Chloro Ligands Research Articles

DNA Cleavage by Structurally Characterized Dinuclear Copper(II) Complexes Based on Triazine

AbstractThe reaction of 2‐chloro‐4,6‐bis(di‐2‐picolylamino)‐1,3,5‐triazine (bdpaTCl) with copper(II) perchlorate and copper(II) chloride afforded two dinuclear complexes [Cu2(μ‐bdpaTCl)(μ‐OH)2(H2O)0.5(ClO4)0.5](ClO4)1.5·(H2O)1.5 (1) and [Cu2(μ‐bdpaTCl)Cl4]·2CH3OH (2), respectively. These complexes were characterized by IR, UV/Vis, and EPR spectroscopy, single‐crystal X‐ray crystallography, and temperature dependence magnetic susceptibility measurements (2–300 K) as well as by electrochemical and molar conductivity measurements. In 1, each of the three N‐donor atoms of the binucleating bdpaTCl ligand coordinate to CuII ions, which are further bridged by two OH– anions in a distorted five‐coordinate geometry. In addition, each CuII ion forms a Cu–O semicoordinate bond with an aqua ligand or perchlorato anion. The Cu···Cu distance across the hydroxido bridges is 2.9698(11) Å. In 2, the bdpaTCl ligand acts as bis‐tridentate ligand connecting the two CuII ions, and the five‐coordinate geometry around each copper center is achieved by two terminal chloro ligands. Magnetic measurements revealed strong antiferromagnetic coupling in 1 (J = –311.2 cm–1) and very weak coupling in 2 (J = –2.4 cm–1). DNA cleavage by these two complexes has been investigated (pH = 7.0, 37 °C). Although the bridged dihydroxido complex 1 did not show any detectable cleavage for DNA, significant cleavage was observed with the tetrachloro complex 2. Under pseudo‐Michaelis–Menten kinetic conditions, the kinetic parameters kcat = 2.53 × 10–5 s–1 and KM = 1.44 × 10–4 M were determined for 2. The kcat value corresponds to a 2.5 × 106 fold rate enhancement over noncatalyzed DNA. Electrophoretic experiments conducted in the presence and absence of oxidative scavengers DMSO, KI, and NaN3, and radical promoter H2O2 provide evidence for the oxidative cleavage of DNA by hydroxy radicals and hydrogen peroxide species.

Group 6 Complexes with Iron and Zinc Heterometals: Understanding the Structural, Spectroscopic, and Electrochemical Properties of a Complete Series of MM···M′ Compounds

Binuclear quadruply bonded complexes Cr(2)(dpa)(4) (1, dpa = 2,2'-dipyridylamide), Mo(2)(dpa)(4) (2), and W(2)(dpa)(4) (3) react with anhydrous FeCl(2), yielding heterometallic compounds CrCrFe(dpa)(4)Cl(2) (4), MoMoFe(dpa)(4)Cl(2) (5), and WWFe(dpa)(4)Cl(2) (6). These molecules are structurally similar, having a linear M≡M···Fe chain that is axially capped by chloride ions and is equatorially supported by the helically twisted dpa ligands. A structurally related zinc analog, CrCrZn(dpa)(4)Cl(2) (7), can be prepared upon metalation of 1 with ZnCl(2). This reaction also persistently produces a 2:1 adduct of ZnCl(2) with 1, [Cr(2)(dpa)(4)](ZnCl(2))(2) (8), which is in equilibrium with 7 and has the two zinc ions bound externally to the Cr(2) core and axial bridging chloro ligands attached to each Cr ion. The sole isolable product of the addition of ZnCl(2) to 3 is a 1:1 adduct, [W(2)(dpa)(4)]ZnCl(2) (9). The structurally related chain complexes 4, 5, 6, and 7 are characterized by X-ray crystallography, UV-vis spectroscopy, cyclic voltammetry, and (57)Fe Mössbauer spectroscopy for the iron complexes in order to gain insights into the nature of heterometallic interactions, electronic excited states, and redox properties of these compounds, which have implications for all other M≡M···M' molecules. Additionally, NMR spectroscopy has been used to gain insight into the mechanism of the metalation of 1 by Zn(II).

Control of the Mutual Arrangement of Cyclometalated Ligands in Cationic Iridium(III) Complexes. Synthesis, Spectroscopy, and Electroluminescence of the Different Isomers

Synthetic control of the mutual arrangement of the cyclometalated ligands (C^N) in Ir(III) dimers, [Ir(C^N)(2)Cl](2), and cationic bis-cyclometalated Ir(III) complexes, [Ir(C^N)(2)(L^L)](+) (L^L = neutral ligand), is described for the first time. Using 1-benzyl-4-(2,4-difluorophenyl)-1H-1,2,3-triazole (HdfptrBz) as a cyclometalating ligand, two different Ir(III) dimers, [Ir(dfptrBz)(2)Cl](2), are synthesized depending on the reaction conditions. At 80 °C, the dimer with an unusual mutual cis-C,C and cis-N,N configuration of the C^N ligands is isolated. In contrast, at higher temperature (140 °C), the geometrical isomer with the common cis-C,C and trans-N,N arrangement of the C^N ligand is obtained. In both cases, an asymmetric bridge, formed by a chloro ligand and two adjacent nitrogens of the triazole ring of one of the cyclometalated ligands, is observed. The dimers are cleaved in coordinating solvents to give the solvento complexes [Ir(dfptrBz)(2)Cl(S)] (S = DMSO or acetonitrile), which maintain the C^N arrangement of the parent dimers. Controlling the C^N ligand arrangement in the dimers allows for the preparation of the first example of geometrical isomers of a cationic bis-cyclometalated Ir(III) complex. Thus, N,N-trans-[Ir(dfptrBz)(2)(dmbpy)](+) (dmbpy = 4,4'-dimethyl-2,2'-bipyridine), with cis-C,C and trans-N,N arrangement of the C^N ligands, as well as N,N-cis-[Ir(dfptrBz)(2)(dmbpy)](+), with cis-C,C and cis-N,N C^N ligand orientation, are synthesized and characterized. Interestingly, both isomers show significantly different photophysical and electroluminescent properties, depending on the mutual arrangement of the C^N ligands. Furthermore, quantum chemical calculations give insight into the observed photophysical experimental data.

Aqua and Diethyl Ether PNNP Complexes of Ruthenium(II): Structure and Solution Behavior

Addition of water to CD2Cl2 solutions of the five-coordinate complex [RuCl(PNNP)]PF6 (2) (formed by treating [RuCl2(PNNP)] (1) with TlPF6 (1 equiv) in dichloromethane) yields the aqua complexes cis-β-[RuCl(OH2)(PNNP)]PF6 (3) and trans-[RuCl(OH2)(PNNP)]PF6 (4) in a 6:1 ratio (PNNP is the chiral ligand (1S,2S)-N,N′-bis[o-(diphenylphosphino)benzylidene]cyclohexane-1,2-diamine). An excess of H2O (10 equiv) is needed for quantitative conversion of 2. The cis-β isomer 3 is more labile than the trans analogue 4 and is in slow-regime chemical exchange with five-coordinate 2 in CD2Cl2. The trans aqua complex 4 does not dissociate in CDCl3 over 6 h, but undergoes rapid equilibration with 2 and 3 upon dissolution in CD2Cl2. The X-ray structure of (Λ)-cis-β-3 shows an intramolecular hydrogen bond between the aqua and the chloro ligands. The elusive Et2O adduct [RuCl(OEt2)(PNNP)]PF6 (5), obtained by treating 1 with (Et3O)PF6 (1 equiv) in dichloromethane, is formed as the cis isomer only. At room temperature, 5 exists ...

Preparation and Structural Features of Cu(I)Cu(II) Coordination Polymers Obtained by Using Tripodal Complexes as Bridging Ligands

Abstract A tripodal complex [CuCl(tpmtm)] (tpmtm: tris(2-pyrimidylthio)methanide) is used to synthesize coordination polymers. The tripodal complex unit worked as bidentate, tridentate, or tetradentate bridging ligands for [CunClm] units via coordination of three outer nitrogen atoms of the tpmtm ligand and also an axial chloro ligand. X-ray crystallography exhibited that obtained coordination polymers contained novel structures of [CunClm] moieties such as chloride-bridged linear CuICuIICuI and CuICuIICuIICuI and cage-shaped CuICuIICuIICuI mixed-valence copper cluster units. The relationship between the numbers of the outer coordination sites on the tripodal complex and structures of the coordination polymers is observed showing that participation in the coordination of two, three, or four outer coordination sites on the tripodal complex afforded the one-dimensional chain, two-dimensional sheet, or three-dimensional structures, respectively.

Crystal Structure and Spectroscopic Properties of Bis[trans‐dichlorobis(2,2‐dimethylpropane‐1,3‐diamine)chromium(III)] Tetrachlorozincate

AbstractThe structure of trans‐[Cr(Me2tn)2Cl2]2ZnCl4 (Me2tn = 2,2‐dimethylpropane‐1,3‐diamine) was determined by a single‐crystal X‐ray diffraction study at 173 K. The analysis reveals that there are three crystallographically independent chromium(III) complex cations in the title compound. The chromium(III) atoms are coordinated by four nitrogen atoms of Me2tn and two chlorine atoms in a trans arrangement, displaying a distorted octahedral geometry. The two six‐membered chelate rings in three complex cations are oriented in an anti chair–chair conformation with respect to each other. The Cr–N and Cr–Cl bond lengths average 2.0862(2) and 2.3112(6) Å, respectively. The ZnCl42– have slightly distorted tetrahedral arrangement with Zn–Cl lengths and the Cl–Zn–Cl angles are influenced by hydrogen bonding. The resolved absorption maxima in the electronic d–d spectrum were fitted with a secular determinant for a quartet energy state of the d3 configuration in a tetragonal field. It is confirmed that the nitrogen atoms of the Me2tn ligand are strong σ donors, but the chloro ligands have weak σ‐ and π donor properties toward the chromium(III) ion.

Bis(2-pyridyl-κN)amine]chlorido(η6-hexamethylbenzene)ruthenium(II) hexafluoridophosphate dichloromethane solvate

In the title half-sandwich complex, [RuCl(η6-C12H18)(C10H9N3)]PF6·CH2Cl2, the ruthenium(II) ion is four-coordinated by a chloro, a hexa­methyl­benzene and a bidentate N,N′-chelating di(pyridin-2-yl)amine ligand. In the crystal, the amino N—H group forms a hydrogen bond with the chloro ligand of a neighbouring complex, thus forming chains along the b axis. Weak inter­molecular C—H⋯F and C—H⋯ Cl contacts are also observed.

Coordination chemistry of 1,4-bis[bis(2-pyridylmethyl)aminomethyl]benzene with copper(II)

The interaction of 1,4-bis[bis(2-pyridylmethyl)aminomethyl]benzene ( p-Xy DPA) with CuCl 2·2H 2O has resulted in the isolation of the dinuclear compound [Cu 2( p-Xy DPA)Cl 4]·H 2O ( 1). When the reaction was performed in presence of sodium perchlorate, sodium azide, sodium dicyanamide (Nadca) and disodium squarate (Na 2C 4O 4) the compounds [Cu 2( p-Xy DPA)(ClO 4) 2Cl 2] ( 2), [Cu 2( p-Xy DPA)(N 3) 4]·2H 2O ( 3), [Cu 2( p-Xy DPA)(dca) 4]·4H 2O ( 4), and [Cu 2( p-Xy DPA)Cl 2(H 2O) 2](C 4O 4)·5.4H 2O ( 5) were obtained, respectively. The complexes were characterized by IR and UV–vis. spectroscopy. The visible spectra of the complexes revealed the square pyramidal geometry around the central Cu 2+ ions. The molecular structures of the complexes 2, 3, 4 and 5 were determined by single crystal X-ray crystallography. This study revealed the dinuclear nature of the complexes and showed that the Cu(II) centers have distorted five-coordinate square pyramidal geometry with N 3-donor atoms of the dipicolyl amine arms and the remaining coordination positions are occupied by the chloro and perchlorato ligands in 2, the monodentate azido ligands in 3 or the monodentate terminal nitrile dca in 4 and by the chloro and aqua ligands in 5 with the squarate dianion as counter ion.

Towards New Molecular Photocatalysts for CO2 Reduction: Photo‐Induced Electron Transfer versus CO Dissociation within [Os(NN)(CO)2Cl2] Complexes

Optical excitation in the visible region of trans-(Cl)-[Os(bpy)(CO)(2)Cl(2)] (bpy=2,2'-bipyridine; C1) and trans-(Cl)-[Os(dmbpy)(CO)(2)Cl(2)] (dmbpy=4,4'-dimethyl 2,2'-bipyridine; C2) is known to induce the common CO dissociation reaction. However, the quantum yield of the reactions is less than 0.15, although C1 and C2 display pronounced photoluminescence in the visible region at room temperature with a lifetime of few tens of nanoseconds. Taking into account the characteristics of their emitting state, we have investigated the capability of C1 and C2 to act as a photosensitiser in redox reactions in different solvents (MeCN, PrCN and DMF). The efficient oxidation and reduction of both complexes under continuous irradiation in the presence of a sacrificial electron acceptor or donor is reported here. The photo-induced transformations and the nature of the resulting compounds were analysed by UV/Vis and IR spectroscopies and cyclic voltammetry. Photo-induced oxidation of C1 and C2 leads to the corresponding monocarbonyl oxidised species, whereas photo-induced reduction under argon leads mainly to the formation of the corresponding Os-bonded molecular wires P1 and P2 after exchange of two electrons associated with the loss of two chloro ligands. The chemical yield of the latter reaction (around 65%) becomes quantitative by adding [Ru(bpy)(3)](2+) as an external redox photosensitiser. This behaviour has been used to photocatalyse the two electron, two proton conversion of CO(2) to CO. Turnover numbers (TON) of 11.5 and 19.5 have been obtained respectively for C1 and C2 after 4.5 h of irradiation under CO(2) in DMF with triethanolamine as the electron donor. TON can be slightly increased by adding [Ru(bpy)(3)](2+) to the solution.

Exchange of isonitrile ligands in the complex [Mo(O)Cl(CNMe)4]+ by the tetraphos ligand prP4: Stereochemical influences on the reaction course

Reaction of [Mo(O)Cl(CNMe)4]+ with the linear tetraphos ligand meso and rac prP4 leads to a mixture of [Mo(O)Cl(κ4-meso-prP4)]+ and [Mo(O)Cl(CNMe)(κ3-rac-prP4)]+ which are identified by X-ray structural analysis and/or 31P NMR spectroscopy. In the meso κ4-product both of the phenyl groups of the central phosphorus atoms are oriented towards the oxo ligand whereas in the rac κ3-product one of these phenyl groups is oriented to the oxo and the other to the chloro ligand. The origin of the different coordination modes lies in the different steric demands of the oxo and chloro ligands. The influences of the steric interactions are enhanced by the fact that exchange of the fourth isonitrile is difficult. This hypothesis is supported by the preparation of the complex [Mo(O)Cl(CNMe)(dpepp)]PF6 whose isonitrile ligand is inert towards exchange by monophosphines, even under drastic conditions.

The Crystal Structure of {[Pt(9S3)Cl2]2[Pt(9S3)2]}Cl2·4H2O: An Improved Synthesis of [Pt(9S3)Cl2

We wish to report the crystal structure for a solid-state solution, {[Pt(9S3)Cl2]2[Pt(9S3)2]}Cl2·4H2O (1), which contains two different complexes of Pt(II) with the trithiacrown 9S3 (1,4,7-trithiacyclononane). One complex [Pt(9S3)Cl2] is neutral and contains a Pt(II) center with a single 9S3 ligand and two coordinated chloro ligands. The second Pt(II) complex is a dication and contains two coordinated 9S3 ligands and two non-coordinating chloride anions. There are two crystallographically equivalent [Pt(9S3)Cl2] complexes present for every single [Pt(9S3)2]2+ cation. Four water solvent molecules are also present. In the neutral complex ([Pt(9S3)Cl2], the Pt(II) center is surrounded by a cis-[S2Cl2 + S1] ligand environment formed by the two chloro ligands and two of the three sulfur atoms from the 9S3 ligand. These two sulfurs are positioned 2.225(2) and 2.242(2) A from the Pt(II), but the third sulfur shows a long distance interaction at 3.311(2) A to form an elongated square pyramidal structure. This axial Pt–S distance is the longest observed in 57 crystal structures of Pt(II) 9S3 complexes. The cation [Pt(9S3)2]2+ displays two centrosymmetrically coordinated 9S3 ligands forming a [S4 + S2] environment with an elongated octahedral shape. In the dication, the two equatorial Pt–S distances are 2.297(2) and 2.306(2) A with the axial sulfur at 3.065(2) A. The most interesting intermolecular aspects of the structure are hydrogen bonding interactions between two of the water molecules and two chloride counter-ions, resulting in a nearly square O2Cl2 ring. This ring shares an edge with a six-membered ring formed by four waters and two chlorides which are hydrogen bonded. The hydrogen bonding interactions, which result from the presence of water in the crystal, appear to be an important component in stabilizing the lattice for the unusual solid-state solution structure. Crystal Data for (1): P2 1 /n, a = 7.8327(10) A, b = 25.152(4) A, c = 12.382(2) A, V = 2314.3(6) A3, Z = 2. We also report an improved synthetic procedure for the preparation of two thiacrown complexes [Pt(9S3)Cl2] and [Pt(10S3)Cl2], which are commonly used as precursors for other heteroleptic thioether complexes. The new syntheses proceed at room temperature without the need for long reflux times and produce large crystals which are easily isolable without filtration. The simplicity of these new preparations results in improved yields over previously employed methods. The title complex crystallizes to form a solid-state solution of two different Pt(II) thiacrown complexes, [Pt(9S3)Cl2] and [Pt(9S3)]2+.

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.

Novel neutral hexacoordinate benzamidinatosilicon(iv) complexes with SiN3OF2, SiN3OCl2, SiN3OBr2, SiN5O and SiN3O3 skeletons

The neutral pentacoordinate monoamidinatosilicon(IV) complex 1 (SiN(2)Cl(3) skeleton) and the neutral hexacoordinate monoamidinatosilicon(IV) complexes 2-9 (SiN(3)OF(2), SiN(3)OCl(2), SiN(3)OBr(2), SiN(5)O and SiN(3)O(3) skeletons) were synthesised and characterised by elemental analyses, single-crystal X-ray diffraction (except for 1) and NMR spectroscopy in the solid state and in solution. Compounds 2-9 contain one bidentate monoanionic N,N'-diisopropylbenzamidinato ligand, one bidentate monoanionic ligand derived from 8-hydroxyquinoline and (i) two identical monoanionic ligands (F, Cl, Br, N(3), NCO, NCS, OSO(2)CF(3)) or (ii) one bidentate dianionic benzene-1,2-diolato ligand. The dynamic behavior of 2-4 (SiN(3)OX(2) skeleton; X = F, Cl, Br) and 9 (SiN(3)O(3)) in solution was studied by multinuclear variable-temperature NMR experiments. Compound 1 was synthesised by reaction of SiCl(4) with the corresponding lithium amidinate, and compound 2 was obtained by reaction of 1 with 8-hydroxyquinoline and triethylamine. Compound 2 served as the starting material in the syntheses of 3-9, in which the two chloro ligands of 2 were substituted by two identical (pseudo)halogeno ligands, two trifluoromethanesulfonato ligands or one benzene-1,2-diolato ligand. Compounds 3 and 4 contain the novel SiN(3)OBr(2) and SiN(3)OF(2) skeletons, while compounds 5-7 are the first neutral hexacoordinate silicon(IV) complexes with an SiN(5)O skeleton.

Analysis of M⋯H–Si interactions in [{M(CpSiMe2H)Cl3}2], (M = Zr, Hf, Ti and Mo) complexes

For the d(0) complex [{Zr(CpSiMe(2)H)Cl(3)}(2)] which contains a linear Si-H···Zr interaction across the dimer, DFT calculations are in good agreement with X-ray structures. The BP86 functional shows a slightly stronger interaction than B3LYP but for qualitative purposes either functional is sufficient. QTAIM analysis shows a bond critical point (bcp) for the interaction, a small negative value for the total energy density [H((r))] and the H atomic basin decreases in energy, E(H), and atomic volume compared to the free ligand. NBO analysis showed E(2) for Si-H σ to Zr(dz(2)) donation at 42.8 kcal mol(-1) and a 34% spatial overlap for the interaction consistent with an inverse hydrogen bond. The Wiberg bond index for the interaction is 0.1735 (0.7205 for the Si-H bond), ν((Si-H)) and (1)J((Si-H)) at 2060 cm(-1) and 145.4 Hz compared to 2183 cm(-1) and 172.1 Hz in the free ligand. Using a "synthesis by computation" approach to forming like complexes, similar features were found for [{Hf(CpSiMe(2)H)Cl(3)}(2)]. The titanium complex [{Ti(CpSiMe(2)H)Cl(3)}(2)] does not contain any Si-H···Ti interaction as rotation about the C-Si bond of the ligand occurs to place the Si-H bond hydrogen closer to a terminal chloro ligand across the dimer. An increase in electron density on the metal in the d(2) complex [{Mo(CpSiMe(2)H)Cl(3)}(2)] results in a stronger interaction with a distinct QTAIM analysis bcp [ρ((r)) 0.0448 a.u.], a small negative value for H((r)) and a much reduced H atomic volume. NBO analysis shows E(2) for Si-H σ to Mo(dz(2)) donation at 143.1 kcal mol(-1) and a 29% spatial overlap. Mo(dz(2)) to Si-H σ* donation (back donation) is minimal [E(2) 1.3 kcal mol(-1), ~1% spatial overlap]. The Wiberg bond index is 0.3114 (0.5667 for the Si-H bond), ν((Si-H)) 2015 cm(-1) and (1)J((Si-H)) 120.6 Hz.

Metallomacrocycle or coordination polymer: Spacer-directed self-assembly of transition-metal complexes based on flexible bis(benzotriazole) ligands

Three structurally related flexible bis(benzotriazole) ligands, 1,2-bis(benzotriazol-1-yl)ethane (L11), 1,5-bis(benzotriazol-1-yl)-3-oxapentane (L22) and 1,8-bis(benzotriazol-1-yl)-3,6-dioxaoctane (L33), have been synthesized. They were reacted with AgNO3 and CuCl2·2H2O at room temperature, resulting in the formation of six novel complexes: {[AgL11(NO3)(CH3CN)]}n (1), [Ag2(L22)3](NO3)2 (2), {[Ag2(L33)2(NO3)2]}n (3), {[CuL11Cl2]}n (4), [Cu2(L22)2Cl4] (5), and [Cu2(L33)2Cl4(DMF)2] (6). All complexes have been characterized by X-ray diffraction analysis. In 1 and 4, they exhibit similar coordination modes in which each ligand links two metal ions to form a 1D non-linear coordination polymeric chain. In 2, two AgI centers are close coupled by Ag⋯Ag interaction and three bridging ligands to form a dinuclear cation. The structure of 3 reveals the dinuclear cluster units, formed by two ligands and two AgI ions, are linked by anions to self-assemble a 1D chain. Complex 5 is an isolated dinuclear structure, in which ligands and bridging chloro ligands act as the organic clips to bridge two CuII centres. But in 6, a pair of ligands takes on the conformation to connect two metal ions to form bimetallic a macrocyclic architecture. These results unequivocally indicate that the influence of flexible ligand spacers, which bring structural varieties for the same metal ion, is the key factor governing the molecular architectures. Moreover, the thermal stability of 1–3 and 4–6 in the solid state has also been compared.

One-dimensional cadmium(II)/bicinate(−1) complexes : The role of the alkali metal ion used in the reaction medium

The initial employment of N,N-bis(2-hydroxyethyl)glycine (bicine; bicH3) in CdCl2 chemistry is reported, and the syntheses, IR spectra and crystal structures of the 1D coordination polymers [CdCl(bicH2)]n·nH2O (1·H2O) and [CdNaCl2(bicH2)(MeOH)]n (2) are described. The identity of the products depends on the solvent, the reaction temperature and the alkali metal ion of the base used. The structure of 1·H2O consists of zig-zag chains. The 7-coordinate CdII atoms are bridged by η1:η1:μ2 carboxylate groups of the 2.21111 (Harris notation) bicH2− ligand. The coordination geometry of the metal center can be either described as a very distorted pentagonal bipyramidal or as a distorted capped octahedral. In the structure of 2 the CdII atoms form an almost linear chain with neighboring NaI atoms on opposite sites of the chain. Every pair of CdII atoms is linked by two chloro ligands and the two oxygen atoms of the bicinate carboxylate group. The CdII and NaI atoms are bridged by one μ2 carboxylate bicinate oxygen and one μ3 chloro ligand. The 3.21,211121212 coordination mode of bicH2− is unprecedented. The CdCl4(Ocarboxylate)2 and Na(Ohydroxyl)2(Ocarboxylate)(OMeOH)NCl coordination spheres are octahedral and trigonal prismatic, respectively. IR data of the complexes are discussed in terms of the coordination modes of bicH2− and the known structures.

Synthesis and X-ray crystal structure of dichloro[S-1-phenyl-N-(S-pyrrolidin-2-ylmethyl)ethanamine]zinc(II) and its catalytic application to rac-lactide polymerization

New dichloro zinc(II) complex ligated by the homochiral bidentate ligand S-1-phenyl-N-(S-pyrrolidin-2-ylmethyl)ethanamine (PPMA) was synthesized and characterized by X-ray crystallography. The geometry of the (PPMA)ZnCl2 is a distorted tetrahedron comprising of zinc metal as a center linked with two N atoms of the PPMA in a bidentate coordination mode along with two chloro ligands. The catalytic capacity of the complex was evaluated in ring opening polymerization (ROP) of rac-lactide. The active catalyst species was generated in situ by treating MeLi to complex (PPMA)ZnCl2. The dimethyl derivative of the (PPMA)ZnCl2 showed highly activity in ROP of rac-lactide and gave preference to heterotactic polylactide.

Mechanism of Selective Halogenation by SyrB2: A Computational Study

The mechanism of the chlorination reaction of SyrB2, a representative α-ketoglutarate dependent halogenase, was studied with computational methods. First, a macromolecular model of the Michaelis complex was constructed using molecular docking procedures. Based on this structure, a smaller model comprising the first- and some of the second-shell residues of iron and a model substrate was constructed and used in DFT investigations on the reaction mechanism. Computed relative energies and Mössbauer isomer shifts as well as quadrupole splittings indicate that the two oxoferryl species observed experimentally are two stereoisomers resulting from an exchange of the coordination sites occupied by the oxo and chloro ligands. In principle both Fe(IV)═O species are reactive and decay to Fe(III)Cl (OH)/carbon radical intermediates via C-H bond cleavage. In the final rebound step, which is very fast and thus precluding equilibration between the two forms of the radical intermediate, the ligand (oxo or chloro) placed closest to the carbon radical (trans to His235) is transferred to the carbon. For the native substrate (L-Thr) the lowest barrier for C-H cleavage was found for an isomer of the oxoferryl species favoring chlorination in the rebound step. CASPT2 calculations for the spin state splittings in the oxoferryl species support the conclusion that once the Fe(IV)═O intermediate is formed, the reaction proceeds on the quintet potential energy surface.

Ruthenium(II) thiacrown complexes: Synthetic, spectroscopic, electrochemical, DFT, and single crystal X-ray structural studies of [Ru([15]aneS 5)Cl](PF 6)

We wish to report the synthesis of the Ru(II) crown thioether complex, (1,4,7,10,13-pentathiacyclopentadecane)chlororuthenium(II) hexafluorophosphate, [Ru([15]aneS 5)Cl](PF 6), and a study of its properties utilizing single crystal X-ray diffraction, electronic spectroscopy, NMR spectroscopy, density functional theory calculations and cyclic voltammetry. The crystal structure shows a single [15]aneS 5 macrocycle and a chloro ligand coordinated in a distorted octahedral fashion around the ruthenium(II) center. A significant shortening (0.15 Å) of the trans Ru–S bond length occurs in this complex compared to the related PPh 3 complex (2.4458(10) to 2.283(1) Å) due to the differences in the trans influence of the two ligands. 13C NMR spectroscopy demonstrates that the structure of [Ru([15]aneS 5)Cl] + is retained in solution. As expected for a Ru(II) complex, the electronic absorption spectrum shows two d– d transitions at 402 and 331 nm. These are red-shifted compared to hexakis(thioether)ruthenium(II) complexes and consistent with the weaker ligand field effect of the chloro ligand. The electrochemical behavior of the complex in acetonitrile shows a single one-electron reversible oxidation–reduction at +0.722 V versus Fc/Fc + which is assigned as the Ru(II)/Ru(III) couple. DFT calculations for [Ru([15]aneS 5)Cl] + show a HOMO with orbital contributions from a t 2 g type orbital of the Ru ion, a π component from a p orbital of the axial S atom of [15]aneS 5, and a p orbital of the chloro ligand while the LUMO consists of orbital contributions of d x 2 - y 2 orbital of the Ru center and p orbitals of the four equatorial S donors.

ChemInform Abstract: Aspects of the Solution Chemistry of trans-Diammineplatinum(II) Complexes.

A convenient method for small-scale preparations of trans-[PtCl2(NH3)2] (e.g., for preparing 15N-labeled compounds) is to heat [Pt(NH3)4]Cl2 at 190-195°C, under vacuum. 15N and 195Pt NMR spectra have been used to characterize in solution trans-diammineplatinum(II) complexes with aqua, chloro, nitrato, sulfato, acetato, and phosphato ligands. A solution of trans-[Pt(OH)(H2O)(NH3)2]+ allowed to stand gives a precipitate [{trans-Pt(μ-OH)(NH3)2}n] (NO3)n. 15N NMR spectra have been used to determine acid dissociation constants for trans-[Pt(H2O)2(15NH3) 2]2+ (pKa1 4.35, pKa2 7.40) and for trans-[PtCl(H2O)(15NH3)2] + (pKa1 5.63).