Change In Coordination Mode Research Articles

Theoretical Insights on Improving Amidoxime Selectivity for Potential Uranium Extraction from Seawater.

Extraction of uranium from seawater is one of the important ways to solve the shortage of terrestrial uranium resources. Thereinto, the competition between uranyl and vanadium cations is a significant challenge in the commonly used amidoxime-based adsorbents for extracting uranium from seawater. An in-depth understanding of the extraction behaviors of modified amidoxime groups with uranyl and vanadium ions is one of the effective means to design and develop efficient adsorbents for selective uranium sequestration. In this work, we have designed and systematically investigated the alkyl and amino functionalized amidoxime, (Z)-2-amino-N'-hydroxy-N,N-dimethylbenzimidamide (L1), and its phenyl and methoxy derivatives ((Z)-3-amino-N'-hydroxy-N,N-dimethyl-2-naphthimidamide (L2) and (Z)-2-amino-N'-hydroxy-4-methoxy-N,N-dimethylbenzimidamide (L3)) by quantum chemistry calculations. In the uranyl complexes, the amidoxime groups prefer to act as η2-coordinated ligands as the amidoximes increase, and there exist substantial hydrogen bond interactions, which are different from the vanadium complexes. Various bonding analyses show that the L1 ligand possesses a stronger binding affinity to UO22+, and the -C6H5 and -CH3O substituent groups seem to have no effect on the improvement of extraction ability. Thermodynamic analysis confirms that the L1 ligand has a stronger extraction capability to uranyl ion compared to L2 and L3. According to the calculations of the vanadium (V) (VO2+ and VO3+) complexes with the L1 ligand, L1 is more likely to react with [H2VO4]- and [HVO4]2- to form VO2+ complexes. Expectantly, thermodynamic analysis displays a higher extraction capacity for uranyl ions than vanadium ions. Therefore, these alkyl and amino functionalized amidoxime ligands demonstrate high selectivity for uranyl over vanadium ions, which is mainly due to the coordination mode changes of these ligands toward vanadium in conjunction with the considerable hydrogen bonds in the uranyl complexes. These results are expected to afford useful clues for the design of efficient adsorbents for uranium extraction from seawater.

Self-assembled mononuclear complexes: open metal sites and inverse dimension-dependent catalytic activity for the Knoevenagel condensation and CO2 cycloaddition.

To lessen the greenhouse effect, measures such as improving the recovery of crude oil and converting carbon dioxide (CO2) into valuable chemicals are necessary to create a sustainable low-carbon future. To this end, the development of efficient new oil-displacing agents and CO2 conversion has aroused great interest in both academia and industry. The Knoevenagel condensation and CO2 cycloaddition are the key reactions to solve the above problems. Four Cu- or Zn-based molecular complexes built from different ligands possessing hydrophilic-hydrophobic layers and different dimensionalities were chosen as solid catalysts for this study. Structural analysis revealed the presence of hydrophilic-hydrophobic layers and open metal sites in the low-dimensional complexes. To obtain deep insight into the reaction mechanism, first-principles density functional theory (DFT) calculations were carried out. These calculations confirmed that in the Knoevenagel condensation reaction, the final formation of benzylidenemalononitrile is the rate-determining step (an energy barrier (ΔE) value of 73.2 kJ mol-1). The zero-dimensional (0D) Cu molecular complex with unsaturated metal centers, hydrophilic and hydrophobic layers, exhibited higher catalytic activity (yield: 100%, temperature: room temperature, and time: 2 h) compared with one- and two-dimensional Cu complexes. In the presence of a 0D Zn complex co-catalyzed with Br- in the CO2 cycloaddition reaction, the ΔE value reduces to 35.5 kJ mol-1 for the ring opening of styrene oxide (SO), which is significantly lower than Br- catalyzed (80.9 kJ mol-1) reactions. The roles of unsaturated metal centers, hydrophilic-hydrophobic layers and dimensionality in the Knoevenagel condensation and CO2 cycloaddition were explained in the results of structure-activity relationships.

Synthesis, Structure and Cytotoxicity of N,N and N,O-Coordinated RuII Complexes of 3-Aminobenzoate Schiff Bases against Triple-negative Breast Cancer.

Half-sandwich RuII complexes, [(YZ)RuII (η6 -arene)(X)]+, (YZ=chelating bidentate ligand, X=halide), with N,N and N,O coordination (1-9) show significant antiproliferative activity against the metastatic triple-negative breast carcinoma (MDA-MB-231). 3-aminobenzoic acid or its methyl ester is used in all the ligands while varying the aldehyde for N,N and N,O coordination. In the N,N coordinated complex the coordinated halide(X) is varied for enhancing stability in solution (X=Cl, I). Rapid aquation and halide exchange of the pyridine analogues, 2 and 3, in solution are a major bane towards their antiproliferative activity. Presence of free -COOH group (1 and 4) make complexes hydrophilic and reduces toxicity. The imidazolyl 3-aminobenzoate based N,N coordinated 5 and 6 display better solution stability and efficient antiproliferative activity (IC50 ca. 2.3-2.5 μM) compared to the pyridine based 2 and 3 (IC50 >100 μM) or the N,O coordinated complexes (7-9) (IC50 ca. 7-10 μM). The iodido coordinated, 6, is resistant towards aquation and halide exchange. The N,O coordinated 7-9 underwent instantaneous aquation at pH 7.4 generating monoaquated complexes stable for at least 6 h. Complexes 5 and 6, bind to 9-ethylguanine (9-EtG) showing propensity to interact with DNA bases. The complexes may kill via apoptosis as displayed from the study of 8. The change in coordination mode and the aldehyde affected the solution stability, antiproliferative activity and mechanistic pathways. The N,N coordinated (5 and 6) exhibit arrest in the G2/M phase while the N,O coordinated 8 showed arrest in the G0/G1 phase.

Mono- and oligonuclear complexes based on a o-vanillin derived Schiff-base ligand: Synthesis, crystal structures, luminescent and electrochemical properties

A new synthetic approach for homo- and heteronuclear complexes, based on N,N′-bis[(3-methoxysalicylideneamino)-propyl]-piperazine (H2L) Schiff-base ligand, has been developed. The ligand has been crystallized in the form H2L·2DMSO and its structure has been solved. Using this ligand, the following complexes have been synthesized: [CoL](ClO4) (1), [Zn2L(CH3COO)2]·2H2O (2), [Cu3L2(NO3)2] (3) and [LaCu6L4(H2O)2(NO3)2](NO3)5·15H2O (4). The 1–4 complexes were characterized by elemental analysis, X-ray crystallography, infrared and diffuse reflectance spectroscopy. The crystallographic investigations revealed that H2L presents the stable chair conformation of the piperazine ring, while its coordination mode changes according to the nature of the metal ion and counterion, respectively, allowing the formation of mono- (1) and oligonuclear (2–4) complexes. Compound 1 consists of a mononuclear complex cation, where the double-deprotonated ligand (L2−) encapsulates the trivalent cobalt ion. In compound 2, L2− acts as a symmetrical binucleatig ligand through the two N2O sets disposed on each side of the piperazine ring and coordinates two zinc(II) ions. Compounds 3 and 4 contain trinuclear units where two ligand molecules coordinate unsymmetrically three CuII ions, with the N3O donor set wrapped around the peripheral CuII and the remaining NO sets bound to the central CuII ion. Two such trinuclear moieties coordinate the LaIII ion in crystal 4. Electrochemical behavior of compounds 1 and 3 and luminescent properties of compound 2 are discussed.

Role of sulfur atoms in the adsorption of antimony by greigite

In this work, greigite (Fe3S4) and magnetite (Fe3O4) is used as a carrier to study the role of sulfur (S) in the adsorption of antimony (Sb) by greigite. Results show that the synthesized Fe3S4 has stronger adsorption ability to Sb(III)/Sb(V) than its oxide counterpart Fe3O4. The Langmuir maximum adsorption capacities of Fe3S4 to Sb(III) and Sb(V) are 178.87 and 163.52 mg/g, respectively. Change in coordination mode caused by the substitution of S to O is the main reason for the enhancement in Sb(III)/Sb(V) adsorption ability. Sb(III)/Sb(V) adsorb on the Fe–Fe bridge site on (311) plane of Fe3O4, while Fe–S is adsorb at the top site on the (311) plane of Fe3S4; the latter has higher adsorption affinity to Sb than the former. The oxidative conducts of Fe3S4 are only elemental sulfur and lepidocrocite (γ-FeOOH), and no sulfur-containing compounds are identified. This work is expected to provide new understanding to the role of anion in spinel materials.

Kinetics and mechanisms of homogeneous catalytic reactions. Part 16. Regioselective hydrogenation of quinoline catalyzed by dichlorotris(triphenylphosphine)ruthenium(II)

The complex RuCl2(PPh3)3 (1) showed to be an efficient and regioselective precatalyst for the hydrogenation of quinoline (Q) to 1,2,3,4-tetrahydroquinoline (THQ) at P = 5.0–6.5 at m and T = 140−167 °C. This reaction showed to be first order on catalyst concentration and fractional order on dissolved hydrogen concentration (1.84). However, different to other Ru, Os, Rh and Ir precatalysts, the reaction showed an inverse fractional order on Q concentration (-0.44). The rate law may be written as: r = {KoK1k2/(Ko + [Q]+ KoK1[H2])}[Ru][H2]2. Coordination chemistry and theoretical DFT studies allowed us to propose a detailed catalytic cycle for this reaction. Under the hydrogenation conditions, the ruthenium precursor 1 is totally transformed to RuCl2(κN-Q)2(PPh3)2 (3) and subsequently to RuHCl(κN-Q)2(PPh3)2 (4) by heterolytic addition of H2. Complex 4 reversibly dissociates a Q ligand to generate RuHCl(κN-Q)(PPh3)2, which was proposed as the catalytically active species (CAS) entering to the catalytic cycle. The reversible addition of hydrogen yields a species containing a κN-1,2-dihydroquinoline (κN-DHQ) ligand (possibly through the coordination of hydrogen, migration of hydride to the N atom of Q ligand and posterior DHQ reductive elimination); this species suffers a change of coordination mode from κN- to an olefin-like η2-DHQ. Posteriorly, the addition of a second molecule of H2, considered the rate-determining step, generates a THQ species (probably through migration of hydride to C3 of DHQ ligand followed by the heterolytic addition of hydrogen). The cycle is completed by the substitution of the THQ ligand by a new Q molecule, therefore regenerating the CAS.

Alternative (κ1-N:η6-arene vs.κ2-N,N) coordination of a sterically demanding amidinate ligand: are size and electronic structure of the Ln ion decisive factors?

The amine elimination reaction of equimolar amounts of ansa-bis(amidine) C6H4-1,2-{NC(tBu)NH(2,6-iPr2C6H3)}2 (L1H) and [(Me3Si)2N]2Yb(THF)2 affords a bis(amidinate) YbII complex [C6H4-1,2-{NC(tBu)N(2,6-iPr2C6H3)}2]Yb(THF) (1) in 68% yield. Complex 1 features a rather rare η1-amido:η6-arene coordination of both amidinate fragments to the YbII ion, resulting in the formation of a bent bis(arene) structure. Oxidation of 1 by I2 regardless of the molar ratio of reagents (2 : 1 or 1 : 1) leads to the formation of the YbIII species [{(2,6-iPr2C6H3)[double bond, length as m-dash]NC(tBu)NH}-C6H4-1,2-{NC(tBu)N(2,6-iPr2C6H3)}]YbI2(THF)2 (2) in which only one amidinate fragment is coordinated to the ytterbium ion in κ2-N,N'-chelating coordination mode, while the second NCN fragment is protonated in the course of the reaction and is not bound to the metal ion. The outcome of the salt metathesis reaction of LaCl3 with lithium amidinates [C6H4-1,2-{NC(tBu)N(2,6-R2C6H3)}2Li2] (R = Me, iPr) is proven to be strongly affected by the substituent 2,6-R2C6H3 on the amidinate nitrogens. When R = iPr, the salt metathesis reaction occurs smoothly and results in the formation of an ate-chloro-amidinate complex [C6H4-1,2-{NC(tBu)N(2,6-iPr2C6H3)}2]La(μ2-Cl)Li(THF)(μ2-Cl)2Li(THF)2 (3) in which the LaIII ion is coordinated by both amidinate fragments in a "classic"κ2-N,N'-chelating fashion. In the case of R = Me, the reaction requires prolonged heating for completion. Moreover, the salt metathesis reaction is accompanied by the fragmentation of the ligand and affords a trinuclear chloro-amidinate complex [C6H4-1,2-{NC(tBu)N(2,6-Me2C6H3)}2]La{[(tBu)C(N-2,6-Me2C6H3)2]La(THF)}2(μ2-Cl)4(μ3-Cl)2 (4) containing one dianionic ansa-bis(amidinate) and two monoanionic [(tBu)C(N-2,6-Me2C6H3)2] amidinate fragments. DFT calculations are conducted to determine the factor that governs this change in coordination mode and, in particular, the effect of the metal oxidation state.

Lead(II) Coordination Sphere and Ligand Coordination Mode Changes During Removal of Water Molecule by Solid‐state Thermal Conversion

The solid‐state conversion of a 3D lead(II) coordination polymer, [Pb(1,4‐BDC)(H2O)]n (1) microstructures (1,4‐H2BDC = 1,4‐benzenedicarboxylic acid) with PbO7 coordination sphere, was synthesized by a sonochemical process to a 3D [Pb(1,4‐BDC)]n (2) coordination polymer with nanoparticle morphology and the same coordination environment was observed upon thermal treatment and dehydration. The color of this compound did not change during the process. This process is irreversible and compound 2 cannot absorb water again. Adsorption and desorption of water in these lead(II) coordination polymers were studied by IR spectroscopy, thermo gravimetric and differential thermal analyses (TG‐DTA), X‐ray powder diffraction (XRD), and scanning electron microscopy (SEM).

Hydrolysis reaction promotes changes in coordination mode of Ru(II)/acylthiourea organometallic complexes with cytotoxicity against human lung tumor cell lines

In this study, Ru(II)-arene complexes with acylthiourea ligands of the type [Ru(η6‑p‑cymene)(PPh3)(T)Cl]PF6(1–5) and [Ru(η6‑p‑cymene)(PPh3)(T)]PF6(1a, 4a), where PPh3 = triphenylphosphine and T = N‑acyl‑N′(monosubstituted)thiourea, were synthesized and characterized, and their cytotoxic properties were also evaluated. 1a and 4a were obtained from the hydrolysis reaction of 1 and 4. All complexes showed unusual coordination modes for acylthiourea ligands, which are coordinated in a monodentate fashion (S) in 1–5, while they found to be bidentate (S,N), in 1a and 4a. To the best of our knowledge, 1a and 4a are the first crystallographically reported ruthenium compounds with acylthiourea coordinated via S and N(amide) atoms. The cytotoxicity of the compounds was evaluated in human lung cells, A549 and MRC-5. The IC50 values ranging from 0.25 to 0.61 μM after 48 h incubation in lung cancer cells indicate that the compounds showed high cytotoxicity with values significantly lower than the reference drug, cisplatin (11.84 μM). Interaction studies were carried out using human serum albumin (HSA) and DNA. All complexes showed similar cytotoxic activity, however complex 1a, which is the hydrolysis product of 1, presented the highest activity and selectivity among all seven compounds synthesized here. Complexes 1 and 1a inhibited the colony formation decreasing the colony size and inducing morphology changes in A549 cells. These complexes induced apoptosis cell death and promoted cell cycle arrest in the Sub-G1 phase with a decrease in the cell number at the S phase.

Thorium(IV) and Uranium(IV) trans-Calix[2]benzene[2]pyrrolide Alkyl and Alkynyl Complexes: Synthesis, Reactivity, and Electronic Structure

The first thorium(IV) and uranium(IV) hydrocarbyl complexes of a trans-calix[2]benzene[2]pyrrolide macrocycle can use ligand noninnocence to enable multiple C–H bond activation reactions at the metal. Both alkyl and alkynyl complexes supported by the L dianion and L–2H tetraanion are reported. The ThIV and UIV monoalkyl-ate complexes [M(L–2H)An(R)] (M = K for R = CH2Ph, M = Li for R = Me, CH2SiMe3), in which the ligand aryl groups are metalated, add C–H bonds of terminal alkynes across the metal and ligand, forming the AnIV-alkynyl complexes [(L)An(C≡CR′)2] (R′ = SiMe3, SiiPr3). This ligand reprotonation from (L–2H)4– to (L)2– is accompanied by a change in coordination mode of the ligand from η5:η1:η5:η1 to η5:η5. Alternatively, the original alkyl group can be retained if the ligand is reprotonated using [Et3NH][BPh4], affording the ThIV cations [(L)Th(R)][BPh4] (R = CH2Ph, N(SiMe3)2). Here, ligand rearrangement to the κ1:η6:κ1:η6 coordination mode occurs. These complexes provide rare examples of bis(aren...

Heterospin MnIII complex as a reaction product of the redox-induced change in the ligand coordination mode

The reaction of MnII chloride with imino nitroxide radical, 2-(2-hydroxy-5-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl (HL2), affords the MnIII complex [MnL22L3]·Me2CO, a distinctive feature of which is the simultaneous presence in the ligand shell of both the initial imino nitroxide and the product of its reduction 2-(2-hydroxy-5-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide (HL3). The reaction involves the oxidation of MnII to MnIII and the reduction of the imino nitroxide radical to the corresponding amidine oxide along with a change in the coordination mode of the heterocyclic ligand on going from L2 to L3. The MnIII ion forms with L2 six-membered metallocycles typical of Schiff bases, whereas with L3 MnIII forms a seven-membered metallocycle due to the coordination of L3 by oxygen atoms of the phenol and N-oxide It was found in a similar reaction of NiII chloride with imino nitroxide HL2 that no oxidation of the metal occurred and bis(chelate) [NiL22(H2O)2]·2Me2CO was formed in the solid phase. The molecular and crystal structures of the compounds were determined, and their magnetic properties were studied.

An unsymmetrical phosphonium diylide with a fluorenylidene subunit and its lithium complexes

The phosphonium ylide MePh2P(flu) (3) (flu = C13H8, fluorenylidene) was conveniently prepared by reaction of Ph2P(fluH) (1) (fluH = C13H9, fluorenyl) with iodomethane, followed by subsequent dehydrohalogenation of the resulting phosphonium salt [MePh2P(fluH)]I (2) by potassium tert-butoxide. Compound 3 was further deprotonated by n-butyllithium, yielding the corresponding lithium complex [Li{CH2PPh2(flu)}(tmeda)] (4) in presence of N,N,N′,N′-tetramethylethylenediamine (tmeda). This mononuclear lithium compound contains the monoanionic chelating diylidic ligand. An exchange of the neutral bidentate tmeda by tridentate N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (pmdta) enforces a change in coordination mode. Consequently, the diylide is monodentate in [Li{CH2PPh2(flu)}(pmdta)] (5). Compounds 1–5 were characterized by NMR spectroscopy and single-crystal X-ray diffraction experiments.

Reactivity of the drug methimazole and its iodine adduct with elemental zinc

The reactivity of zinc complexes with N,S-donor molecules may be of relevance to the study of Zn-metalloproteins and -metalloenzymes. In this context, the zinc complex [Zn(MeImSH)2I2] was synthesised by the reaction of zinc powder with the 1 : 1 iodine adduct of the drug methimazole [(MeImSH)·I2]. The molecular structure of the complex, elucidated by X-ray diffraction analysis, showed a tetrahedral zinc(II) centre coordinated by two neutral methimazole units (through the sulfur atoms) and two iodides. From the reaction of MeImSH and Zn powder, the complex [Zn(MeImSH)(MeImS)2] (MeImS = deprotonated form of methimazole) was separated and characterised. An analysis of the crystal packing of the neutral complexes [Zn(MeImSH)2X2] (X = I, Br and Cl) and the ionic complex [Zn(MeImSH)3I]I showed that in all of the complexes the sulfur atom, in addition to binding to the metal centre, contributes to the formation of 1-D chains built via C(4)–H⋯S and N–H⋯X interactions in the neutral complexes, and via C(4)–H⋯S and N–CH3⋯S interactions in the ionic complex [Zn(MeImSH)3I]I. The deprotonation/protonation of the coordinated methimazole units can modulate the coordination environment at the Zn core. From the reaction of complex [Zn(MeImSH)3I]I with a strong non-coordinating organic base, we have shown that, as a consequence of the NH deprotonation of methimazole S-coordinated to zinc(II), the ligand coordination mode changes from S-monodentate to N,S-bridging. Correspondingly, in the complex [Zn(MeImSH)(MeImS)2], the MeImS that displays the N,S-bridging mode at zinc can be N-protonated and thereby changes to the S-monodentate coordination.

Boron-Dipyrromethene-Functionalized Hemilabile Ligands as “Turn-On” Fluorescent Probes for Coordination Changes in Weak-Link Approach Complexes

Herein we report a new class of hemilabile ligands with boron-dipyrromethene (Bodipy) fluorophores that, when complexed to Pt(II), can signal changes in coordination mode through changes in their fluorescence. The ligands consist of phosphino-amine or phosphino-thioether coordinating moieties linked to the Bodipy's meso carbon via a phenylene spacer. Interestingly, this new class of ligands can be used to signal both ligand displacement and chelation reactions in a fluorescence "turn-on" fashion through the choice of weakly binding heteroatom in the hemilabile moiety, generating up to 10-fold fluorescence intensity increases. The Pt(II) center influences the Bodipy emission efficiency by regulating photoinduced electron transfer between the fluorophore and its meso substituent. The rates at which the excited Bodipy-species generate singlet oxygen upon excitation suggest that the heavy Pt(II) center also influences Bodipy's emission efficiency by affecting intersystem crossing from the Bodipy excited singlet to excited triplet states. This signaling strategy provides a quantitative read-out for changes in coordination mode and potentially will enable the design of new molecular systems for sensing and signal amplification.

Synthesis and structures of urea-coordinated dinickel(II) complexes with binucleating ligand 1,3-bis(N-(2-(dimethylamino)ethyl)-N-methylamino)propan-2-ol (HL1) and its analogs

New urea-coordinated dinickel(II) complexes with binucleating ligands—HL1, which contains dimethylaminoethyl arms, and its analogs HL2, which features bis(methoxyethyl) arms, and HL3, which contains one dimethylaminoethyl arm and one bis(methoxyethyl) arm—all of which contain a 2-hydroxytrimethylene bridge between the two chelating sites, were synthesized. The structures of [Ni2L1(μ-CH3COO)(CH3COO)(urea)(EtOH)]BPh4·EtOH (2), [Ni2L1(μ-Cl)2(urea)(CH3CN)]BPh4·H2O (3), [Ni2L2(H2O)2(urea)Cl](BPh4)2·H2O (5), and [Ni2L3(μ-CH3COO)2(urea)]BPh4 (7) were revealed by X-ray crystallography, as well as those of their parent dinickel(II) complexes, [Ni2L1(μ-CH3COO)(CH3COO)(H2O)2]BPh4 (1), [Ni2L2(μ-CH3COO)2]BPh4·CH3CN (4), and [Ni2L3(μ-CH3COO)(CH3COO)(EtOH)]BPh4 (6). One urea molecule was coordinated to one dinuclear nickel(II) ion, forming intramolecular hydrogen bonds with a μ-acetato bridge (2, 7), a μ-chloro bridge (3), and coordinated chloro and aqua ligands (5). The formation of 7 from the reaction of 6 with urea was associated with a change in coordination mode from a non-bridging acetato ligand to a μ-acetato ligand. Magnetic measurements revealed a weak antiferromagnetic interaction between the two nickel(II) ions in 1 (J=−16.7cm−1) and 2 (J=−15.0cm−1).

Evaluation of the H2dedpa Scaffold and its cRGDyK Conjugates for Labeling with 64Cu

Studies of the acyclic ligand scaffold H(2)dedpa and its derivatives with the peptide cRGDyK for application in copper radiopharmaceuticals are described. Previously shown to be a superb ligand for (67/68)Ga, the chelate is now shown to coordinate (64)Cu in its derivatized and nonderivatized forms rapidly under mild reaction conditions (10 min, RT, pH 5.5 10 mM sodium acetate buffered solution). The hexadentate, distorted octahedral coordination of H(2)dedpa is confirmed in the corresponding solid state X-ray crystal structure of [Cu(dedpa)]. Cyclic voltammetry determined the reduction potential of [Cu(dedpa)] to be below values found for common bioreductants. Reduction and reoxidation were irreversible but reproducible, indicating a potential change of coordination mode upon reduction of Cu(II) to Cu(I). The thermodynamic stability constant log K(CuL) was determined to be 19.16(5), comparable to other frequently used (64)Cu chelates. Serum stability of the (64)Cu labeled chelate revealed only 3% transchelation/association to serum proteins after 2 h, while the conjugates reveal 10% ([Cu(RGD1)]) and 6% ([Cu(RGD2)]) transchelation at the same time point.

Allosteric Effects in a Ditopic Ligand Containing Bipyridine and Tetra-aza-crown Donor Units

Artificial allosterism: A ditopic ligand, which contains both bipyridine and tetra-aza-crown binding sites, coordinates one Cu(II) through all four N-donors of the tetradentate aza-crown unit. Reaction at the bipyridine site with another Cu(II) allosterically changes the aza-crown from being a tetradentate to a tridentate N-donor unit, a change in coordination mode that causes the successive binding of two Cu(II) ions to proceed with severe negative cooperativity (see scheme).

Synthesis of 1‐Aza‐2‐borabutatriene Rhodium Complexes by Thermal Borylene Transfer from [(OC)5MoBN(SiMe3)2

Borylene on me: An unprecedented borylene transfer to metal-carbon double bonds afforded the title compounds. Preliminary studies revealed a thermally induced change of coordination mode from BC to CC and subsequent highly stereoselective CH activation by the BC bond. [(η5-C5H5)Rh(PCy3){(B,C-η2)-(SiMe3)2N=B=CCH2)}] and its rearrangement product were both characterized by X-ray crystallography (see picture).

Reversible solid state structural transformation of a polyhapto lead(ii) polymeric chain to a tetrahapto lead(ii) two-dimensional network by thermal dehydration with no change in nanoplate morphology

A reversible solid state structural transformation of a new 1D lead(II) coordination polymer [Pb(MPOAc)2(H2O)]n (1), (MPOAc−: mono phenyl acetate) involving in situ ligand synthesis with O7Pb⋯C6 coordination sphere to a 2D supramolecular network [Pb(MPOAc)2]n (2) with O6Pb⋯C4 coordination environment has been observed upon heating and dehydration. This change in coordination-mode was confirmed by single-crystal X-ray diffraction analyses of compounds 1 and 2. Thermogravimetric (TG) and differential thermal analyses (DTA) were employed to study the thermal stabilities of compounds 1 and 2. Powder X-ray diffraction experiments showed that the structural transformation occurs in the batch powder samples and lead to monophasic products. Nanoplates of compound 1 were synthesized by a microwave-assisted process and characterized by scanning electron microscopy (SEM), powder X-ray diffraction, IR spectroscopy and elemental analyses. The SEM images showed that no morphology change occurs during this solid state structural transformation.

Irreversible transformation of chiral to achiral polymorph of K[Co(HCOO)3]: synthesis, structures, and magnetic properties

We report the rare observation of an irreversible transformation from a chiral to an achiral crystal through the syntheses of two polymorphs of K[Co(HCOO)(3)], and their characterization using single and powder crystal X-ray diffractions, infrared spectroscopy, thermal analyses, and the study of their magnetic properties. The kinetic phase (1), obtained under a high concentration of reactants, has a chiral (4(9)·6(6)) framework and adopts the hexagonal space-group P 6(3)22. The thermodynamic phase (2), obtained from dilute solution, has an achiral (4(12)·6(3)) framework and adopts a monoclinic space group C 2/c. Once 1 has crystallized out from the concentrated solution, it dissolves slowly at the expense of the formation of 2. In the solid state 1 is irreversibly transformed to 2 very slowly at ambient conditions. The transformation is accompanied by an increase of the crystal density, a change of coordination mode of some formates from anti-anti to syn-anti and a change in the coordination number of K from 6 to 8. 1 is a spin-canted antiferromagnet (T(N) = 8.3 K) displaying two steps in the isothermal magnetization at 2 K, a spin-flop at 1.2 kOe and a flip to paramagnetic phase at 42.0 kOe. 2 is an antiferromagnet (T(N) = 2.0 K). Thermal properties and IR spectra of the two polymorphs have been studied, showing some differences.