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The complexes of the formula [(η6-arene)Ru(L)Cl]PF6, where arene is benzene (bz) or p-cymene (cym) and L is 2,(2′-pyridyl)quinoline (pqn), were synthesized and characterized by means of NMR spectroscopic techniques, HR-ESI mass spectrometry and, in the case of [(η6-cym)Ru(pqn)Cl]PF6, by X-ray single crystal diffraction. Their resistance in hydrolysis was also studied. A comparative NMR study of their 9-methylguanine (9-MeG) complexes, [(η6-arene)Ru(pqn)(9-MeG)](PF6)2, with similar diimine complexes revealed that the unimpeded rotation of 9-MeG is hindered by interactions between the 9-MeGO6 and the p-cymene aromatic proton H2 and, by the bulky shape of the pqn. This conformation forces the 9-MeGH8 to be in close proximity to the aromatic ring system of pqn. NMR spectroscopic techniques lead to the conclusion that the strong shielding effect on 9-MeGH8 depends on the extension of the aromatic system of the ligand. Also, we conclude that the strong deshielding on the 9-MeGNH1 is influenced by both the N7 ruthenation of 9-MeG and the addendum electron density in the 9-MeG ring system, due to the proximity to the aromatic ring system of pqn.

The synthesis and the characterization of (RuCp)-[12]CycloParaPhenylene complexes of the general formula [([12]CPP)(RuCp)n](PF6)n (n = 1–3, 4–6 and 9–12) was achieved by the reaction of [(η5-Cp)Ru(CH3CN)3](PF6) with [12]CPP in dry acetone. The number n of the (RuCp) substitutions on [12]CPP varied depending on the reaction molar ratio, producing mixtures with average (RuCp) moieties, ω1:1 = 2.9, ω1:6 = 4.9, ω1:12 = 10, which were analyzed by 1H NMR spectroscopy and high-resolution ESI mass spectrometry. The [([12]CPP)(RuCp)n]Cln (n = 4–6) was transformed to its corresponding [Cl]− salt which was stable in aqueous solution in the dark, but released (RuCp) solvolyzed species upon UV (365 nm) irradiation. The addition of 9-MeG in an aqueous solution containing [([12]CPP)(RuCp)n]Cln (n = 4–6) which was subsequently irradiated with UV (365 nm) formed adducts between the released (RuCp) and the 9-MeG, where 9-MeG was coordinated through N7. This may be useful in the application of full-sandwich ruthenium-arene complexes in cancer photodynamic therapy.

Mixed ligand cyclopalladated complexes with 2-phenylpyridine (ppy) and 2,9-dimethyl-1,10-phenanthroline (ncp), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (bcp), 4,7-diphenyl-1,10-phenanthroline (bphen) were synthesized and characterized. The crystal structures of [Pd(ppy)(ncp)Cl] (1), [Pd(ppy)(ncp)Η2O]PF6·0.5(CH3CH2)O (3) and {[Pd(ppy)(ncp)]2(μ-Cl)}PF6 (4) were determined by single-crystal diffraction methods. In all cases, the results showed a pseudo-pentacoordinated palladium environment due to the anisobidentate binding of the 2,9-dimethyl-1,10-phenanthroline. The structures of the complexes in acetone solution were studied using NMR spectroscopic techniques, mass spectrometry and conductivity measurements. The results revealed the retention of their solid-state structure. The complexes (1), (4) and [Pd(ppy)(phen)]PF6, (6) were examined for their activity in the hydroxylation reaction of 2-phenylpyridine using NMP (N-methyl-2-pyrrolidone) and molecular oxygen as oxidant. The complex [Pd(ppyO)(phen)]PF6 (8), was isolated from the hydroxylation reaction mixture and could potentially imply that the reaction mechanism includes the formation of high-valent palladium species with Pd-OH bond(s).

Ruthenium η6-arene compounds of the general formula [(η6-arene)Ru(L)Cl](PF6), (1)PF6–(4)PF6, (η6-arene is benzene (bz) or p-cymene (cym), L is 2-(2′-pyridyl)quinoxaline (pqx) or 2-(2′-pyridyl)benzo [g]quinoxaline (pbqx)) and [(η6-cym)Ru(L)(9MeG)](PF6)2, (L is 2-(2′-pyridyl)quinoxaline (pqx), 2-(2′-pyridyl)benzo [g]quinoxaline (pbqx), 2,2′-bipyridine (bpy), 9MeG is 9-methylguanine), (5)(PF6)2–(7)(PF6)2, were synthesized and characterized by spectroscopic and analytical techniques. The molecular structures of the complexes (1)–(4), determined by single-crystal X-ray analysis of the hexafluorophospate salts, are also reported. In (5)(PF6)2–(7)(PF6)2, the nucleobase 9MeG binds to ruthenium through N7. Based on 1H NMR spectroscopy, a strong shielding effect between the aromatic ring system of the quinoxaline or benzo[g]quinoxaline moiety of the ligands pqx and pbqx and the H8 of 9MeG was observed. The complexes (1)–(4) are highly cytotoxic as chloride salts, against various cancer cell lines, with their IC50 values observed at less than 1 μΜ.

The homoleptic [Ru(trpyCO-TrpCONH2)2](PF6)2 (1), [Ru(trpyCO-Gly-TrpCONH2)2](PF6)2 (2) and the heteroleptic complexes [Ru(trpy)(trpyCO-TrpCONH2)](PF6)2 (3), [Ru(trpy)(trpyCO-Gly-TrpCONH2)](PF6)2 (4), where trpyCO-TrpCONH2 and trpyCO-Gly-TrpCONH2 are 2,2′:6′,2″-terpyridine-4-carboxylic acid-tryptophanamide and 2,2′:6′,2″-terpyridine-4-carboxylic acid-glycyl-tryptophanamide respectively, were synthesized and characterized by various spectroscopic and analytical techniques. The interactions of complexes (1) and (4) with the oligonucleotide d(5′-CGCGAATTCGCG-3′)2 were studied by means of NMR spectroscopy. Both complexes bound very weakly to the oligonucleotide, perturbing slightly the helix from B-form, probably through electrostatic interactions between the positive charge of the complexes and the DNA phosphates. In the case of complex (1), the conjugated tryptophane did not approach the oligonucleotide helix, as in the case of complex (4), the unsubstituted trpy of which was clearly orientated towards the oligonucleotide helix. These observations indicate that the bulky substitute on the ligand trpy reduces the binding affinity of the complexes to DNA, allowing only electrostatic interactions. However, complex (4) shows high cytotoxicity against LMS, MCF-7, U2OS and K562 cancer cell lines, with IC50 values ranging 0.464–0.925 μM, which can be attributed to a non classical mechanism for metal based anticancer agents.

Pd(II) complexes of various donor atom ligands posses anti-tumor and anti-viral. -malarial, -fungal and -microbial activities. This review focuses on such properties of Pd(II) complexes and makes comparisons with similar properties of other metals. In the first part, the anti-viral, anti-fungal and anti-microbial activities of new I'd(H) complexes are described, classified according to the ligands used, namely; sulfur donors, ligands used as drugs, Schiff bases ligands and miscellaneous. The second part describes the anti-tumor properties of new Pd(II) complexes, similarly classified with sulfur and nitrogen and other donor ligands. The results are summarized in 1st and 2nd tables in this article which also contain all Pd(II) complexes described in Ref. [A. Garoufis. S.K. Hadjikakou, N. Hadjiliadis, in: M. Gielen, E.R.T. Tiekink (Eds.), Metals in Medicine, Palladium (Pd), in Metallotherapeutic Drugs and Metal-based Diagnostic Agents: The Use of Metals in Medicine, John Wiley & Sons, Ltd., 2005, p. 399 (Chapter 21)1 for comparison and clearly demonstrate the anti-tumor, anti-fungal, -viral, -microbial properties of several of them, as compared to those of other metals and especially to those of cisplatin. These promising results are encouraging further research in this field, for future applications. (C) 2008 Elsevier B.V. All rights reserved. Coordination Chemistry Reviews

The novel lanthanide(III) complexes [La(NO(3))(3)(H(2)O)L] 1, and [Ln(NO(3))(3)L] (Ln=Pr 2, Sm 3, Gd 4) where L=N,N'-bis(pyridin-2-ylmethylene)benzene-1,2-diamine, have been obtained by direct reaction of the Schiff base ligand and the corresponding hydrated lanthanide(III) nitrates in methanol. All complexes were characterized spectroscopically and thermogravimetrically. Complex 3 was also characterized with crystallographic studies. In the molecular structure of 3, Sm(III) is surrounded by all four nitrogen atoms of the Schiff base and six oxygen atoms belonging to three bidentate chelating nitrato ligands. (C) 2002 Elsevier Science B.V. All rights reserved. Inorganic Chemistry Communications

Reaction of Co(II) perchlorate hexahydrate and anhydrous Co(II) chloride with the ligand 2-(2′-pyridyl)quinoxaline (L) leads to the formation of the novel five- and six-coordinated complexes CoLCl2(DMF) (1) and [CoL2(H2O)2](ClO4)2·H2O·2CH3OH (2), correspondingly. The crystal structures of the above complexes show a trigonal bipyramidal geometry around the metal atom for complex 1 and a distorted octahedral geometry for complex 2.

Complexes of 2-(2′-pyridyl)quinoxaline (L) with R2SnCl2 (R=Me, Et, Bun) have been synthesized and characterized using IR, far-IR, 119Sn Mossbauer, 1H and 13C spectroscopies. The X-ray crystal structure of Et2SnCl2L shows a bidentate chelating behaviour of L, which is observed in all the diorganotin compounds presented. Interaction of the ligand L with SnCl4 resulted in the formation of a salt with the formula [(LH)2]2+[SnCl6]2−. Solution studies of the complexes R2SnCl2L (R=Me, Et, Bun) revealed partial dissociation of the ligand in chloroform.

The reaction of MnCl2.4H(2)O with the biheteroaromatic ligand (L), formed the dinuclear complex bis[aquachloro-2-(2'-pyridyl)quinoxaline]di-mu-chloro dimanganese {[Mn2L2Cl4(H2O)(2)]}, which was studied in the solid state by thermal techniques [thermogravimetry (TG), differential thermogravimetry (DTG) and differential thermal analysis (DTA)], spectroscopy (IR, far-IR, electronic spectra), magnetic susceptibility, X-ray diffraction methods as well as in methanolic solution by electrospray mass spectrometry (ES-MS). The X-ray crystal structure showed two manganese(II) ions bridged by two chloro ligands with a terminal chloride, a water molecule and a chelating molecule of L, completing a six-coordinate octahedral geometry around each metal centre. The complex in methanolic solution decomposes, forming various monomeric species, as observed from both conductivity measurements and ES-MS. Anions of the general formula [(MnCl2)Cl](n)(-), where n=1, 2, 3, 4 and 5, were also observed in the negative ES mode. (C) 1999 Elsevier Science Ltd. All rights reserved. Polyhedron

The preparation and the characterization of Ni2+ and Fe2+ complexes of the neutral, N-4(-) non-macrocyclic Shiff base ligand, L = 1,2-bis-(2'-pyridylmethyleneimino)benzene of formulae FeLCl2 and [NiL(H2O)(2)]Cl-2(-) are reported. The structure of the Ni complex, [NiL(H2O)(2)]Cl-2, has been determined by X-ray diffraction methods. The nickel atom has a six coordinate NiN4O2 chromophore with distorted octahedral coordination. The ligand L acts as tetradentate chelate, with the ligated atoms in an essentially planar arrangement around the metal with the remaining-axial coordination sites occupied by water ligands. In addition a series of ligand-bridged LMCl2 oligomeric complexes of the type {[LME]Cl-2}(n) (M = Ni, Fe, Cu and E = pyrazine, 4,4'-bipyridine, 1,4-dicyanobenzene, 1,4-cyanopyridine), have been synthesized and characterized by elemental analysis, solid state conductivity, magnetic susceptibility measurements and IR, UV-VIS and ES-MS spectroscopic techniques. Doping of these complexes with iodine exhibited conductivities in the solid state comparable to similar dimethylglyoxime derivative complexes. (C) 1998 Elsevier Science Ltd. All rights reserved. Polyhedron

The preparation and the characterization of nickel(II) complexes with the neutral, N4 non-macrocyclic Schiff base ligands L1=1,2-bis(2′-pyridylbenzyleneimino)benzene and L2=1,2-bis(2′-pyridylethyleneimino)benzene, of formulae Ni(LX)Cl2 are reported. The structure of the complex, [Ni(L1)Cl2] · EtOH, has been determined by X-ray diffraction methods. The nickel atom has a six coordinate NiN4Cl2chromophore with distorted octahedral coordination, while the ligand L acts as a tetradentatechelate, with the ligated atoms in an essentially planar arrangement around the metal and the remaining axial coordination sites occupied by chloro ligands. The reactions of the above complexes and that of Ni(L3)Cl2 with 1,4-phenyldiisocyanide (phdi) formed polymeric compounds of the type [(LX)Ni(phdi)]nCl2n which have been characterized by elemental analysis, magnetic susceptibility measurements, IR and UV-Visspectroscopic techniques. The solid state electrical conductivity of the polymeric complexes was approximately 10−7 (Ω · m)−1, which further increased by partial oxidation with I2.

Cu(NO3)2·3H2O reacts with 1 equiv. of the tetradentate Schiff base N,N′-bis[1–(2–pyridyl)ethylidene]ethane-1,2–diamine (LA) in refluxing acetone to yield the [CuLA(ONO2)(H2O)](NO3) complex in ca. 80% yield. The structure of this salt has been determined by single-crystal X-ray crystallography. The copper is six-coordinated with the LA ligand in the equatorial plane and weakly bonded aqua and nitrato ligands above and below this plane. The complex cation is hydrogen-bonded to the nitrate counter-ion. The complex was also characterized by elemental analyses, molar conductivity, room-temperature magnetic susceptibility and spectroscopic (i.r., far-i.r., u.v.–vis, e.s.r.) studies. The data are discussed in terms of the nature of bonding and the known structure.

The Ru-containing modified silica [Ru-II(terpy)(4'Mebpy/4CONH(CH2)(3)SiO3/2)Cl](+)m center dot zSiO(2) has been prepared by covalent attachment on silica surface of biomimetic [Ru-II(terpy)(4-CO2H-4'-Mebpy)Cl](+). complex through the formation of a pseudo-peptide bond. The catalytic ability of bio-derived silica for alkene oxidation with (HOOBu)-Bu-t has been evaluated exhibiting significant efficiency and, in some cases, showing increased activity compared vs. the corresponding 'net' [Ru-II(terpy)(4-CO2H-4'-Mebpy)Cl](+) complex. The data supported that the covalently attached ruthenium complex preserves the catalytic behaviour of the 'net' ruthenium complex indicating that the presented grafting process was successful. (C) 2012 Elsevier Ltd. All rights reserved. Polyhedron

Complexes of the general formulae [Pt(trpy)(cpy)]NO3, where cpy = pyridine-2-carboxylic acid, pyridine-3-carboxylic and pyridine-4-carboxylic acid (1)–(3), have been synthesized and characterized. The molecular structure of (3) has been determined by X-ray single crystal diffraction. The resin-immobilized ligand Lys-Lys-4-CO-py (L) interacts with the [Pt(trpy)H2O](NO3)2 via solid phase synthesis, forming the complex [Pt(trpy)(4-CO-py-Lys1-Lys2CONH2)](NO3)4, which has been characterized by 1H NMR and mass spectrometry.

The 2:1 and 1:1 reactions of MeHgI with 2-(2'-pyridyl)quinoxaline (L) in methanol led to Hg-C bond cleavage and yielded the dinuclear complex [Hg(2)I(4)L(2)] as one of the products. The crystal structure of this compound shows a chelating behaviour of L and different (terminal, asymmetric bridging) iodide coordination modes. Some spectroscopic characteristics of the dimer and the biological relevance of this reaction are also reported. Polyhedron

The reactions of ZnX2 and CdX2 (X = Cl, Br, I) with the biheteroaromatic ligand 2-(2′-pyridyl)quinoxaline (L) were studied in ethanolic solutions. The new complexes [ZnX2L] (X = Cl, Br, I), [CdI2L] and [Cd2X4L2] were isolated and characterized by elemental analyses, conductivity measurements, X-ray powder patterns, thermal methods (TG/DTG, DTA) and spectroscopic (IR, far-IR, Raman, 1H NMR) studies. The X-ray crystal structure of [ZnCl2L]·0.5MeOH shows a distorted tetrahedral geometry around the zinc(II) atom. The ligand L acts as a bidentate chelate with ligand atoms being the pyridine nitrogen and one of the quinoxaline nitrogens. A monomeric pseudo-tetrahedral structure is also assigned for [ZnBr2] and [MI2L] (M = Zn, Cd). Dimeric structures are proposed for the chloro and bromo cadmium(II) compounds, in which the two metal centres are bridged by two halo ligands, with a terminal halide and a chelating molecule of L completing five-coordination at each metal. All data are discussed in terms of the nature of bonding and known and assigned structures. A complex with the empirical formula Cd2Cl4L was isolated during the thermal decomposition of [Cd2Cl4L2]; the vibrational study of this thermally stable intermediate shows that L acts as a tridentate bridging ligand. The crystal structure of [Hg2Br4L2], which was not available when the results of the HgX2/L chemistry had been published, is also described.

The mercury(II) complexes [Hg 2 X 4 L 2 ] (X = Cl, Br) and [HgI 2 L], where L is 2-(2′-pyridyl)quinoxaline, have been prepared and studied by a combination of conductivity measurements and FT-IR and far-IR, Raman and 1 H NMR spectroscopy. The structures of the free ligand L and [Hg 2 Cl 4 L 2 ] have been determined from three-dimensional X-ray data collected by counter methods. Compound L crystallizes in space group P 2 1 / c with a = 4.163(2), b = 16.953(4), c = 14.509(3) A, β = 94.79(2)° and Z =4. The complex [Hg 2 Cl 4 L 2 ] crystallizes in space group P 2 1 / n with a = 7.627(3), b = 15.617(4), c = 11.099(4),β=92.03(3)° and Z = 2. In free L, the pyridine nitrogen and the nearest quinoxaline nitrogen are located on the opposite side of the carboncarbon bond which connects the two rings; the reverse conformation has been observed on complexation. The structure of [Hg 2 Cl 4 L 2 ] consists of two Hg(II) centres bridged by two chloro ligands, with a terminal chloride and a chelating molecule of L completing five-coordination at each metal. The geometry at mercury is a distorted trigonal bipyramid with the bridging chlorides occupying apical and equatorial sites of each Hg(II) atom. The bromo compound is isostructural with [Hg 2 Cl 4 L 2 ], while a monomeric pseudotetrahedral structure is assigned for the iodo complex in the solid state.

Transition metal(II) chloro complexes of the new Schiff base ligand 1,2-bis(2′-pyridylmethyleneimino)benzene (L), derived from 2-pyridinecarboxaldehyde and 1,2-phenylenediamine, were prepared. Compounds of [MnLCl2]-H2O, [CoLCl2]·2H2O, [NiLCl2] and [Zn3L2Cl4]Cl2 were prepared. Details are given of the formation of the complex [Cu(L·EtOH)Cl2], in which one molecule of EtOH adds across only one of the Schiff base {ie531-01} groups to give the coordinated ligand L·EtOH. The rationalization of this type of reaction by considering the steric requirements of the ligand is given. The complexes were characterized by elemental analyses, conductivity measurements, thermal techniques, mass spectra, magnetic susceptibilities and spectroscopic (i.r., ligand field, e.s.r., 1H n.m.r.) studies. The nitrogen donor atoms of the tetradentate ligands L and L·EtOH are assumed to adopt an essentially planar arrangement about manganese(II), cobalt(II), nickel(II) and copper(II), with the remaining axial coordination sites occupied by chloro ligands to yield high-spin octahedral molecules. A trinuclear structure, based on tetrahedrally coordinated metal ions, is proposed for the zinc(II) complex.

The complexes [MLCl2] (M=Co, Ni, Cu, Zn), where L is the new ligand 2-(2′-pyridyl)quinoxaline derived unexpectedly from 2-acetylpyridine and 1,2-phenylenediamine, were isolated. The ligand and its complexes have been characterized by a variety of physical and spectroscopic techniques. L behaves as a bidentate chelating ligand in the monomeric pseudotetrahedral Zn∥ compound; all three nitrogen atoms of L are involved in coordination in the polymeric Co∥, Ni∥ and Cu∥ complexes giving five-coordinate (Co∥) or six-coordinate (Ni∥, Cu∥) structures.

The complexes of the general formulae [Ru(terpy)(dcbpy)X](q) (dcbpy = 4,4'-dicarboxy-2,2'-bipyridine; X = Cl(-), 1; NO(+), 2: No(2)(-), 3: q = 1+, 3+ and 1-, respectively) have been synthesized and characterized. The DNA binding properties of structurally similar complexes [Ru(terpy)(dcbpy)NO(2)](-), 3, [Ru(terpy)(4-CO(2)-4'-Mebpy)NO(2)], 4, and [Ru(terpy)(bpy)NO(2)](+), 5, were studied, and their DNA affinities (K(b)) were calculated as 6 +/- 0.3 x 10(4) M(-1), 8 +/- 1.1 x 10(4) M(-1) and 9.7 +/- 0.02. 10(6) M(-1). The structural and spectroscopic properties of complexes 3-5 were investigated by DFT and TD DFT electronic structure calculations. The equilibrium geometries of complexes 3-5 in vacuum correspond to a distorted octahedral stereochemistry. The high-lying peaks of the absorption spectra of the complexes, ranging from 440 to 529 nm, are assigned to MLCT/LLCT transitions. These transitions are red-shifted upon adding carboxy substituents to the bipyridine ligand while the low-lying LLCT transitions, absorbing at 779 and 659 turn, are blue-shifted. Noteworthy is the excellent agreement of the TD DFT simulated absorption spectra in aqueous solution with the experimental ones. (C) 2008 Elsevier B.V. All rights reserved. Inorganic Chemistry Communications

The Pd(II) and Pt(II) complexes with triazolopyrimidine C-nucleosides L-1 (5,7-dimethyl-3-(2',3',5'-tri-O-benzoyl-beta-D-ribofuranosyl-s-triazolo)[4,3-a]pyrimidine), L-2 (5,7-dimethyl-3-beta-D-ribofuranosyl-s-triazolo [4,3-a]pyrimidine) and L-3 (5,7-dimethyl[1,5-a]-s-triazolopyrimidine), [Pd(en)(L-1)](NO3)(2), (Pd(bpy)(L-1)](NO3)(2), cis-Pd(L-3)(2)Cl-2, [Pd-2(L-3)(2)Cl-4]center dot H2O, cis-Pd(L-2)(2)Cl-2 and [Pt-3(L-1)(2)Cl-6] were synthesized and characterized by elemental analysis and NMR spectroscopy. The structure of the [Pd-2(L-3)(2)Cl-4]center dot H2O complex was established by Xray crystallography. The two L-3 ligands are found in a head to tail orientation, with a (PdPd)-Pd-... distance of 3.1254(17) angstrom.L-1 coordinates to Pd(II) through N8 and N1 forming polymeric structures. L-2 coordinates to Pd(II) through N8 in acidic solutions (0.1 M HCl) forming complexes of cis-geometry. The Pd(II) coordination to L-2 does not affect the sugar conformation probably due to the high stability of the C-C glycoside bond. (c) 2006 Elsevier B.V. All rights reserved. Inorganica Chimica Acta

The 1:1 reactions of FeCl2 . 4H(2)O and FeCl3 with the biheteroaromatic ligand 2-(2'-pyridyl)quinoxaline (L) were studied in methanol. The new complexes [Fe2Cl4L2] (1) and [Fe2Cl4L2]Cl-2 (2) were isolated and characterized by elemental analyses, conductivity measurements, magnetic susceptibilities at room temperature and spectroscopic (IR, far-IR, ligand field, Fe-57 Mossbauer) techniques. The X-ray crystal structure of 1 consists of two Fe-II centres bridged by two chloro ligands, with a terminal chloride and a chelating molecule of L completing five-coordination at each metal. The geometry at iron is distorted trigonal bipyramidal with the bridging chlorides occupying apical and equatorial sites of each Fe-II atom. A five-coordinate dinuclear structure is also assigned for the cation of complex 2. All data are discussed in terms of the nature of bonding and known or assigned structures. (C) 1998 Elsevier Science Ltd. All rights reserved. Polyhedron

The 1:1 and 1:2 reactions of [MX4](2-)(M=Pd, Pt; X=Cl, Br) with the biheteroaromatic ligand 2-(2'-pyridyl)quinoxaline (L) were studied. The new complexes [PdCl2L] (1), [PdL2]Cl-2 (2), [PtCl2L] (3), [PdBr2L] (4) and [PtBr2L] (5) were isolated and studied by a combination of conductivity measurements, X-ray powder patterns, thermal techniques (TG/DTG, DTA) and spectroscopy (IR, far-IR, Raman). Compounds 1 and 2 have also been characterized by using H-1 and C-13 NMR spectroscopies. The complex [PdCl2L] crystallizes in space group P2(1)/c with a=9.842(1), b=10.223(1), c=15.130(1) A, beta=122.70(1)degrees, V=1281.0(6) A(3) and Z=4. Refinement of the structure gave a final R factor of 0.017 (R-w=0.024) for 2050 unique reflections having I>2.0 sigma(I). The X-ray crystal structure of 1 shows a slightly distorted square planar geometry around the Pd-II atom. The ligand L behaves as a bidentate chelate with the ligated atoms being the pyridine nitrogen and the nearest quinoxaline nitrogen. Similar monomeric, square planar structures are also assigned for 3, 4 and 5. A trans square planar structure is proposed for the [PdL2](2+) cation in 2. All data are discussed in terms of the nature of bonding and known and assigned structures. Compounds with the empirical formulae PtCl2L0.5 (3a) and PtBr2L0.25 (5c) were isolated during the thermal decomposition of 3 and 5; the vibrational studies of these thermally stable intermediates show that L acts as a tridentate bridging ligand and support complicated polymeric structures. The H-1 NMR study of the I:1 [PdI(dien)]I/L (dien=diethylenetriamine) reaction solution in DMSOd(6)/MeOD reveals a monodentate quinoxaline coordination of L. Inorganica Chimica Acta

The 1:1 reaction of Hg(ClO 4 ) 2 ·3H 2 O with 2-(2′-pyridyl)quinoxaline(L) in acetone leads to isolation of [Hg(CH 2 COCH 3 )(ClO 4 L] 2 ; the X-ray crystal structure determination together with 1 H- and 13 C-NMR spectra reveal the presence of the coordinated 2-oxopropyl anion. L coordinates in a bidentate, highly asymmetric mode.

The first 1:2 metal complexes of 2-(2'-pyridyl) quinoxaline (L) have been isolated. The physical and spectroscopic characteristics of the compounds [MCl(2)L(2)] (M=Ni, Cu, Cd) and [Cu(1)L(2)](PF6) are described. The structure of the copper(I) complex has been determined by X-ray diffraction methods. Crystals are orthorhombic, space group P-cnb with a=11.014(2), b=12.886(2), c=17.806(4) Angstrom, V=2527.1(9) Angstrom(3) and Z=4. Refinement of the structure gave a final R factor of 0.046 (R(w)=0.041) for 814 unique reflections having I>2.0 sigma(I). The ligand L acts as a bidentate chelate, the ligated atoms being the pyridine nitrogen and the nearest quinoxaline nitrogen. The structure of [CuL(2)](+) consists of a distorted tetrahedral arrangement around the copper(I) atom with Cu-N bond lengths of 2.023(6) and 2.059(5) Angstrom, and the N-Cu-N angle of the chelating ligand equal to 80.6(2)degrees. A monomeric trans pseudo-octahedral stereochemistry is assigned for the [MCl(2)L(2)] complexes. Inorganica Chimica Acta

Ternary complexes of formulae [Cu(dipeptide)(nucl)(2)]Cl-2 . xH(2)O with dipeptides glycyl-glycine (Gly-Gly), glycyl-L-alanine (Gly-Ala), glycyl-L-valine (Gly-Val), glycyl-L-leucine (Gly-Leu) and nucl inosine (ino) and guanosine (guo) were isolated from a water:ethanol (2:1) solution and characterized with elemental analysis, conductivity measurements, IR, electronic and ESR spectra. At low pH values ( 4 the dipeptides coordinate through the (-NH2) terminal and the deprotonated amide (-N-) groups. The pK(a) values for these deprotonations were estimated with electronic spectra and increase with the increase of the side chain of the dipeptides, due to steric reasons. At higher pH values one nucleoside molecule is liberated and replaced by the terminal deprotonated carboxylate group of the dipeptides. The pK values for these transformations were calculated with ESR spectra and follow the same trend as for the deprotonation constants and for the same reason. Polyhedron

Preparation de nouveaux complexes cis-Pt(ino) 2 Cl 2 , cis-[Pt(ino) 2 (ala)]Cl, cis-[Pt(ino) 2 (alaH)Cl]Cl et cis-[Pd(gua) 2 (isoleuc)]Cl