes of the type [Cu(en)₂(H₂O)₂]X₂·nH₂O (n=1 for nic; n=0 for isonic). The analogous reaction of CuX₂·nH₂O with diethylenetriamine (dien) in a molar ratio of 1:1 leads to the formation of square-pyramidal pentacoordinated complexes of the type [CuX(dien)(H₂O)]X. On the other hand, the reaction of equimolar quantities of copper(II) nitrate and dien with nicotinate anions (equimolar quantities of pyridinecarboxylic acid and NaOH) in ethanolic solutions gives a solid monomeric complex [Cu(nic)(NO₃)dien)(H₂O)]·H₂O in which the coordination polyhedron around the Cu(II) atom is a (4+1+1) distorted tetragonal bipyramid. Based on the molecular structure the electronic and IR spectra are discussed. Moreover, the results of the quantitative determination of antimicrobial activity of the isonic complexes [Cu(isonic)₂(H₂O)₄], [Cu(en)₂(H₂O)₂](isonic)₂, [Cu(isonic)(dien)(H₂O)](isonic), as well as isonicotinic acid, ethylenediamine and diethylenetriamine alone are discussed.     

Synthesis, crystal structure and imine bond activation of a copper(II) Schiff base complex

A new copper(II) complex [Cu(HL)(ClO₄)](ClO₄) (1), where HL is a multidentate Schiff base N,N′-(2-hydroxypropane-1,3-diyl)bis(pyridine-2-aldimine), is prepared, structurally characterized by X-ray crystallography and its spectral and electrochemical properties studied. The complex forms a one-dimensional chain in the solid state structure in which the monomeric Cu(HL) units are linked by the perchlorate ligand. The complex has an axially elongated six coordinate geometry (4+2) with a CuN₄O₂ core in which the Schiff base ligand displays a tetradentate mode of bonding in the basal plane. The axial ligand is perchlorate with a significantly long Cu–O bond of ca. 2.6 Å. The one-electron paramagnetic complex displays a cyclic voltammetric response for the Cu(II)/Cu(I) couple at 0.01 V versus SCE in MeCN–0.1 M TBAP. The azomethine bond of the Schiff base in 1 on treatment with H₂O₂ undergoes oxidative conversion to form a bis(picolinato)copper(II) · dihydrate species through the formation of an amido intermediate as evidenced from the solution infrared spectral studies.     

A kinetic and spectroscopic study on the copper catalyzed oxidative coupling polymerization of 2,6-dimethylphenol. X-ray structure of the catalyst precursor tetrakis (N-methylimidazole) bis(nitrato) copper(II)

The complex of copper(II) nitrate with N-methylimidazole (Nmiz) ligand has been studied as a catalyst for the oxidative coupling of 2,6-dimethylphenol by means of kinetic and spectroscopic measurements. The order of the reaction in copper is fractional and depends on the N/Cu ratio and the base/Cu ratio, indicating that there are at least two possible rate-determining steps, i.e. the formation of a dinuclear copper species and the phenol oxidation. EPR spectroscopy performed on frozen solutions with varying ligand to copper ratios shows that all Cu(II) is converted into the precursor complex at a ratio of 4 to 1, whereas in kinetic experiments, maximum activity and selectivity are reached only at a ratio of at least 30 to 1. Base is needed as a co-catalyst, and the maximum reaction rate is reached at a base to copper ratio of 1.8 to 1. The solid-state X-ray structure of the catalyst precursor complex has been determined to be [Cu(Nmiz)₄(NO₃)₂], monoclinic, space group P2₁/n, a = 8.452(1) Å, b = 10.376(2)Å, c = 12.821(2)Å, β = 94.88(2) °, Z = 1, R = 0.049 for 3525 reflections. This structure consists of an axially elongated octahedral CuN₄O₂ chromophore, which is in agreement with frozen-solution EPR spectra. Investigations under conditions where water and dioxygen were carefully excluded, have shown that for the phenol oxidation step the presence of dioxygen is not required. However, the reaction does require a trace of water (or hydroxide) to form the reactive intermediate. A modified reaction mechanism for the oxidative coupling is presented with special attention to the first steps of the reaction and the equilibrium species present in solution. The role of dioxygen appears to be only to reoxidize the formed Cu(I) species and to regenerate base.     

Novel liquid-crystalline derivatives of transition metals. The effect of the molecular geometry of the ligands on the mesogenic properties of tetracoordinated copper(II) complexes

The synthesis, characterization and thermal behaviour of several new series of copper(II) complexes derived from carbonylic compounds and their Schiff's bases are reported. The complexes are of two types; [Cu(C₆H₃O(R)-C(X) = O)₂], (type I) and [Cu(C₆H₃O(R)-C(X) = N-R')₂] (type II) where R = - OOC-C₆H₄OC₁₀H₂₁-p, and the position of R is 4 or 5; R' = CH₃, n-C₁₀H₂₁, p-n-C₁₀H₂₁O(C₆H₄)-; X = H, CH₃. In type I complexes, only the compound with X = H and R in position 5 showed mesomorphism. For type II complexes, all the Schiff's bases complexes of copper(II) derived from 2,4-dihydroxybenzaldehyde showed thermotropic mesophases (smectic C and nematic), whereas the complexes derived from 2,5-dihydroxybenzaldehyde were only mesogenic when the imine was derived from methylamine. None of the complexes derived from the ketone (2,4 or 2,5-dihydroxy derivatives) showed liquid-crystalline properties. X-ray studies of four complexes of type II were carried out. The anisotropy of the magnetic susceptibility has a negative sign for complexes with R in position 4 and a positive sign for 2,5-derivative complexes. The relationship between molecular structure and mesomorphic behaviour is discussed.     

Structural, spectral and antimicrobial studies of copper(II) complexes of 2-benzoylpyridine N(4)-cyclohexyl thiosemicarbazone

Six new copper(II) complexes of 2-benzoylpyridine N(4)-cyclohexyl thiosemicarbazone (HL) have been synthesized and characterized by different physicochemical techniques like molar conductivity measurements, magnetic studies and electronic, infrared and EPR spectral studies. Five of the complexes have been found to possess the stoichiometry [CuLX], where X = Cl (1), Br (2), NO₃ (3), NCS (4), N₃ (5). The complex prepared from copper sulfate has the composition [Cu₂L₂SO₄] · (H₂O)₂ (6). In all the complexes the deprotonated ligand, L and the anion were found to be coordinated to the Cu(II) ion. The terdentate nature of the ligand is evident from the IR spectra. The metal ligand bonding parameters evaluated from the EPR spectra indicate strong in-plane σ and in-plane π bonding. The magnetic and spectroscopic data indicate a square planar geometry for complexes 1, 3, 4 and 5, while the complexes 2 and 6 are assigned a square pyramidal geometry. Crystal structure of the complex [CuLCl] reveals two molecules per asymmetric unit of a monoclinic lattice, with space group symmetry P2₁/n. The complexes [ CuLBr ₂] (2) and [CuLNCS] (4) crystallized into triclinic lattices with space group . Compound 2 exists as a thiolate bridged copper(II) dimer. The antimicrobial activity of the ligand and the copper complexes were tested against five types of bacteria isolated from clinical samples. The complexes were found to be active against Bacillus sp., Vibrio cholera O1, Staphylococcus aurus and Salmonella paratyphi.     

Spectroscopic and magnetic properties of copper(II) complexes derived from pyridine-2-carbaldehyde thiosemicarbazone. Structures of [Cu(NO3)(C7H8N4S)(H2O)](NO3) and [{Cu(NCS)(C7H7N4S)}2]

Complexes with the formula CuX(L) (X=N₃ 1, NCO 2 and NCS 3) and [Cu(NO₃)(HL)(H₂O)](NO₃) 4, where HL=C₇H₈N₄S, (pyridine-2-carbaldehyde thiosemicarbazone), have been characterised. Single-crystal X-ray diffraction studies on compounds 3 and 4 have been carried out. The structure of compound 4 consists of monomeric distorted square pyramidal copper(II) species. The copper(II) ions are coordinated to the NNS atoms from the tridentate thiosemicarbazone ligand and one oxygen atom of a nitrate group in the equatorial position. The oxygen atom of the water molecule occupies the apical position. The structure of compound 3 consists of non-centrosymmetric {Cu₂(μ-SR)₂} entities in which the copper(II) ions exhibit five-coordinate square–pyramidal geometry. The thiosemicarbazone ligand and one nitrogen atom from the thiocyanate ion are in a basal position. The sulfur atom of the tridentate ligand acts as a bridge occupying the apical position. Structural and spectroscopic results suggest the presence of relevant σ ligand-to-metal charge transfer and metal-to-ligand π-backdonation character in these compounds. The ESR spectra of compounds 3 and 4 show rhombic symmetry. For complexes 1 and 2 the ESR spectra exhibit axial signals. Magnetic measurements on compounds 1, 2 and 3 show antiferromagnetic couplings. The susceptibility data were fitted by the Bleaney–Bowers’ equation for copper(II) dimers. The obtained J/k values are −4.22, −6.10 and −7.33 K for compounds 1, 2 and 3, respectively.     

Reactivity of ruthenium complexes with uninegative (X,S)-donor ligands (X = S,P)—II. Phosphine substitution in [Ru(S,S)2(PR3)2] derivatives. Crystal structure of trans-bis(O-ethyldithiocarbonate)bis(dimethylphenylphosphine)-ruthenium(II)

The complexes [Ru(S,S)₂(PPh₃)₂] [S,S = EtCOCS₂⁻, (CH₂)₄NCS₂⁻] react with a variety of tertiary phosphines with the substitution of triphenylphosphine and the formation of [Ru(S,S)₂(PR₃)₂]. The reaction occurs with the formation ofthe cis isomer, except for the complex with PMe₂Ph that gives rise to the trans isomer as the crystal structure shows. The effect of the different phosphines on the ruthenium complex is analysed in terms of the spectroscopic and electrochemical properties of the isolated compounds. The cyclic voltammetric studies of the cis complexes show that isomerization to the trans isomer occurs on oxidation. This isomerization is not observed in the trans-[Ru(S,S)₂(PMe₂Ph)₂] complexes that give rise to stable trans-ruthenium(II)/ruthenium(III) couples. In a similar way the diphosphine complexes afford a quasi-reversible cis-ruthenium(II)/ruthenium(III) process.     

Synthesis, spectral and structural characterization of two polymeric 1:1 complexes of 2,3-dimethylpyridine and 5-ethyl-2-methylpyridine with copper(II) azide; Cu(2,3-dimethylpyridine) (N3)2 and Cu(2-methyl-5-ethylpyridine) (N3)2

Two new 1:1 ligand complexes of copper(II) azide with disubstituted pyridine ligands, namely catena-di-μ(1,3)-azido-[di-μ(1,1)-azidobis(2,3-lutidine)dicopper(II)] (1) and catena-di-μ(1,1)-azido[di-μ(1,1)-azidobis(2-methyl-5-ethylpyridine)dicopper(II)] (2), have been synthesized and characterized by spectroscopic and X-ray crystallographic methods. The polymeric complex 1 features monodentate 2,3-lut ligands, centrosymmetric di-μ(1,1)-azido-bridged Cu₂N₂ rings, distorted square-pyramidal copper(II) coordination geometry and di-μ(1,3)-azido bridges which link the centrosymmetric binuclear Cu₂(2,3-lut)₂(N₃)₂ moieties to form sheets within the ab plane. In the monoclinic crystals of complex 2, the copper(II) centres are pentacoordinated via N(11), N(21), N(11b) and N(21a) from the azido ligands [Cu---N distances 1.971(5)–2.286(5) Å] and N(1) from the organic molecule at a Cu---N bond length of 2.001(5) Å. Both azido ligands function as μ(1,1) bridges to form chains of polyhedra along the short a-axis of the unit cell. The IR absorption spectra reveal that each of these complexes contains two independent azide ligands. The solid and solution electronic spectra of complexes 1 and 2 show at least three and two strong absorption bands, respectively, associated with N₃⁻ → Cu^II charge transfer transitions. The EPR spectra of powder samples and DMSO solutions at room temperature were recorded and are discussed.     

Discotic liquid crystals of transition metal complexes X. Phthalocyanine derivatives substituted with n-alkyloxyphenyl side chains

Octakis(alkyloxyphenyl)-phthalocyanine derivatives ((C_nOph)₈PcH₂ n = 8, 10 12 and 18), their corresponding copper (II) complexes ((C_nOph)₈PcCu, n = 10, 12 and 18) and octakis(2-ethylhexyl)-PcH₂ have been synthesized and their mesomorphic properties characterized. (C_nOph)₈PcH₂, (n = 12 and 18) exhibit hexagona disordered columnar mesophases whereas (C_nOph)₈PcCu (n = 12 and 18) yields a rectangular disordered columnar liquid crystal. An alkylphenyl-oxymethyl derivative, (C₁₂phOCH₂)₈PcH₂, was synthesized to determine the influence of the connecting link between the side chains and the phthalocyanine macrocycle on the mesomorphic properties.     

Transition metal coordination compounds of a chelating imidazole-thioether ligand. The X-ray crystal structure of (1,6-bis(4(5)-imidazolyl)-2,5-dithiahexane)bis(nitrato)copper(II)

Transition metal coordination compounds with the novel N₂S₂-donor ligand 1,6-bis(4(5)-imidazolyl)-2,5-dithiahexane (abbreviated bhdhx) with general formulae M(bhdhx)(NO₃)₂(M = Co, Ni, Cu) and M(bhdhx)(H₂O)₂(BF₄)₂ (M = Cu, Zn) have been isolated. In all compounds the ligand is tetradentate with both thioether sulphurs and imidazole nitrogens coordinating. In all compounds the metal ions are six-coordinated in a distorted octahedral geometry with either nitrates or water molecules as the fifth and sixth ligands. This is confirmed by the ligand field spectra, which agree with a distorted octahedral coordination. The distortion from octahedral, indicated by the ligand field spectrum of the cobalt nitrate compound is such that the S atoms of the ligands must be at a very large distance from the metal ion. A single crystal of Cu(bhdhx)(NO₃)₂ was used in a structure determination: orthorhombic space group Pbcn, a = 14.351(5), b = 8.554(3), c = 13.057(4) Å, Z = 4, and T = 293 K. The structure was solved by heavy atom techniques and refined by least-squares methods to a residual R value of 0.033 for 847 significant reflections. The copper ion is at a special position on a two-fold axis, which causes a two-fold symmetry in the ligand. The coordination geometry of the copper atom is distorted octahedral with the two nitrates and the two thioether sulphurs in a cis position, and the imidazole nitrogens trans. The copper to nitrogen distances are 1.933(4) Å, the copper to sulphur distances are 2.495(1) Å, and the copper to oxygen distances are 2.280(3) Å.     

Phenylbis(2- pyridyl)phosphine: P- vs. N,N′-coordination in carbonylmolybdenum-(O) and -(II) complexes

The first carbonyl molybdenum-(O) and -(II) complexes with phenylbis(2-pyridyl)phosphine (PPhpy₂) have been synthesized. PPhpy₂ reacts with [Mo(CO)₅(NCMe)] to give [Mo(CO)₅(PPhpy₂-P)]. With [Mo(CO)₄(NBD)] (NBD = norbornadiene) it gives [Mo(CO)₄(PPhpy₂-P)₂] when a 2 : 1 ratio is used, or [MO(CO)₄(py₂PhP---N,N′)] for a 1 : 1 ratio. Decarbonylation of any of these pyridylphosphine complexes leads to an oligomer of formula {MO(CO)₃(μ-PPhpy₂)}_n, which is also obtained after heating [MO(CO)₆] in solution with an equimolar amount of PPhpy₂. The oligomer undergoes oxidative addition by iodine or allylbromide to give [MoI₂(CO)₃(py₂PhP---N,N′)], or [MoBr(η³-CH₂CHCH₂)(CO)₂(py₂PhP---N,N′)], respectively. These complexes are also obtained by addition of equimolar amounts of PPhpy₂ to solutions of [MoI₂(CO)₃(NCMe)₂] and MoBr(η³-CH₂CH CH₂)(CO)₂(NCMe)₂, respectively. The ligand tends to act as a P-donor towards molybdenum(O) substrates, and as a chelating N,N′-donor in molybdenum (II) complexes.     

Iron(III), cobalt(II,III), copper(II) and zinc(II) complexes of 2-pyridineformamide 3-piperidylthiosemicarbazone

Reduction of 2-cyanopyridine by sodium in the presence of 3-piperidylthiosemicarbazide produces 2-pyridineformamide 3-piperidylthiosemicarbazone, HAmpip. Complexes with iron(III), cobalt(II,III) copper(II) and zinc(II) have been prepared and characterized by molar conductivities, magnetic susceptibilities and spectroscopic techniques. In addition, the crystal structures of HAmpip, [Fe(Ampip)₂]ClO₄, [Cu(HAmpip)Cl₂]·CH₃OH and [Zn(HAmpip)Br₂]·C₂H₆SO have been determined. Coordination is via the pyridyl nitrogen, imine nitrogen and thiolato or thione sulfur when coordinating as the anionic or neutral ligand, respectively.     

Redox potential, ligand and structural effects in rhodium(I) complexes

The electrochemical behaviour of the set of tetracoordinate rhodium(I) complexes [Rh(O^∩O)(CO)L] [O^∩O=MeC(O)CHC(O)Me (acac), L=CO (1), P(NC₄H₄)₃ (2), PPh(NC₄H₄)₂ (3), PPh₂(NC₄H₄) (4), PPh₃ (5), PCy₃ (6), P(OPh)₃ (7) or PPh₂(C₆H₄OMe-4) (8); O^∩O=PhC(O)CHC(O)Me (bac), L=CO (9) or PPh₃ (10); O^∩O=PhC(O)CHC(O)CF₃(bta), L=CO (11) or PPh₃ (12)] and of the pentacoordinate [RhH(CO)L₃] [L=P(NC₄H₄)₃ (13), PPh₃ (14), P(OPh)₃ (15) or P(OC₆H₄Me-4)₃ (16)] and [RhHL₄] [L=PPh₃ (17) or P(OC₆H₄Me-3)₃ (18)] was studied by cyclic voltammetry and controlled potential electrolysis, in aprotic medium, at a Pt electrode. They present a single-electron oxidation wave (I) (irreversible or quasi-reversible) that can be followed, at a higher potential, by a second and irreversible one (II). The values of first oxidation potential for the tetracoordinate complexes fit the additive Lever's electrochemical parameterisation, and the ligand electrochemical Lever E_L and Pickett P_L parameters were estimated for the N-pyrrolyl phosphines PPh_n(NC₄H₄)_3−n (n=0, 1 or 2) and for the organophosphines PCy₃ and PPh₂(C₆H₄OMe-4), the former behaving as weaker net electron donors (the electron donor ability decreases with the increase of the number of N-pyrrolyl groups) than the latter phosphines. The pentacoordinate hydride complexes 13–18 fit a distinct relationship which enabled the estimate of the E_L ligand parameter for the phosphites P(OC₆H₄Me-3)₃ and P(OC₆H₄Me-4)₃. Electrochemical metal site parameters were obtained for the square planar and the pentacoordinate Rh(I)/Rh(II) couples and, for the former, the redox potential is shown to present a much higher sensitivity to a change of a ligand than the octahedral redox couples investigated so far. Linear relationships were also observed between the oxidation potential and the P_L ligand parameter (for the series [Rh(acac)(CO)L]) or the infrared ν(CO) frequency, and a generalisation of the former type of correlation is proposed for series of square-planar 16-electron complexes [M′_SL] with a common 14-electron T-shaped binding metal centre {M′_S}. Oxidation of 5 by Ag[PF₆] leads to the dimerisation of the derived Rh(II) species.     

Three new polynuclear tetracarboxylato-bridged copper(II) complexes: Syntheses, X-ray structure and magnetic properties

The synthesis, crystal structure and magnetic measurements of three new polynuclear tetracarboxylato-bridged copper(II) complexes, i.e. {[Cu₄(phen)₂(μ-O₂CC₂H₅)₈] · (H₂O)}_n (1), [Cu₂(μ-O₂CC₆H₄OH)₄(C₇H₇NO)₂] · 6H₂O (2) and [Cu₂(μ-O₂CCH₃)₄(C₇H₇NO)₂] (3) (phen = 1,10-phenanthroline, O₂CC₆H₄OH = 3-hydroxy benzoate, C₇H₇NO = 4-acetylpyridine) are reported. All compounds consist of dinuclear units, in which two Cu(II) ions are bridged by four syn,syn-η¹:η¹:μ carboxylates, showing a paddle-wheel cage type with a square-pyramidal geometry, arranged in different ways. The structure of compound 1 consists of an one-dimensional structure generated by an alternating classical dinuclear paddle-wheel unit and an unusual dinuclear Cu₂(μ-OCOC₂H₅)₂(μ-O₂CC₂H₅)₂(phen)₂unit, which are connected to each other via a syn,anti-triatomic propionato bridge in an axial-equatorial configuration. The adjacent chains are connected to generate a 2D structure through the face-to-face π–π interaction between phen rings. Structures of compounds 2 and 3 both consist of a symmetric dinuclear Cu(II) carboxylate paddle-wheel core and pyridyl nitrogen atoms of 4-acetylpyridine ligand at the apical position, and just differ in the substituents of the equatorial ligands.

The magnetic properties have been measured and correlated with the molecular structures. It is found that in the two classical paddle-wheel compounds the Cu(II) ions are strongly antiferromagnetically coupled with J = −278.5 and −287.0 cm⁻¹ for complexes 2 and 3, respectively. In compound 1 the magnetic susceptibility could be fitted with two different, independent Cu(II) units, one strongly coupled and one weakly coupled; the paddle-wheel dinuclear unit has the strongest antiferromagetic coupling with a value for J of −299.5 cm⁻¹, whereas the Cu(II) ions in the propionato-bridged dinuclear unit of 1 display a very weak antiferromagnetic coupling with a value for J = −0.75 cm⁻¹, due to the orthogonality of the magnetic orbitals. Also the exchange within the chain is therefore very weak. The magneto-structural correlations for complexes 1, 2, and 3 are discussed on the basis of the structural parameters and magnetic data for the complexes.