The synthesis and characterisation of some MnLnX2 complexes (n = 1, L = pyridine, 4-pyrrolidinopyridine,X = Cl,Br, I,NCS; n = 1, L = EtOH,X = Cl,Br; n = 2, L = EtOH,X = I,NCS)

Mono-ligand complexes MnLX₂ (L = pyridine, 4-pyrrolidinopyridine, X = Cl, Br, I, NCS) have been prepared. The pyridine complexes contain only bridging halide and pseudohalide groups, whereas the 4-py complexes contain both bridging and terminal bound anions. Ethanol is coordinated in Mn(EtOH)X₂ (X=C1, Br) and Mn(EtOH)₂X₂ (X=I, NCS). Although the MnLX₂ complexes have the same stoichiometry as the Mn(PR₃)X₂complexes none show any activity towaxds binding dioxygen either in the solid state or in solution.     

Co-ordination compounds derived from dimethylhydrazones of cyclohexane-1,2-dione, 2-acetyl- and 2-benzoylpyridines and 4-bezoylpyridine

The 1,1-dimethylhydrazones of cyclohexane-1,2-dione (CDDMH), 2-acetylpyridine (APDMH) and 2-benzoylpyridine (2BPDMH) from tetrahedral complexes MX₂L (M = Co(II), Zn(II); X = Cl, Br) in which the ligand is chelating through the methylene nitrogen atoms (CDDMH) or one methylene and one pyridine nitrogen atom (APDMH, 2BPMDH). Octahedral complexes CoX₂L₂ (X = Cl, NCS; L = APDMH, 2BPDMH) have also been isolated but no tris-ligand complexes. The ligand 4-benzoylpyridine-dimethylhydrazone (4BPDMH) does not chelate but forms tetrahedral complexes MX₂(4BPDMH)₂ in which the unidentate ligand co-ordinates through the pyridine nitrogen atom.     

Synthesis and characterization of new ruthenium(II) complexes containing coupled di(2-pyridyl) and 1,3-dithiole units

Two new ruthenium (II) complexes containing coupled di(2-pyridyl) and 1,3-dithiole units, cis-[Ru(Medpydt)₂(NCS)₂] (2, Medpydt = dimethyl 2-(di(2-pyridyl)methylene)-1,3-dithiole-4,5-dicarboxylate) and cis-[Ru(H₂dpydt)₂(NCS)₂] (3, H₂dpydt = 2-(di(2-pyridyl)methylene)-1,3-dithiole-4,5-dicarboxylate), have been synthesized and characterized. The structure of complex 2 has been determined by X-ray crystallography. There exist intermolecular H-bonding interactions between carbomethoxy groups on neighboring pyridine rings giving rise to 2D H-bonded arrays. The metal-to-ligand charge-transfer (MLCT) absorptions were observed around 480 nm. Redox properties of ruthenium complexes have been investigated by cyclic voltammetry. Solar cells involving thin films of anatase TiO₂ impregnated with cis-[Ru(H₂dpydt)₂(NCS)₂] were prepared, and the photovoltaic performance was preliminarily investigated.     

Synthesis, characterization and properties of iron(II) complexes with a series of tripodal ligands based on the parent ligand tris(2-pyridylmethyl)amine

Iron(II) complexes of the type [Fe(L)(NCS)₂] with the tripodal ligand apme (apme = N¹-(2-aminoethyl)-N¹-(2-pyridyl-methyl)-1,2-ethanediamine) as well as with its derivatives were prepared and structurally characterized. The bond distances thus obtained showed that all complexes investigated were high-spin at the respective temperature. Furthermore [Fe(Me₄apme)(NCS)₂] was analyzed using Mößbauer spectroscopy that showed that this complex remains in its high-spin state over the entire temperature range.     

Effect of H-bonding on the ambivalence of SCN towards copper(II)

Condensations of 2-(2-aminoethyl)pyridine with 4-methylimidazole-5-carboxaldehyde and 1-methyl-2-imidazolecarboxaldehyde generate the tridentate N donor ligands L and L′ respectively. Reactions of Cu(NCS)₂ with L and L′ yield respectively CuL(SCN)(NCS) (1) containing a CuN₄S core and CuL′(NCS)₂ (2) having a CuN₅ core. Both the cores are square pyramidal with SCN⁻ bound in 1 at the axial position through the S end. This differential behaviour of SCN⁻ in the two complexes despite the ligands being very similar, is investigated by DFT calculations at the B3LYP/TZV level. It is found that DFT calculations predict isolation of the Cu(ligand)(NCS)₂ species for both the ligands L and L′. Presence of an offsetting intermolecular H-bonding between the N atom of the thiocyanate and the N-H proton of the ligand L of an adjacent molecule makes the binding of SCN⁻ via the S end feasible in 1 resulting in the H-bonded dimer Cu₂L₂(SCN)₂(NCS)₂. The strength of the H-bond is estimated as 27.1 kJ mol⁻¹ from the DFT calculations. The question of such H-bonding does not arise with L′ as it lacks in a similar H atom. Dimeric 1 represents a case of two non-interacting spins.     

New ruthenium sensitizers containing styryl and antenna fragments

Amphiphilic ligands 4′-((4-(5-pyridin-4-yloxy)pentyloxy)styryl)-4-methyl-2,2′-bipyridine (L1), 4,4′-bis((E)-4-(5-(pyridin-4-yloxy)pentyloxy)styryl)-2,2′-bipyridine (L2), 4′-(4-(5-(4′-cyano-4-biphenoxy)pentyloxy)styryl)-4-methyl-2,2′-bipyridine (L3), and 4′-(4-(5-(zinc tetrakis-5,10,15-tritolyl-20-(4-hydroxyphenyl)porphyrin)pentyloxy)styryl)-4-methyl-2,2′-bipyridine (L4) and their heteroleptic ruthenium(II) complexes of the types [Ru(L1)(L)(NCS)₂] (D20), [Ru(L2)(L)(NCS)₂] (D21), [Ru(L3)(L)(NCS)₂] (D22), and [Ru(L4)(L)(NCS)₂] (D23) (where L = 4,4′-bis(carboxylic acid)-2,2′-bipyridine) have been synthesized, as photosensitizers for nanocrystalline dye-sensitized solar cells. All complexes D20-D23 exhibit a broad MLCT band around 520-530 nm in DMF and an emission band around 740-790 nm in DMF. We have studied photovoltaic performances based on the newly synthesized dyes. Under standard AM 1.5 sunlight, the dye D20 gave a short-circuit photocurrent density of 13.31 mA/cm², an open-circuit voltage of 0.64 V, and a fill factor of 0.68, corresponding to an overall conversion efficiency of 5.81%.     

Metal Complexes of 2-Amino-5-nitrothiazole

The preparation and characterisation of complexes of 2-amino-5-nitrothiazole (ANT) with Co(II), Ni(II), Cu(II), Cd(II), Cu(I) and Ag(I) are described. From spectral data it is inferred that the complexes fall into two groups: those in which ANT is bound through the ring nitrogen, and those in which the exocyclic amine group is bound to the metal ion. In the former group are complexes of the type MCl₂(ANT)₂ (M  Co, NJ, Cu, Cd); compounds containing methanol, NiBr₂(ANT)₃(MeOH), Ni- (NCS)₂(ANT)₂(MeOH)₂, Ni(NCS)₂(ANT)₂(MeOH); and AgNO₃(ANT)₂, Cu(AcO)₂(ANT) and CuCl- (ANT)₂ In the latter group are complexes prepared from and containing N,N′-dimethylformamide: CoSO₄(ANT)₂(DMF)₂, NiSO₄(ANT)₂(DMF)₂, NiCl₂- (ANT)₂(DMF)₂, CuSO₄(ANT)(DMF) and CuCl₂- (ANT)(DMF). The probable structures of the nickel and cobalt complexes are discussed. The coordination chemistry of the thiazole group and the effect of the electron withdrawing nitro-group are discussed.     

Reaction of methanol ligated manganese(II) silanethiolate with pyridine related ligands - Different structures of complexes with MnNO2S2 kernel

The reaction of [Mn{SSi(OBu^t)₃}₂(MeOH)₄] with pyridine and its three monosubstituted methyl derivatives leads to the formation of two distinct types of complexes, although both with the MnO₂NS₂ kernel. The first two compounds (with pyridine or 2-picoline) contain two silanethiolate ligands, heterocyclic base and two methanol molecules. In the second case (3- and 4-picoline) the role of O-donor and simultaneously S-donor ligand is fulfilled by tri-tert-butoxysilanethiolate rest which under favorable conditions can serve as a chelating agent.     

Interaction of copper(II) with the non-steroidal anti-inflammatory drugs naproxen and diclofenac: synthesis, structure, DNA- and albumin-binding

Copper(II) complexes with the non-steroidal anti-inflammatory drugs (NSAIDs) naproxen and diclofenac have been synthesized and characterized in the presence of nitrogen donor heterocyclic ligands (2,2′-bipyridine, 1,10-phenanthroline or pyridine). Naproxen and diclofenac act as deprotonated ligands coordinated to Cu(II) ion through carboxylato oxygens. The crystal structures of (2,2′-bipyridine)bis(naproxenato)copper(II), , (1,10-phenanthroline)bis(naproxenato)copper(II), and bis(pyridine)bis(diclofenac)copper(II), have been determined by X-ray crystallography. The UV study of the interaction of the complexes with calf-thymus DNA (CT DNA) has shown that the complexes can bind to CT DNA with (2,2′-bipyridine)bis(naproxenato)copper(II) exhibiting the highest binding constant to CT DNA. Competitive study with ethidium bromide (EB) indicates that the complexes can displace the DNA-bound EB suggesting strong competition with EB. The cyclic voltammograms of the complexes recorded in the presence of CT DNA have shown that the complexes can bind to CT DNA by the intercalative binding mode which has also been verified by DNA solution viscosity measurements. The NSAID ligands and their complexes exhibit good binding propensity to human or bovine serum albumin protein having relatively high binding constant values. The biological properties of the previously reported complexes [Cu₂(naproxenato)₄(H₂O)₂], [Cu₂(diclofenac)₄(H₂O)₂] and [Cu(naproxenato)₂(pyridine)₂(H₂O)] have been also evaluated. The dinuclear complexes exhibit similar affinity for CT DNA as the 2,2′-bipyridine or 1,10-phenanthroline containing complexes. The pyridine containing complexes exhibit the lowest affinity for CT DNA and the lowest ability to displace EB from its EB-DNA complex.     

A study of 2-cyanopyridine addition products in the coordination sphere of Ni(II)

The coordination of 2-cyanopyridine molecule to Ni(II) atom promotes a nucleophilic addition of solvent molecules (water, methanol, ethanol) to the nitrile group. The addition of water leads to the formation of solid complexes containing pyridine-2- carboxamide as a chelate ligand. An analogous reaction of 2-cyanopyridine with NiX₂ (X = Cl, Br, I, NCS) in methanolic solutions gives, however, complexes containing two or three molecules of O-methylpyridine-2-carboximidate. No nucleophilic addition of solvent occurred with 3- and 4-cyanopyridine under the same reaction conditions.The complexes under study exhibit an octahedral geometry. The structure and the mode of the ligand coordination have been determined by IR spectra.     

Synthesis and characterization of phosphorescent iridium complexes containing trifluoromethyl-substituted phenyl pyridine based ligands

Several iridium complexes containing trifluoromethyl-substituted phenyl pyridine based ligands have been synthesized and characterized to try to investigate the effect of trifluoromethyl group and its position on physical properties. The complexes have the general structure of (C-N)₂Ir(LX), where the C-N are 2-phenylpyridine (ppy), 2-(3,5-bis-trifluoromethylphenyl)pyridine (fmppy), 2-(3,5-bis-trifluoromethylphenyl)-4-methylpyridine (fmpmpy), 2-(3,5-bis-trifluoromethylphenyl)-5-trifluoromethylpyridine (tfmppy) and the LX are 2-picolinic acid (pic) and acetylacetonate (acac). The (tfmppy)₂Ir(pic) was characterized using X-ray crystallography. The absorption, emission, and thermostability of the complexes were systematically investigated. Introduction of CF₃ substituents into 2-phenylpyridine in (ppy)₂Ir(pic) lead to some decrease in the sublimation temperature, which is more suitable to devices fabrication. The experimental results revealed that the emissive colors of these complexes could be finely tuned by suitable incorporation of trifluoromethyl substituents on the 2-phenylpyridine ligand, obtaining bright green-blue emission λ_max values from 471 to 489 nm in CH₂Cl₂ solution at room temperature, with high solution quantum efficiencies ranging from 0.37 to 1.89 relative to Ir(ppy)₃.     

Synthetic, EPR spectroscopic, magnetic and X-ray crystallographic structural studies on copper(II) complexes of the tridentate N2S donor ligand formed from 6-methyl-2-formylpyridine and S-methyldithiocarbazate (Hmpsme)

New copper(II) complexes of general empirical formula, Cu(mpsme)X · xCH₃COCH₃ (mpsme = anionic form of the 6-methyl-2-formylpyridine Schiff base of S-methyldithiocarbazate; X = Cl, N₃, NCS, NO₃; x = 0, 0.5) have been synthesized and characterized by IR, electronic, EPR and susceptibility measurements. Room temperature μ_eff values for the complexes are in the range 1.75-2.1 μ_B typical of uncoupled or weakly coupled Cu(II) centres. The EPR spectra of the [Cu(mpsme)X] (X = Cl, N₃, NO₃, NCS) complexes reveal a tetragonally distorted coordination sphere around the mononuclear Cu(II) centre. We have exploited second derivative EPR spectra in conjunction with Fourier filtering (sine bell and Hamming functions) to extract all of the nitrogen hyperfine coupling matrices. While the X-ray crystallography of [Cu(mpsme)NCS] reveals a linear polymer in which the thiocyanate anion bridges the two copper(II) ions, the EPR spectra in solution are typical of a magnetically isolated monomeric Cu(II) centres indicating dissociation of the polymeric chain in solution. The structures of the free ligand, Hmpsme and the {[Cu(mpsme)NO₃] · 0.5CH₃COCH₃}₂ and [Cu(mpsme)NCS]_n complexes have been determined by X-ray diffraction. The {[Cu(mpsme)NO₃] 0.5CH₃COCH₃}₂ complex is a centrosymmetric dimer in which each copper atom adopts a five-coordinate distorted square-pyramidal geometry with an N₂OS₂ coordination environment, the Schiff base coordinating as a uninegatively charged tridentate ligand chelating through the pyridine and azomethine nitrogen atoms and the thiolate, an oxygen atom of a unidentate nitrato ligand and a bridging sulfur atom from the second ligand completing the coordination sphere. The [Cu(mpsme)(NCS)]_n complex has a novel staircase-like one dimensional polymeric structure in which the NCS⁻ ligands bridge two adjacent copper(II) ions asymmetrically in an end-to-end fashion providing its nitrogen atom to one copper and the sulfur atom to the other.     

Main group metal halide complexes with sterically hindered thioureas. VIII. Complexes of lead(II) halides with 1,3-dimethyl-2(3H)-imidazolethione

Two new complexes of 1,3-dimethyl-2(3H)- imidazolethione (dmit) and lead(II) halides have been synthesized and characterized. Addition of dmit in molar excess to PbX₂ (X = Cl, Br, I, SCN) solutions in hot water yielded PbCl₂dmit and Pb(NCS)₂(dmit)₂. No adducts were isolated for PbBr₂ or PbI₂. Complexes were characterized via standard methods including both solid state and solution state information. Both complexes were high melting solids and appeared to be polymeric in the solid state, and IR data indicated polymerization occurred through halogen (of pseudohalogen) bridges only. Thiocyanate was N-bonded to the metal. Solution studies concluded that both were dissociated in DMF with PbCl₂dmit being a non-electrolyte and Pb(NCS)₂(dmit)₂ acting like a 1:1 electrolyte.     

Synthesis, structure, and properties of monomeric Fe(II), Co(II), and Ni(II) complexes of neutral N-(aryl)-2-pyridinecarboxamides

We have prepared and structurally characterized six-coordinate Fe(II), Co(II), and Ni(II) complexes of types [M^II(HL¹)₂(H₂O)₂][ClO₄]₂ (M = Fe, 1; Co, 3; and Ni, 5) and [M^II(HL²)₃][ClO₄]₂ · MeCN (M = Fe, 2 and Co, 4) of bidentate pyridine amide ligands, N-(phenyl)-2-pyridinecarboxamide (HL¹) and N-(4-methylphenyl)-2-pyridinecarboxamide (HL²). The metal centers in bis(ligand)-diaqua complexes 1, 3 and 5 are coordinated by two pyridyl N and two amide O atoms from two HL¹ ligands and six-coordination is completed by coordination of two water molecules. The complexes are isomorphous and possess trans-octahedral geometry. The metal centers in isomorphous tris(ligand) complexes 2 and 4 are coordinated by three pyridyl N and three amide O atoms from three HL² ligands. The relative dispositions of the pyridine N and amide O atoms reveal that the pseudo-octahedral geometry have the meridional stereochemistry. To the best of our knowledge, this work provides the first examples of structurally characterized six-coordinate iron(II) complexes in which the coordination is solely by neutral pyridine amide ligands providing pyridine N and amide O donor atoms, with or without water coordination. Careful analyses of structural parameters of 1-5 along with that reported in the literature [M^II(HL¹)₂(H₂O)₂][ClO₄]₂ (M = Cu and Zn) and [Co^III(L²)₃] have allowed us to arrive at a number of structural correlations/generalizations. The complexes are uniformly high-spin. Spectroscopic (IR and UV/Vis) and redox properties of the complexes have also been investigated.     

The coordination chemistry of N-(2-pyridyl)pyridine-2′-carboxamide; A potentially tridentate ligand containing one secondary amide and two 2-pyridyl donor groups

New complexes of the general compositions M(LH)X₂ (M = Co, Zn; X = Cl, Br, I), Zn(LH)(NCS)₂, Zn(LH)(NO₃)₂ ·H₂O, Cu(LH)X₂ (X = Cl, Br, ONO₂), Ni(LH)Cl₂·H₂O, Co(LH)₂X₂ (X = NCS, ONO ₂), Ni(LH)₂X₂ (X = Cl, Br, NCS, ONO₂), Pt(LH)₂Cl₂ and MLCl·nH₂O (M = Ni, Cu, Pd; n = 2, 3), where LH = N-(2-pyridyl)pyridine-2′-carboxamide, have been isolated. The complexes were characterized by elemental analyses, conductivity measurements, X-ray powder patterns, thermal methods, magnetic susceptibilities and spectroscopic (IR, ligand field, ¹H NMR) studies. Pseudotetrahedral, square planar, square pyramidal and distorted octahedral stereochemistries are tentatively assigned in the solid state. Most complexes appear to be monomeric, while polymeric structural types are attributed for Ni(LH)Cl₂·H₂O and CuLCl·2H₂O. The neutral amide group of LH is coordinated to Co(II), Ni(II), Cu(II) and Zn(II) through oxygen, while N-coordination is observed for PdLCl·2H₂O. The amide group of L⁻ is bound to different Cu(II) atoms in CuLCl·2H₂O through both its nitrogen and oxygen. The rare O-coordination of the deprotonated amide bound is proposed for NiLCl· 3H₂O. The N(1) atom is not involved in coordination except in the complexes Ni(LH)Cl₂·H₂O, NiLCl· 3H₂O and CuLCl·2H₂O, where both pyridine residues are coordinated. The variation in structural types observed is believed to be a consequence of the stereochemical adaptability of the ligand to the electronic demands of the metal ions.     

Synthesis of a novel pyridine-diamino bridged diphosphine ligand and its macrocyclic metal complexes

A novel long chain diphosphine ligand with a pyridine-diamino bridge, 2,6-bis(N-benzyl-N-diphenylphosphinomethylamino)pyridine (PNP1), was prepared conveniently using the Mannich reaction of HPPh₂ with paraformaldehyde and 2,6-bis(N-benzylamino)pyridine in high yield. Reactions of the ligand with metal complexes, M(COD)Cl₂ (M = Pd, Pt), M(CH₃CN)₄ClO₄ (M = Cu, Ag) and M(CO)₆ (M = Mo, W) afforded the corresponding 10-numbered monometallic macrocyclic complexes with an uncoordinated pyridyl bridge. The monometallic chelate PdCl₂(PNP1) continued to react with Ag⁺ or Cu⁺ giving the μ-Cl bridged bicyclic metallic complex (μ-Cl)₂[PdCl(PNP1)]₂. The diphenylphosphine group coordinated with metal ion in cis-form in all the 10-numbered macrocyclic metal complexes. Ligand PNP1 and another known analogous 2,6-bis(N-diphenylphosphinoamino)pyridine (PNP2) reacted with Au(SMe₂)Cl giving the corresponding bimetallic Au₂Cl₂(PNP1) and Au₂Cl₂(PNP2), respectively. The latter bimetallic complexes continued to react with Ag⁺ and diphosphine ligand to give the corresponding bimetallic macrocyclic complexes Au₂(ligand)₂(ClO₄)₂. All the complexes were characterized and the structures of some complexes were confirmed by X-ray single crystallography determination.     

Synthesis of some ruthenium complexes with mixed diimine ligands

The use of Ru(DMSO)₄Cl₂ and Ru(PY)₄Cl₂ (DMSO=dimethyl sulphoxide; Py=pyridine) in synthesizing mixed ligand complexes is reported. The bidentate ligands used are of the diimine type, namely, 2,2′-bipyrimidine (bpm); 3,6-di-(2-pyridyl)-1,2,4, 5-tetrazine (dpt); 2,3-bis(2-pyridyl)-5,6-dihydropyrazine (dhp); 2,3-bis(2-pyridyl)-pyrazine (dpp); 2,3-bis-(2-pyridyl)-quinoxaline (dpq); 2,3,5,6-tetrakis(2-pyridyl)-pyrazine (tpp). Characterization of the complexes has been accomplished using elemental analysis, conductivity, IR and UV-Vis spectroscopy.     

Triazamacrocyclic complexes with 8- and 9-membered chelate rings. Preparation, structures and agostic interactions in complexes of 1,5,9-triazacyclotetradecane and 1,5,9-triazacyclopentadecane

Cobalt(II), copper(II) and nickel(II) complexes of the ligands 1,5,9-triazacyclotetradecane (tatd) and 1,5,9-triazacyclopentadecane (tapd), which have 8- and 9-membered chelate rings, respectively, have been prepared and characterised. Crystal structures of [Ni(tatd)(NCS)₂]·H₂O and [Co(tatd)(NCS)₂] have been determined. The nickel(II) complex has a distorted square pyramidal geometry and the cobalt(II) complex has a distorted trigonal bipyramidal geometry. Agostic interactions between a hydrogen on the central carbon of the 8-membered chelate ring and the metal ion are observed in both complexes.     

The isolation and structural characterization of copper(II) complexes obtained by oxidation of the 2,6-bis(dicyclohexylphosphinomethyl)pyridine and 2-(diisopropylphosphinomethyl)-1-methylimidazole ligands

The reactions of [Cu(NCCH₃)₄]BF₄ with 2,6-(dicyclohexylphosphinomethyl)pyridine and 2-(diisopropylphosphinomethyl)-1-methylimidazole afford Cu(I) species that convert slowly to the Cu(II) complexes [CuCl{Cy₂P(O)CH₂pyCH₂P(O)Cy₂}(H₂O)]BF₄ and [Cu{MelmCH₂P(O)Prⁱ₂}₂](BF₄)₂, respectively, when their solutions are exposed to air. The structures of the Cu(II) complexes have been established by X-ray crystallography.     

Bis(isocyclam)dicopper(II) complexes with a linear methylene chain bridge

New binucleating ligands, bis(isocyclam) with a linear methylene chain bridge, n-bicy (n = 2, 3, 4) and their copper(II) complexes, Cu₂(n-bicy)(ClO₄)₄· xH₂O and Cu₂(n-bicy)(NCS)₄·yH₂O have been synthesized. The magnetic moments of these complexes were normal, but the presence of magnetic coupling between copper(II) ions were clearly demonstrated by the hyperfine structure in the ESR spectra.