Monodentate Ancillary Ligands Research Articles

Antiprotozoal Pt(II) Complexes as Luminophores Bearing Monodentate P/As/Sb-Based Donors: An X-ray Diffractometric, Photoluminescence, and 121Sb-Mössbauer Spectroscopic Study with TD-DFT-Guided Interpretation and Predictive Extrapolation toward Bi.

In this study, it is demonstrated that the radiative rate constant of phosphorescent metal complexes can be substantially enhanced using monodentate ancillary ligands containing heavy donor atoms. Thus, the chlorido coligand from a Pt(II) complex bearing a monoanionic tridentate C^N*N luminophore ([PtLCl]) was replaced by triphenylphosphane (PPh3) and its heavier pnictogen congeners (i.e., PnPh3 to yield [PtL(PnPh3)]). Due to the high tridentate-ligand-centered character of the excited states, the P-related radiative rate is rather low while showing a significant boost upon replacement of the P donor by heavier As- and Sb-based units. The syntheses of the three complexes containing PPh3, AsPh3, and SbPh3 were completed by unambiguous characterization of the clean products using exact mass spectrometry, X-ray diffractometry, bidimensional NMR, and 121Sb-Mössbauer spectroscopy (for [PtL(SbPh3)]) as well as steady state and time-resolved photoluminescence spectroscopies. Hence, it was shown that the hybridization defects of the Vth main-group atoms can be overcome by complexation with the Pt center. Notably, the enhancement of the radiative rate constants mediated by heavier coligands was achieved without significantly influencing the character of the excited states. A rationalization of the results was achieved by TD-DFT. Even though the Bi-based homologue was not accessible due to phenylation side reactions, the experimental data allowed a reasonable extrapolation of the structural features whereas the hybridization defects and the excited state properties related to the Bi-species and its phosphorescence rate can be predicted by theory. The three complexes showed an interesting antiprotozoal activity, which was unexpectedly notorious for the P-containing complex. This work could pave the road toward new efficient materials for optoelectronics and novel antiparasitic drugs.

Luminescent Platinum(II) Complexes with Terdentate N∧C∧C Ligands.

The synthesis, structure, and luminescence of Pt(II) complexes of the type [Pt(N∧C∧C)(L)] are reported, where N∧C∧C is a terdentate ligand resulting from the cycloplatination of 2-(3,5-diphenoxyphenyl)pyridine or 2-(4,4″-dimethyl-[1,1':3',1″-terphenyl]-5'-yl)pyridine, and L represents a monodentate ancillary ligand, which can be γ-picoline, 4-pyridinecarboxaldehyde, PPh3, n-butyl or 2,6-dimethylphenyl isocyanide, CO, or the N-heterocyclic carbenes 1-butyl-3-methylimidazol-2-ylidene or 4-butyl-3-methyl-1-phenyl-1H-1,2,3-triazol-5-ylidene. Derivatives bearing CO, isocyanides, or carbenes showed the highest stabilities in solution, whereas the pyridine and PPh3 derivatives establish ligand-exchange equilibria in acetonitrile. Different supramolecular structures are observed in the solid state, which largely depend on the nature of the ancillary ligand. Isocyanides and CO favor π interactions between the aromatic rings, metallophilic Pt···Pt contacts, or a combination of both. In contrast, pyridine ligands may lead to bimolecular assemblies driven by C-H···O, C-H···Pt, or C-H/π hydrogen bonds. Luminescence was examined in fluid solution, poly(methyl methacrylate) matrices, and the solid state at 298 K, and in 2-methyltetrahydrofuran glasses at 77 K. The majority of derivatives show highly efficient emissions from 3ILCT/MLCT or 3ILCT/MLCT/LLCT excited states of monomeric species. The formation of excimers and different types of emissive aggregates are demonstrated, which lead to red-shifted emissions of different origins and characteristics depending on the involved noncovalent interactions.

Site-specific covalent metalation of DNA oligonucleotides with phosphorescent platinum(ii) complexes.

Phosphorescent Pt(II) complexes, composed of a tridentate N^N^C donor ligand and a monodentate ancillary ligand, were covalently attached to DNA oligonucleotides. Three modes of attachment were investigated: positioning the tridentate ligand as an artificial nucleobase via a 2'-deoxyribose or a propane-1,2-diol moiety and orienting it towards the major groove by appending it to a uridine C5 position. The photophysical properties of the complexes depend on the mode of attachment and on the identity of the monodentate ligand (iodido vs. cyanido ligand). Significant duplex stabilization was observed for all cyanido complexes when they are attached to the DNA backbone. The luminescence strongly depends on whether a single or two adjacent complexes are introduced, with the latter showing an additional emission band indicative of excimer formation. The doubly platinated oligonucleotides could be useful as ratiometric or lifetime-based oxygen sensors, as the green photoluminescence intensities and average lifetimes of the monomeric species are drastically boosted upon deoxygenation, whereas the red-shifted excimer phosphorescence is nearly insensitive to the presence of triplet dioxygen in solution.

Comparative Coordination Chemistry of PNP and SNS Pincer Ruthenium Complexes

Ruthenium carbonyl complexes supported by PNP pincer ligands are prominent catalysts for a range of hydrogenation and dehydrogenation reactions. Recently, Ru complexes with cheaper, more air stable SNS pincer ligands have emerged as attractive alternatives for the development of improved catalysts. However, there is currently a paucity of information on how the replacement of the phosphine donors in PNP ligands with the sulfur donors in SNS ligands influences the synthesis, structure, and electronic properties of the resulting metal complexes. Herein, the coordination chemistry of a series of Ru carbonyl complexes with SNS pincer ligands has been systematically compared with related PNP-ligated species. Three different SNS pincer ligands were explored including a pyridyl based NC5H3{CH2(StBu)}2 ligand and two aliphatic ligands, HN{CH2CH2(StBu)}2 and NCH3{CH2CH2(StBu)}2, along with different combinations of monodentate ancillary ligands. The geometric structures of the SNS and PNP Ru complexes were studied using NMR spectroscopy and X-ray crystallography. Additionally, the redox properties and electronic structures of these complexes were probed through a combination of cyclic voltammetry and DFT calculations. Overall, differences between SNS and PNP complexes extend well beyond simply modulating inductive donation to the metal and include changes in synthetic outcomes, as well as variations in geometry that impact redox behavior. Our study reveals fundamental information about the coordination chemistry of the SNS ligand, which may aid in interpreting catalytic results.

Compensation of Hybridization Defects in Phosphorescent Complexes with Pnictogen-Based Ligands-A Structural, Photophysical, and Theoretical Case-Study with Predictive Character.

In this work, for the first time, the comparative use of P-, As-, and Sb-based ligands in phosphorescent coordination compounds is reported toward new coordination chemical concepts in the design and realization of tailored triplet emitters with nonconventional elements. By means of spectroscopic, X-ray diffractometric, and quantum-chemical methods, we reconstructed the nature of the chemical bonds as well as the influence of the increasingly heavy elements on the photoexcited state properties, which were correlated with the hybridization and polarizability of the pnictogen atoms (Pn). In particular, we elucidated the structural and photophysical properties of a series of homologous Pt(II) complexes with monodentate ancillary ligands based on group 15 elements, namely P, As, and Sb. Six coordination compounds bearing tridentate dianionic 2,6-bis(1H-1,2,4-triazol-5-yl)pyridine luminophoric pincer ligands bearing either CF3 or tBu moieties on the triazole rings along with triphenylpnictogens (PnPh3) as monodentate ancillary ligands ([CF3/Pn] or [tBu/Pn], respectively) have been investigated. The electron donating or withdrawing effect of the peripheral substituent (tBu vs. CF3, respectively) and its influence on the bonding, crystal packing as well as the excited state energies and lifetimes was assessed in fluid solutions, frozen glassy matrices, amorphous solids, and crystalline phases. A progressively red-shifted phosphorescence was observed with increasing atomic number along with a growing compensation of hybridization defects upon coordination of the Pn atom to the Pt(II) center. The change of molecular geometry of the PnPh3 unit upon complexation was extrapolated to predict the structural and excited state characteristics of the Bi-based analogues, which according to DFT calculations should be stable species and are the subject of ongoing synthetic efforts. In general, we envisage the use of these ligands for the relativistic enhancement of radiative deactivation rate processes, especially if Bi-based s-orbitals participate on the bond with the metal center, paving the road toward novel coordination compounds using abundant elements with high spin-orbit coupling for sustainable electroluminescent devices.

Synthesis and investigation of enhanced luminescence of Ln(III)-complexes containing fluorinated β-diketone and oxygen donor ancillary ligands for efficient advanced displays

2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedione (fod) fluorinated β-diketone had been used to prepare a series of Ln3+ (Eu or Tb) ternary complexes with monodentate ancillary ligands such as aqua, urea, triphenylphosphineoxide (TPPO) and pyridine-N-oxide (PNO). Prepared ternary materials Eu(fod)3.(aqua)2 (1), Tb(fod)3.(aqua)2 (2), Eu(fod)3.(urea)2 (3), Tb(fod)3.(urea)2 (4), Eu(fod)3.(TPPO)2 (5), Tb(fod)3.(TPPO)2 (6), Eu(fod)3.(PNO)2 (7), Tb(fod)3.(PNO)2 (8) were illustrated through various structural and photo-physical spectroscopic practices. Emission measurement showed characteristics strong emission in red aa well as green spectral region accredited to the electric dipole 5D0→7F2 and 5D4→7F5 hypersensitive transitions of Eu3+ and Tb3+ ions respectively. An inclusive comparative investigation of enhancement features in the luminescence intensity had been carried out to determine the role of ancillary ligands. Improved luminosity was achieved as auxiliary ligands not only substituted the solvent molecules in coordination sphere but also indirectly sensitize metal ion through transfer of energy to emissive level of respective Ln3+ ion from triplet state of ligand. Decay curve specified uniformity in chemical environment around central metal ion. Efficient red and green light materials could be successfully used for fabricating OLEDs.

Intense red luminescent materials of ternary Eu3+ complexes of oxide ligands for electroluminescent display devices

Solid ternary compounds of Eu(III) with fluorinated β-diketone (4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)-1,3-hexanedione) (Hfth) and heteroaromatic monodentate ancillary ligands (aqua/triphenylphosphineoxide/pyridine-N-oxide/2-pyridionl-N-Oxide) were prepared for red color emissive materials. The luminescence characteristics of prepared compounds were illustrated using absorption and emission spectral measurements which specified that the β-diketone ligand could effectively sensitized the central europium ion meant for the improved emission of the light. Due to interaction metal complexes displays distinguished effectual on photoluminescence efficacy (η) as well as Judd Ofelt luminous factor (Ω2). An extensive relative approach of enhancement in luminescent behavior of the synthesized metal complexes had been carried out by replacing aqua ligand in the inner coordination sphere of conventionally prepared parent aqua complex with others ancillary oxide ligands to make metal complex co-coordinatively saturated as well as suitable for fabricating electroluminescent display devices.

Highly efficient blue-emitting of bis-cyclometalated tetravalent platinum (IV) complexes: A theoretical study

Pt(IV) complexes bespeak the prospect as phosphorescent materials because of their excellent properties, whereas the reports of excavating potential properties for Pt(IV) complexes in phosphorescence are limited. To address this issue, a DFT/TDDFT calculation has been applied on two series of biscyclometalated Pt(IV) complexes ([Pt(ppy)2XCl], where X = -CH3(1-Me); -CF3(1a-CF3); -CN(1a-CN), -(CH3)3 (1b-tBu); -CH2NH2(1b-AMe); -C6H5(2-Ph); -C6F5(2a-C6F5) and -2,4,6-(CH3)3C6H5 (2b-Mes)) to shed light on the effects of systematic single monodentate ancillary ligand modifications on structure and photophysical properties. The calculated results confirm that all complexes displayed blue emission in dichloromethane solution with varying emission efficiencies that were found to be influenced by the electronic nature of the ancillary ligand. The stronger the electron-releasing ability and the smaller degree of extended conjugation in the monodentate ancillary ligand can give rise to intensive the radiative decay. Regardless of whether π conjugation exists or not, increasing electron-withdrawing character in ancillary ligand of parent complexes 1-Me ([Pt(ppy)2CH3Cl]) or 2-Ph ([Pt(ppy)2C6H5Cl]) can be unbeneficial for the nonradiative decay process. In addition, the results demonstrate that complexes 1a-CN ([Pt(ppy)2CNCl]) exhibits a better blue phosphorescent material with a higher quantum yield.So far, there has been no theoretical study that systematically focuses on biscyclometalated Pt(IV) complexes. Our research provides a strong impetus to further optimize the phosphorescence efficiencies based on Pt(IV) complexes.

Influence of the monodentate ancillary ligand on the photophysical properties of Pt(II) complexes bearing a symmetric dianionic tridentate luminophore

Abstract Herein we present a study of the influence of the ancillary ligand on the photophysical properties of Pt(II) complexes with a symmetric tridentate luminophore. Starting from a previously used bulky triphenylphosphane (PPh3) as the monodentate ancillary ligand, progressively smaller ancillary ligands were introduced, namely a PPh2Me and a PPhMe2 and finally compared with a planar 4-amylpyridine. We observed that the emission wavelength of the monomer was not influenced by the monodentate ligand, and that excimer formation only occurs for the fully planar complex. Surprisingly, intermolecular deactivation pathways can be largely suppressed even with the smallest phosphane. This knowledge is important for the design and realization of triplet emitters for optoelectronic devices.

Correlating the Structural and Photo­physical Features of Pincer Luminophores and Monodentate Ancillary Ligands in PtII Phosphors

AbstractInvited for the cover of this issue are Prof. Luisa De Cola and Priv.‐Doz. Cristian A. Strassert from the Westfälische Wilhelms‐Universität Münster, Germany. The cover image shows a series of bright PtII complexes with improved excited state properties.

Correlating the Structural and Photo­physical Features of Pincer Luminophores and Monodentate Ancillary Ligands in PtII Phosphors (Eur. J. Inorg. Chem. 36/2015)

Correlating the Structural and Photo­physical Features of Pincer Luminophores and Monodentate Ancillary Ligands in Pt^II Phosphors (Eur. J. Inorg. Chem. 36/2015)

Correlating the Structural and Photo­physical Features of Pincer Luminophores and Monodentate Ancillary Ligands in PtII Phosphors

AbstractPhosphorescent PtII complexes featuring pincer luminophores of 2,6‐bis(1,2,4‐triazolyl)pyridine (H2L1) and 2,6‐bis(pyrazolyl)pyridine (H2L3) with a bulky adamantyl or tolyl substituent (H2L4) are systematically compared, and their structural features are correlated with their photophysical properties. The combination with 4‐amylpyridine (Py), triphenylphosphine (P) or benzimidazol‐2‐ylidene (N‐heterocyclic carbene, NHC) donors as monodentate ancillary ligands gave a series of highly luminescent triplet emitters with variable aggregation properties. The molecular structures of four of these complexes, namely, Pt‐L1‐P, Pt‐L1‐NHC, Pt‐L3‐P, and Pt‐L4‐P were garnered from single‐crystal X‐ray diffraction analysis. The coordination complexes displayed green phosphorescence in solution and in the solid state. In doped poly(methyl methacrylate) (PMMA) matrices, most of the complexes exhibited high phosphorescence quantum yields, which reached 59 % for Pt‐L3‐P. A comparative analysis between the spectroscopic data and the computed parameters derived from time‐dependent density functional theory (TD‐DFT) calculations suggests that the emission originates from metal‐perturbed ligand‐centered excited triplet states (3MP‐LC). The radiationless deactivation rate constants of the emissive states can be correlated with the aggregation properties derived from the substitution pattern at the tridentate luminophores and the ancillary ligands, whereas the radiative rate constants are determined by the electronic structures of the complexes. We found that PtII complexes containing pyrazolate donors showed an enhanced charge‐transfer character in the excited state, whereas bulky adamantyl moieties and triphenylphosphine ancillary ligands suppress bimolecular aggregation and quenching phenomena.

Preparation and first biological evaluation of novel Re-188/Tc-99m peptide conjugates with substance-P

IntroductionNew 188Re and 99mTc peptide conjugates with substance- P (SP) were prepared and biologically evaluated. The radiopharmaceuticals have been labelled with the [M≡N]2+ (M=99mTc, 188Re) core using a combination of π-donor tridentate and π-acceptor monodentate ancillary ligands. MethodsThe new radiopharmaceuticals have been prepared through a two-step reaction by simultaneous addition of the tridentate and monodentate ligands to a vial containing a preformed [M≡N]2+ core. The tridentate ligand was formed by linking two cysteine residues to the terminal arginine of the undecapeptide SP, whereas the monodentate ligand was a tertiary phosphine. The preparation of the corresponding Re-188 derivative required developing a more complex chemical procedure to obtain the [Re≡N]2+ core in satisfactory yields. Characterization of the resulting products was obtained by chromatographic methods. Biological evaluation was performed for both Tc-99m and Re-188 derivatives by in-vitro studies on isolated cells expressing NK1-receptors. In-vivo imaging in mice was carried out using a small-animal YAP(S)PET tomograph. ConclusionNew Tc-99m and Re-188 peptide radiopharmaceuticals with SP have been prepared in high-yield and with high-specific activity. Both Tc-99m and Re-188 peptide radioconjugates exhibit high affinity for NK1 receptors, thus giving further evidence to the empirical rule that structurally related Tc-99m and Re-188 radiopharmaceuticals exhibit identical biological properties.

Synthesis, Characterisation, Interaction with DNA, Cytotoxicity, and Apoptotic Studies of Ruthenium(II) Polypyridyl Complexes

We report the synthesis and characterisation of two new ruthenium(ii) polypyridyl complexes containing monodentate ancillary ligands [Ru(L)4(4HEPIP)], where L = 4-aminopyridine (1) or pyridine (2) and 4HEPIP = 2-(4-hydroxy-3-ethoxyphenyl)-1H-imidazo[4,5-f][1,10](phenanthroline). These complexes were characterised by elemental analysis and ultraviolet-visible, infrared, and 1H NMR spectroscopy. The binding properties of the two complexes towards calf thymus (CT)-DNA were investigated with different spectrophotometric methods, viscosity measurements, and salt dependent studies. Experimental results indicated that the complexes interact with CT-DNA base pairs by intercalation. Upon irradiation at 365 nm, these complexes efficiently cleave pBR322 DNA from super coiled form I to nicked form II. Their cytotoxicity on different cancer cell lines such as A549, Du145, and HeLa was investigated. The IC50 values are 39.5, 28.3, and 27.3 μM for complex 1, and 55, 67.9, and 47.9 μM for complex 2 respectively. Cellular uptake and apoptosis induced by these complexes was also studied.

A Highly Efficient Titanium Catalyst for the Synthesis of Ultrahigh‐Molecular‐Weight Polyethylene (UHMWPE)

Long chain running: The polymerization performance of guanidinato titanium(IV) olefin catalysts is tuned by monodentate ancillary ligands. Polymerization activities of up to 8800 kgPE molcat.−1 h−1 bar−1 together with molecular weights of 2500 kg mol−1 were observed (see figure; d-MAO=dry methylalumoxane). Ligand transfer of the additional donor ligands has to be avoided.

Characterization of Low Energy Charge Transfer Transitions in (terpyridine)(bipyridine)Ruthenium(II) Complexes and their Cyanide-Bridged Bi- and Tri-Metallic Analogues

The lowest energy metal-to-ligand charge transfer (MLCT) absorption bands found in ambient solutions of a series of [Ru(tpy)(bpy)X](m+) complexes (tpy = 2,2':3',2''-terpyridine; bpy = 2,2'-bipyridine; and X = a monodentate ancillary ligand) feature one or two partly resolved weak absorptions (bands I and/or II) on the low energy side of their absorption envelopes. Similar features are found for the related cyanide-bridged bi- and trimetallic complexes. However, the weak absorption band I of [(bpy)(2)Ru{CNRu(tpy)(bpy)}(2)](4+) is missing in its [(bpy)(2)Ru{NCRu(tpy)(bpy)}(2)](4+) linkage isomer demonstrating that this feature arises from a Ru(II)/tpy MLCT absorption. The energies of the MLCT band I components of the [Ru(tpy)(bpy)X](m+) complexes are proportional to the differences between the potentials for the first oxidation and the first reduction waves of the complexes. Time-dependent density functional theory (TD-DFT) computational modeling indicates that these band I components correspond to the highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) transition, with the HOMO being largely ruthenium-centered and the LUMO largely tpy-centered. The most intense contribution to a lowest energy MLCT absorption envelope (band III) of these complexes corresponds to the convolution of several orbitally different components, and its absorption maximum has an energy that is about 5000 cm(-1) higher than that of band I. The multimetallic complexes that contain Ru(II) centers linked by cyanide have mixed valence excited states in which more than 10% of electronic density is delocalized between the nearest neighbor ruthenium centers, and the corresponding stabilization energy contributions in the excited states are indistinguishable from those of the corresponding ground states. Single crystal X-ray structures and computational modeling indicate that the Ru-(C≡N)-Ru linkage is quite flexible and that there is not an appreciable variation in electronic structure or energy among the conformational isomers.

Facile Synthesis and Characterization of Phosphorescent Pt(N∧C∧N)X Complexes

In order to investigate the ground state and excited state properties of Pt(N(∧)C(∧)N)X, we have prepared a series of Pt complexes, where N(∧)C(∧)N aromatic chelates are derivatives of m-di(2-pyridinyl)benzene (dpb) and X are monoanionic and monodentate ancillary ligands including halide and phenoxide. Facile synthesis of platinum m-di(2-pyridinyl)benzene chloride and its derivatives, using controlled microwave heating, was reported. This method not only shortened the reaction time but also improved the reaction yield for most of the Pt complexes. Two Pt(N(∧)C(∧)N)X complexes have been structurally characterized by X-ray crystallography. The change of functional group does not affect the structure of the core Pt(N(∧)C(∧)N)Cl fragment. Both molecules pack as head-to-tail dimers, each molecule of the dimer related to the other by a center of inversion. The electrochemical studies of all Pt complexes demonstrate that the oxidation process occurs on the metal-phenyl fragment and the reduction process is associated with the electron accepting groups like pyridinyl groups and their derivatives. The maximum emission wavelength of the Pt(N(∧)C(∧)N)X complexes ranges between 471 and 610 nm, crossing the spectrum of visible light. Most of the Pt complexes are strongly luminescent (Φ = 0.32-0.63) and have short luminescence lifetimes (τ = 4-7 μs) at room temperature. The lowest excited state of the Pt(N(∧)C(∧)N)X complexes is identified as a dominant ligand-centered (3)π-π* state with some (1)MLCT/(3)MLCT character, which appears to have a larger (1)MLCT component than their bidentate and tridentate analogs. This results in a high radiative decay rate and high quantum yield for Pt(dpb)Cl and its analogs. However, the excited state properties of the Pt(N(∧)C(∧)N)X complexes are strongly dependent on the nature of the electron-accepting groups and substituents to the metal-phenyl fragment. A rational design will be needed to tune the emission energies of the Pt(N(∧)C(∧)N)X complexes over a wide range while maintaining their high luminescent efficiency.

Controlling the dimensionalities and structures of homochiral Zn(ii) and Cd(ii) compounds of N-(p-tosyl)-S-carboxymethyl-l-cysteinevia tuning the connecting modes of metal ions and chiral linkers by different kinds of ancillary ligands

A new ligand of N-(p-tosyl)-S-carboxymethyl-L-cysteine (Ts-cmc) was prepared. The reactions of Ts-cmc with Zn(II) or Cd(II) salts in the absence or presence of ancillary ligands provided five homochiral coordination polymers [Cd(Ts-cmc)]n (1), [Cd(Ts-cmc)(4,4′-bipy)(H2O)]n (2), [Zn2(Ts-cmc)2(4,4′-bipy)2(H2O)2]n (3), [Cd(Ts-cmc)(Im)(H2O)]n (4) and [Zn(Ts-cmc)(Im)(H2O)]n (5) and one discrete dinuclear compound [Zn2(Ts-cmc)2(2,2′-bipy)2(H2O)2]·2H2O (6) (4,4′-bipy = 4,4′-bipyridine, Im = imidazole and 2,2′-bipy = 2,2′-bipyridine). Complexes 1–4 crystallize in a chiral space groupP21, but 5 and 6 in chiral space groupsP212121 and C2, respectively. The interaction of 5-connected Cd(II) ions and Ts-cmc ligands of 1 without the help of any ancillary ligands led to the construction of a 2D network with 1D helices. With the aid of the bridging ancillary ligand of 4,4′-bipy another kind of 2D homochiral network was established for 2 and 3 with 4-connected metal ions and 2-connected Ts-cmc ligands. However the introduction of a monodentate ancillary ligand of imidazole into the reaction system gave a 1D double-chain made from 3-connected Cd(II) ions and Ts-cmc ligands for 4 and a 1D helix constructed from 2-connected metal ions and Ts-cmc ligands for 5. Furthermore, the chelating ancillary ligand of 2,2′-bipy resulted in the formation of a chiral discrete dinuclear structure (6) with 2-connected metal ions and Ts-cmc ligands. It was revealed that the introduction of bridging, monodentate or chelating ancillary ligands into the reaction system leads to the change of connecting modes for metal ions and Ts-cmc linkers from 5- to 2-connected modes reaching the goal of controlling the growth of dimensionalities and structures of homochiral metal-frameworks. An investigation of the fluorescence of the Cd(II) compounds as well as the free ligands indicates the emission bands of the Cd(II) compounds are due to the intraligand transmission.

Homonuclear and heteronuclear complexes of a four-armed octadentate ligand: synthetic control based on matching ligand denticity with metal ion coordination preferences

The octadentate ligand 1,2,4,5-tetrakis-[3-(2-pyridyl)pyrazol-1-yl]benzene (L), with four bidentate arms radiating from a central phenyl ring, combines with 6-coordinate and 4-coordinate metal ions (as their tetrafluoroborate salts) in different ways according to the coordination number preferences of the metal ions. The four bidentate arms are not ideally matched to the requirement of octahedral metal ions, such that complexes with Cd(ii), such as tetranuclear [Cd(4)L(2)(micro-F)(2)(solv)(4)](BF(4))(6) (solv = MeOH or MeCN), and Co(ii)/Ni(ii), such as hexanuclear [Co(6)L(4)(micro-F)(2)][BF(4)](10), require monodentate ancillary ligands (solvent molecules or fluoride ions) to provide coordinative saturation. In contrast, a mixture of octahedral [M = Co(ii) or Ni(ii)] and tetrahedral [Ag(i)] metal ions reacts with L to afford the simpler trinuclear heterometallic complexes [Co(2)AgL(2)](BF(4))(5) in which the requirements of the metal ions (for 3 + 3 + 2 bidentate arms) are matched by two four-armed ligands. The maximum site occupancy principle can accordingly be used to direct self-assembly of heterometallic complexes.

Organometallic Chemistry of Amidate Complexes. Accelerating Effect of Bidentate Ligands on the Reductive Elimination of N-Aryl Amidates from Palladium(II)

We report a series of arylpalladium complexes of acetamidate, sulfonamidate, and deprotonated oxazolidinone ligands that undergo reductive elimination with rates and yields that depend on the binding mode of the ancillary and amidate ligands. Complexes of the acetamidate ligands containing the bidentate phosphines DPPF and Xantphos as ancillary ligands undergo reductive elimination. The rate and yield were higher from the complex ligated by Xantphos, which contains a larger bite angle. In contrast, the analogous amidate complex containing a single sterically hindered monodentate ligand and a kappa2-bound amidate ligand does not undergo reductive elimination. This trend of faster reductive elimination from complexes containing bidentate ancillary ligands than from a complex with a single monodentate ancillary ligand is unusual and is consistent with an effect of the denticity of the ancillary ligand on the binding mode of the amidate. Complexes of sulfonamidate ligands underwent reductive elimination faster than complexes of acetamidates, and reductive elimination occurred from complexes containing both bidentate and monodentate ancillary ligands. Like reductive elimination from the acetamidate complexes, reductive eliminations from the sulfonamidate complexes were faster when the complexes possessed bidentate Xantphos and kappa1-sulfonamidate ligands.