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A series of mercury(II) complexes, [Hg(N N)(SCN) 2 ] (N N is 4,4′-dimethyl-2,2′-bipyridine in 1 , 5,5′-dimethyl-2,2′-bipyridine in 2 , 6,6′-dimethyl-2,2′-bipyridine in 3 and 6-methyl-2,2′-bipyridine in 4 ), were prepared from the reactions of Hg(SCN) 2 with mentioned ligands in methanol. Suitable crystals of these complexes were obtained for X-ray diffraction measurement by methanol diffusion into a DMSO solution. The four complexes were thoroughly characterized by spectral methods (IR, UV–Vis, 13 C{ 1 H}NMR, 1 H NMR and luminescence), elemental analysis (CHNS) and single crystal X-ray diffraction. The X-ray structural analysis indicated that in the structures of these complexes, the mercury(II) cation is four-coordinated in a distorted tetrahedral configuration by two S atoms from two thiocyanate anions and two N atoms from one chelating 2,2′-bipyridine derivative ligand. Also, in these complexes intermolecular interactions, for example C H⋯N hydrogen bonds (in 1 – 4 ), C H⋯S hydrogen bonds (in 1 , 2 and 4 ), π … π interactions (in 2 – 4 ), Hg⋯N interactions (in 2 ) and S⋯S interactions (in 4 ), are effective in the stabilization of the crystal structures and the formation of the 3D supramolecular complexes. Furthermore, the luminescence spectra of the title complexes show that the intensity of their emission bands are stronger than the emission bands for the free bipyridine derivative ligands. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electronic aspects of Cu(I) and Cu(II) metal complexes. • Intricate mechanisms of helicate formation and chiral separation. • Generation of reactive oxygen species (ROS) from copper complexes. • Oxygen reduction and water oxidation mediated by copper complexes. • Charge injection onto TiO 2 by copper complexes and ultrafast rearrangement of copper complexes structures. Copper complexes are highly versatile species that find promising uses in broad fields such as catalysis, drug design, and bioinorganic applications. However, copper complexes display a rich chemical behavior in solution due to their oxidation-state dependent geometrical rearrangements that make it daunting to the inexperienced. This review summarizes the advances in the synthesis of copper complexes containing phenanthroline- and bipyridine-like ligands covering from the electronic aspects of Cu(I) and Cu(II) metal ions to the intricate mechanisms of helicate formation and generation of reactive oxygen species (ROS). To illustrate the complexity of Cu complexes and strategies to address it, we will focus on three main aspects of their chemistry: 1) their electronic/geometric structure relationships, 2) the formation and behavior of helicates, and 3) oxygen reaction chemistry with copper complexes. In the first case, g values from EPR spectroscopy are discussed as a powerful method to elucidate the molecular structure of different copper complexes using crystal field approximations and the R parameter. Also, we correlate these with the geometries and the electronic properties observed for different copper species. In the second case, we cover structural changes observed in helicates from the synthesis of tetracoordinate ligands to trimetallic species. We consider relevant equilibria in the helicates, and we discuss the chiral separation of diastereosimers and their properties. In addition, we summarize oxygen reduction by copper(I) complexes and the oxygen adducts determined for hydroxyl and peroxyl radicals in different solvents. Their water oxidation chemistry and the concept of "autoreduction" that many copper complexes have is addressed. Lastly, we revised photoinduced charge transfer activates the electron transfer mechanisms proposed for copper complexes onto support TiO 2 receiving charge injection from copper photosensitizers for use in solar cells. We describe the generation of reactive oxygen species and their detection by EPR. While the reader may find different challenges in their research on coordination chemistry, these three illustrations provide solid examples of how ligand field theory, crystal structure, and spin characterization are used to solve concrete problems posed by Cu chemistry. We hope this review will help jumpstart the novice chemist into the fascinating chemistry of Cu complexes and provide new discussion and conceptual tools to more advanced researchers. [ABSTRACT FROM AUTHOR]

Complexes of Co(iii) containing mixed chelating diimine and o-quinone ligand sets are of fundamental interest on account of their fascinating magnetic and electronic properties. Whilst complexes of this type containing one diimine and two o-quinone ligands have been studied extensively, those with the reverse stoichiometry (two diimines and one o-quinone) are much rarer. Herein, we describe a ready route to the synthesis of the complex [CoIII(o-catecholate) (2,2′-bipyridine)2]+ (1), and also report the synthesis of [CoIII(o-catecholate)(5,5′-dimethyl-2,2′-bipyridine)2]+ (2) and [CoIII(o-benezenedithiolate)(5,5′-dimethyl-2,2′-bipyridine)2]+ (3) for the first time. Spectroscopic studies show that complex 2 displays intriguing solvatochromic behaviour as a function of solvent hydrogen bond donation ability, a property of this type of complex which has hitherto not been reported. Time-dependent density function theory (TD-DFT) shows that this effect arises as a result of hydrogen bonding between the solvent and the oxygen atoms of the catecholate ligand. In contrast, the sulfur atoms in the benzenedithiolate analogue 3 are much weaker acceptors of hydrogen bonds from the solvent, meaning that complex 3 is only very weakly solvatochromic. Finally, we show that complex 2 has some potential as a molecular probe that can report on the composition of mixed solvent systems as a function of its absorbance spectrum. [ABSTRACT FROM AUTHOR]

Reaction of 6-methoxy-2,2′-bipyridine (bpy 6OMe ) with the electron-rich platinum(II) complex [Pt(Me) 2 (DMSO) 2 ] gave the rollover cyclometalated complex [Pt(κ 2 -N,C-bpy 6OMe -H) (Me) (DMSO)] under mild conditions. The occurrence of rollover cyclometalation was demonstrated by single crystal X-ray diffraction structure determination. In contrast, reaction of bpy 6OMe with [Pt(Ph) 2 (DMSO) 2 ] and [Pt(Cl) 2 (DMSO) 2 ] under mild conditions gave only adduct species of the type [Pt(X) 2 (bpy 6OMe )] (X = Ph, Cl). Under harsher conditions, activation of a C H bond in the methoxy substituent yielded the terdentate cyclometalated complex [Pt (κ 3 -N,N,C-bpy 6OMe -H)Cl]. Finally, reaction of Pd(II) and Au(III) derivatives invariably gave adduct species, with the exception of the dimeric complex [Pd(κ 2 -N,C-bpy 6OMe -H) (OAc)] 2 , which, however, was not isolated in pure form. The reactivity of bpy 6OMe , as emerged from this study, was compared with that of the corresponding disubstituted ligand 6,6′-dimethoxy-2,2′-bipyridine, previously studied by us. [ABSTRACT FROM AUTHOR]

Electronic structures of ruthenium complexes [Ru(bpy) 2 (L)] 2+ were studied by DFT calculations, where bpy is 2,2′-bipyridine and L's are its derivatives. They are parent ( 1 ) and five complexes with L = 4,4′-dimethyl-2,2′-bipyridine ( 2 ), 6,6′-dimethyl-2,2′-bipyridine ( 3 ), biquinoline ( 4 ), 5-nitro-1,10-phenanthroline ( 5 ) and two acetonitrile molecules ( 6 ). These complexes were characterized by ESI-MS, 1 H NMR, UV–vis spectroscopy and elementary analysis. The crystal structures of 3· (PF 6 ) 2 , 4· (PF 6 ) 2 , 5· (PF 6 ) 2 and 6· (PF 6 ) 2 were also determined. Spin densities were analyzed to characterize the excited triplet states in those complexes. It was found that the complexes have three triplet (called here 3 MLCT, 3 MC 1 and 3 MC 2 ) states. The 3 MC 1 and 3 MC 2 states have elongated Ru N bonds and large spin densities on Ru 2+ . Those states are stable and would lead to the nonradiative relaxation to the ground state. In particular, those of 3 , 5 and 6 are very stable, which results in their poor quantum yields ( Φ < 0.01) of the emissions. In contrast, both 1 and 2 showed the 3 MLCT states. Energy gaps between triplet and ground states were compared with energies corresponding to wavelengths of emission spectra of 1 – 5 . Good agreement between the calculated and the experimental energies was found. Moreover, dual emission which depends on the excitation wavelength was observed in complex 4 . [ABSTRACT FROM AUTHOR]

The interaction of MnCl2with the non-steroidal anti-inflammatory drug sodium diclofenac in the presence of 2,2′-bipyridine and pyridine resulted in the formation of cationic and neutral mononuclear complexes [Mn(diclofenac)(2,2′-bipyridine)(H2O)2] (diclofenac) (1) and [Mn(diclofenac)2(pyridine)2(H2O)2] (2), respectively. The structure of1was characterized by X-ray crystallography. In a preliminary attempt to evaluate the biological properties and possible application, the interaction of the complexes with calf-thymus DNA and human or bovine serum albumins was monitored. Additionally, the ability of the compounds to scavenge radicals such as 1,1-diphenyl-picrylhydrazyl, 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), and hydroxyl radicals was evaluated; the complexes were more potent scavengers than free sodium diclofenac. [ABSTRACT FROM AUTHOR]

[Ni(5,5′-dmbipy)Cl]·3HO ( 1) complex was obtained from the reaction of NiCl·6HO with 5,5′-dimethyl-2,2′-bipyridine (5,5′-dmbipy) in a mixture of CHOH/CHCN. This complex was characterized by elemental analysis, IR, UV-Vis and luminescence spectroscopy, and its structure was determined by the single-crystal diffraction method. The Ni atom has a distorted octahedral coordination by four N atoms from two 5,5′-dmbipy ligands and two Cl anions. [ABSTRACT FROM AUTHOR]

The binuclear complex {[UO(5,5′-dmbpy)(NO)](μ-O)}, where 5,5′-dmbpy is 5,5′-dimethyl-2,2′-bipyridine, was prepared by reaction of UO(NO).6HO with 5,5′-dimethylbipyridine in 1:1 methanol-acetonitrile. The complex was characterized by FT-IR and UV-visible spectroscopy, cyclic voltammetry (CV), and single-crystal X-ray diffraction analysis. The crystal data for {[UO(5,5′-dmbpy)(NO)](μ-O)} at 25 °C are: monoclinic, space group P2 /n with a = 9.8(7) Å, b = 16.0 (12) Å, c = 10.3 (8) Å, β = 111.023(9)° and Z = 2. [ABSTRACT FROM AUTHOR]

The sulfonated bipyridine derivative disodium 6,6′-bis(sulfonatomethyl)-2,2′-bipyridine [Na2(smbipy)] was synthesized, and its complexation behaviour towards divalent 3d metals in aqueous solution was explored. The complexes of late 3d metals [M(smbipy)(H2O)2] ·H2O (M = Co, Ni, Zn) and [Cu(smbipy)(H2O)] are sparingly soluble in water, and their crystal structures show fourfold equatorial coordination (κ4 N, N′, O, O′) of the smbipy ligand. Ammonia-rich solutions of the NiII and CuII aqua complexes yield the decomplexation products [Ni(NH3)6](smbipy), [Ni(NH3)5(H2O)](smbipy) and [Cu(NH3)4](smbipy) ·2H2O. Buffered solutions with a reduced ammonia content lead to [Ni(smbipy)(NH3)2] and [Cu(smbipy)(NH3)3] ·2H2O, and the latter shows twofold coordination of the smbipy ligand through the nitrogen atoms only (κ2 N, N′). When nearly quantitative amounts of ammonia are applied, two closely related complexes with the core motif [(smbipy)Cu(μ-OH)2Cu] form. Crystal structures of all complexes were obtained, and their features are discussed. [ABSTRACT FROM AUTHOR]

Five new [Pt(NN)(dtoc)] complexes (1-5; NN = diimine: 2,2'-bipyridine and its 4,4'-alkyl/aryl-substituted derivatives or 1,10-phenanthroline; dtoc2- = 1,2-dithiolate-1,2-closo-dicarbadodecaborane) have been synthesized and characterized by spectroscopic and electrochemical methods, and by means of X-ray diffraction in the case of complexes 1 and 4. Hybrid DFT and time-dependent (TD) DFT calculations were performed on complexes 1-5 and the previously reported complex [Pt(Ph2phen)(dtoc)] (6; Ph2phen = 4,7-diphenyl-1,10-phenanthroline) both in the gas phase and in the presence of several solvents (CH2Cl2, CHCl3, CH3CN, acetone, THF, DMF, DMSO, and toluene) to gain an insight into the electronic structure of the complexes and explain their experimental features. Theoretical calculations allowed for the determination of structure-property relationships within the series of the six complexes considered, and the prediction of their second order nonlinear optical (SONLO) properties by evaluating their first static hyperpolarizabilities (ßtot). [ABSTRACT FROM AUTHOR]

Abstract: Coordination chemistry of 2,2′-bipyridine bearing an ortho-substituted phenyl group at the 6-position, i.e., 6-(o-X-phenyl)-2,2′-bipyridine (MeO-L: X = OMe; Me2N-L: X = NMe2) with [Ru(ttpy)Cl3] (ttpy = 4′-(4-tolyl)-2,2′;6′,2″-terpyridine) was investigated. The reaction of MeO-L and [Ru(ttpy)Cl3] in the presence of N-methylmorpholine afforded demethylated, O-coordinated complex [Ru(O-L)(ttpy)]+ (O-L: X = O) as well as the cyclometalated, C-coordinated complex [Ru(MeO-L)(ttpy)]+. On the other hand, reaction of Me2N-L and [Ru(ttpy)Cl3] in the presence of N-methylmorpholine afforded only N-coordinated complex [Ru(Me2N-L)(ttpy)]2+. The crystal structures, spectroscopic and redox properties were examined supplemented by DFT calculations. The spectroscopic and redox properties of RuN are more or less similar to those of [Ru(ttpy)Cl3]. On the other hand, the properties of RuC and RuO are mutually similar but significantly different from those of RuN. The anionic ligand in RuC and RuO raises the HOMO energy as compared to the neutral ligand in RuN, which is manifested in negatively shifted redox potentials, particularly the oxidation potentials, and thus, the red shift in the visible absorption band. Relevance of these complexes to sensitizers for dye-sensitized solar cells is briefly discussed. [Copyright &y& Elsevier]

A novel class of luminescent gold(III) complexes containing various tridentate cyclometalaring ligands derived from 6-phenyl-2,2'-bipyridine and alkynyl ligands, [Au- (RC∧N∧N)(C≡C-R')]PF6, has been successfully synthesized and characterized. One of the complexes has also been determined by X-ray crystallography. Electrochemical studies show a ligand-centered reduction originated from the cyclometalaring RC∧N∧N ligands as well as an alkynyl-centered oxidation. The electronic absorption and photoluminescence properties of the complexes have also been investigated. In acetonitrile at room temperature, the complexes show intense absorption at higher energy region with wavelength shorter than 320 nm, and a moderately intense broad absorption band at 374-- 406 nm, assigned as the metal-perturbed intraligand π--π* transition of the cyclometalating RC∧N∧N ligand, with some charge transfer character from the aryl ring to the bipyridine moiety. Most of the complexes have been observed to show vibronicstructured emission bands at 469--550 nm in butyronitile glass at 77 K, assigned to an intraligand excited state of the RC∧N∧N ligand, with some charge transfer character from the aryl to the bipyridyine moiety. Insights into the origin of the absorption and emission have also been provided by density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. [ABSTRACT FROM AUTHOR]