Variations in the copper(I)-copper(I) distances in multinuclear clusters with identical coordination geometries. Short metal-metal contacts induced by oligomerization

Factors contributing to the variations in the Cu(I)-Cu(I) distances in two clusters with identical ligand and coordination geometries have been analyzed. While the hexamer, 4, exhibits metal-metal distances in the range 2.81-3.25 Angstrom, shorter contacts are found in the corresponding tetramer, 3 (2.60-2.77 Angstrom). EHT calculations reveal relatively little attractive interactions in the corresponding Cu-4(4+) and Cu-6(6+) cores. Introduction of the ligands lowers the reduced overlap populations between the metals further. MNDO calculations with model electrophiles have been carried out to determine the bite angle requirements of the ligands. These are satisfactorily met in the structures of both 3 and 4. The key geometric feature distinguishing 3 and 4 is the Cu-S-Cu angle involving the bridging S- unit. In 4, the corresponding angles are about 90 degrees, while the values in 3 are smaller (70-73 degrees). Wider angles are computed to be energetically favored and are characterized by an open three-center bond and a long Cu-Cu distance. The bridging angles are suggested to be primarily constrained by the mode of oligomerization. Implications of these results for the stability and reactivity of these clusters and for short metal-metal distances in d(10) systems in general are discussed.

Coordination aggregation of mesoaryl substituted porphyrins

Synthesis of the free-base tetrakis (3'-nitro/aminophenyl), (H2TNP/H(2)TAP) has been accomplished and its coordination behaviour towards Mg(II), Co(II), Zn(II) and Ag(II) ions is investigated. Optical and magnetic resonance properties of the metal derivatives MTNP and MTAP reveal that the aminoporphyrins exist as aggregates in solution. The aggregation is promoted by the coordination of the peripheral amino groups to neighbouring metalloporphyrins. Possible structures of aggregated species are proposed from the model studies.

Facial Coordination in BIS[BIS(Benzimidazol-2-Ylmethyl)Amine]Copper(II) Perchlorate Dihydrate - Synthesis, Structure, Spectra and Redox Behavior

The 1:1 and 1:2 cooper(II) complexes with the tridentate compound bis(benzimidazol-2-ylmethyl)amine (L(1)) and its benzimidazole (L(2)) and amine (L(3)) N-methyl-substituted derivatives have been prepared and their spectroscopic properties studied. While the 1:1 complexes are of the type CuLX(2) nH(2)O (X = C/O-4(-), NO3-, Cl- or Br-), the 1:2 complexes are of the type CuL(2) (ClO4)(2) nH(2)O (L = L(1) or L(3), n = 0-4). In all these complexes L acts as a tridentate ligand with the amine nitrogen and both the benzimidazole nitrogens co-ordinating to Cu-II. The complex [CuL(2)(1)][ClO4](2) 2H(2)O crystallises in the monoclinic space group P2(1)/c with a = 9.828(2), b = 9.546(2) and c = 19.906(2) Angstrom and beta = 95.71(1)degrees, for Z = 2. The R value is 0.0635 for 2180 significant reflections. The copper(II) ion has an elongated octahedral geometry with four equatorial benzimidazole and two long-distance axial amine N donors. The Cu-N-bzim and Cu-N-amine distances are 2.011(4) and 2.597(6) Angstrom respectively. Factors favouring facial co-ordination to tridentate ligands are discussed. The 1:1 complexes involve meridonal co-ordination of the ligands, with square-based geometry as revealed by ligand-field and EPR spectral properties. The NMe substitution as in CuL(3)(ClO4)(2) confers low V ($) over tilde$$(max) and high E(1/2) for the cu(II)-Cu-I couple. Most of the 1:1 complexes are less reversible but exhibit E(1/2) values more positive than those of the corresponding 1:2 complexes.

Organometallic Chemistry of Diphosphazanes. 11. Reactions of fac-[Mo(CO)3(MeCN){.eta.2-Ph2PN(Pri)PPh(DMP)}] (DMP = 3,5-Dimethyl-1-Pyrazolyl) with Diphosphazanes and Diphosphinoalkanes and Oxidative Addition with Iodine

The use of fac-[Mo(CO)(3)(MeCN)(eta(2)-L(1))] (1a) {L(1) = Ph(2)PN(Pr-i)PPh(DMP)}(2) as a precursor to metalloligands and bimetallic, heterotrimetallic, and heptacoordinated complexes is reported. The reaction of 1a with diphosphazane, dppa, or a diphosphinoalkane such as dppm or dppe yields the fac-eta(1)-diphosphine substituted metalloligands, fac-[Mo(CO)(3)(eta(2)-L(1))(eta(1)-PXP)] {PXP = dppa (2), dppm (3), and dppe (4)}. These undergo isomerization to yield the corresponding mer-diphosphine complexes (5-7). Oxidation of the uncoordinated phosphorus atom of the mer-eta(1)-dppm-substituted complex eventually provides mer-[Mo(CO)(3)-(eta(2)-L(1)){eta(1)-Ph(2)PCH(2)P(O)Ph(2)}](8). The structure of the latter complex has been confirmed by single crystal X-ray diffraction {triclinic system, P ($) over bar 1; a = 11.994(3), b = 14.807(2), c = 15.855(3) Angstrom; alpha = 114.24(1), beta = 91.35(2), and gamma = 98.95(1)degrees; Z = 2, 4014 data (F-0 > 5 sigma(F-0)), R = 0.066, R(W) = 0.069}. Treatment of the dppe metalloligand 7 with [PtCl2(COD)] yields the heterotrimetallic complex cis-[PtCl2{mer-[Mo(CO)(3)(eta(2)-L(1))(eta(1)-dppe]}(2)] (9). Attempts to prepare a related trimetallic complex with the dppm-containing metalloligand were unsuccessful; only the tetracarbonyl complex cis-[Mo(CO)(4)(eta(2)-L(1))] (1b) and cis-[PtCl2(eta(2)-dppm)] were obtained. Reaction of la with dppe in the ratio 2:1 yields the mer-mer dinuclear complex [{mer-[Mo(CO)(3)(eta(2)-L(1))]}(2)(mu-dppe)] (10) bridged by dppe. Oxidation of 1a with iodine yields the Mo(II) heptacoordinated complex [MoI2(CO)(2)(eta(3)-L(1))] (11) with tridentate PPN coordination. The same Mo(II) complex 11 is also obtained by the direct oxidation of the tetracarbonyl complex cis-[Mo(CO)(4)(eta(2)-L(1))] (1b) with iodine. The structure of 11 has been confirmed by X-ray diffraction studies {monoclinic system, Cc; a = 10.471(2), b = 19.305(3), c = 17.325(3) Angstrom; beta = 95.47(2)degrees; Z = 4, 3153 data (F-0 > 5 sigma(F-0)), R = 0.049, R(W) = 0.051}. This complex exhibits an unusual capped-trigonal prismatic geometry around the metal. A similar heptacoordinated complex 12 with a chiral diphosphazane ligand {L(3) = (S,R)-P(h)2PN-(*CHMePh)*PPh(DMP)} has also been synthesized.

Coordination driven self-assembly of metallamacrocycles using ambidentate linkers and self-selection of single linkage isomer

Nicotinate-N-oxide and isonicotinate-N-oxide have been employed to synthesize four heterometallic metallamacrocycles (dppf)(2)Pd-2(nicotinate-N-oxide)(2)](OTf)(2) (1), (dppf)(2)Pt-2(nicotinate-N-oxide)(2)](OTf)(2) (2), (dppf) 2Pd2(isonicotinate-N-oxide)(2)](OTf)(2) (3) and (dppf)(2)Pt-2(isonicotinate-N-oxide)(2)](OTf)(2) (4). The complexes represent the first examples of metallamacrocycles driven by solely Pd(II)/Pt(II)-O coordination using carboxylate-N-oxide donor. All the complexes 1-4 are characterized by IR, UV-Vis, multinuclear NMR spectroscopic and ESI-MS studies. The molecular structures of the complexes 1 and 3 are unambiguously determined by single crystal X-ray diffraction analysis. Despite the possibility of formation of several linkage isomers due to ambidentate nature of the donors, exclusive formation of 2 + 2] self-assembled single isomeric metallamacrocycle in each case is interesting observation. (C) 2011 Elsevier B.V. All rights reserved.

Structural model for the Cu-B site of dopamine beta-hydroxylase: Crystal structure of a copper(II) complex showing N3OS coordination with an axial sulfur ligation

A copper(II) complex containing a NSO-donor Schiff base and NN-donor 2,2'-bipyridine has been prepared and structurally characterized. The square pyramidal complex with an axial sulfur ligation is a structural model for the CUB site of dopamine-hydroxylase in its oxidized form. The copper(II) complex is catalytically active in the oxidation of ascorbic acid by dioxygen mediated by a copper(I) species which is proposed to have a four-coordinate structure with a N3S coordination geometry.

Ternary copper(II) complexes of thiosemicarbazones and heterocyclic bases showing N3OS coordination as models for the type-2 centers of copper monooxygenases

Six ternary copper(II) complexes of general formulation [CuLB] (1-6), where L is dianionic ONS-donor thiosemicarbazones derived from the condensation of salicylaldehyde with thiosemicarbazides and B is NN-donor heterocyclic bases like 2,2'-bipyridine, 1,10-phenanthroline and 2,9-dimethyl-1,10-phenanthroline, are prepared from a reaction of copper(II) acetate hydrate with the heterocyclic base (B) and the thiosemicarbazone (H2L) in MeOH, and structurally characterized by X-ray diffraction technique. Crystal structures of the complexes display a distorted square-pyramidal (4 + 1) coordination geometry having the ONS-donor thiosemicarbazone bonded at the basal plane. The chelating heterocyclic bases exhibit axial-equatorial mode of bonding. The complexes are one-electron paramagnetic and they show axial X-band EPR spectra in DMF-toluene glass at 77 K giving g(parallel to)(A(parallel to)) and g(perpendicular to) values of similar to2.2 (175 x 10(-4) cm(-1)) and similar to2.0 indicating a {d(x2-y2)}(1) ground state. The complexes show a d-d band near 570 nm and a charge transfer band near 400 nm in DMF. The complexes are redox active and exhibit a quasireversible Cu(II)-Cu(I) couple in DMF-0.1 M tetrabutylammonium perchlorate near 0.1 V vs. SCE. They are catalytically active in the oxidation of ascorbic acid in presence of dioxygen. The complexes with a CuN3OS coordination model the ascorbate oxidation property of dopamine beta-hydroxylase and peptidylglycine a-hydroxylating monooxygeanase. (C) 2003 Elsevier Science B.V. All rights reserved.

Coordination-driven self-assembly of 2D-metallamacrocycles using a shape-selective Pt(2)(II)-organometallic 90 degrees acceptor: design, synthesis and sensing study

Synthesis of a series of two-dimensional metallamacrocycles via coordination-driven self-assembly of a shape-selective Pt(2)(II)-molecular building unit incorporating carbazole-ethynyl functionality is described. An equimolar (1 : 1) combination of a Pt(2)(II)-organometallic 90 degrees acceptor, 1, with rigid linear ditopic donors (L(a) and L(b)) afforded [4 + 4] self-assembled octanuclear molecular squares, 2 and 3, in quantitative yields, respectively [L(a) = 4,4'-bipyridine; L(b) = trans-1,2-bis(4-pyridyl)ethylene]. Conversely, a similar treatment of 1 with an amide-based unsymmetrical flexible ditopic donor, L(c), resulted in the formation of a [2 + 2] self-sorted molecular rhomboid (4a) as a single product [L(c) = N-(4-pyridyl)isonicotinamide]. Despite the possibility of several linkage isomeric macrocycles (rhomboid, triangle and square) due to the different connectivity of L(c), the formation of a single and symmetrical molecular rhomboid (4a) as the only product is an interesting observation. All the self-assembled macrocycles (2, 3 and 4a) were fully characterized by multinuclear NMR ((1)H and (31)P) and ESI-MS analysis. Further structural insights about the size and shape of the macrocycles were obtained through energy minimization using density functional theory (DFT) calculations. Decoration of the starting carbazole building unit with Pt-ethynyl functionality enriches the assemblies to be more p-electron rich and luminescent in nature. Macrocycles 2 and 3 could sense the presence of electron deficient nitroaromatics in solution by quenching of the initial intensity upon gradual addition of picric acid (PA). They exhibited the largest quenching response with high selectivity for nitroaromatics compared to several other electron deficient aromatics tested.

Self-assembly of Ru-4 and Ru-8 assemblies by coordination using organometallic Ru(II)(2) precursors: Synthesis, characterization and properties

Coordination-driven self-assembly of binuclear half-sandwich p-cymene ruthenium(II) complexes [Ru-2(mu-eta(4)-C2O4)(MeOH)(2)(eta(6)-p-cymene)(2)](O3SCF3)(2) (1a) or [Ru-2(mu-eta(4)-N,N'-diphenyloxamidato)(MeOH)(2)(eta(6)-p-cymene)(2)]( O3SCF3)(2) (1b) separately with an imidazole-based tetratopic donor L in methanol affords two tetranuclear metallamacrocycles 2a and 2b, respectively. Conversely, the similar combination of L with 2,5-dihydroxy-1,4-benzoquinonato (dhbq) bridged binuclear complex [Ru-2(mu-eta(C6H2O4)-C-4)(MeOH)(2)(eta(6)-p-cymene)(2)](O3SCF3)(2) (1c) in 1:2 molar ratio resulted in an octanuclear macrocyclic cage 2c. All the self-assembled macrocycles 2a-2c were isolated as their triflate salts in high yields and were characterized fully by multinuclear (H-1, C-13 and F-19) NMR, infrared (IR) and electrospray ionization mass spectrometry (ESIMS). In addition, the molecular structure of macrocycle 2a was established unequivocally by single-crystal X-ray diffraction analysis and adopts a tetranuclear rectangular geometry with the dimensions of 5.53 angstrom x 12.39 angstrom. Furthermore, the photo-and electrochemical properties of these newly synthesized assemblies have been studied by using UV-vis absorption and cyclic voltammetry analysis.

Three-Component Self-Assembly of a Series of Triply Interlocked Pd12 Coordination Prisms and Their Non-Interlocked Pd6 Analogues

Template-assisted formation of multicomponent Pd6 coordination prisms and formation of their self-templated triply interlocked Pd12 analogues in the absence of an external template have been established in a single step through Pd?N/Pd?O coordination. Treatment of cis-[Pd(en)(NO3)2] with K3tma and linear pillar 4,4'-bpy (en=ethylenediamine, H3tma=benzene-1,3,5-tricarboxylic acid, 4,4'-bpy=4,4'-bipyridine) gave intercalated coordination cage [{Pd(en)}6(bpy)3(tma)2]2[NO3]12 (1) exclusively, whereas the same reaction in the presence of H3tma as an aromatic guest gave a H3tma-encapsulating non-interlocked discrete Pd6 molecular prism [{Pd(en)}6(bpy)3(tma)2(H3tma)2][NO3]6 (2). Though the same reaction using cis-[Pd(NO3)2(pn)] (pn=propane-1,2-diamine) instead of cis-[Pd(en)(NO3)2] gave triply interlocked coordination cage [{Pd(pn)}6(bpy)3(tma)2]2[NO3]12 (3) along with non-interlocked Pd6 analogue [{Pd(pn)}6(bpy)3(tma)2](NO3)6 (3'), and the presence of H3tma as a guest gave H3tma-encapsulating molecular prism [{Pd(pn)}6(bpy)3(tma)2(H3tma)2][NO3]6 (4) exclusively. In solution, the amount of 3' decreases as the temperature is decreased, and in the solid state 3 is the sole product. Notably, an analogous reaction using the relatively short pillar pz (pz=pyrazine) instead of 4,4'-bpy gave triply interlocked coordination cage [{Pd(pn)}6(pz)3(tma)2]2[NO3]12 (5) as the single product. Interestingly, the same reaction using slightly more bulky cis-[Pd(NO3)2(tmen)] (tmen=N,N,N',N'-tetramethylethylene diamine) instead of cis-[Pd(NO3)2(pn)] gave non-interlocked [{Pd(tmen)}6(pz)3(tma)2][NO3]6 (6) exclusively. Complexes 1, 3, and 5 represent the first examples of template-free triply interlocked molecular prisms obtained through multicomponent self-assembly. Formation of the complexes was supported by IR and multinuclear NMR (1H and 13C) spectroscopy. Formation of guest-encapsulating complexes (2 and 4) was confirmed by 2D DOSY and ROESY NMR spectroscopic analyses, whereas for complexes 1, 3, 5, and 6 single-crystal X-ray diffraction techniques unambiguously confirmed their formation. The gross geometries of H3tma-encapsulating complexes 2 and 4 were obtained by universal force field (UFF) simulations.

Coordination-Driven Self-Assembly of 2D-Metallamacrocycles Using a New Carbazole-Based Dipyridyl Donor: Synthesis, Characterization, and C-60 Binding Study

A new carbazole-based 90 degrees dipyridyl donor 3,6-di(4-pyridylethynyl)carbazole (L) containing carbazole-ethynyl functionality is synthesized in reasonable yield using the Sonagashira coupling reaction. Multinuclear NMR, electrospray ionization-mass spectrometry (ESI-MS), including single crystal X-ray diffraction analysis characterized this 90 degrees building unit. The stoichiometry combination of L with several Pd(II)/Pt(II)-based 90 degrees acceptors (1a-1d) yielded 2 + 2] self-assembled metallacycles (2a-2d) under mild conditions in quantitative yields 1a = cis-(dppf)Pd(OTf)(2); 1b = cis-(dppf)Pt(OTf)(2); 1c = cis-(tmen)Pd(NO3)(2); 1d = 3,6-bis{trans-Pt(C C) (PEt3)(2)(NO3))carbazole]. All these macrocycles were characterized by various spectroscopic techniques, and the molecular structure of 2a was unambiguously determined by single crystal X-ray diffraction analysis. Incorporation of ethynyl functionality to the carbazole backbone causes the resulted macrocycles (2a-2d) to be pi-electron rich and thereby exhibit strong emission characteristics. The macrocycle 2a has a large internal concave aromatic surface. The fluorescence quenching study suggests that 2a forms a similar to 1:1 complex with C-60 with a high association constant of K-sv = 1.0 X 10(5) M-1.

Highly luminescent and thermally stable lanthanide coordination polymers designed from 4-(dipyridin-2-yl)aminobenzoate: efficient energy transfer from Tb3+ to Eu3+ in a mixed lanthanide coordination compound

Herein, a new aromatic carboxylate ligand, namely, 4-(dipyridin-2-yl)aminobenzoic acid (HL), has been designed and employed for the construction of a series of lanthanide complexes (Eu3+ = 1, Tb3+ = 2, and Gd3+ = 3). Complexes of 1 and 2 were structurally authenticated by single-crystal X-ray diffraction and were found to exist as infinite 1D coordination polymers with the general formulas {Eu(L)(3)(H2O)(2)]}(n) (1) and {Tb(L)(3)(H2O)]center dot(H2O)}(n) (2). Both compounds crystallize in monoclinic space group C2/c. The photophysical properties demonstrated that the developed 4-(dipyridin-2-yl)aminobenzoate ligand is well suited for the sensitization of Tb3+ emission (Phi(overall) = 64%) thanks to the favorable position of the triplet state ((3)pi pi*) of the ligand the energy difference between the triplet state of the ligand and the excited state of Tb3+ (Delta E) = (3)pi pi* - D-5(4) = 3197 cm(-1)], as investigated in the Gd3+ complex. On the other hand, the corresponding Eu3+ complex shows weak luminescence efficiency (Phi(overall) = 7%) due to poor matching of the triplet state of the ligand with that of the emissive excited states of the metal ion (Delta E = (3)pi pi* - D-5(0) = 6447 cm(-1)). Furthermore, in the present work, a mixed lanthanide system featuring Eu3+ and Tb3+ ions with the general formula {Eu0.5Tb0.5(L)(3)(H2O)(2)]}(n) (4) was also synthesized, and the luminescent properties were evaluated and compared with those of the analogous single-lanthanide-ion systems (1 and 2). The lifetime measurements for 4 strongly support the premise that efficient energy transfer occurs between Tb3+ and Eu3+ in a mixed lanthanide system (eta = 86%).

Solid State and Solution Mediated Multistep Sequential Transformations in Metal-Organic Coordination Networks

Sequential transformation in a family of metal-organic framework compounds has been investigated employing both a solid-state as well as a solution mediated route. The compounds, cobalt oxy-bis(benzoate) and manganese oxybis(benzoate) having a two-dimensional structure, were reacted with bipyridine forming cobalt oxy-bis(benzoate)-4,4'-bipyridine and manganese oxy-bis(benzoate)-4,4'-bipyridine, respectively. The bipyridine containing compounds appear to form sequentially through stable intermediates. For the cobalt system, the transformation from a two-dimensional compound, Co(H2O)(2)(OBA)] (OBA = 4,4'-oxy-bis(benzoate)), I, to two different three-dimensional compounds, Co(bpy)(OBA)]center dot bpy, II, (bpy = 4,4'-bipyridine) and Co(bpy)(0.5)(OBA)], III, and reversibility between II and III have been investigated. In the manganese system, transformation from a two-dimensional compound, Mn(H2O)(2)(OBA)], Ia, to two different three-dimensional compounds, Mn (bpy)(OBA)]center dot bpy, Ha and Ha to Mn(bpy)(0.5)(OBA)], Ilia, has been investigated. It has also been possible to identify intermediate products during these transformation reactions. The possible pathways for the formation of the compounds were postulated.

Coordination self-assembly of tetranuclear Pt(II) macrocycles with an organometallic backbone for sensing of acyclic dicarboxylic acids

Coordination self-assembly of a series of tetranuclear Pt(II) macrocycles containing an organometallic backbone incorporating ethynyl functionality is presented. The 1 : 1 combination of a linear acceptor 1,4-bistrans-Pt(PEt3)(2)(NO3)(ethynyl)]benzene (1) with three different dipyridyl donor `clips' (L-a-L-c) afforded three 2 + 2] self-assembled Pt-4(II) macrocycles (2a-2c) in quantitative yields, respectively L-a = 1,3-bis-(3-pyridyl)isothalamide; L-b = 1,3-bis(3-pyridyl)ethynylbenzene; L-c = 1,8-bis(4-pyridyl)ethynylanthracene]. These macrocycles were characterized by multinuclear NMR (H-1 and P-31); ESI-MS spectroscopy and the molecular structures of 2a and 2b were established by single crystal X-ray diffraction analysis. These macrocycles (2a-2c) are fluorescent in nature. The amide functionalized macrocycle 2a is used as a receptor to check the binding affinity of aliphatic acyclic dicarboxylic acids. Such binding affinity is examined using fluorescence and UV-Vis spectroscopic methods. A solution state fluorescence study showed that macrocycle 2a selectively binds (K-SV = 1.4 x 10(4) M-1) maleic acid by subsequent enhancement in emission intensity. Other aliphatic dicarboxylic acids such as fumaric, succinic, adipic, mesaconic and itaconic acids caused no change in the emission spectra; thereby demonstrating its potential use as a macrocyclic receptor in distinction of maleic acid from other aliphatic dicarboxylic acids.