Dalton Transactions

doi: 10.1039/b603061kpmid: N/A

doi: 10.1039/b603062apmid: N/A

doi: 10.1039/b603063gpmid: N/A

Hamacek, Josef; Borkovec, Michal; Piguet, Claude

doi: 10.1039/b518461dpmid: 16538265

During the past 15 years, coordination chemistry has rapidly developed toward multicomponent assemblies involving several ligands and metal ions, which are connected intra- or intermolecular processes. The fascinating structural aspect of these complexation reactions has been early recognized for the design of sophisticated (supra)molecular architectures with novel topologies and functions, while the concomitant energetic part only recently emerged as a potential tools for controlling and programming self-assemblies. In this Perspective, we focus on the modelling of the free energy changes accompanying self-assembly processes. Starting with the original protein-ligand model borrowed from biology, which describes complicated multicomponent assemblies, we present (i) its adaptation to coordination chemistry and (ii) its significance for addressing cooperativity as an extra energy cost resulting from intercomponent interactions. An additional entropic concept arising from the separation of intra- and intermolecular complexation processes is then discussed, together with its explicit consideration for modeling multicomponent complexation reactions. Finally, both aspects ( cooperativity and intra-/intermolecular connections) are combined in the extended site binding model, which is able to dissect free energy changes occurring in sophisticated metal–ligand assemblies with a minimum set of microscopic parameters. Applications to experimental complexation reactions of increasing complexity are systematically discussed, and illustrate the potential and limitations of each model.

Price, Jason R.; Lan, Yanhua; Jameson, Geoffrey B.; Brooker, Sally

doi: 10.1039/b516997fpmid: 16538266

Silver() complexes of the two closely related linear bis-bidentate pyridazine-based Schiff-base ligands and exhibit very different solid state molecular architectures, easily deformed grid . side-by-side, due to steric and electronic factors.

Antiñolo, Antonio; García-Yuste, Santiago; Lopez-Solera, Maria Isabel; Otero, Antonio; Pérez-Flores, Juan C.; Reguillo-Carmona, Rebeca; Villaseñor, Elena

doi: 10.1039/b517307hpmid: 16538267

The niobium phosphido complex [Nb(η-CHSiMe)(CNXylyl)(PPh)] () undergoes an unusual cycloaddition reaction with electron-deficient alkynes to give the novel five-membered heteroniobacycles [Nb(η-CHSiMe)(κ-C(N(Xylyl))C(COMe)C(R)PPh-κ)] (R = H and R = Me ).

Iwatsuki, Satoshi; Itou, Tomohiro; Ito, Hideaki; Mori, Hiroki; Uemura, Kuzuhiro; Yokomori, Yushinobu; Ishihara, Koji; Matsumoto, Kazuko

doi: 10.1039/b515743apmid: 16538268

Head-to-head bis(α-pyridonato)-bridged bis(ethylenediamine)dipalladium(), HH-[Pd(en)(α-pyridonato)](ClO), was synthesized and structurally characterized by X-ray crystallography. The H NMR spectra show that the head-to-head (HH) dimer produces the head-to-tail (HT) dimer and monomers ([Pd(en)(α-pyridone)], [Pd(en)(HO)(α-pyridone)], [Pd(en)(HO)], ) in aqueous solution, and the relative amount of dimers to monomers is dependent on the total concentration of the HH dimer dissolved as well as the acidity of the solution. It was found that the formation of the HH and HT dimers from the monomers is fast, and the HT dimer is produced from the HH dimer only coexisting monomers, , there is no direct isomerization path between the HH and HT dimers. The kinetic analyses for the HH ⇌ HT isomerization reaction with time-resolved H NMR measurements revealed that the reaction proceeds first-order kinetics, which was explained based on a relaxation process. The rate determining step for HH ⇌ HT isomerization is the reaction step between the mono-α-pyridone complex and the bis-α-pyridone complex, [Pd(en)(HO)(α-pyridone)]+α-pyridone ⇌ [Pd(en)(α-pyridone)].

Tjahjono, Martin; Allian, Ayman D.; Garland, Marc

doi: 10.1039/b515298dpmid: 16538269

Two experimental multi-component organometallic systems were studied, namely, (1) a non-reactive system consisting of [Mo(CO)], [Mn(CO)], and [Re(CO)] in toluene under argon at 298.15 K and 0.1 MPa and (2) a reactive system consisting of [Rh(CO)] + PPh→ [Rh(CO)PPh] + CO in n-hexane under argon at 298.15 K and 0.1 MPa. The mole fractions of all solutes were less than 140 × 10 in system (1) and less than 65 × 10 in system (2). Simultaneous FTIR spectroscopic measurements and on-line oscillatory U-tube density measurements were performed on the multi-component solutions. A newly developed response surface methodology was applied to the data sets to determine the individual limiting partial molar volumes of all constituents present as well as the reaction volume. The limiting partial molar volumes obtained for system (1) were 176.4 ± 2.5, 265.1 ± 2.4, and 276.8 ± 2.4 cm mol for [Mo(CO)], [Mn(CO)], and [Re(CO)], respectively and are consistent with independent binary experiments. The limiting partial molar volumes obtained for system (2) were 310.7 ± 2.7, 219.8 ± 2.2 and 461.5 ± 4.5 cm mol for [Rh(CO)], PPh and [Rh(CO)PPh], respectively. In addition, a reaction volume Δ equal to −17.0 ± 5.7 cm mol was obtained. The present results demonstrate that both partial molar volumes and reaction volumes can be obtained directly from multi-component organometallic solutions. This development provides a new tool for physico-chemical determinations relevant to a variety of solutes and their reactions.

Barnes, Nicholas A.; Godfrey, Stephen M.; Halton, Ruth T. A.; Mushtaq, Imrana; Pritchard, Robin G.; Sarwar, Shamsa

doi: 10.1039/b516784apmid: 16538270

The synthesis and characterisation of PhSeBr () directly from the reaction of PhSe with dibromine is reported. The solid-state structure of consists of four PhSeBr units linked by weak selenium–selenium bonds [3.004(2)–3.051(2) Å] into a Se square, and is structurally analogous to the previously reported PhTeI. The reactions of PhSeBr with a variety of tertiary phosphines have been undertaken, resulting in the formation of compounds of formula RPSe(Ph)Br. X-Ray crystallographic analysis of three of the compounds reveals different structural isomers. PhPSe(Ph)Br () is a charge-transfer (CT) compound [Se–Br 3.0020(8) Å], with an essentially linear P–Se–Br bond angle, 172.15(4)° and T-shaped geometry at selenium. MePSe(Ph)Br () also contains the selenium atom in a T-shaped geometry, consistent with a CT formulation, although the Se–Br distance of 3.327(3) Å is considerably longer than observed for . In contrast, CyPSe(Ph)Br () is an ionic phosphonium salt, [CyPSePh]Br with no short Se–Br interactions. Geometry at selenium is bent, as expected for an ionic compound. These results are discussed with reference to the previously reported iodo-compounds PhPSe(Ph)I and [(MeN)PSe(Ph)]I.

Biver, Tarita; Lombardi, Dario; Secco, Fernando; Rosaria Tiné, Maria; Venturini, Marcella; Bencini, Andrea; Bianchi, Antonio; Valtancoli, Barbara

doi: 10.1039/b512820jpmid: 16538271

The macrocyclic polyamine 2,5,8,11,14-pentaaza[15]-[15](2,9)[1,10]phenanthrolinophane (neotetren) is studied in its ability to coordinate Cu() even at very low pH values and to interact, as a metal complex, with DNA. The kinetics and equilibria for 1 : 1 and 2 : 1 metal–ligand complexes formation are studied by the stopped-flow method and UV spectrophotometry. Differently protonated complexes are formed, with rate constants much lower than that of water exchange at copper() and other Cu()/amine systems, this behaviour being ascribed to ring effects and intra-molecular hydrogen bonds. Concerning the DNA/copper()–neotetren complexes interaction, analysis of data suggests an intercalative mode of binding. The kinetic results for both DNA/CuL and DNA/CuL systems agree with the sequence D + S ⇄ D,S ⇄ DS where the metal complexes (D) react with the DNA sites (S) leading to fast formation of an externally bound form (D,S) which is converted into an intercalated complex (DS). A very slow process is also detected and ascribed to a conformational change in the polynucleotide secondary structure where the metal centre plays a crucial role. Chromatographic experiments demonstrate that both the investigated Cu()/L complexes are able to cleave DNA, but only in the presence of hydrogen peroxide.