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1.  Supramolecular architectures and structural diversity in a series of lead (II) Chelates involving 5-Chloro/Bromo thiophene-2-carboxylate and N,N’-donor ligands 
Lead is a heavy toxic metal element in biological systems and is one of the major pollutants as a result of its widespread use in industries. In spite of its negative roles the coordination chemistry of Pb(II) complexes is a matter of interest. The N,N’-bidentate aromatic bases such as BPY,4-BPY and PHEN (BPY = 2,2′bipyridine, 4-BPY = 4,4′-dimethyl-2,2′-bipyridine, PHEN = 1,10-Phenanthroline) are widely used to build supramolecular architectures because of their excellent coordinating ability and large conjugated system that can easily form π-π interactions among their aromatic moieties. A series of novel Pb(II) complexes in concert with 5-CTPC, 5-BTPC (5-CTPC = 5-chlorothiophen-2-carboxylate, 5-BTPC = 5-bromothiophen-2-carboxylate) and corresponding bidentate chelating N.N′ ligands have been synthesized and characterized.
Five new Pb (II) complexes [Pb(BPY)(5-CTPC)2] (1), [Pb(4-BPY)(5-CTPC)2] (2), [Pb2(PHEN)2(5-CTPC)4] (3), [Pb(4-BPY)(5-BTPC)2] (4) and [Pb2(PHEN)2(5-BTPC)2(ACE)2] (5) have been synthesized. Even though in all these complexes the molar ratio of Pb, carboxylate, N,N-chelating ligand are the same (1:2:1), there is a significant structural diversity. These complexes have been characterised and investigated by elemental analysis, IR, 1H-NMR,13C-NMR, TGA, and photoluminescence studies. Single crystal X-ray diffraction studies reveal that complexes (1, 2) and (4) are mononuclear while (3 and 5) are dinuclear in nature which may result from the chelating nature of the ligands, various coordination modes of the carboxylates, and the coordination geometry of the Pb(II) ions.
The observation of structures 2,4 and 3,5 show the structural changes made just chloro/bromo substituent of the thiophene ring. A detailed packing analysis has been undertaken to delineate the role of valuable non covalent interactions like X…π, H…X, (X = Cl/Br). A quadruple hydrogen bond linking the monomeric units and generating a supramolecular architecture is observed in (1). The metal bite unit comprised of PbN2C2 (i.e. Pb-N-C-C-N-Pb) is the repeating unit in all the five complexes and they have almost same geometrical parameters. This metal bite has been identified as the self assembly unit in complexes.
PMCID: PMC3766206  PMID: 23945397
Metal bite; Lone pair; Phenanthroline; 5-chlorothiophen-2-carboxylic acid; Pb(II); Halogen bonding
2.  Synthesis, Characterization, and Reactivity of Cobalt(III)–Oxygen Complexes Bearing a Macrocyclic N-Tetramethylated Cyclam Ligand 
Mononuclear metal–dioxygen species are key intermediates that are frequently observed in the catalytic cycles of dioxygen activation by metal-loenzymes and their biomimetic compounds. In this work, a side-on cobalt-(III)–peroxo complex bearing a macro-cyclic N-tetramethylated cyclam (TMC) ligand, [CoIII(15-TMC)(O2)]+, was synthesized and characterized with various spectroscopic methods. Upon protonation, this cobalt(III)–peroxo complex was cleanly converted into an end-on cobalt(III)–hydroperoxo complex, [CoIII(15-TMC)(OOH)]2+. The cobalt(III)–hydroperoxo complex was further converted to [CoIII(15-TMC-CH2-O)]2+ by hydroxylation of a methyl group of the 15-TMC ligand. Kinetic studies and 18O-labeling experiments proposed that the aliphatic hydroxylation occurred via a CoIV–oxo (or CoIII–oxyl) species, which was formed by O–O bond homolysis of the cobalt(III)–hydroperoxo complex. In conclusion, we have shown the synthesis, structural and spectroscopic characterization, and reactivities of mono-nuclear cobalt complexes with peroxo, hydroperoxo, and oxo ligands.
PMCID: PMC3928501  PMID: 24038300
aliphatic hydroxylation; bioinorganic chemistry; cobalt; macrocyclic ligands; oxygen
3.  Synthesis and Biological Activity of Manganese (II) Complexes of Phthalic and Isophthalic Acid: X-Ray Crystal Structures of [Mn(ph)(Phen)2(H2O)]· 4H2O, [Mn(Phen)2(H2O)2]2(Isoph)2(Phen)· 12H2O and {[Mn(Isoph)(bipy)]4· 2.75biby}n(phH2 = Phthalic Acid; isoph = Isophthalic Acid; phen = 1,10-Phenanthroline; bipy = 2,2-Bipyridine) 
Metal-Based Drugs  2000;7(5):275-288.
Manganese(II) acetate reacts with phthalic acid (phH2) to give [Mn(ph)]·0.5H2O (1). Reaction of 1 with 1,10-phenanthroline produces [Mn(ph)(phen)]·2H2O (2) and [Mn(ph)(phen)2(H2O)]·4H2O (3). Reaction of isophthalic acid (isophH2) with manganese(II) acetate results in the formation of [Mn(isoph)]·2H2O (4). The addition of the N,N-donor ligands 1,10-phenanthroline or 2,2'-bipyridine to 4 leads to the formation of [Mn2 (isoph)2(phen)3)]·4H2O (5), [(Mn(phen)2(H2O)2]2(isoph)2(phen)·12H2O (6) and {[Mn(isoph)(bipy)]4·2.75 biby}n (7), respectively. Molecular structures of 3, 6 and 7 were determined crystallographically. In 3 the phthalate ligand is bound to the manganese via just one of its carboxylate groups in a monodentate mode with the remaining coordination sites filled by four phenanthroline nitrogen and one water oxygen atoms. In 6 the isophthalates are uncoordinated with the octahedral manganese center ligated by two phenanthrolines and two waters. In 7 the Isophthalate ligands act as bridges resulting in a polymeric structure. One of the carboxylate groups is chelating a single manganese with the other binding two metal centres in a bridging bidentate mode. The phthalate and isophthalate complexes, the metal free ligands and a number of simple manganes salts were each tested for their ability, to inhibit the growth of Candida albicans. Only the “metal free” 1,10-phenanthroline and its manganese complexes were found to be active.
PMCID: PMC2365232  PMID: 18475957
4.  Ruthenium Dihydroxybipyridine Complexes are Tumor Activated Prodrugs Due to Low pH and Blue Light Induced Ligand Release 
Journal of inorganic biochemistry  2013;130:10.1016/j.jinorgbio.2013.10.008.
Ruthenium drugs are potent anti-cancer agents, but inducing drug selectivity and enhancing their modest activity remain challenging. Slow Ru ligand loss limits the formation of free sites and subsequent binding to DNA base pairs. Herein, we designed a ligand that rapidly dissociates upon irradiation at low pH. Activation at low pH can lead to cancer selectivity, since many cancer cells have higher metabolism (and thus lower pH) than non-cancerous cells. We have used the pH sensitive ligand, 6,6′-dihydroxy-2,2′-bipyridine (66′bpy(OH)2), to generate [Ru(bpy)2(66′(bpy(OH)2)]2+, which contains two acidic hydroxyl groups with pKa1 = 5.26 and pKa2 = 7.27. Irradiation when protonated leads to photo-dissociation of the 66′bpy(OH)2 ligand. An in-depth study of the structural and electronic properties of the complex was carried out using X-Ray crystallography, electrochemistry, UV/visible spectroscopy, and computational techniques. Notably, Ru-N bond lengths in the 66′bpy(OH)2 complex are longer (by ~0.3 Å) than in polypyridyl complexes that lack 6 and 6′ substitution. Thus, the longer bond length predisposes the complex for photo-dissociation and leads to the anti-cancer activity. When the complex is deprotonated, the 66′bpy(O−)2 ligand molecular orbitals mix heavily with the ruthenium orbitals, making new mixed metal-ligand orbitals that lead to a higher bond order. We investigated the anti-cancer activities of [Ru(bpy)2(66′(bpy(OH)2)]2+, [Ru(bpy)2(44′(bpy(OH)2)]2+, and [Ru(bpy)3]2+ (44′(bpy(OH)2 = 4,4′-dihydroxy-2,2′-bipyridine) in HeLa cells, which have a relatively low pH. It is found that [Ru(bpy)2(66′(bpy(OH)2)]2+ is more cytotoxic than the other ruthenium complexes studied. Thus, we have identified a pH sensitive ruthenium scaffold that can be exploited for photo-induced anti-cancer activity.
PMCID: PMC3882005  PMID: 24184694
prodrug; anti-cancer; ruthenium; polypyridyl; light-activated; pH-selective
5.  Tetra­ethyl­ammonium (2,2′-bipyridine)tetra­cyanidocobaltate(III) sesquihydrate acetonitrile solvate 
The title complex, (C8H20N)[Co(CN)4(C10H8N2)]·CH3CN·1.5H2O, consists of tetra­ethyl ammonium cations, mononuclear [CoIIIbpy(CN)4]− anions and uncoordinated water and acetonitrile mol­ecules. The CoIII atom is six-coordinated by two 2,2′-bipyridine (bpy) N atoms and four cyanide C atoms in a distorted octa­hedral geometry. The acute bite angle of the chelating bpy [82.28 (8)°] is the main factor accounting for this distortion. In addition, the tetra­ethyl­ammonium cation is significantly disordered [occupancy ratio 0.611 (3):0.389 (3)]. The presence of water mol­ecules, one of which is disordered over two positions about an inversion center, results in the formation of a network of O—H⋯N hydrogen bonds involving the cyanide N atoms.
PMCID: PMC2983854  PMID: 21580557
6.  Crystal structure of [(1,2,3,4,11,12-η)-anthracene]tris­(tri­methyl­stann­yl)cobalt(III) 
The first reported structure of a cobalt complex containing an η6-anthracene ligand is presented. The anthracene ligand is nearly flat and coordinates the metal asymmetrically, such that the ring junction carbon atoms are slightly further from the cobalt center than are the other four.
The asymmetric unit of the title structure, [Co(η6-C14H10){Sn(CH3)3}3], contains two independent mol­ecules. Each anthracene ligand is η6-coordinating to a CoIII cation and is nearly planar [fold angles of 5.4 (3) and 9.7 (3)°], as would be expected for its behaving almost entirely as a donor to a high-oxidation-state metal center. The slight fold in each anthracene ligand gives rise to slightly longer Co—C bond lengths to the ring junction carbon atoms than to the other four. Each CoIII cation is further coordinated by three Sn(CH3)3 ligands, giving each mol­ecule a three-legged piano-stool geometry. In each of the two independent mol­ecules, the trio of SnMe3 ligands are modeled as disordered over two positions, rotated by approximately 30%, such that the C atoms nearly overlap. In one mol­ecule, the disorder ratio refined to 0.9365 (8):0.0635 (8), while that for the other refined to 0.9686 (8):0.0314 (8). The mol­ecules are well separated, and thus no significant inter­molecular inter­actions are observed. The compound is of inter­est as the first structure report of an η6-anthracene cobalt(III) complex.
PMCID: PMC4257331  PMID: 25484731
crystal structure; cobalt; anthracene; tri­methyl­stannyl ligands; flat-slipped coordination mode; NMR data
7.  Bis(acetato-κO)bis­(pyridine-2-aldoxime-κ2 N,N′)nickel(II) 
In the mononuclear title compound, [Ni(CH3COO)2(C6H6N2O)2], the NiII atom is coordinated by two pyridine-2-aldoxime (PaoH) ligands and two acetate groups, with cis coordination for the pairs of identical ligands. While each acetate group binds to the NiII atom by one O atom, each PaoH chelates the NiII atom through two N atoms. The O atom on PaoH is not deprotonated and does not participate in bonding to the NiII atom. Thus, the NiII atom exhibits an octa­hedral environment. Intra­molecular O—H⋯O hydrogen-bonding inter­actions and inter­molecular C—H⋯O hydrogen-bonding inter­actions are present in the structure. Adjacent mol­ecules pack along [100] through van der Waals forces.
PMCID: PMC3344309  PMID: 22590075
8.  Bis[μ-2-(4-hy­droxy­phen­yl)acetato]-κ3 O,O′:O;κ3 O:O,O′-bis­{aqua­(4,4′-bipyridine-κN)[2-(4-hy­droxy­phen­yl)acetato-κ2 O,O′]samarium(III)} monohydrate 
The dinuclear title complex, [Sm2(C8H7O3)6(C10H8N2)2(H2O)2]·H2O, contains two SmIII atoms, six deprotonated p-hy­droxy­phenyl­acetic acid (PAA) mol­ecules, two 4,4′-bipyridine (bipy) mol­ecules, two coordinated water mol­ecules and one solvent water molecule. Each SmIIIion is nine-coordinated by seven O atoms from four PAA ligands, one water O atom and one N atom from a bipy ligand in a distorted geometry. The PAA ligands are coordinated to the SmIII ion in bridging and bridging tridentate modes. The asymmetric unit also contains one uncoordinated water mol­ecule. The occurrence of numerous O—H⋯O and O—H⋯N hydrogen bonds involving coordinated and non-coordinated water mol­ecules builds up an intricate three-dimensional network.
PMCID: PMC3011563  PMID: 21589216
9.  Slow Hydrogen Transfer Reactions of Oxo— and Hydroxo— Vanadium Compounds: the Importance of Intrinsic Barriers 
Reactions are described that interconvert vanadium(IV) oxo-hydroxo complexes [VIVO(OH)(R2bpy)2]BF4 (1a-c) and vanadium(V) dioxo complexes [VVO2(R2bpy)2]BF4 (2a-c) [R2bpy = 4,4′-di-t-butyl-2,2′-bipyridine (tBu2bpy), a; 4,4′-dimethyl-2,2′-bipyridine (Me2bpy), b; 2,2′-bipyridine (bpy), c]. These are rare examples of pairs of isolated, sterically unencumbered, first-row metal-oxo/hydroxo complexes that differ by a hydrogen atom (H+ + e−). The VIV– tBu2bpy derivative 1a has a useful 1H NMR spectrum, despite being paramagnetic. Complex 2a abstracts H• from organic substrates with weak O–H and C–H bonds, converting 2,6-tBu2-4-MeO-C6H2OH (ArOH) and 2,2,6,6-tetramethyl-N-hydroxy-piperidine (TEMPOH) to their corresponding radicals ArO• and TEMPO, hydroquinone to benzoquinone, and dihydroanthracene to anthracene. The equilibrium constant for 2a + ArOH ⇋ 1a + ArO• is (4 ± 2) × 10−3, implying that the VO–H bond dissociation free energy (BDFE) is 70.6 ± 1.2 kcal mol−1. Consistent with this value, 1a is oxidized by 2,4,6-tBu3C6H2O•. All of these reactions are surprisingly slow, typically occurring over hours at ambient temperatures. The net hydrogen-atom pseudo-self-exchange 1a + 2b ⇋ 2a + 1b, using the tBu- and Me-bpy substituents as labels, also occurs slowly, with kse = 1.3 × 10−2 M−1 s−1 at 298 K, ΔH‡ = 15 ± 2 kcal mol−1, and ΔS‡= 16 ± 5 cal mol−1 K. Using this kse and the BDFE, the vanadium reactions are shown to follow the Marcus cross relation moderately well, with calculated rate constants within 102 of the observed values. The vanadium self-exchange reaction is ca. 106 slower than that for the related RuIVO(py)(bpy)22+ / RuIIIOH(py)(bpy)22+ self-exchange. The origin of this dramatic difference has been probed with DFT calculations on the self-exchange reactions of 1c + 2c and on mono-cationic ruthenium complexes with pyrrolate or fluoride in place of the py ligands. The calculations reproduce the difference in barrier heights and show that transfer of a hydrogen atom involves more structural reorganization for vanadium than the Ru analogs. The vanadium complexes have larger changes in the metal–oxo and metal–hydroxo bond lengths, which is traced to the difference in d-orbital occupancy in the two systems. This study thus highlights the importance of intrinsic barriers in the transfer of a hydrogen atom, in addition to the thermochemical (bond strength) factors that have been previously emphasized.
PMCID: PMC2735118  PMID: 19292442
10.  Bis[bis­(2,2′-bi­pyridine-κ2 N,N′)(carbon­ato-κ2 O,O′)cobalt(III)] 2-{4-[(carboxyl­atometh­yl)carbamo­yl]benz­amido}­acetate hexa­hydrate 
The complex cation of the title compound, [Co(CO3)(C10H8N2)2]2(C12H10N2O6)·6H2O, contains a CoIII atom with a distorted octa­hedral coordination environment formed by four N atoms from two bidentate 2,2′-bi­pyridine ligands and one bidentate carbonate anion. The asymmetric unit is completed by one-half of the 2-({4-[(carboxyl­atometh­yl)carbamo­yl]phen­yl}formamido)­acetate dianion, which is located on a centre of inversion, and by three water mol­ecules. Two [Co(CO3)(C10H8N2)2]+ cations are connected through C—H⋯O contacts by the uncoordinating anions. The aromatic rings of the 2,2′-bi­pyridine ligands and di­acetate anions are involved in π–π stacking and C—H⋯π inter­actions. The centroid–centroid distances are in the range 3.4898 (4)–3.6384 (5) Å. The crystal structure is stabilized by further O—H⋯O and N—H⋯O hydrogen bonds, which give rise to a three-dimensional supra­molecular network.
PMCID: PMC4011312  PMID: 24860299
11.  Poly[[dodeca­aqua­(μ4-benzene-1,4-dicarboxyl­ato)(μ2-4,4′-bipyridine-κ2 N:N′)dicerium(III)] bis­(benzene-1,4-dicarboxyl­ate)] 
The asymmetric unit of the title compound, {[Ce2(C8H4O4)(C10H8N2)(H2O)12](C8H4O4)2}n, consists of half a CeIII cation, a quarter of a coordinated benzene-1,4-dicarboxyl­ate (bdc2−) dianion, a quarter of a 4,4′-bipyridine (bpy) mol­ecule, three water mol­ecules and a half of an uncoordinated benzene-1,4-dicarboxyl­ate dianion. The CeIII ion is located on a twofold rotation axis and exhibits a distorted trigonal prism square-face tricapped coordination geometry. The coordinated and uncoordinated bdc2− ions and the bpy mol­ecule lie about special positions of site symmetries 2/m, m and 2/m, respectively. The CeIII ions are bridged by the bdc2− and bpy ligands, giving a sheet structure parallel to the ac plane. The uncoordinated bdc2− dianion exists between the sheets and links the sheets by inter­molecular O—H⋯O hydrogen bonds between the uncoordinated bdc2− and coordinated water mol­ecules. A π–π stacking inter­action between the uncoordinated bdc2− dianion and the bpy ligand [centroid–centroid distance = 3.750 (4) Å] is also observed.
PMCID: PMC3344367  PMID: 22590133
12.  Characterization of proton coupled electron transfer in a biomimetic oxomanganese complex: Evaluation of the DFT B3LYP level of theory 
The capabilities and limitations of the Becke-3–Lee–Yang–Parr (B3LYP) density functional theory (DFT) for modeling proton coupled electron transfer (PCET) in the mixed-valence oxomanganese complex 1 [(bpy)2MnIII(μ-O)2MnIV(bpy)2]3+ (bpy = 2,2'-bipyridyl) are analyzed. Complex 1 serves as a prototypical synthetic model for studies of redox processes analogous to those responsible for water oxidation in the oxygen-evolving complex (OEC) of photosystem II (PSII). DFT B3LYP free energy calculations of redox potentials and pKa's are obtained according to the thermodynamic cycle formalism applied in conjunction with a continuum solvation model. We find that the pKa's of the oxo-ligands depend strongly on the oxidation states of the complex, changing by approximately 10 pH units (i.e., from pH~2 to pH~12) upon III,IV→III,III reduction of complex 1. These computational results are consistent with the experimental pKa's determined by solution magnetic susceptibility and near-IR spectroscopy as well as with the pH dependence of the redox potential reported by cyclic voltammogram measurements, suggesting that the III,IV→III,III reduction of complex 1 is coupled to protonation of the di-μ-oxo bridge as follows: [(bpy)2MnIII(μ-O)2 MnIV(bpy)2]3++H++e−→[(bpy)2MnIII(μ-O)(μ-OH)MnIII(bpy)2]3+. It is thus natural to expect that analogous redox processes might strongly modulate the pKa's of oxo and hydroxo/water ligands in the OEC of PSII, leading to deprotonation of the OEC upon oxidation state transitions.
PMCID: PMC2896228  PMID: 20607115
13.  catena-Poly[[di­aqua­[μ2-4-(4-carb­oxy­phen­oxy)benzoato](μ2-4,4′-oxydibenzo­ato)praseodymium(III)] monohydrate] 
In the title compound, {[Pr(C14H8O5)(C14H9O5)(H2O)2]·H2O}n, the PrIII cation is eight-coordinated by six carboxyl O atoms from both a monoanionic 4-(4-carb­oxy­phen­oxy)benzoate and a dianionic 4,4′-oxydibenzoate ligand (four bridging with two from a bidentate chelate inter­action), and two O-atom donors from water mol­ecules. A single water mol­ecule of solvation is also present. The complex units are linked through carboxyl O:O′ bridges giving a two-dimensional sheet polymer lying parallel to (001). An overall three-dimensional network structure is generated through inter­molecular carb­oxy­lic acid and water O—H⋯O hydrogen bonds and weak C—H⋯O inter­actions.
PMCID: PMC3884249  PMID: 24454025
14.  Tris(2,2′-bipyridine-κ2 N,N′)cobalt(III) bis­[bis­(pyridine-2,6-dicarboxyl­ato-κ3 O 2,N,O 6)cobaltate(III)] perchlorate dimethyl­formamide hemisolvate 1.3-hydrate 
In the title compound, [Co(C10H8N2)3][Co(C7H3NO4)2]2(ClO4)·0.5C3H7NO·1.3H2O, the CoIII atom in the complex cation is pseudoocta­hedrally coordinated by six N atoms of three chelating bipyridine ligands. The CoIII atom in the complex anion is coordinated by two pyridine N atoms and four carboxyl­ate O atoms of two doubly deprotonated pyridine-2,6-dicarboxyl­ate ligands in a distorted octa­hedral geometry. One dimethyl­formamide solvent mol­ecule and two water mol­ecules are half-occupied and one water mol­ecule is 0.3-occupied. O—H⋯O hydrogen bonds link the water mol­ecules, the perchlorate anions and the complex anions. π–π inter­actions between the pyridine rings of the complex anions are also observed [centroid–centroid distance = 3.804 (3) Å].
PMCID: PMC3470129  PMID: 23125573
15.  Chloridobis(ethyl­enediamine-κ2 N,N′)(n-pentyl­amine-κN)cobalt(III) dichloride monhydrate 
The title complex, [CoCl(C5H13N)(C2H8N2)2]Cl2·H2O, comprises one chloridobis(ethyl­enediamine)(n-pentyl­amine)cobalt(III) cation, two chloride counter-anions and a water mol­ecule. The CoIII atom of the complex is hexa­coordinated by five N and one Cl atoms. The five N atoms are from two chelating ethyl­enediamine and one n-pentyl­amine ligands. Neighbouring cations and anions are connected by N—H⋯Cl and N—H⋯O hydrogen bonds to each other and also to the water mol­ecule.
PMCID: PMC2969482  PMID: 21582753
16.  Di-μ2-acetato-diacetato-bis­{μ2-3,3′,5,5′-tetra­meth­oxy-2,2-[ethane-1,2-diylbis(nitrilo­methyl­idyne)]diphenolato}tricobalt(II,III) dichloro­methane disolvate 
The trinuclear title compound, [Co3(CH3COO)4(C20H22N2O6)2]·2CH2Cl2, contains mixed-valence cobalt ions in the following order CoIII–CoII–CoIII where all the three cobalt ions are hexa­coordinated. The central cobalt ion is situated on an inversion centre and is in an all-oxygen environment, coordinated by four phenolate O atoms and two O atoms from bridging acetate groups, while the terminal cobalt ion is hexa­coordinated by two phenolate O atoms, two acetate O atoms and two imine N atoms. This complex contains a high-spin central CoII and two terminal low-spin CoIII i.e. CoIII(S = 0)–CoII(S = 3/2)-CoIII(S = 0). There are weak inter­molecular C—H⋯O inter­actions involving the meth­oxy groups, as well as inter­molecular C—H⋯O inter­actions involving the acetate anions. In addition, the dichoromethane solvate mol­ecules are held in place by weak C—H⋯Cl inter­actions.
PMCID: PMC3052101  PMID: 21522241
17.  [2-(2-Carboxy­phen­yl)benzoato]bis­(1,10-phenanthroline)zinc(II) 2-(2-carboxy­phen­yl)benzoate monohydrate 
In the title compound, [Zn(C14H9O4)(C12H8N2)2](C14H9O4)·H2O, the ZnII atom of the complex cation is six-coordinated in an octa­hedral geometry by four N atoms from two 1,10-phenanthroline ligands and two O atoms of a carboxyl­ate group from a singly deprotonated diphenic acid. The phenanthroline and carboxylate ligands act as chelating ligands. The dihedral angles between the two benzene rings in the deprotonated diphenic acid groups are 81.05 (2) (ligand) and 89.10 (2)° (anion). O—H⋯O and C—H⋯O hydrogen bonds link the components into a three-dimensional network.
PMCID: PMC2961034  PMID: 21201991
18.  (Carbonato-κ2 O,O′)bis­(1,10-phenan­throline-κ2 N,N′)cobalt(III) nitrate monohydrate 
The crystal structure of the title compound, [Co(CO3)(C12H8N2)2]NO3·H2O, consists of CoIII complex cations, nitrate anions and uncoordinated water mol­ecules. The CoIII cation is chelated by a carbonate anion and two phenanthroline ligands in a distorted octa­hedral coordination geometry. A three-dimensional supra­molecular structure is formed by O—H⋯O and C—H⋯O hydrogen bonding, C—H⋯π and aromatic π–π stacking [centroid–centroid distance = 3.995 (1)Å] inter­actions.
PMCID: PMC2980272  PMID: 21579944
19.  Synthesis, Structural and Spectroscopic Characterization, and Reactivities of Mononuclear Cobalt(III)-Peroxo Complexes 
Journal of the American Chemical Society  2010;132(47):16977-16986.
Metal-dioxygen adducts are key intermediates detected in the catalytic cycles of dioxygen activation by metalloenzymes and biomimetic compounds. In this study, mononuclear cobalt(III)- peroxo complexes bearing tetraazamacrocyclic ligands, [Co(12-TMC)(O2)]+ and [Co(13-TMC)(O2)]+, were synthesized by reacting [Co(12-TMC)(CH3CN)]2+ and [Co(13-TMC)(CH3CN)]2+, respectively, with H2O2 in the presence of triethylamine. The mononuclear cobalt(III)-peroxo intermediates were isolated and characterized by various spectroscopic techniques and X-ray crystallography, and the structural and spectroscopic characterization demonstrated unambiguously that the peroxo ligand is bound in a side-on η2 fashion. The O-O bond stretching frequency of [Co(12-TMC)(O2)]+ and [Co(13- TMC)(O2)]+ was determined to be 902 cm−1 by resonance Raman spectroscopy. The structural properties of the CoO2 core in both complexes are nearly identical; the O-O bond distances of [Co(12-TMC)(O2)]+ and [Co(13-TMC)(O2)]+ were 1.4389(17) Å and 1.438(6) Å, respectively. The cobalt(III)-peroxo complexes showed reactivities in the oxidation of aldehydes and O2-transfer reactions. In the aldehyde oxidation reactions, the nucleophilic reactivity of the cobalt-peroxo complexes was significantly dependent on the ring size of the macrocyclic ligands, with the reactivity of [Co(13-TMC)(O2)]+ > [Co(12-TMC)(O2)]+. In the O2-transfer reactions, the cobalt(III)-peroxo complexes transferred the bound peroxo group to a manganese(II) complex, affording the corresponding cobalt(II) and manganese(III)- peroxo complexes. The reactivity of the cobalt-peroxo complexes in O2-transfer was also significantly dependent on the ring size of tetraazamacrocycles, and the reactivity order in the O2-transfer reactions was the same as that observed in the aldehyde oxidation reactions.
PMCID: PMC2995300  PMID: 21062059
20.  Bis[4-chloro-2-(quinolin-8-yl­imino­meth­yl)phenolato-κ3 N,N′,O]cobalt(III) trichlorido­methano­lcobaltate(II) 
The reaction of 4-chloro-2-(quinolin-8-yl­imino­meth­yl)phenol (HClQP) with cobalt(II) dichloride hexa­hydrate in methanol/chloro­form under solvothermal conditions yielded the title compound, [Co(C16H10ClN2O)2][CoCl3(CH3OH)]. The CoIII atom is six-coordinated in a slightly distorted octa­hedral geometry by four N atoms and two O atoms of two tridentate HClQP ligands, which are nearly perpendicular to each other, making a dihedral angle of 86.95°. The CoII atom is four-coordinated by three Cl atoms and one O atom from a methanol ligand in a distorted tetra­hedral geometry. The crystal packing is consolidated by inter­molecular O—H⋯Cl, C—H⋯Cl and C—H⋯O hydrogen bonds, forming a three-dimensional supra­molecular structure, in which [CoIICl3(CH3OH)] anions are connected via O—H⋯Cl and C—H⋯Cl hydrogen bonds into centrosymmetric dimers. Neighboring cobalt(III) complexes form dimers through C—H⋯O hydrogen bonds, as well as π–π stacking [centroid–centroid distances = 3.30 (2) Å] between the planar quinoline systems of one HClQP ligand and the phenolate ring of another.
PMCID: PMC3647815  PMID: 23723781
21.  Aqua­bis(2,2′-bipyridine-κ2 N,N′)(1H-indole-2-carboxyl­ato-κO)nickel(II) 1H-indole-2-carboxyl­ate dihydrate 
The hydro­thermal reaction of Ni2(OH)2CO3 with 2,2′-bipyridine and 2-indolyl-formic acid in CH3OH/H2O at 423 K for 7 d produced the novel NiII complex [Ni(C9H6NO2)(C10H8N2)2(H2O)](C9H6NO2)·2H2O. The asymmetric unit of the title compound consists of a monovalent [Ni(L)(bpy)2(H2O)]+ cation (bpy is 2,2′-bipyridine and L is 1H-indole-2-carboxyl­ate), an L anion and two solvent water mol­ecules. In the [Ni(L)(bpy)2(H2O)]+ cations, the Ni atom coordinates to four N atoms from the two bpy ligands and two O atoms, one from a L anion and the other from a water mol­ecule to complete an significantly distorted NiN4O2 octa­hedron. The coordinated and solvate water mol­ecules form an extensive series of O—H⋯O hydrogen bonds. N—H⋯O and C—H⋯O hydrogen bonds are also present and the mol­ecules are inter­linked, forming a three-dimensional network.
PMCID: PMC2967892  PMID: 21581519
22.  Tetra­aqua­bis­[1-(3-carb­oxy­phen­yl)-4,4′-bipyridin-1-ium-κN 1′]zinc bis­(4,5-carb­oxy­benzene-1,2-dicarboxyl­ate) 2.5-hydrate 
In the complex cation of the title compound, [Zn(C17H13N2O2)2(H2O)4](C10H4O8)2·2.5H2O, the ZnII atom, lying on an inversion center, is coordinated by two N atoms from two N-(3-carb­oxy­phen­yl)-4,4′-bipyridin-1-ium ligands and four water mol­ecules in a distorted octa­hedral geometry. The pyromellitate anion is double deprotonated. O—H⋯O and C—H⋯O hydrogen bonds connect the cations, anions and uncoordinated water mol­ecules into a three-dimensional supra­molecular network. One of the two lattice water molecules shows an occupancy of 0.25. An intra­molecular O—H⋯O hydrogen bond is present in the anion.
PMCID: PMC3238626  PMID: 22199517
23.  Crystal structure of di-μ-hydroxido-bis{[N,N′-bis­(2,6-di­methyl­phen­yl)pentane-2,4-diiminato(1–)]zinc} 
The title compound, [Zn2(C21H25N2)2(OH)2], is a binuclear zinc complex formed by two bidentate β-diketiminate (nacnac) ligands and two μ-hydroxide O atoms, bridging two mononuclear units into a centrosymmetric dimeric unit. Each Zn2+ cation is coordinated by two N-donor atoms from the nacnac ligand and two O-donor atoms of hydroxide anions to give a distorted tetra­hedral coordination environment. The Zn—O bond lengths are 1.9643 (13) and 2.0022 (14) Å, and the two Zn—N bond lengths are 1.9696 (14) and 1.9823 (14) Å. The distance between the two Zn2+ cations in the dimer is 2.9420 (4) Å. Although hydroxide groups are present in the complex, no classical hydrogen-bonding inter­ations are observed because of the bulky β-diketiminate ligands.
PMCID: PMC4186180  PMID: 25309180
crystal structure; zinc; hydroxide bridging ligand; β-diketiminate ligand
24.  Poly[bis(2,2′-bipyridine-κ2 N,N′)heptadeca-μ-oxido-tetraoxidodicopper(II)divanadate(IV)hexavanadate(V)] 
In the title complex, [Cu2V8O21(2,2′-bpy)2]n (bpy = bipyridine, C10H8N2), the asymmetric unit contains four independent V atoms briged by 11 O atoms, one of which lies on an inversion center, and a [Cu(2,2′-bpy)]2+ unit. Three V atoms in the polyoxoanion exhibit distorted tetra­hedral coordination geometries while the fourth V atom adopts a trigonal-bipyramidal geometry. The Cu atom adopts a square-pyramidal geometry being coordinated by two nitro­gen donors of a 2,2′-bpy ligand, and three bridging O atoms which are linked with V atoms. The V8 polyoxoanion is connected to [Cu(2,2′-bpy)]2+ cations, resulting in a two-dimensional layer structure extending parallel to (010). C—H⋯O hydrogen bonding consolidates the structure.
PMCID: PMC2980047  PMID: 21579931
25.  A one-dimensional polymeric cobalt(III)–potassium complex with 18-crown-6, cyanide and porphyrinate ligands 
The reaction of CoII(TpivPP) {TpivPP is the dianion of 5,10,15,20-tetra­kis­[2-(2,2-di­methyl­propanamido)­phen­yl]por­ph­yrin} with an excess of KCN salts and an excess of the 18-crown-6 in chloro­benzene leads to the polymeric title compound catena-poly[[dicyanido-2κ2 C-(1,4,7,10,13,16-hexa­oxa­cyclo­octa­decane-1κ6 O){μ3-(2α,2β)-5,10,15,20-tetra­kis­[2-(2,2-di­methyl­propanamido)­phen­yl]porphyrinato-1κO 5:2κ4 N,N′,N′′,N′′′:1′κO 15}cobalt(III)potassium] dihydrate], {[CoK(CN)2(C12H24O6)(C64H64N8O4]·2H2O}n. The CoIII ion lies on an inversion center, and the asymmetric unit contains one half of a [CoIII(2α,2β-TpivPP)(CN)2]− ion complex and one half of a [K(18-C-6]+ counter-ion (18-C-6 is 1,4,7,10,13,16-hexa­oxa­cyclo­octa­deca­ne), where the KI ion lies on an inversion center. The CoIII ion is hexa­coordinated by two C-bonded axial cyanide ligands and the four pyrrole N atoms of the porphyrin ligand. The KI ion is chelated by the six O atoms of the 18-crown-6 mol­ecule and is further coordinated by two O atoms of pivalamido groups of the porphyrin ligands, leading to the formation of polymeric chains running along [011]. In the crystal, the polymeric chains and the lattice water mol­ecules are linked by N—H⋯O and O—H⋯N hydrogen bonds, as well as weak C—H⋯O, O—H⋯π and C—H⋯π inter­actions into a three-dimensional supra­molecular architecture.
PMCID: PMC3998383  PMID: 24764938

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