Synthesis, crystal structure, spectroscopic and photoluminescence studies of manganese(II), cobalt(II), cadmium(II), zinc(II) and copper(II) complexes with a pyrazole derived Schiff base ligand

Varying coordination modes of the Schiff base ligand H₂L [5-methyl-1-H-pyrazole-3-carboxylic acid (1-pyridin-2-yl-ethylidene)-hydrazide] towards different metal centers are reported with the syntheses and characterization of four mononuclear Mn(II), Co(II), Cd(II) and Zn(II) complexes, [Mn(H₂L)(H₂O)₂](ClO₄)₂(MeOH) (1), [Co(H₂L)(NCS)₂] (2), [Cd(H₂L)(H₂O)₂](ClO₄)₂ (3) and [Zn(H₂L)(H₂O)₂](ClO₄)₂ (4), and a binuclear Cu(II) complex, [Cu₂(L)₂](ClO₄)₂ (5). In the complexes 1-4 the neutral ligand serves as a 3N,2O donor where the pyridine ring N, two azomethine N and two carbohydrazine oxygen atoms are coordinatively active, leaving the pyrazole-N atoms inactive. In the case of complex 5, each ligand molecule behaves as a 4N,O donor utilizing the pyridine N, one azomethine N, the nitrogen atom proximal to the azomethine of the remaining pendant arm and one pyrazole-N atom to one metal center and the carbohydrazide oxygen atom to the second metal center. The complexes 1-4 are pentagonal bipyramidal in geometry. In each case, the ligand molecule spans the equatorial plane while the apical positions are occupied by water molecules in 1, 3 and 4 and two N bonded thiocyanate ions in 2. In complex 5, the two Cu(II) centers have almost square pyramidal geometry (τ = 0.05 for Cu1 and 0.013 for Cu2). Four N atoms from a ligand molecule form the basal plane and the carbohydrazide oxygen atom of a second ligand molecule sits in the apex of the square pyramid. All the complexes have been X-ray crystallographically characterized. The Zn(II) and Cd(II) complexes show considerable fluorescence emission while the remaining complexes and the ligand molecule are fluorescent silent.     

Structural and spectral studies of nickel(II) complexes with N(4),N(4)-(butane-1,4-diyl) thiosemicarbazones

Nickel(II) complexes of quinoline-2-carbaldehyde N(4),N(4)-(butane-1,4-diyl) thiosemicarbazone (HL¹) and 2-benzoylpyridine N(4),N(4)-(butane-1,4-diyl) thiosemicarbazone (HL²) have been synthesized and physico-chemically characterized by means of partial elemental analyses, molar conductance measurements, magnetic measurements, electronic and infrared spectral studies. Three complexes were given the formulae [Ni(HL¹)₂]Cl₂ (1), [Ni(HL²)L²]ClO₄ · 7H₂O (2) and [NiL²Cl] · 0.5H₂O (3). The structure of compound 1 has been solved by single crystal X-ray crystallography and is found to be distorted octahedral. Compound 2, when crystallized in DMSO solution, got deprotonated to form a new compound [Ni(L²)₂] (2a), with a distorted octahedral Ni(II) center. In compound 1, HL¹ coordinates to the metal in the thione form, while in compounds 2a and 3, HL² coordinates in its deprotonated thiolate form.     

Nickel(II) and zinc(II) complexes of N-substituted di(2-picolyl)amine derivatives: Synthetic and structural studies

The interaction of di(2-picolyl)amine (1) and its secondary N-substituted derivatives, N-(4-pyridylmethyl)-di(2-picolyl)amine (2), N-(4-carboxymethyl-benzyl)-di(2-picolyl)amine (3), N-(4-carboxybenzyl)-di(2-picolyl)amine (4), N-(1-naphthylmethyl)-di(2-picolyl)amine (5), N-(9-anthracenylmethyl)-di(2-picolyl)amine (6), 1,4-bis[di(2-picolyl)aminomethyl]benzene (7), 1,3-bis[di(2-picolyl)aminomethyl]benzene (8) and 2,4,6-tris[di(2-picolyl)amino]triazine (9) with Ni(II) and/or Zn(II) nitrate has resulted in the isolation of [Ni(1)(NO₃)₂], [Ni(2)(NO₃)₂], [Ni(3)(NO₃)₂], [Ni(4)(NO₃)₂]·CH₃CN, [Ni(5)(NO₃)₂], [Ni(6)(NO₃)₂], [Ni₂(7)(NO₃)₄], [Ni₂(8)(NO₃)₄], [Ni₃(9)(NO₃)₆]·3H₂O, [Zn(3)(NO₃)₂]·0.5CH₃OH, [Zn(5)(NO₃)₂], [Zn(6)(NO₃)₂], [Zn(8)(NO₃)₂] and [Zn₂(9)(NO₃)₄]·0.5H₂O. X-ray structures of [Ni(4)(NO₃)₂]·CH₃CN, [Ni(6)(NO₃)₂] and [Zn(5)(NO₃)₂] have been obtained. Both nickel complexes exhibit related distorted octahedral coordination geometries in which 4 and 6 are tridentate and bound meridionally via their respective N₃-donor sets, with the remaining coordination positions in each complex occupied by a monodentate and a bidentate nitrato ligand. For [Ni(4)(NO₃)₂]·CH₃CN, intramolecular hydrogen bond interactions are present between the carboxylic OH group on one complex and the oxygen of a monodentate nitrate on an adjacent complex such that the complexes are linked in chains which are in turn crosslinked by intermolecular offset π-π stacking between pyridyl rings in adjacent chains. In the case of [Ni(6)(NO₃)₂], two weak CH?O hydrogen bonds are present between the axial methylene hydrogen atoms on one complex and the oxygen of a monodentate nitrate ligand on a second unit such that four hydrogen bonds link pairs of complexes; in addition, an extensive series of π-π stacking interactions link individual complex units throughout the crystal lattice. The X-ray structure of [Zn(5)(NO₃)₂] shows that the metal centre once again has a distorted six-coordinated geometry, with the N₃-donor set of N-(1-naphthylmethyl)-di(2-picolyl)amine (5) coordinating in a meridional fashion and the remaining coordination positions occupied by a monodentate and a bidentate nitrato ligand. The crystal lattice is stabilized by weak intermolecular interactions between oxygens on the bound nitrato ligands and aromatic CH hydrogens on adjacent complexes; intermolecular π-π stacking between aromatic rings is also present.     

Copper(II) complexes of N(4)-substituted thiosemicarbazones derived from pyridine-2-carbaldehyde: Crystal structure of a binuclear complex

Ten copper(II) complexes {[CuL¹Cl] (1), [CuL¹NO₃]₂ (2), [CuL¹N₃]₂ · 2/3H₂O (3), [CuL¹]₂(ClO₄)₂ · 2H₂O (4), [CuL²Cl]₂ (5), [CuL²N₃] (6), [Cu(HL²)SO₄]₂ · 4H₂O (7), [Cu(HL²)₂] (ClO₄)₂ · 1/2EtOH (8), [CuL³Cl]₂ (9), [CuL³NCS] · 1/2H₂O (10)} of three NNS donor thiosemicarbazone ligands {pyridine-2-carbaldehyde-N(4)-p-methoxyphenyl thiosemicarbazone [HL¹], pyridine-2-carbaldehyde-N(4)-2-phenethyl thiosemicarbazone [HL²] and pyridine-2-carbaldehyde N(4)-(methyl), N(4)-(phenyl) thiosemicarbazone [HL³]} were synthesized and physico-chemically characterized. The crystal structure of compound 9 has been determined by X-ray diffraction studies and is found that the dimer consists of two square pyramidal Cu(II) centers linked by two chlorine atoms.     

Nickel(II) and zinc(II) complexes with N-(5,6-dihydro-4H-1,3-thiazin-2-yl)-2-aminobenzimidazole (BzTz): Synthesis,spectral and structural characterization

The reaction of nickel and zinc chlorides and nitrates with the ligand N-(5,6-dihydro-4H-1,3-thiazin-2-yl)-2-aminobenzimidazole (BzTz) leads to the formation of the new complexes: [NiCl₂(BzTz)₂] (1), [Ni(NO₃)(BzTz)₂(H₂O)₃](NO₃) (2), [ZnCl₂(BzTz)₂] (3) and [Zn(NO₃)₂(BzTz)₂] (4). They have been characterized by spectroscopic methods (electronic, infrared and NMR) and magnetic susceptibility measurements. Additionally, the crystal structures of the complexes 1 and 3 have been determined by X-ray single-crystal diffraction. The ligand exhibits the N-benzimidazole coordination mode on interacting with the metal centers. The X-ray structure of the complexes 1 and 3 reveals a distorted tetrahedral coordination geometry around the metal center, with the metallic atoms coordinated to two chlorine atoms and two benzimidazole nitrogen atoms. These two complexes are isostructural, crystallizing in the monoclinic system and Cc space group. In complex 2 the geometry around the nickel atom could be described as a distorted octahedron whereas in case of complex 4 the zinc atom is in a distorted tetrahedral environment.     

Synthesis and structure of highly substituted pyrazole ligands and their complexes with platinum(II) and palladium(II) metal ions

Reaction of 3-methoxycarbonyl-2-methyl- or 3-dimethoxyphosphoryl-2-methyl-substituted 4-oxo-4H-chromones 1 with N-methylhydrazine resulted in the formation of isomeric, highly substituted pyrazoles 4 (major products) and 5 (minor products). Intramolecular transesterification of 4 and 5 under basic conditions led, respectively, to tricyclic derivatives 7 and 8. The structures of pyrazoles 4a (dimethyl 2-methyl-4-oxo-4H-chromen-3-yl-phosphonate) and 4b (methyl 4-oxo-2-methyl-4H-chromene-3-carboxylate) were confirmed by X-ray crystallography. Pyrazoles 4a and 4b were used as ligands (L) in the formation of ML₂Cl₂ complexes with platinum(II) or palladium(II) metal ions (M). Potassium tetrachloroplatinate(II), used as the metal ion reagent, gave both trans-[Pt(4a)₂Cl₂] and cis-[Pt(4a)₂Cl₂], complexes with ligand 4a, and only cis-[Pt(4b)₂Cl₂] isomer with ligand 4b. Palladium complexes were obtained by the reaction of bis(benzonitrile)dichloropalladium(II) with the test ligands. trans-[Pd(4a)₂Cl₂] and trans-[Pd(4b)₂Cl₂] were the exclusive products of these reactions. The structures of all the complexes were confirmed by IR, ¹H NMR and FAB MS spectral analysis, elemental analysis and Kurnakov tests.     

Structural and spectral studies on manganese(II) complexes of di-2-pyridyl ketone N(4)-methyl and N(4)-ethyl thiosemicarbazones

Four manganese(II) complexes of di-2-pyridyl ketone N(4)-methyl (HDpyMeTsc) and N(4)-ethyl thiosemicarbazones (HDpyETsc) were synthesized and physico-chemically characterized by means of partial elemental analyses, molar conductance measurements, electronic, infrared and EPR spectral studies. The complexes are represented as [Mn(DpyMeTsc)₂] (1), [Mn(HDpyMeTsc)Cl₂] (2), [Mn(HDpyMeTsc)₂](ClO₄)₂ · H₂O (3) and [Mn(DpyETsc)₂] · 2H₂O (4). The crystal structure of [Mn(DpyMeTsc)₂] was established by single crystal X-ray diffraction studies. The compound crystallizes into a monoclinic lattice with P2₁/n space group. Manganese(II) exists in a distorted octahedral geometry in the complex.     

Crystal structure, spectroscopy and magnetism of trinuclear nickel(II), cobalt(II) complexes and their solid solution

Four new complexes [Ni₃(μ-L)₆(H₂O)₆](NO₃)₆·6H₂O (1), [Co₃(μ-L)₆(H₂O)₆](NO₃)₆·6H₂O (2), [Ni₃(μ-L)₆(H₂O)₄(CH₃OH)₂](NO₃)₆·4H₂O (3), [Co₃(μ-L)₆(H₂O)₄(CH₃OH)₂](NO₃)₆·4H₂O (4) (L = 4-amino-3,5-dimethanyl-1,2,4-triazole) were synthesized and structurally characterized by X-ray single-crystal diffraction. The structural analyses show that complex 1 and 2 are isomorphous; complex 3 and 4 are isomorphous. Four complexes all consist of the linear trinuclear cations ([M₃(μ-L)₆(H₂O)₆]⁶⁺ (M = Ni,Co) for 1 and 2; [M₃(μ-L)₆(H₂O)₄(CH₃OH)₂]⁶⁺ (M = Ni,Co) for 3 and 4), NO₃⁻ anions and crystallized water molecules. In the trinuclear cations, the central M(II) ions and two terminal M(II) ions are bridged by three triazole ligands. Other eleven solid solution compounds which are isomorphous with complex 3 and 4 were obtained by using different ratio of Ni(II) and Co(II) ions as reactants and ICP result indicates that ligand L has higher selectivity of Ni(II) ions than that of Co(II) ions. The magnetic analysis was carried out by using the isotropic spin Hamiltonian ? = −2J(?₁?₂ + ?₂?₃) (for complexes 1 and 3) and simultaneously considering the temperature dependent g factor (for complexes 2 and 4). Both the UV-Vis spectra and the magnetic properties of the solid solutions can be altered systematically by adjusting the Co(II)/Ni(II) ratio.     

Complexes of Co(II), Ni(II) and Cu(II) with lapachol

Complexes of naturally occurring hydroxynaphtho-quinone, lapachol (2-hydroxy-3(3-methyl-2-buthenyl)-1,4-naphthoquinone = HL) with Co(II), Ni(II) and Cu(II) have been prepared by reaction of the corresponding acetates with the ligand (HL) in ethanol. The molecular and crystal structures were determined for [CoL₂(EtOH)₂] (1), [NiL₂(EtOH)₂] (2), and [CuL₂(py)₂] (3). In all cases the deprotonated lapachol behaves as chelating bidentate ligand. The complexes were also characterized by elemental analyses, cyclic voltammetry, and FAB-MS.     

Synthesis and properties of new Mo(II) complexes with N-heterocyclic and ferrocenyl ligands

New Mo(II) complexes with 2,2′-dipyridylamine (L1), [Mo(CH₃CN)(η³-C₃H₅)(CO)₂(L1)]OTf (C1a) and [{MoBr(η³-C₃H₅)(CO)₂(L1)}₂(4,4′-bipy)](PF₆)₂ (C1b), with {[bis(2-pyridyl)amino]carbonyl}ferrocene (L2), [MoBr(η³-C₃H₅)(CO)₂(L2)] (C2), and with the new ligand N,N-bis(ferrocenecarbonyl)-2-aminopyridine (L3), [MoBr(η³-C₃H₅)(CO)₂(L3)] (C3), were prepared and characterized by FTIR and ¹H and ¹³C NMR spectroscopy. C1a, C1b, L3, and C2 were also structurally characterized by single crystal X-ray diffraction. The Mo(II) coordination sphere in all complexes features the facial arrangement of allyl and carbonyl ligands, with the axial isomer present in C1a and C2, and the equatorial in the binuclear C1b. In both C1a and C1b complexes, the L1 ligand is bonded to Mo(II) through the nitrogen atoms and the NH group is involved in hydrogen bonds. The X-ray single crystal structure of C2 shows that L2 is coordinated in a κ²-N,N-bidentate chelating fashion. Complex C3 was characterized as [MoBr(η³-C₃H₅)(CO)₂(L3)] with L3 acting as a κ²-N,O-bidentate ligand, based on the spectroscopic data, complemented by DFT calculations.The electrochemical behavior of the monoferrocenyl and diferrocenyl ligands L2 and L3 has been studied together with that of their Mo(II) complexes C2 and C3. As much as possible, the nature of the different redox changes has been confirmed by spectrophotometric measurements. The nature of the frontier orbitals, namely the localization of the HOMO in Mo for both in C2 and C3, was determined by DFT studies.     

Syntheses,characterization and crystal structures of mixed-ligand Cu(II), Ni(II) and Mn(II) complexes of N-(1-phenyl-3-methyl-4-propenylidene-5-pyrazolone)-salicylidene hydrazide containing ethanol or pyridine as a co-ligand

Five new mixed-ligand complexes [CuL(EtOH)] (1), [NiL(EtOH)₃] (2), [Mn₂L₂(μ₂-EtOH)₂(EtOH)₂] (3), [CuL(Py)] · MeOH (4) and [NiL(Py)₃] (5) (L²⁻ = N-(1-phenyl-3-methyl-4-propenylidene-5-pyrazolone)-salicylidene hydrazide anion, Py = pyridine) have been synthesized and characterized by elemental analyses, IR spectra, thermal analyses and single crystal X-ray diffraction. The crystallographic structural analyses of these complexes reveal that the ligand (H₂L) itself undergoes isomerization from the keto form to the enol form in the reaction, then loses two protons and acts as a double negatively charged tridentate chelating agent coordinated to the metal ion in the solution. The final results show that when a co-ligand was present in the synthetic reaction, other coordination sites around the metal ions Cu²⁺ and Ni²⁺ were completed either by the ethanol or pyridine molecules under the common solvent reaction or solvothermal syntheses conditions, respectively. In the case of the Mn²⁺ ion, it was still coordinated with the solvent molecules regardless of whether it was synthesized under the common solvent reaction or solvothermal syntheses with pyridine. The reason for this difference might be attributed to the fact that the coordination modes and bonding effect of the co-ligand with the metal ions are different, the final complexes tend to form the most stable compound.     

Synthesis, spectral characterization and crystal structure of copper(II) complexes of 2-benzoylpyridine-N(4)-phenylsemicarbazone

An interesting series of nine new copper(II) complexes [Cu₂L₂(OAc)₂]·H₂O (1), [CuLNCS]·½H₂O (2), [CuLNO₃]·½H₂O (3), [Cu(HL)Cl₂]·H₂O (4), [Cu₂(HL)₂(SO₄)₂]·4H₂O (5), [CuLClO₄]·½H₂O (6), [CuLBr]·2H₂O (7), [CuL₂]·H₂O (8) and [CuLN₃]·CH₃OH (9) of 2-benzoylpyridine-N(4)-phenyl semicarbazone (HL) have been synthesized and physico-chemically characterized. The tridentate character of the semicarbazone is inferred from IR spectra. Based on the EPR studies, spin Hamiltonian and bonding parameters have been calculated. The g values, calculated for all the complexes in frozen DMF, indicate the presence of the unpaired electron in the d_x²-y² orbital. The structure of the compound, [Cu₂L₂(OAc)₂] (1a) has been resolved using single crystal X-ray diffraction studies. The crystal structure revealed monoclinic space group P2₁/n. The coordination geometry about the copper(II) in 1a is distorted square pyramidal with one pyridine nitrogen atom, the imino nitrogen, enolate oxygen and acetate oxygen in the basal plane, an acetate oxygen form adjacent moiety occupies the apical position, serving as a bridge to form a centrosymmetric dimeric structure.     

Synthesis, spectral and structural studies of 1-ethoxycarbonyl-piperazine-4-carbodithioate and its Co(III), Zn(II) and Cd(II) complexes

The new complexes [Co(ecpzdtc)₃] (2) [Zn(ecpzdtc)₂(py)] (3) and [Cd(ecpzdtc)₂(py)]·H₂O (4) have been synthesized from sodium 1-ethoxycarbonyl-piperazine-4-carbodithioate [(Na⁺(ecpzdtc)⁻]. The ligand and the complexes have been characterized by elemental analyses, IR, magnetic susceptibility and single crystal X-ray data. The [Zn(ecpzdtc)₂(py)] and [Cd(ecpzdtc)₂(py)]·H₂O complexes contain pyridine as the co-ligand. [Co(ecpzdtc)₃] (2) crystallizes in the monoclinic system, whereas [Zn(ecpzdtc)₂(py)] (3) and [Cd(ecpzdtc)₂(py)]·H₂O (4) crystallize in the triclinic system. The sulfur donor sites of the bidentate ligand chelate the metal center, forming a four-membered CS₂M ring. The cobalt complex has a distorted octahedral geometry, the zinc complex is almost between trigonal bipyramidal and square pyramidal, whereas the cadmium complex is square pyramidal. The crystal structures of all the complexes are stabilized by various types of inter and intramolecular hydrogen bonding.     

Synthesis and crystal structure characterization of iron(II), cobalt(II) and nickel(II) complexes with 1,3-bis(2-pyridylmethylthio)propane

Three new mononuclear complexes of nitrogen–sulfur donor sets, formulated as [Fe^II(L)Cl₂] (1), [Co^II(L)Cl₂] (2) and [Ni^II(L)Cl₂] (3) where L = 1,3-bis(2-pyridylmethylthio)propane, were synthesized and isolated in their pure form. All the complexes were characterized by physicochemical and spectroscopic methods. The solid state structures of complexes 1 and 3 have been established by single crystal X-ray crystallography. The structural analysis evidences isomorphous crystals with the metal ion in a distorted octahedral geometry that comprises NSSN ligand donors with trans located pyridine rings and chlorides in cis positions. In dimethylformamide solution, the complexes were found to exhibit Fe^II/Fe^III, Co^II/Co^III and Ni^II/Ni^III quasi-reversible redox couples in cyclic voltammograms with E_1/2 values (versus Ag/AgCl at 298 K) of +0.295, +0.795 and +0.745 V for 1, 2 and 3, respectively.     

Spectral and structural studies of nickel(II) complexes of salicylaldehyde 3-azacyclothiosemicarbazones

Mononuclear nickel(II) complexes with two ONS donor thiosemicarbazone ligands {salicylaldehyde 3-hexamethyleneiminyl thiosemicarbazone [H₂L¹] and salicylaldehyde 3-tetramethyleneiminyl thiosemicarbazone [H₂L²]} have been prepared and physico-chemically characterized. IR and electronic spectra of the complexes have been obtained. The thiosemicarbazones bind to the metal as dianionic ONS donor ligands in all the complexes except in [Ni(HL¹)₂] (1). In compound 1, the ligand is coordinated as a monoanionic (HL⁻) one. The magnetic susceptibility measurements indicate that all the complexes are mononuclear and are diamagnetic. The complexes were given the formulae [Ni(HL¹)₂] (1), [NiL¹py] (2), [NiL¹α-pic] (3), [NiL¹γ-pic] · H₂O (4), [NiL²py] (5) and [NiL²γ-pic] (6). The structures of compounds 2 and 3 have been solved by single crystal X-ray crystallography and were found to be distorted square planar in geometry with coordination of azomethine nitrogen, thiolato sulfur, phenolato oxygen and pyridyl nitrogen atoms.     

Synthesis,characterization and antimicrobial activity of Ni(II) and Zn(II) complexes with N′,N′-bis[(1E)-1-(2-pyridyl)ethylidene]propanedihydrazide. Crystal structures of two highly solvated bimetallic complexes of Ni(II)

The bimetallic [Ni₂(H₂L2)₂](ClO₄)₄ (1), [Ni₂(HL2)(H₂L2)](ClO₄)₃ (2) and [Zn₂(H₂L2)₂](BF₄)₄ (3) complexes (H₂L2 = N′,N′²-bis[(1E)-1-(2-pyridyl)ethylidene]propanedihydrazide) were synthesized and characterized. The structure of complexes (1) and (2) was established by X-ray analysis. NMR spectroscopy was used for the characterization of complex (3). The complexes (1) and (2) were obtained from the same synthetic reaction and two crystal types of these complexes have been isolated during the fractional crystallization process.     

Synthesis, characterization, structures and cytotoxic activity of palladium(II) and platinum(II) complexes containing bis(2-pyridylmethyl)amine and saccharinate

New palladium(II) and platinum(II) complexes containing bis(2-pyridylmethyl)amine (bpma) and saccharinate (sac), [Pd(bpma)(sac)](sac)·2H₂O (1), [Pt(bpma)(sac)](sac)·2H₂O (2), [Pd(bpma)Cl](sac)·2H₂O (3) and [Pt(bpma)(sac)]Cl·1.5H₂O (4), were synthesized and characterized by elemental analysis, IR, NMR and TG-DTA. A single-crystal X-ray analysis of 3 and 4 proved a distorted square-planar geometry around the metal ions with one tridentate bpma ligand and one Cl or sac monoanion. The [Pd(bpma)Cl]⁺ ions in 3 form dimers by intermolecular N-H?Cl and Pd?Pd interactions. The cations reside in the centers of a hydrogen-bonded honeycomb network formed by the uncoordinated sac ions and the lattice water molecules, while the cations of 4 are connected by N-H?Cl and OW-H?O hydrogen bonds into one-dimensional chains. Cyclic planar tetrameric and trimeric water clusters were observed in 3 and 4, respectively. Cytotoxicity of 1-4 was tested against A549, C6 and CHO cells. Although 2 and 4 have no cytotoxicity, the best results were achieved for 1 and 3. In particular, the cyctotoxic activity of 3 is comparable to cisplatin.     

Syntheses,structures and hydrolytic properties of copper(II) complexes of asymmetrically N-functionalised 1,4,7-triazacyclononane ligands

A series of new asymmetrically N-substituted derivatives of the 1,4,7-triazacyclononane (tacn) macrocycle have been prepared from the common precursor 1,4,7-triazatricyclo[5.2.1.0^4,10]decane: 1-ethyl-4-isopropyl-1,4,7-triazacyclononane (L1), 1-isopropyl-4-propyl-1,4,7-triazacyclononane (L2), 1-(3-aminopropyl)-4-benzyl-7-isopropyl-1,4,7-triazacyclononane (L3), 1-benzyl-4-isopropyl-1,4,7-triazacyclononane (L4) and 1,4-bis(3-aminopropyl)-7-isopropyl-1,4,7-triazacyclononane (L5). The corresponding monomeric copper(II) complexes were synthesised and were found to be of composition: [Cu(L1)Cl₂] · 1/2 H₂O (C1), [Cu(L4)Cl₂] · 4H₂O (C2), [Cu(L3)(MeCN)](ClO₄)₂ (C3), [Cu(L5)](ClO₄)₂ · MeCN · NaClO₄ (C4) and [Cu(L2)Cl₂] · 1/2 H₂O (C5). The X-ray crystal structures of each complex revealed a distorted square-pyramidal copper(II) geometry, with the nitrogen donors on the ligands occupying 3 (C1 and C2), 4 (C3) or 5 (C4) coordination sites on the Cu(II) centre. The metal complexes were tested for the ability to hydrolytically cleave phosphate esters at near physiological conditions, using the model phosphodiester, bis(p-nitrophenyl)phosphate (BNPP). The observed rate constants for BNPP cleavage followed the order k_C1 ≈ k_C2 > k_C5 ? k_C3 > k_C4, confirming that tacn-type Cu(II) complexes efficiently accelerate phosphate ester hydrolysis by being able to bind phosphate esters and also form the nucleophile necessary to carry out intramolecular cleavage. Complexes C1 and C2, featuring asymmetrically disubstituted ligands, exhibited rate constants of the same order of magnitude as those reported for the Cu(II) complexes of symmetrically tri-N-alkylated tacn ligands (k ∼ 1.5 × 10⁻⁵ s⁻¹).     

Syntheses,EPR spectral studies and crystal structures of manganese(II) complexes of neutral N,N donor bidentate Schiff bases and azide/thiocyanate as coligand

Four manganese(II) complexes Mn₂(paa)₂(N₃)₄ (1), [Mn(paa)₂(NCS)₂]·³/₂H₂O (2), Mn(papea)₂(NCS)₂ (3), [Mn(dpka)₂(NCS)₂]·¹/₂H₂O (4) of three neutral N,N donor bidentate Schiff bases were synthesized and physico-chemically characterized by means of partial elemental analyses, electronic, infrared and EPR spectral studies. Compounds 3 and 4 were obtained as single crystals suitable for X-ray diffraction. Compound 4 recrystallized as Mn(dpka)₂(NCS)₂. Both the compounds crystallized in the monoclinic space groups P2₁ for 3 and C2/c for 4. Manganese(II) is found to be in a distorted octahedral geometry in both the monomeric complexes with thiocyanate anion as a terminal ligand coordinating through the nitrogen atom. EPR spectra in DMF solutions at 77 K show hyperfine sextets with low intensity forbidden lines lying between each of the two main hyperfine lines and the zero field splitting parameters (D and E) were calculated.     

Synthesis and structural characterization of novel ruthenium(II) complexes featuring an N,N,O-scorpionate ligand: A versatile synthetic precursor for open-face scorpionatoruthenium(II) complexes

The syntheses and characterization of novel ruthenium(II) complexes containing bis(3,5-dimethylpyrazol-1-yl)acetato (bdmpza), a new class of scorpionate ligands, are reported herein. [RuCl(bdmpza)(η⁴-1,5-cyclooctadiene)] (1) was found to be a versatile precursor to synthesize a wide range of new ruthenium(II) complexes with the bdmpza ligand. The treatment of 1 with pyridine (py), diphenylphosphinoethane (dppe), 2,2′-bipyridyl (bpy), 1,10-phenanethroline (phen), or bispicolylamine (Hbpica) in refluxing N,N-dimethylformamide resulted in displacement of the 1,5-cyclooctadiene ligand to afford [RuCl(bdmpza)(py)₂] (2), [RuCl(bdmpza)(dppe)] (3), [RuCl(bdmpza)(bpy)] (4), [RuCl(bdmpza)(phen)] (5), and [Ru(bdmpza)(Hbpica)]Cl (6Cl) in good yields, respectively. The structures of 1–4, and 6 were determined by X-ray structure analyses.