Coordinated Metal Centers Research Articles

Electron-density distributions in selected ferrocenyl-pyrazolyl late transition-metal complexes.

57Fe Mössbauer spectroscopy has been used to study electronic dispersions in complexes of Fe, Co, Ni and Pd anchored onto 3-ferrocenyl-5-methylpyrazolylmethylenepyridine and 3-ferrocenylpyrazolylmethylenepyridine ligands. Mössbauer spectroscopy shows that pyrazolyl-derivatizing of ferrocene increases the electron-density at the Fe-centre as well as facilitating the Fe to cyclopentadienyl ring back-donation of electron-density. The coordination of the ferrocenyl-pyrazolyl ligand to transition metals such as Fe, Co, Ni and Pd reduces the electron-density at the Fe-centre of the ferrocenyl moiety while increasing the electron-density at the coordinated metal centre, especially in the Fe complexes. The electron-density change at the coordination metal centre is inversely proportional to the electronegativity of the halide substituent. Furthermore, the type of substituent (Me or H) at position 5 on the pyrazolyl moiety has an influence on the electron density at the ferrocenyl-Fe and the coordinated metal centre. The methyl group as a substituent reduces the π-acceptor ability of the pyrazolyl and therefore increases the electron-density at the ferrocenyl-Fe centre. However, when the substituent is hydrogen, the electron-density at the coordination metal centre increases. Similarly, for other metals (i.e., Co, Ni and Pd) the electron density at the ferrocenyl-Fe is also significantly reduced upon coordination of the ligand to the metal. Additionally, Mössbauer experiments reveal a trivalent Fe species in the synthesized complexes which is not discerned by X-ray and elemental analysis. The species has been identified as the oxidative product [Fe(iii)X4]- where X = Cl or Br. The study also highlights and cautions on the possibility of photo-oxidation processes involving both ferrocene and the coordinating Fe-halides under standard lighting conditions with possible contributions from aerated solvents.

Investigating the geometrical preferences of a flexible benzimidazolone-based linker in the synthesis of coordination polymers.

A series of new group 2 coordination polymers, MgL ={MgL(H2O)(DMF)0.75}∞, CaL = {CaL(DMF)2}∞, SrL = {SrL(H2O)0.5}∞ and BaL = {BaL(H2O)0.5}∞, were synthesized using a flexible benzimidazolone diacetic acid linker (H2L) in which the two carboxylic acid binding sites are connected to a planar core via {–CH2–} spacers that can freely rotate in solution. In a ‘curiosity-led' diversion from group 2 metals, the first row transition metal salts Mn2+, Cu2+ and Zn2+ were also reacted with L to yield crystals of MnL = {MnL(DMF)(H2O)3.33}∞, Cu3L2 = {Cu3L2(DMF)2(CHO2)2}∞ and ZnL = {ZnL(DMF)}∞. Crystal structures were obtained for all seven materials. All structures form as two-dimensional sheets and contain six-coordinate centres, with the exception of ZnL, which displays tetrahedrally coordinated metal centres, and Cu3L2, which contains square planar coordinated metal centres and Cu paddle-wheels. In each structure, the linker adopts one of two distinct conformations, with the carboxylate groups either cis or trans with respect to the planar core. All materials were also characterized by powder X-ray diffraction and thermogravimetric analysis.

The Use of Resorcinarene Cavitands in Metal‐Based Catalysis

Catalytic chemistry involving coordination complexes based on resorcinarene cavitands has been little explored in comparison to the many studies concerning the use of such ligands in classical coordination chemistry or host–guest chemistry. The potential utility of resorcinarene cavitands in catalysis arises essentially from two features: (1) their ability to function as ligands suitable for metal confinement and thus to make reactions either shape selective or to enhance their rates through supramolecular assistance by the receptor subunit; (2) their ability to enforce steric interactions with a coordinated metal center and thereby favor carbon–carbon bond forming reactions. To date, limited use has been made of cavitands as platforms for the attachment of different ligating sites, in particular for the generation of multifunctional ligands giving rise to anchimeric assistance in catalytic reactions. This review is intended to show the promise that exists in this area. As generic cavitands can be easily expanded to result in large bowl‐shaped structures as well as capsular containers, it may be anticipated that future work in this field will focus on the synthesis of sophisticated, metallated microreactors (possibly made water‐soluble) for highly selective transformations, including polymerizations.

Porous Hydrogen-Bonded Organic Frameworks.

Ordered porous solid-state architectures constructed via non-covalent supramolecular self-assembly have attracted increasing interest due to their unique advantages and potential applications. Porous metal-coordination organic frameworks (MOFs) are generated by the assembly of metal coordination centers and organic linkers. Compared to MOFs, porous hydrogen-bonded organic frameworks (HOFs) are readily purified and recovered via simple recrystallization. However, due to lacking of sufficiently ability to orientate self-aggregation of building motifs in predictable manners, rational design and preparation of porous HOFs are still challenging. Herein, we summarize recent developments about porous HOFs and attempt to gain deeper insights into the design strategies of basic building motifs.

CuII and ZnII β-diketonate coordination polymers based on pyrimidin-2-amine, pyrazine and 1,2-bis(4-pyridyl)ethane.

Copper(II) and zinc(II) bis(4,4,4-trifluoro-1-phenylbutane-1,3-dionato) compounds with pyrimidin-2-amine (pyr2a), pyrazine (pyz) and 1,2-bis(4-pyridyl)ethane (dpet) were prepared and solid-state structures of coordination polymers [M(tfpb)2(pyr2a)]∞ [M = Cu (1), Zn (2); tfpb = 4,4,4-trifluoro-1-phenylbutane-1,3-dionate], [M(tfpb)2(pyz)]∞ [M = Cu (3), Zn (4a, 4b)] and [Cu(tfpb)2(dpet)]∞ (5), respectively, were determined by single-crystal X-ray analysis. The coordination of metal centers in all compounds is octahedral with nitrogen ligands occupying the axial positions. Compound (1) crystallizes in the triclinic space group P\bar 1, whereas (2) crystallizes in the monoclinic space group P2/n. Differences are due to the different orientation of adjacent M(tfpb)2 units, whereas the orientation of pyrimidin-2-amine is the same in both compounds. Polymeric chains in (1) and (2) contain intramolecular N-H...O hydrogen bonding between amino and carbonyl groups. Room-temperature structures (3) and (4a) are isomorphous adopting the monoclinic space group C2/m; however, on cooling crystals (4a) to 150 K a single-crystal-to-single-crystal transformation to (4b) possessing the triclinic space group P\bar 1 was observed. Compound (5) crystallizes in the triclinic space group P\bar 1 and contains a parallel aggregation of chains in contrast to the known structure of the non-fluorinated benzoylacetonato ligand, where chains aggregate in a perpendicular fashion. In the compounds studied intramolecular C-H...O and/or C-H...F interactions are present. The neighboring chains are linked by π...π interactions and in some compounds also by C-H...π interactions [(1), (4b), (5)].

Identification of different coordination geometries by XAFS in copper(II) complexes with trimesic acid

X-ray absorption spectroscopy (XAS) is very useful in revealing the information about geometric and electronic structure of a transition-metal absorber and thus commonly used for determination of metal-ligand coordination. But XAFS analysis becomes difficult if differently coordinated metal centers are present in a system. In the present investigation, existence of distinct coordination geometries around metal centres have been studied by XAFS in a series of trimesic acid Cu(II) complexes. The complexes studied are: Cu3(tma)2(im)6 8H2O (1), Cu3(tma)2(mim)6 17H2O (2), Cu3(tma)2(tmen)3 8.5H2O (3), Cu3(tma) (pmd)3 6H2O (ClO4)3 (4) and Cu3(tma)2 3H2O (5). These complexes have not only Cu metal centres with different coordination but in complexes 1–3, there are multiple coordination geometries present around Cu centres. Using XANES spectra, different coordination geometries present in these complexes have been identified. The variation observed in the pre-edge features and edge features have been correlated with the distortion of the specific coordination environment around Cu centres in the complexes. XANES spectra have been calculated for the distinct metal centres present in the complexes by employing ab-initio calculations. These individual spectra have been used to resolve the spectral contribution of the Cu centres to the particular XANES features exhibited by the experimental spectra of the multinuclear complexes. Also, the variation in the 4p density of states have been calculated for the different Cu centres and then correlated with the features originated from corresponding coordination of Cu. Thus, these spectral features have been successfully utilized to detect the presence of the discrete metal centres in a system. The inferences about the coordination geometry have been supported by EXAFS analysis which has been used to determine the structural parameters for these complexes.

A Family of Homo‐ and Heteroscorpionate Ligands: Applications to Bioinorganic Chemistry

In this brief review we focus on a few examples of how a family of homo‐ and heteroscorpionate ligands allow us to examine how changes in reactivity, structure, or physical/chemical properties around biologically interesting N2X coordinated metal centers vary as a function of donor atom, charge, hydrophobicity, hydrogen bonding, etc., in a way previously unavailable. Such a family of ligands is the bioinorganic chemists answer to site‐directed mutagenesis. Here we focus on two bioinorganic examples i.e. models for molybdoenzymes and zinc metalloproteins.

A versatile hard-soft N/S-ligand for metal coordination and cluster formation.

Deprotonation of the thialdiphosphazane [S[double bond, length as m-dash]PH(μ-N(t)Bu)]2 with a range of metal-bases gives the stable dianion [S-P(μ-N(t)Bu)]2(2-), which is valence-isoelectronic with the widely-used [RN-P(μ-NR)]2(2-) ligand. Structural studies show that the new ligand has adaptable hard-soft character with respect to the coordinated metal centre and that its multidentate nature can be exploited to construct large cage architectures.

Stacking Interactions Drive Selective Self-Assembly and Self-Sorting of Pyrene-Based M(II)4L6 Architectures.

Subcomponent self-assembly of two isomeric bis(3-aminophenyl)pyrenes, 2-formylpyridine and the metal ions Fe(II), Co(II), and Zn(II) led to the formation of two previously unidentified structure types: a C2-symmetric M(II)4L6 assembly with meridionally coordinated metal centers, and a C3-symmetric self-included M(II)4L6 assembly with facially coordinated metal centers. In both structures the meta linkages within the ligands facilitate π-stacking between the pyrene panels of the ligands. A C2h-symmetric M(II)2L2 box was also obtained, which was observed to selectively bind electron-deficient aromatic guests between two parallel pyrene subunits. Similar donor-acceptor interactions drove the selective self-assembly of a singular M(II)4L4L'2 architecture incorporating both a pyrene-containing diamine and an electron-deficient NDI-based diamine. This heteroleptic architecture was shown to be thermodynamically favored over the corresponding homoleptic M(II)4L6 and M(II)4L'6 complexes, which were nonetheless stable in each others' absence. By contrast, an isomeric pyrene-based diamine was observed to undergo narcissistic self-sorting in the presence of the NDI-based diamine.

Investigations on the influence of the metal center coordination on the magnetic properties of Mn thiocyanato coordination polymers

Reaction of manganese(II) thiocyanate with the monodentate ligand 4-benzylpyridine (bp) leads to the formation of two compounds of composition Mn(NCS)2(4-benzylpyridine)4 (1-bp) and Mn(NCS)2(4-benzylpyridine)2 (2-bp). Compound 1-bp forms discrete complexes in which the Mn cations are coordinated by four 4-benzylpyridine ligands and two terminal N-bonding thiocyanato anions within slightly distorted octahedra. In compound 2-bp the metal cations are surrounded by two cis-coordinating 4-benzylpyridine ligands, two cis-coordinating S-bonded thiocyanato anions and two trans-coordinating N-bonded anionic ligands. The Mn cations are linked into zig–zag-like chains by pairs of μ-1,3-bridging anionic ligands. DTA–TG measurements on 1-bp prove that 2-bp is obtained as intermediate. Magnetic measurements on the chain compound 2-bp show dominating antiferromagnetic interactions between the Mn centers. On cooling a maximum is observed in the susceptibility curve indicative for an antiferromagnetic transition. The results of the magnetic measurements are compared with those obtained for other Mn thiocyanato chain compounds in which the thiocyanato anions are trans-coordinated.

The role of chloride in the mechanism of O(2) activation at the mononuclear nonheme Fe(II) center of the halogenase HctB.

Mononuclear nonheme Fe(II) (MNH) and α-ketoglutarate (α-KG) dependent halogenases activate O2 to perform oxidative halogenations of activated and nonactivated carbon centers. While the mechanism of halide incorporation into a substrate has been investigated, the mechanism by which halogenases prevent oxidations in the absence of chloride is still obscure. Here, we characterize the impact of chloride on the metal center coordination and reactivity of the fatty acyl-halogenase HctB. Stopped-flow kinetic studies show that the oxidative transformation of the Fe(II)-α-KG-enzyme complex is >200-fold accelerated by saturating concentrations of chloride in both the absence and presence of a covalently bound substrate. By contrast, the presence of substrate, which generally brings about O2 activation at enzymatic MNH centers, only has an ∼10-fold effect in the absence of chloride. Circular dichroism (CD) and magnetic CD (MCD) studies demonstrate that chloride binding triggers changes in the metal center ligation: chloride binding induces the proper binding of the substrate as shown by variable-temperature, variable-field (VTVH) MCD studies of non-α-KG-containing forms and the conversion from six-coordinate (6C) to 5C/6C mixtures when α-KG is bound. In the presence of substrate, a site with square pyramidal five-coordinate (5C) geometry is observed, which is required for O2 activation at enzymatic MNH centers. In the absence of substrate an unusual trigonal bipyramidal site is formed, which accounts for the observed slow, uncoupled reactivity. Molecular dynamics simulations suggest that the binding of chloride to the metal center of HctB leads to a conformational change in the enzyme that makes the active site more accessible to the substrate and thus facilitates the formation of the catalytically competent enzyme–substrate complex. Results are discussed in relation to other MNH dependent halogenases.

Role of the Coordination Center in Photocurrent Behavior of a Tetrathiafulvalene and Metal Complex Dyad

Small organic molecule-based compounds are considered to be promising materials in photoelectronics and high-performance optoelectronic devices. However, photoelectron conversion research based on functional organic molecule and metal complex dyads is very scarce. We design and prepare a series of compounds containing a tetrathiafulvalene (TTF) moiety substituted with pyridylmethylamide groups of formulas [Ni(acac)2L]·2CH3OH (1), [Cu2I2L2]·THF·2CH3CN (2), and [MnCl2L2]n·2nCH3CH2OH (3) (L = 4,5-bis(3-pyridylmethylamide)-4',5'-bimethylthio-tetrathiafulvalene, acac = acetylacetone) to study the role of the coordination center in photocurrent behavior. Complex 1 is a mononuclear species, and complex 2 is a dimeric species. Complex 3 is a two-dimensional (2-D) coordination polymer. Spectroscopic and electrochemical properties of these complexes indicate that they are electrochemically active materials. The tetrathiafulvalene ligand L is a photoelectron donor in the presence of electron acceptor methylviologen. The effect of metal coordination centers on photocurrent response behavior is examined. The redox-active metal coordination centers should play an important role in improvement of the photocurrent response property. The different morphologies of the electrode films reflect the dimensions in molecular structures of the coordination compounds.

Theoretical investigations of the structures and electronic spectra of Zn(II) and Ni(II) complexes with cyclohexylamine-N-dithiocarbamate

The ground-state structures of two ligands cyclohexylamine-N-dithiocarbamate (L) and PPh3 and four complexes [Zn(L)2] (A), [Ni(L)2] (B), [Zn(L)2PPh3] (C), and [Ni(L)2PPh3] (D) are optimized by M06, B3LYP, and B3PW91 methods with the same mixed basis set. As compared with the experimental data of other complexes containing the Ni–P bond, the result obtained by M06/6-31+G(d)-LANL2DZ method is finally regarded as accurate and reliable for this project. Based on the optimized geometries, the compositions of molecular orbitals are analyzed and the absorption spectra are simulated. When one more ligand PPh3 is coordinated, the lowest-lying transition energy presents red-shift; while it shows blue-shift when the metal coordination center change from Ni to Zn with the same ligands. The detailed transition characters related with the absorption spectrum are assigned. In all the key transitions, it is hard to find the contribution from Zn atom. On the contrary, the d orbital of Ni atom contributes a lot for the HOMO and LUMO of complexes B and D. Consequently, the transition characters of Zn(II) and Ni(II) complexes are different.

Octamolybdate-Based Metal–Organic Framework with Unsaturated Coordinated Metal Center As Electrocatalyst for Generating Hydrogen from Water

Two octamolybdate-based MOFs with unsaturated coordinated metal centers formulated as Cu(3)(Mo(8)O(26))(H(2)O)(2)(OH)(2)(L1)(4) (L1 = 4H-4-amino-1,2,4-triazole) (1) and Ag(4)(Mo(8)O(26))(L2)(2.5)(H(2)O) (L2 = 3,5-dimethyl-4-amino-4H-1,2,4-triazole) (2) were synthesized and structurally characterized by single-crystal X-ray diffractions. Complex 1 exhibits a 1D chain-like structure. In complex 2, 1D Ag-octamolybdate chains in the ac plane are covalently embedded into the 2D Ag-L2 layer, and the Ag-octamolybdate chains in the bc plane covalently link the 2D layers into 3D architecture. The two complexes both exhibit electrocatalytic activities toward generating H(2) from water with lowered overpotentials and enhanced currents, and the Cu complex exhibits better electrocatalytic activity toward generating H(2) from water than the Ag complex.

Synthesis, molecular structure and electrochemistry of gold(I) complexes with 1-(diphenylphosphino)-1′-[(diphenylphosphino)methyl]ferrocene

Depending on the reaction stoichiometry, 1-(diphenylphosphino)-1′-[(diphenylphosphino)methyl]-ferrocene (1) reacts with [AuCl(tht)] (tht = tetrahydrothiophene) to afford an insoluble polymer formulated as [AuCl(1)]n (2) or ligand-bridged digold(I) complex, [(μ-1)(AuCl)2] (3). The latter compound readily undergoes metathesis reactions with anionic reagents such as in situ generated acetylides, thiocyanate or N,N-diethyldithiocarbamate to give the corresponding digold(I) complexes [(μ-1)(AuY)2], where Y is CCPh (4), CCFc (5; Fc = ferrocenyl), SCN (6), and Et2NCS2 (7). Similar reaction of 3 with a dithiolate formed from propane-1,3-dithiol and sodium methoxide affords a macrocyclic bis-chelate [(μ-1)(AuSCH2CH2CH2SAu)] (8). Compounds 2–8 have been characterized by spectroscopic methods (multinuclear NMR, ESI, MS, UV–vis and IR) and by elemental analysis, and the molecular structures of 3·½C2H4Cl2, 4·2CHCl3, 7·2CHCl3, and 8 have been determined by single-crystal X-ray diffraction analysis. Cyclic voltammetric study revealed that ligand 1 undergoes a one-electron oxidation at the ferrocene unit, which is associated with some chemical complications resulting presumably from the presence of the lone electron pair at phosphorus. After coordination to Au(I)L fragments bearing simple auxiliary ligands (e.g., in 3, 4, and 6), the FeII/FeIII redox process becomes reversible and appears shifted to more positive potentials owing to an electron density transfer from the diphosphine ligand to the coordinated metal centers. For compounds 5 and 7, this redox change is accompanied by additional waves attributable to oxidation of ferrocenyl groups in the terminal ferrocenylethynyl groups and to redox changes occurring at the Au-bound carbamate ligands, respectively.

A Charge‐Transfer Challenge: Combining Fullerenes and Metalloporphyrins in Aqueous Environments

A series of truly water-soluble C(60)/porphyrin electron donor-acceptor conjugates has been synthesized to serve as powerful mimics of photosynthetic reaction centers. To this end, the overall water-solubility of the conjugates was achieved by adding hydrophilic dendrimers of different generations to the porphyrin moiety. An important variable is the metal center of the porphyrin; we examined zinc(II), copper(II), cobalt(II), nickel(II), iron(III), and manganese(III). The first insights into electronic communication between the electron donors and the electron acceptors came from electrochemical assays, which clearly indicate that the redox processes centered either on C(60) or the porphyrins are mutually affected. Absorption measurements, however, revealed that the electronic communication in terms of, for example, charge-transfer features, remains spectroscopically invisible. The polar environment that water provides is likely to be a cause of the lack of detection. Despite this, transient absorption measurements confirm that intramolecular charge separation processes in the excited state lead to rapid deactivation of the excited states and, in turn, afford the formation of radical ion pair states in all of the investigated cases. Most importantly, the lifetimes of the radical ion pairs were found to depend strongly on several aspects. The nature of the coordinated metal center and the type of dendrimer have a profound impact on the lifetime. It has been revealed that the nature/electronic configuration of the metal centers is decisive in powering a charge recombination that either reinstates the ground state or any given multiplet excited state. Conversely, the equilibrium of two opposing forces in the dendrimers, that is, the interactions between their hydrophilic regions and the solvent and the electronic communication between their hydrophobic regions and the porphyrin and/or fullerene, is the key to tuning the lifetimes.

Precursor-Directed Assembly of Complex Oxide Nanobeads: The Role of Strongly Coordinated Inorganic Anions

The use of an inorganic perrhenate ligand in the structure of early-transition-metal alkoxide precursors permits to achieve uniform self-assembly of the primary nanoparticles produced by their hydrolysis. The latter has been carried out in a hydrocarbon reaction medium by the addition of water with vigorous stirring, either in the pure form or in solutions in parent alcohols. The self-assembly is guided by the surface charge enhanced by the presence of strongly coordinated anions as determined by zeta potential measurements. The aggregation process has been followed in real time by nanoparticle tracking analysis (NanoSight technique). The reaction products are spherical aggregates with a size that can be efficiently controlled through the polarity of the reaction medium. The produced nanobeads have been characterized by TEM, SEM-EDS, DLS, nitrogen adsorption, and FTIR. The coordination of metal centers has been investigated using EXAFS spectroscopy. The aggregates remain amorphous on thermal treatment of up to 700 °C (24 h treatment) but crystallize when treated at 1000 °C. This latter process is associated with the total loss of rhenium content and offers early-transition-metal oxides as products.

Structural evidence of [Rh(Thio) 6] 3+ and [Rh(Thio) 5Cl] 2+ cations in three novel ionic systems based on Co(III) dioximates

Multicomponent mixed metal ionic-type dioximates, [Со(DH) 2(Thio) 2][Rh(Thio) 6][BF 4] 4 ( 1), [Со(DH) 2(Thio) 2][Rh(Thio) 6][TiF 6] 2·H 2O ( 2) and [Со(NioxH) 2(Thio) 2] 2[Rh(Thio) 5Cl][TiF 6] 2·CH 3OH·3H 2O ( 3), where DH 2 is dimethylglyoxime, NioxH 2 is 1.2-cyclohexanedionedioxime, and Thio is thiourea, were synthesized and their structures were determined by an X-ray method. Compounds 1–3 consist of two different mononuclear coordination cations with cobalt(III) and rhodium(III) as octahedrally coordinated metal centers and fluorine-containing anions as counterions. In the studied systems, Rh(III) mostly binds Thio ligands instead of dioximes, while a typical bis-dioximate in trans geometry is formed by Co(III) with two Thio ligands placed in axial positions. A structural characterization of coordination cations [Rh(Thio) 6] 3+ and [Rh(Thio) 5Cl] 2+ is given for the first time. The interactions and arrangement of the components in crystals 1–3 are discussed.

Self-assembly of d–f coordination frameworks based on 1H-benzimidazole-5-carboxylic acid: synthesis, structure and luminescence

By the addition of different secondary ligands [acetate (OAc), Br− and oxalate (ox)], or by the absence of such ligands, four different types of heterometallic coordination compounds were obtained by reaction of 1H-benzimidazole-5-carboxylic acid (H2bic) with transition metal (d) and lanthanide (f) ions under hydrothermal conditions, namely, [TbAg3(Hbic)2(bic)2]·4H2O (1), [LnCu2(Hbic)4Br] [Ln = Er (2), Ln = Yb (3)], [EuAg2(Hbic)2(bic)(OAc)(H2O)] (4), [TbAg(Hbic)3·(ox)0.5] (5). Compounds 1, 2 and 3 stand out by having octahedrally coordinated lanthanide centers rather than the more usual 8 or 9 coordinated metal centers. Complex 1 exhibits an interesting 2D wave-like layered network constructed from infinite six-coordinated terbium carboxylate chains and Ag3(Hbic)2(bic)2 units. Isostructural compounds 2 and 3 display two-dimensional (2D) mildly ruffled sheets constructed by interconnecting μ2-Br ligands to adjacent ribbon-shaped Cu2(Hbic)4 chains. Addition of auxiliary acetate and oxalate ions led to lanthanide ions with normal coordination numbers, and Eu2(OAc)2 and Tb(ox) subunits are formed. Complex 4 is a 2D structure with a (4,4) net that is constructed by interlinking dinuclear Eu2(OAc)2 subunits with Ag2(bic)(Hbic)2(H2O) subunits. Complex 5 represents a 2D heterometallic coordination framework with an (8,3) net that is constructed by interconnection of Ag(Hbic)3 subunits and Tb(ox) subunits. The luminescence properties of 1, 4 and 5 are discussed.

Transition metal complexes of the novel hexadentate ligand 1,4-bis(di(N-methylimidazol-2-yl)methyl)phthalazine

The novel polydentate ligand 1,4-bis(di(N-methylimidazol-2-yl)methyl)phthalazine, bimptz, has been synthesized and its coordination chemistry was investigated. Bimptz is neutral and contains a central phthalazine unit, to which two di-(N-methylimidazol-2-yl)methyl groups are attached in the 1,4-positions. This ligand therefore provides up to 6 donor sites for coordination to metal ions. A series of metal complexes of bimptz was prepared and their molecular structures were determined by X-ray diffraction. Upon reaction of bimptz with two equivalents of MnCl(2)·4H(2)O, CoCl(2)·6H(2)O and [Ru(dmso)(4)Cl(2)], the dinuclear complexes [Mn(2)(bimptz)(µ-Cl)(2)Cl(2)] (1), [Co(2)(bimptz)(CH(3)OH)(2)(µ-Cl)(2)](PF(6))(2) (3) and [Ru(2)(bimptz)(dmso)(2)(µ-Cl)(2)](PF(6))(2) (4), respectively, were isolated. The latter were found to have similar solid state structures with octahedrally coordinated metal centers bridged by the phthalazine unit and two chloro ligands. The cobalt and ruthenium complexes 3 and 4 were isolated as PF(6)(-) salts and contain neutral methanol and dmso ligands, respectively, at the terminal coordination sites of the metal centres. The mononuclear ruthenium complex [Ru(Hbimptz)(2)](PF(6))(4) (6) was obtained from the reaction of two equivalents bimptz with [Ru(dmso)(4)Cl(2)]. In complex 6, three donor sites per ligand molecule are used for coordination of the Ru(ii) center. In each bimptz ligand, one of the remaining, dangling N-methylimidazole rings is protonated and forms a hydrogen bond with the unprotonated N-methylimidazole ring of the other bimptz ligand.