Search tips
Search criteria

Results 1-25 (401334)

Clipboard (0)

Related Articles

1.  Synthesis and Structural Characterization of a Metal Cluster and a Coordination Polymer Based on the [Mn6(μ4-O)2]10+ Unit 
A new 1-D coordination polymer {[Mn6O2(O2CMe)10(H2O)4]·2.5H2O}∞ (1·2.5H2O)∞ and the cluster [Mn6O2(O2(O2CPh)10 (py)2(MeCN)(H2O)]·2MeCN (2·2MeCN) are reported. Both compounds were synthesized by room temperature reactions of [Mn3(μ3-O)(O2CR)6(L)2(L′)] (R = Me, L = L′ = py, (1·2.5H2O)∞; R = Ph, L = py, L′ = H2O, 2·2MeCN) in the presence of 3-hydroxymethylpyridine (3hmpH) in acetonitrile. The structures of these complexes are based on hexanuclear mixed-valent manganese carboxylate clusters containing the [Mn4IIMn2III(μ4-O)2]10+ structural core. (1·2.5H2O)∞ consists of zigzag chain polymers constructed from [Mn6O2(O2CMe)10(H2O)4] repeating units linked through acetate ligands, whereas 2·2MeCN comprises a discrete Mn6-benzoate cluster.
PMCID: PMC2902058  PMID: 20634987
2.  Single-Molecule Magnetism Properties of the First Strontium-Manganese Cluster [SrMn14O11(OMe)3(O2CPh)18(MeCN)2] 
Inorganic chemistry  2008;47(6):1940-1948.
The preparation and properties of the first strontium-manganese molecular complex are described. The reaction of (NBun4)[Mn4O2(O2CPh)9(H2O)] (4MnIII) with Sr(ClO4)2 in MeCN/MeOH led to the isolation of [SrMn14O11(OMe)3(O2CPh)18(MeCN)2] (1; 13MnIII, MnII). The structure of 1 consists of two [Mn4O3(OMe)] cubane units attached to a central, near-planar, trinuclear [Mn3O4] unit, to which are also attached a Mn and a Sr above the plane and a [Mn2O(OMe)] rhomb below the plane. Peripheral ligation is provided by 18 bridging benzoate and two terminal MeCN groups. Variable-temperature and -field dc magnetization (M) data were collected in the 1.8–10 K and 0.1–4.0 T ranges and fit by matrix diagonalization methods to give S = 9/2, D = –0.50(5) cm–1, and g = 1.88(10), where S is the ground-state spin and D is the axial zero-field splitting parameter. Magnetization versus dc field sweeps at various temperatures and scan rates exhibited hysteresis loops, confirming 1 to be a new single-molecule magnet. Because complex 1 is the initial molecular example of intimately associated Mn and Sr atoms, Sr EXAFS studies have been performed for the first time on a synthetic Sr-containing molecule. This has also allowed comparisons with the EXAFS data on the Sr-substituted water oxidizing complex (WOC) of Photosystem II (PS II), which contains a SrMn4 complex.
PMCID: PMC3962502  PMID: 18281933
3.  Synthesis, X-Ray Structure, and Characterization of Catena-bis(benzoate)bis{N,N-bis(2-hydroxyethyl)glycinate}cadmium(II) 
The reaction of N, N-bis(2-hydroxyethyl)glycine (bicine; bicH3) with Cd(O2CPh)2 · 2H2O in MeOH yielded the polymeric compound [Cd2(O2CPh)2(bicH2)2]n(1). The complex crystallizes in the tetragonal space group P41212. The lattice constants are a = b = 12.737(5) and c = 18.288(7) Å. The compound contains chains of repeating {Cd2(O2CPh)2(bicH2)2} units. One CdII atom is coordinated by two carboxylate oxygen, four hydroxyl oxygen, and two nitrogen atoms from two symmetry-related 2.21111 (Harris notation) bicH2− ligands. The other CdII atom is coordinated by six carboxylate oxygen atoms, four from two bicH2− ligands and two from the monodentate benzoate groups. Each bicinate(-1) ligand chelates the 8-coordinate, square antiprismatic CdII atom through one carboxylate oxygen, the nitrogen, and both hydroxyl oxygen atoms and bridges the second, six-coordinate trigonal prismatic CdII center through its carboxylate oxygen atoms. Compound 1 is the first structurally characterized cadmium(II) complex containing any anionic form of bicine as ligand. IR data of 1 are discussed in terms of the coordination modes of the ligands and the known structure.
PMCID: PMC2952795  PMID: 20976297
4.  Periodic Trends within a Series of Five Coordinate, Thiolate–Ligated [MII(SMe2N4(tren))]+ (M = Mn, Fe, Co, Ni, Cu, Zn) Complexes, Including a Rare Example of a Stable CuII–Thiolate 
Inorganic chemistry  2007;46(22):9267-9277.
A series of five-coordinate thiolate-ligated complexes [MII(tren)N4SMe2]+ (M = Mn, Fe, Co, Ni, Cu, Zn; tren = tris(2-aminoethyl)amine) are reported, and their structural, electronic, and magnetic properties are compared. Isolation of dimeric [NiII(SN4(tren)–RSdang)]2 (“dang”= dangling, uncoordinated thiolate supported by H–bonds) using the less bulky [(tren)N4S]1− ligand, pointed to the need for gem-dimethyls adjacent to the sulfur in order to sterically prevent dimerization. All of the gem-dimethyl derivatized complexes are monomeric, and with the exception of [NiII(SMe2N4(tren)]+, are isostructural and adopt a tetragonally distorted trigonal bipyramidal geometry favored by ligand constraints. The nickel complex uniquely adopts an approximately ideal square pyramidal geometry, and resembles the active site of Ni-superoxide dismutase (Ni-SOD). Even in coordinating solvents such as MeCN, only five-coordinate structures are observed. The MII–S thiolate bonds systematically decrease in length across the series (Mn–S > Fe–S > Co–S > Ni–S ~ Cu–S < Zn–S) with exceptions occurring upon the occupation of σ* orbitals. The copper complex, [CuII(SMe2N4(tren)]+, represents a rare example of a stable CuII–thiolate, and models the perturbed “green” copper site of nitrite reductase. In contrast to the intensely colored, low–spin Fe(III)-thiolates, the M(II)-thiolates described herein are colorless to moderately colored, and high–spin (in cases where more than one spin-state is possible), reflecting the poorer energy match between the metal d– and sulfur–orbitals upon reduction of the metal ion. As the d–orbitals drop in energy proceeding across the across the series M2+ (M= Mn, Fe, Co, Ni, Cu), the sulfur-to-metal charge transfer transition moves into the visible region, and the redox potentials cathodically shift. The reduced M+1 oxidation state is only accessible with copper, and the more oxidized M+4 oxidation state is only accessible for manganese.
PMCID: PMC2532082  PMID: 17867686
5.  Synthesis, characterization and X-ray structural studies of four copper (II) complexes containing dinuclear paddle wheel structures 
Various dinuclear copper (II) complexes with octahedral geometry have been reported. The majority of these complexes contain N containing aromatic rings as axial ligands. There are also a few cases where the solvent used in the reaction occupies the axial position of the dinuclear copper (II) complex. This may occur by planned synthesis or some times by serendipity. Here we report some four copper (II) complexes containing solvent and or N containing heterocyclic ring as the axial ligand.
Four compounds, each containing dinuclear Copper (II) units (with the most robust, frequently occurring paddle wheel structures) were synthesized and characterised by single crystal X-ray diffraction and by IR spectroscopy. The compounds 1 & 2 have the general formula Cu2(RCOO) 4(L)2 [(for (1) RCOO= 4-Chloro Benzoate, L= Isopropanol; for 2 RCOO= Benzoate, L= 2-Amino-4,6-dimethyl pyrimidine )] while 3 & 4 have the general formula, Cu2(RCOO) 4(S)2 Cu2(RCOO) 4(L)2 [RCOO=5-Chloro-thiophene-2-carboxylate L= 2-Amino-4,6-dimethyl pyrimidine, for 3 S= ethanol; for 4 S= methanol ]. A wide range of hydrogen bonds (of the O-H…O, N-H…O and N-H…N type) and π-π stacking interactions are present in the crystal structures.
All compounds contain the dinuclear units, in which two Cu (II) ions are bridged by four syn, syn-η1:η1:μ carboxylates, showing a paddle-wheel cage type with a distorted octahedral geometry. The compounds 1 &2 contain a single dimeric unit while 3 &4 contain two dimeric units. The structures 3 and 4 are very interesting co-crystals of two paddle wheel molecules. Also it is interesting to note that the compounds 3 &4 are isostructural with similar cell parameters. Both the compounds 3 &4 differ in the solvent molecule coordinated to copper in one of the dimeric units. In all the four compounds, each of the copper dimers has an inversion centre. Every copper has a distorted octahedral centre, formed by four oxygen atoms (from different carboxylate) in the equatorial sites. The two axial positions are occupied by copper and the corresponding ligand.
PMCID: PMC3616956  PMID: 23433679
Paddle wheel structures; Cu (II) complexes; Supramolecular architectures; Carboxylates; Crystal structure
6.  Synthesis, Crystal Structures, and DNA Binding Properties of Zinc(II) Complexes with 3-Pyridine Aldoxime 
The employment of 3-pyridine aldoxime, (3-py)CHNOH, in ZnII chemistry has afforded two novel compounds: [Zn(acac)2{(3-py)CHNOH}]·H2O (1·H2O) [where acac− is the pentane-2,4-dionato(-1) ion] and [Zn2(O2CMe)4{(3-py)CHNOH}2] (2). Complex 1·H2O crystallizes in the monoclinic space group P21/n. The ZnII ion is five-coordinated, surrounded by four oxygen atoms of two acac− moieties and by the pyridyl nitrogen atom of the (3-py)CHNOH ligand. Molecules of 1 interact with the water lattice molecules forming a 2D hydrogen-bonding network. Complex 2 crystallizes in the triclinic P-1 space group and displays a dinuclear paddle-wheel structure. Each ZnII exhibits a perfect square pyramidal geometry, with four carboxylate oxygen atoms at the basal plane and the pyridyl nitrogen of one monodentate (3-py)CHNOH ligand at the apex. DNA mobility shift assays were performed for the determination of the in vitro effect of both complexes on the integrity and the electrophoretic mobility of pDNA.
PMCID: PMC2971566  PMID: 21076521
7.  Characterization and Dioxygen Reactivity of a New Series of Coordinatively Unsaturated Thiolate-Ligated Manganese(II) Complexes 
Inorganic chemistry  2012;51(12):6633-6644.
The synthesis, structural, and spectroscopic characterization of four new coordinatively unsaturated mononuclear thiolate-ligated manganese(II) complexes ([MnII(SMe2N4(6-Me-DPEN))](BF4) (1), [MnII(SMe2N4(6-Me-DPPN))](BPh4)•MeCN (3), [MnII(SMe2N4(2-QuinoPN))](PF6)•MeCN•Et2O (4), and [MnII(SMe2N4(6-H-DPEN)(MeOH)](BPh4) (5)) is described, along with their magnetic, redox, and reactivity properties. These complexes are structurally-related to recently reported [MnII(SMe2N4(2-QuinoEN))](PF6) (2) Dioxygen addition to complexes 1-5 is shown to result in the formation of five new rare examples of Mn(III) dimers containing a single, unsupported oxo bridge: [MnIII(SMe2N4(6-Me-DPEN)]2-(μ-O)(BF4)2•2MeOH (6), [MnIII(SMe2N4(QuinoEN)]2-(μ-O)(PF6)2•Et2O (7), [MnIII(SMe2N4(6-Me-DPPN)]2-(μ-O)(BPh4)2 (8), [MnIII(SMe2N4(QuinoPN)]2-(μ-O)(BPh4)2 (9), and [MnIII(SMe2N4(6-H-DPEN)]2-(μ-O)(PF6)2•2MeCN (10). Labeling studies show that the oxo atom is derived from 18O2. Ligand modifications, involving either the insertion of a methylene into the backbone, or the placement of an ortho substituent on the N-heterocyclic amine, are shown to noticeably modulate the magnetic and reactivity properties. Fits to solid-state magnetic susceptibility data show that the Mn(III) ions of μ -oxo dimers 6-10 are moderately antiferromagnetically coupled, with coupling constants (2J) that fall within the expected range. Metastable intermediates, which ultimately convert to μ-oxo bridged 6 and 7, are observed in low-temperature reactions between 1 and 2 and dioxygen. Complexes 3-5, on the other hand, do not form observable intermediates, thus illustrating the effect that relatively minor ligand modifications have upon the stability of metastable dioxygen-derived species.
PMCID: PMC3422664  PMID: 22642272
8.  Structural Characterization of Methanol Substituted Lanthanum Halides 
Polyhedron  2010;29(7):1784-1795.
The first study into the alcohol solvation of lanthanum halide [LaX3] derivatives as a means to lower the processing temperature for the production of the LaBr3 scintillators was undertaken using methanol (MeOH). Initially the de-hydration of {[La(µ-Br)(H2O)7](Br)2}2 (1) was investigated through the simple room temperature dissolution of 1 in MeOH. The mixed solvate monomeric [La(H2O)7(MeOH)2](Br)3 (2) compound was isolated where the La metal center retains its original 9-coordination through the binding of two additional MeOH solvents but necessitates the transfer of the innersphere Br to the outersphere. In an attempt to in situ dry the reaction mixture of 1 in MeOH over CaH2, crystals of [Ca(MeOH)6](Br)2 (3) were isolated. Compound 1 dissolved in MeOH at reflux temperatures led to the isolation of an unusual arrangement identified as the salt derivative {[LaBr2.75•5.25(MeOH)]+0.25 [LaBr3.25•4.75(MeOH)]−0.25} (4). The fully substituted species was ultimately isolated through the dissolution of dried LaBr3 in MeOH forming the 8-coordinated [LaBr3(MeOH)5] (5) complex. It was determined that the concentration of the crystallization solution directed the structure isolated (4 concentrated; 5 dilute) The other LaX3 derivatives were isolated as [(MeOH)4(Cl)2La(µ-Cl)]2 (6) and [La(MeOH)9](I)3•MeOH (7). Beryllium Dome XRD analysis indicated that the bulk material for 5 appear to have multiple solvated species, 6 is consistent with the single crystal, and 7 was too broad to elucidate structural aspects. Multinuclear NMR (139La) indicated that these compounds do not retain their structure in MeOD. TGA/DTA data revealed that the de-solvation temperatures of the MeOH derivatives 4 – 6 were slightly higher in comparison to their hydrated counterparts.
PMCID: PMC2877215  PMID: 20514349
Lanthanum; halides; scintillators; methanol; crystal structure
9.  Iridium(III) Hydrido N-Heterocyclic Carbene–Phosphine Complexes as Catalysts in Magnetization Transfer Reactions 
Inorganic Chemistry  2013;52(23):13453-13461.
The hyperpolarization (HP) method signal amplification by reversible exchange (SABRE) uses para-hydrogen to sensitize substrate detection by NMR. The catalyst systems [Ir(H)2(IMes)(MeCN)2(R)]BF4 and [Ir(H)2(IMes)(py)2(R)]BF4 [py = pyridine; R = PCy3 or PPh3; IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene], which contain both an electron-donating N-heterocyclic carbene and a phosphine, are used here to catalyze SABRE. They react with acetonitrile and pyridine to produce [Ir(H)2(NCMe)(py)(IMes)(PPh3)]BF4 and [Ir(H)2(NCMe)(py)(IMes)(PCy3)]BF4, complexes that undergo ligand exchange on a time scale commensurate with observation of the SABRE effect, which is illustrated here by the observation of both pyridine and acetonitrile HP. In this study, the required symmetry breaking that underpins SABRE is provided for by the use of chemical inequivalence rather than the previously reported magnetic inequivalence. As a consequence, we show that the ligand sphere of the polarization transfer catalyst itself becomes hyperpolarized and hence that the high-sensitivity detection of a number of reaction intermediates is possible. These species include [Ir(H)2(NCMe)(py)(IMes)(PPh3)]BF4, [Ir(H)2(MeOH)(py)(IMes)(PPh3)]BF4, and [Ir(H)2(NCMe)(py)2(PPh3)]BF4. Studies are also described that employ the deuterium-labeled substrates CD3CN and C5D5N, and the labeled ligands P(C6D5)3 and IMes-d22, to demonstrate that dramatically improved levels of HP can be achieved as a consequence of reducing proton dilution and hence polarization wastage. By a combination of these studies with experiments in which the magnetic field experienced by the sample at the point of polarization transfer is varied, confirmation of the resonance assignments is achieved. Furthermore, when [Ir(H)2(pyridine-h5)(pyridine-d5)(IMes)(PPh3)]BF4 is examined, its hydride ligand signals are shown to become visible through para-hydrogen-induced polarization rather than SABRE.
para-Hydrogen enables NMR characterization of the reaction intermediates via signal amplification by reversible exchange.
PMCID: PMC3850244  PMID: 24215616
10.  Strategies for the Hyperpolarization of Acetonitrile and Related Ligands by SABRE 
The Journal of Physical Chemistry. B  2014;119(4):1416-1424.
We report on a strategy for using SABRE (signal amplification by reversible exchange) for polarizing 1H and 13C nuclei of weakly interacting ligands which possess biologically relevant and nonaromatic motifs. We first demonstrate this via the polarization of acetonitrile, using Ir(IMes)(COD)Cl as the catalyst precursor, and confirm that the route to hyperpolarization transfer is via the J-coupling network. We extend this work to the polarization of propionitrile, benzylnitrile, benzonitrile, and trans-3-hexenedinitrile in order to assess its generality. In the 1H NMR spectrum, the signal for acetonitrile is enhanced 8-fold over its thermal counterpart when [Ir(H)2(IMes)(MeCN)3]+ is the catalyst. Upon addition of pyridine or pyridine-d5, the active catalyst changes to [Ir(H)2(IMes)(py)2(MeCN)]+ and the resulting acetonitrile 1H signal enhancement increases to 20- and 60-fold, respectively. In 13C NMR studies, polarization transfers optimally to the quaternary 13C nucleus of MeCN while the methyl 13C is hardly polarized. Transfer to 13C is shown to occur first via the 1H–1H coupling between the hydrides and the methyl protons and then via either the 2J or 1J couplings to the respective 13Cs, of which the 2J route is more efficient. These experimental results are rationalized through a theoretical treatment which shows excellent agreement with experiment. In the case of MeCN, longitudinal two-spin orders between pairs of 1H nuclei in the three-spin methyl group are created. Two-spin order states, between the 1H and 13C nuclei, are also created, and their existence is confirmed for Me13CN in both the 1H and 13C NMR spectra using the Only Parahydrogen Spectroscopy protocol.
PMCID: PMC4315046  PMID: 25539423
11.  Synthesis and Characterization of New Trinuclear Copper Complexes 
Inorganica chimica acta  2012;389:131-137.
This report describes our approach towards modelling the copper cluster active sites of nitrous oxide reductase and the multicopper oxidases/oxygenases. We have synthesized two mesitylene-based trinucleating ligands, MesPY1 and MesPY2, which employ bis(2-picolyl)amine (PY1) and bis(2-pyridylethyl)amine (PY2) tridentate copper chelates, respectively. Addition of cuprous salts to these ligands leads to the isolation of tricopper(I) complexes [(Mes-PY1)CuI3(CH3CN)3](ClO4)3·0.25Et2O (1) and [(Mes-PY2)CuI3](PF6)3 (3) Each of the three copper centers in 1 is most likely four-coordinate, with ligated acetonitrile as the fourth ligand; by contrast, the copper centers in 3 are three-coordinate, as determined by X-ray crystallography The synthesis of [(Mes-PY1)CuII3(CH3CN)2(CH3OH)2](ClO4)6·(CH3OH) (2) was accomplished by addition of three equivalents of the copper(II) salt, Cu(ClO4)2·6H2O, to the ligand. The structure of 2 shows that two of the copper centers are tetracoordinate (with MeCN solvent ligation), but have additional weak axial (fifth ligand) interactions with the perchlorate anions; the third copper is unique in that it is coordinated by two MeOH solvent molecules, making it overall five-coordinate. For complexes 2 and 3, one copper ion center is located on the opposite side of the mesitylene plane as the other two. These observations, although in the solid state, must be taken into account for future studies where intramolecular tricopper(I)/O2 (or other small molecules of interest) interactions in solution are desirable.
PMCID: PMC3389755  PMID: 22773847
trinuclear copper; copper(I) and copper(II); copper clusters; trinucleating ligands; Cu clusters in biology
12.  Aqua­bis(4-methyl­benzoato)-κO;κ2 O,O′-bis­(pyridine-κN)nickel(II) 
In the title mononuclear complex, [Ni(C8H7O2)2(C5H5N)2(H2O)], the NiII atom is in a distorted octa­hedral arrangement, coordinated by three carboxylate O atoms from one bidentate 4-methyl­benzoate ligand and one monodentate 4-methyl­benzoate ligand, two N atoms from pyridine ligands, axially positioned, and a water mol­ecule. The equatorially positioned water mol­ecule and uncoordinated carb­oxylate O atom form an intra­molecular hydrogen bond. An inter­molecular O—H⋯O hydrogen bond between the coordinated water mol­ecule and carboxylate O atom of the 4-methyl­benzoate ligand forms infinite chains along the b axis. These chains are connected by C—H⋯π inter­actions.
PMCID: PMC2961051  PMID: 21202005
13.  Bis(μ-3-hydroxy­benzoato)-κ2 O 1:O 3;κ2 O 3:O 1-bis­[bis­(1H-benzimidazole-κN 3)(3-hydroxy­benzoato-κO)nickel(II)] bis­(1H-benzimidazole-κN 3)bis­(3-hy­droxy­benzoato-κO 1)nickel(II) hexa­hydrate 
The title compound, [Ni2(C7H5O3)4(C7H6N2)4][Ni(C7H5O3)2(C7H6N2)2]·6H2O, is a mononuclear/dinuclear nickel(II) cocrystal, the two mol­ecular species inter­acting through hydrogen bonds that involve the uncoordinated water mol­ecules. In the mononuclear species, the NiII ion, located on an inversion center, is coordinated by two 1H-benzimidazole (bzim) ligands and two 3-hydroxy­benzoate (hba) anions in a square-planar geometry. In the centrosymmetric dinuclear species, the NiII ion is coordinated by two bzim ligands and three hba anions in a square-pyramidal geometry; of the two independent hba anions, one bridges two NiII ions with both carboxylate and hydroxyl groups whereas the other coordin­ates in a unidentate manner to the NiII ion. The apical Ni—Ohydrox­yl bond is 0.39 Å longer than the basal Ni—Ocarbox­yl bonds. The face-to-face separation of 3.326 (9) Å indicates the existence of π–π stacking between parallel bzim ligands of adjacent dinuclear entities. Extensive N—H⋯O and O—H⋯O hydrogen bonds help to stabilize the crystal structure.
PMCID: PMC2960256  PMID: 21201350
14.  Tetra-μ-benzoato-bis­[(6-methyl­quino­line)­copper(II)] 
In the title compound, [Cu2(C7H5O2)4(C10H9N)2], the paddle-wheel-type dinuclear complex is constructed by four bridging benzoate groups and two terminal 6-methyl­quinoline ligands. The asymmetric unit contains one-half of the whole mol­ecule, and there is an inversion center at the mid-point of the Cu⋯Cu bond. The octa­hedral coordination of each Cu atom, with four O atoms in the equatorial plane, is completed by the N atom of the 6-methyl­quinoline mol­ecule [Cu—N = 2.212 (2) Å] and by another Cu atom [Cu⋯Cu = 2.6939 (13) Å]. The Cu atom lies 0.234 Å out of the plane of the four O atoms. The molecular packing is stabilized by one intramolecular C—H⋯O as well as C—H⋯π and π–π interactions.
PMCID: PMC2961840  PMID: 21202752
15.  Bis(μ-2-fluoro­benzoato-1:2κ2 O:O′)(2-fluoro­benzoato-1κ2 O,O′)(2-fluoro­benzoato-2κO)dinicotinamide-1κN 1,2κN 1-dizinc(II)–2-fluoro­benzoic acid (1/1) 
The asymmetric unit of the title compound, [Zn2(C7H4FO2)4(C6H6N2O)2]·C7H5FO2, consists of a binuclear ZnII complex bridged by two carboxyl groups of 2-fluoro­benzoate (FB) anions and a 2-fluoro­benzoic acid mol­ecule. The two bridging FB anions, one chelating FB anion and one nicotinamide (NA) ligand coordinate to one Zn cation with a distorted square-pyramidal geometry, while the two bridging FB anions, one monodentate FB anion and one NA ligand coordinate to the other Zn cation with a distorted tetra­hedral geometry. Within the binuclear mol­ecule, the pyridine rings are oriented at a dihedral angle of 19.41 (14)°. In the crystal structure, the uncoordinated 2-fluorobenzoic acid mol­ecules are linked by O—H⋯O hydrogen bonding, forming centrosymmetric supra­molecular dimers. Inter­molecular N—H⋯O hydrogen bonds link the complex mol­ecules into a three-dimensional network. The π–π contacts between nearly parallel pyridine and benzene rings [dihedral angles of 19.41 (14) and 12.72 (16)°, respectively, centroid–centroid distances = 3.701 (2) and 3.857 (3) Å] may further stabilize the crystal structure. The fluorine atoms in two FB ligands are disordered over two positions, with occupancy ratios of 0.70:0.30.
PMCID: PMC2971791  PMID: 21578633
16.  Structural, Spectroscopic, and Electrochemical Properties of Nonheme Fe(II)-Hydroquinonate Complexes: Synthetic Models of Hydroquinone Dioxygenases 
Using the tris(3,5-diphenylpyrazol-1-yl)borate (Ph2Tp) supporting ligand, a series of mono- and dinuclear ferrous complexes containing hydroquinonate (HQate) ligands have been prepared and structurally characterized with X-ray crystallography. The monoiron(II) complexes serve as faithful mimics of the substrate-bound form of hydroquinone dioxygenases (HQDOs) – a family of nonheme Fe enzymes that catalyze the oxidative cleavage of 1,4-dihydroxybenzene units. Reflecting the variety of HQDO substrates, the synthetic complexes feature both mono- and bidentate HQate ligands. The bidentate HQates cleanly provide five-coordinate, high-spin Fe(II) complexes with the general formula [Fe(Ph2Tp)(HLX)] (1X), where HLX is a HQate(1-) ligand substituted at the 2-position with a benzimidazolyl (1A), acetyl (1B and 1C), or methoxy (1D) group. In contrast, the monodentate ligand 2,6-dimethylhydroquinone (H2LF) exhibited a greater tendency to bridge between two Fe(II) centers, resulting in formation of [Fe2(Ph2Tp)2(μ-LF)(MeCN)] [2F(MeCN)]. However, addition of one equivalent of “free” pyrazole (Ph2pz) ligand provided the mononuclear complex, [Fe(Ph2Tp)(HLF)(Ph2pz)] [1F(Ph2pz)], which is stabilized by an intramolecular hydrogen bond between the HLF and Ph2pz donors. Complex 1F(Ph2pz) represents the first crystallographically-characterized example of a monoiron complex bound to an untethered HQate ligand. The geometric and electronic structures of the Fe/HQate complexes were further probed with spectroscopic (UV-vis absorption, 1H NMR) and electrochemical methods. Cyclic voltammograms of complexes in the 1X series revealed an Fe-based oxidation between 0 and −300 mV (vs. Fc+/0), in addition to irreversible oxidation(s) of the HQate ligand at higher potentials. The one-electron oxidized species (1Xox) were examined with UV-vis absorption and electron paramagnetic resonance (EPR) spectroscopies.
PMCID: PMC3891569  PMID: 22930005
17.  Synthesis and Characterization of Ruthenium Bis(β-diketonato) Pyridine-Imidazole Complexes for Hydrogen Atom Transfer 
Inorganic chemistry  2007;46(26):11190-11201.
Ruthenium bis(β-diketonato) complexes have been prepared at both the RuII and RuIII oxidation levels and with protonated and deprotonated pyridine-imidazole ligands. RuII(acac)2(py-imH) (1), [RuIII(acac)2(py-imH)]OTf (2), RuIII(acac)2(py-im) (3), RuII(hfac)2(py-imH) (4), and [DBU-H][RuII(hfac)2(py-im)] (5) have been fully characterized, including X-ray crystal structures (acac = 2,4-pentanedionato, hfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionato, py-imH = 2-(2′-pyridyl)imidazole, DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene). For the acac-imidazole complexes 1 and 2, cyclic voltammetry in MeCN shows the RuIII/II reduction potential (E1/2) to be −0.64 V vs. Cp2Fe+/0. E1/2 for the deprotonated imidazolate complex 3 (−1.00 V) is 0.36 V more negative. The RuII bis-hfac analogs 4 and 5 show the same ΔE1/2 = 0.36 V but are 0.93 V harder to oxidize than the acac derivatives (0.29 V and −0.07 V). The difference in acidity between the acac and hfac derivatives is much smaller, with pKa values of 22.1 and 19.3 in MeCN for 1 and 4. From the E1/2 and pKa values, the bond dissociation free energies (BDFEs) of the N–H bonds in 1 and 4 are calculated to be 62.0 and 79.6 kcal mol−1 in MeCN – a remarkable difference of 17.6 kcal mol−1 for such structurally similar compounds. Consistent with these values, there is facile net hydrogen atom transfer from 1 to TEMPO• (2,2,6,6-tetramethylpiperidine-1-oxyl radical) to give 3 and TEMPO–H. The ΔG° for this reaction is −4.5 kcal mol−1. Complex 4 is not oxidized by TEMPO• (ΔG° = +13.1 kcal mol−1), but in the reverse direction TEMPO–H readily reduces in situ generated RuIII(hfac)2(py-im) (6). A RuII-imidazoline analog of 1, RuII(acac)2(py-imnH) (7), reacts with 3 equiv of TEMPO• to give the imidazolate complex 3 and TEMPO–H, with dehydrogenation of the imidazoline ring.
PMCID: PMC2596074  PMID: 18052056
18.  Diaqua­bis­(benzoato-κO)bis­[4,4,5,5-tetra­methyl-2-(pyridin-4-yl-κN)imidazoline-1-oxyl 3-oxide]cobalt(II) 
The title compound, [Co(C7H5O2)2(C12H16N3O2)2(H2O)2], was obtained from a conventional solvent evaporation method. The complex mol­ecule is centrosymmetric, so pairs of equivalent ligands lie trans to each other in a slightly distorted octa­hedral CoN2O4 geometry. The CoII ion is coordinated by the pyridine N atoms from NITpPy ligands [NITpPy is 4,4,5,5-tetra­methyl-2-(pyridin-4-yl)imidazoline-1-oxyl 3-oxide), water O atoms and two monodentate benzoate O atoms. The complex mol­ecules are connected by O—H⋯O hydrogen bonds between water mol­ecules and benzoate ligands, forming chains parallel to [100]. π–π stacking inter­actions between the benzoate ligands with centroid–centroid distances of 3.752 (2) Å connect the chains into layers parallel to (10-1).
PMCID: PMC3343890  PMID: 22589858
19.  Syntheses, Spectral Characterization, and Antimicrobial Studies on the Coordination Compounds of Metal Ions with Schiff Base Containing Both Aliphatic and Aromatic Hydrazide Moieties 
An EtOH solution of 3-ketobutanehydrazide and salicylhydrazide on refluxing in equimolar ratio forms the corresponding Schiff base, LH3 (1). The latter reacts with Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Zr(OH)2(IV), MoO2(VI), and UO2(VI) ions in equimolar ratio and forms the corresponding coordination compounds, [M(LH)(MeOH)3] (2, M = Mn, Co, Ni), [Cu(LH)]2 (3), [M′(LH)(MeOH)] (4, M′ = Zn, Cd), [Zr(OH)2(LH)(MeOH)2] (5), [MoO2(LH)(MeOH)] (6), and [UO2(LH)(MeOH)] (7). The coordination compounds have been characterized on the basis of elemental analyses, molar conductance, spectral (IR, reflectance, 1H NMR, ESR) studies, and magnetic susceptibility measurements. They are nonelectrolytes in DMSO. The coordination compounds, except 3, are monomers in diphenyl. They are active against gram-positive bacteria (S. aureus, B. subtilis), gram-negative bacteria (E. coli, P. aeruginosa), and yeast (S. cerevisiae, C. albicans). 1 acts as a dibasic tridentate ONO donor ligand in 2–7 coordinating through its both enolic O and azomethine N atoms. The coordination compounds 2 and 3 are paramagnetic, while rest of the compounds are diamagnetic. A square-planar structure to 3, a tetrahedral structure to 4, an octahedral structure to 2, 6, and 7, and a pentagonal bipyramidal structure to 5 are proposed.
PMCID: PMC3808720  PMID: 24198736
20.  Aqua­bis(1H-imidazole-κN 3)bis­(4-methyl­benzoato)-κO;κO,O′-nickel(II) 
In the mononuclear title compound, [Ni(C8H7O2)2(C3H4N2)2(H2O)], the NiII atom is coordinated by three carboxylate O atoms (from a bidentate 4-methyl­benzoate ligand and a monodentate 4-methyl­benzoate ligand), two N atoms (from two imidazole ligands) and a water mol­ecule in an octa­hedral geometry. Inter­molecular O—H⋯O hydrogen-bonding inter­actions lead to infinite chains, which are further self-assembled into a supra­molecular network through inter­molecular N—H⋯O hydrogen-bonding inter­actions and π–π stacking [centroid–centroid distance = 3.717 (2) Å].
PMCID: PMC2961080  PMID: 21202196
21.  Tetra-μ-benzoato-bis­{[4-(pyrrolidin-1-yl)pyridine]zinc(II)} 
The central part of the title centrosymmetric dinuclear complex, [Zn2(C7H5O2)4(C9H12N2)2], has a paddle-wheel conformation with four benzoate ligands bridging two symmetry-related ZnII ions. The distorted square-pyramidal coordination environment around the ZnII ion is completed by an N atom from a 4-(pyrrolidin-1-yl)pyridine ligand. The Zn⋯Zn separation of 2.9826 (12) Å does not represent a formal direct metal–metal bond. The ZnII ion is displaced by 0.381 (1) Å from the mean plane of the four basal O atoms. Two of the C atoms of the pyrrolidine ring are disordered over two sites with refined occupancies of 0.53 (2) and 0.47 (2).
PMCID: PMC2980161  PMID: 21579957
22.  Tetra-μ-benzoato-bis­[(3-methyl­quinoline)copper(II)](Cu—Cu) 
In the title compound, [Cu2(C7H5O2)4(C10H9N)2], the paddle-wheel-type dinuclear complex mol­ecule contains four bridging benzoate groups and two terminal 3-methyl­quinoline ligands. The asymmetric unit contains one and a half mol­ecules with a total of three independent Cu atoms; there is an inversion center at the mid-point of the Cu⋯Cu bond in one molecule. The octa­hedral coordination of each Cu atom, with four O atoms in the equatorial plane, is completed by an N atom of a 3-methyl­quinoline ligand [Cu—N = 2.190 (4)–2.203 (3) Å] and by another Cu atom [Cu⋯Cu = 2.667 (1) and 2.6703 (7) Å]. The Cu atoms are all ca 0.22 Å out of the plane of the four bonded O atoms.
PMCID: PMC2960550  PMID: 21201597
23.  Bis(μ2-2-chloro­benzoato-κ2 O:O′)bis­[(2-chloro­benzoato-κO)(1,10-phenanthroline-κ2 N:N′)copper(II)] dihydrate 
In the title compound, [Cu2(C7H4ClO2)4(C12H8N2)2]·2H2O, the two crystallographically independent dinuclear complex mol­ecules, A and B, have different Cu⋯Cu separations, viz. 3.286 (1) Å in A and 3.451 (1) Å in B. Both independent mol­ecules reside on inversion centres, so the asymmetric unit contains a half-mol­ecule each of A and B and two water mol­ecules. Each Cu atom has a square-pyramidal environment, being coordinated by two O atoms from two bridging 2-chloro­benzoate ligands, one O atom from a monodentate 2-chloro­benzoate ligand and two N atoms from a 1,10-phenanthroline ligand. The water mol­ecules can also be considered as coordinating ligands, which complete the coordination geometry up to distorted octa­hedral with elongated Cu—O distances, viz. 3.024 (3) Å in A and 2.917 (3) Å in B. In the crystal, weak inter­molecular C—H⋯O inter­actions contribute to the consolidation of the crystal packing.
PMCID: PMC3212258  PMID: 22090915
24.  Aqua­bis(isonicotinamide-κN 1)bis­(4-methyl­benzoato)-κO;κ2 O,O′-cadmium(II) monohydrate 
In the crystal structure of the title compound, [Cd(C8H7O2)2(C6H6N2O)2(H2O)]·H2O, the CdII cation is coordinated by two 4-methyl­benzoate (PMB) anions, two isonicotinamide (INA) ligands and one water mol­ecule in a distorted octa­hedral CdN2O4 geometry. One of PMB ions acts as a bidentate ligand while the other and the two INA are monodentate ligands. An O—H⋯O hydrogen bond links the uncoordinated water mol­ecule to the carboxyl groups of the complex. The dihedral angles between the carboxyl groups and the adjacent benzene rings are 10.28 (11) and 21.24 (9)°, while the two benzene rings and the two pyridine rings are oriented at dihedral angles of 6.90 (4) and 88.64 (4)°, respectively. In the crystal structure, O—H⋯O and N—H⋯O hydrogen bonds link the mol­ecules into a supra­molecular structure. A π–π contact between the benzene rings [centroid–centroid distance = 3.911 (1) Å] may further stabilize the crystal structure. Weak C—H⋯π inter­actions involving the pyridine rings also occur in the crystal structure.
PMCID: PMC2984084  PMID: 21580498
25.  Bis(di­methyl­formamide)­penta­kis­(μ-N,2-dioxido­benzene-1-carb­ox­imidato)tetra­kis­(1-methyl­imidazole)di-μ-propionato-penta­manganese(III)manganese(II)–di­methyl­formamide–methanol (1/0.24/1.36) 
The title compound [Mn6(C7H4NO3)5(C3H5O2)2(C4H6N2)4.17(C3H7NO)1.83]·0.24C3H7NO·1.36CH3OH or Mn(II)(C3H5O2)2[15-MCMn(III)N(shi)-5](Me—Im)4.17(DMF)1.83·0.24DMF·1.36MeOH (where MC is metallacrown, shi3− is salicyl­hydroximate, Me—Im is 1-methyl­imidazole, DMF is N,N-di­methyl­formamide, and MeOH is methanol), contains an MnII ion in the central cavity and five MnIII ions in the MC ring. The central MnII ion is seven coordinate and has a geometry best described as distorted face-capped trigonal prismatic with Φ angles of 6.13, 10.36, and 11.73° and an estimated average s/h ratio of 1.03±0.11. Four of the ring MnIII ions are six coordinate with distorted octa­hedral geometries. Two of the MnIII ions have Λ absolute stereoconfiguration, while the other two MnIII ions have a planar configuration. The fifth MnIII ion is five coordinate and has a distorted square pyramidal geometry with τ = 0.20. Three of the MnIII ions bind one 1-methyl­imidazole ligand. Two of the ring MnIII ions have a 1-methyl­imidazole and a DMF disordered over a coordination site. For one of the ring MnIII ions, the occupancy ratio of the ligands refines to 0.51 (1):0.49 (1) in favor of the DMF. For the other ring MnIII ion, the occupancy ratio of the ligands refines to 0.68 (1):0.32 (1) in favor of the 1-methyl­imidazole. Two propionate anions serve to bridge the central MnII ion between two different MnIII ions. The methyl groups of the bridging propionate anions are disordered over two positions. The methyl group disorder also induces disorder in the H atoms of the adjacent methyl­ene C atom to the same degree. For one of the propionate anions, the occupancy ratio refines to 0.752 (8):0.248 (8) and for the second, the occupancy ratio refines to 0.604 (6):0.396 (6). In addition, the disorder of the methyl group of the latter propionate anion is correlated with a partially occupied [0.604 (6)] methanol mol­ecule. Furthermore, a methanol mol­ecule and a DMF mol­ecule are positionally disordered in the lattice. The occupancy refines to 0.757 (7):0.243 (7) in favor of the methanol mol­ecule. Correlated to the occupancy of the methanol and DMF mol­ecules is a disordered benzene ring of one salicyl­hydroximate ligand. The benzene ring is disordered over two positions with an occupancy ratio of 0.757 (7):0.243 (7). Lastly, the two lattice methanol mol­ecules are hydrogen bonded to the 15-MC-5 mol­ecule. For the partially occupied methanol mol­ecule associated with the disordered propionate anion, the hydroxyl group of the methanol is hydrogen bonded to a carboxyl­ate O atom of the propionate anion. For the partially occupied methanol mol­ecule associated with the partially occupied lattice DMF mol­ecule, the hydroxyl group of the methanol is hydrogen bonded to the phenolate O atom of a salicyl­hydroximate ligand and to the carbonyl O atom of a coordinated DMF mol­ecule.
PMCID: PMC3884426  PMID: 24426984

Results 1-25 (401334)