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[Abstract] We report two novel macrocyclic ligands based on the 1,4-DO2AM platform (1,4-DO2AM = 2,2′-(1,4,7,10-tetraazacyclododecane-1,4-diyl)diacetamide) and containing two benzyl groups attached either to the nitrogen atoms of the macrocyclic unit (1,4-BzDO2AM) or to the amide pendant arms (1,4-DO2AMBz). The protonation constants of the ligands and the stability constants of their Mn2+ complexes were determined using pH potentiometry. The introduction of benzyl groups results in a slight decrease of the stability constants of the Mn2+ complexes and a slight increase of their acid-catalysed dissociation reactions. A detailed relaxometric characterisation of the complexes using nuclear magnetic dispersion relaxation (NMRD) and 17O NMR studies indicated that the increase in molecular weight associated with the presence of benzyl groups results in a remarkable increase of proton relaxivities r1p, which take values of 3.8, 3.5 and 2.5 mM−1 s−1 for [Mn(1,4-BzDO2AM)]2+, [Mn(1,4-DO2AMBz)]2+ and [Mn(1,4-DO2AM)]2+ (at 25 °C and 20 MHz). The [Mn(1,4-BzDO2AM)]2+ and [Mn(1,4-DO2AMBz)]2+ complexes form relatively strong adducts with Human Serum Albumin (HSA) with association constants of (3.9 ± 0.6) × 103 and (2.0 ± 0.3) × 103 M−1, respectively. The interaction with the protein slows down the rotational tumbling of the complex in solution, which results in adducts endowed with remarkably high proton relaxivities (r1pb = 18.5 ± 0.7 and 27.4 ± 1.4 mM−1 s−1 for [Mn(1,4-BzDO2AM)]2+ and [Mn(1,4-DO2AMBz)]2+, respectively). Ministerio de Economía y Competitivad; CTQ2015-71211-REDT Ministerio de Economía y Competitivad; CTQ2016-76756-P

[Abstract] The zero-field splitting (ZFS) parameters of the [Mn(EDTA)(H2O)]2–·2H2O and [Mn(MeNO2A)(H2O)]·2H2O systems were estimated by using DFT and ab initio CASSCF/NEVPT2 calculations (EDTA = 2,2′,2″,2‴-(ethane-1,2-diylbis(azanetriyl))tetraacetate; MeNO2A = 2,2′-(7-methyl-1,4,7-triazonane-1,4-diyl)diacetate). Subsequent molecular dynamics calculations performed within the atom-centered density matrix propagation (ADMP) approach provided access to the transient and static ZFS parameters, as well as to the correlation time of the transient ZFS. The calculated ZFS parameters present a reasonable agreement with the experimental values obtained from the analysis of 1H relaxation data. The correlation times calculated for the two systems investigated turned out to be very short (τc ∼ 0.02–0.05 ps), which shows that the transient ZFS is modulated by molecular vibrations. On the contrary, the static ZFS is modulated by the rotation of the complexes in solution, which for the small complexes investigated here is characterized by rotational correlation times of τR ∼ 35–60 ps. As a result, electron spin relaxation in small Mn2+complexes is dominated by the static ZFS. España. Ministerio de Economía y Competitividad; CTQ2013-43243-P España. Ministerio de Economía y Competitividad; CTQ2015-71211-REDT

International audience; The Y3+ complex of PCTMB, the tri-n-butyl phosphonate ester of pyclen (3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene), was synthesized as well as its Ho3+ and Lu3+ analogues. X-ray diffraction analyses revealed isomorphous dimeric M2(PCTMB)2·9H2O (M = Y, Ho, Lu) structures that crystallize in the centrosymmetric P1 triclinic space group. 1H NMR and UV studies in aqueous solutions indicated that Y3+ complexation is fast, being quantitative in 167 min at pH 3.8 and in 13 min at pH 5.5 (25 °C, acetate buffer, I = 0.150 M, [Y3+] = [PCTMB] = 0.2 mM). 1H NMR DOSY and photon correlation spectroscopy experiments evidenced the formation of aggregates in chloroform with a bimodal distribution that changes slightly with concentration (11-24 and 240-258 nm). The behavior of the acid-assisted dissociation of the complex of Y3+ with PCTMB was studied under pseudo-first-order conditions, and the half-life of the [Y(PCTMB)] complex in 0.5 M HCl at 25 °C was found to be 37 min, a value that decreases to 2.6 min in 5 M HCl. The Y3+ complex of PCTMB is thermodynamically very stable, with a stability constant of log KY-PCTMB = 19.49 and pY = 16.7 measured by potentiometry. 90Y complexation studies revealed fast radiolabeling kinetics; optimal radiolabeling conditions were obtained for 90Y in acetate medium, PCTMB at 10-4 to 10-2 M in acetate buffer pH = 4.75, 15 min at 45-60 °C. In vitro stability studies in human serum showed that [90Y(PCTMB)] is quite stable, with about 90% of the activity still in the form of the radiotracer at 24 h and 80% from 48 h to 72 h. A comparison with other ligands such as PCTA, DOTA, and DTPA already used for in vivo application shows that [90Y(PCTMB)] is an interesting lipophilic and neutral analogue of these reference chelates for therapeutic applications in aqueous and nonaqueous media. © 2016 American Chemical Society.

The most feasible complexes formed between dipicolinic acid and hydrated Fe 2+ cation (namely, [FeL(H 2 O) 3 ] and [FeL 2 ]) have been modeled using density functional theory. A comparison among several computational levels of theory and available X-ray data showed that the B3LYP/6-311G(d) computational level provides accurate geometrical parameters for geometry optimization of complexes. The energetics and thermochemistry of complexation reactions in the gas phase and solvated medium (PCM) were evaluated at the B3LYP/6-311G(d) and B3LYP/6-311++G(2df,pd)//B3LYP/6-311G(d) levels of theory. The calculated thermochemistry data exhibited high complexation energies for both complexes and decreasing in the exothermicity of complexation reactions when PCM model was included in the calculations. The calculated free energy changes of complexation reactions pointed to spontaneous procedures. Detailed analysis of energy levels and major composition of selected frontier orbitals were performed and the results suggested the higher stability for the [FeL(H 2 O) 3 ] system than for [FeL 2 ]. Based on QTAIM, several bond-indexes such as electron density at the bond critical points, the Laplacian of the electron density, ellipticity and the total energy density were utilized to analyze chemical bonding in these complexes. Natural bond orbital (NBO) analysis was carried out to provide more precise insight on the interactions and nature of the bonds established between the ligand and the metal ion.

[Abstract] We report a complete set of magnetic susceptibilities of lanthanide complexes with a macrocyclic ligand based on a 3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane platform containing four hydroxyethyl pendant arms (L1). The [LnL1]3+ complexes are isostructural along the lanthanide series from Ce3+ to Yb3+, with the only structural change observed along the series being the monotonous shortening of the Ln–donor distances due to lanthanide contraction. The 1H NMR spectra point to a D2 symmetry of the [LnL1]3+ complexes in aqueous solution, which provides a unique opportunity for analysis of the rhombic magnetic anisotropies with an unequivocal location of the magnetic axes. The contact contributions for the observed paramagnetic shifts have been estimated with density functional theory calculations on the [GdL1]3+ complex. Subsequently, the pseudocontact shifts could be factored out, thereby giving access to the axial and rhombic contributions of the magnetic susceptibility tensor. Our results show that the calculated magnetic anisotropies do not follow the trends predicted by Bleaney’s theory, particularly in the case of Ho3+ and Er3+ complexes. Ministerio de Economía y Competitividad; CTQ2013-43243-P Ministerio de Ciencia e Innovación; CTQ2011-24487

EuDOTA-tetraamide complexes as paraCEST agents offer an attractive platform for designing biological sensors and responsive agents. The early versions of these agents showed low sensitivity at temperature and power levels suitable for in vivo applications partly due to non-optimal water exchange rates. Here we report two new EuDOTA derivatives having glutamyl-phosphonate side arms that display the slowest water exchange rates of any other paraCEST agent reported so far. The advantages of such systems are demonstrated experimentally both in vitro and in vivo and DFT calculations were performed to help understand the physical-chemical reasons for this interesting behavior.

We present herein the efficient palladium(II)-directed self-assembly in water of a series of nine new diversely functionalized metallacycles, owning hydroxy/alkoxycarbonyl/azidoalkyl exo pendant groups attached to ditopic N-monoalkyl/aryl-4,4'-bipyridinium/2,7-diazapyrenium ligands. The highly convergent and versatile synthetic route for the ligands uses the Zincke reaction between (dinitrophenyl)bipyridinium/diazapyrenium salts and racemic amines as the key step. The stereochemical outcome of the self-assembly of the Pd2L2 species is discussed on the basis of density functional theory quantum-chemical calculations.

Six novel lanthanide metal coordination polymers (LnCPs) [Ln(Hbic)3(H2O)]n [Ln = La (1), Pr (2), Nd (3), Sm (4), Eu (5), Gd (6)] have been synthesized by reaction of 1H-benzimidazole-5-carboxylic acid (H2bic) with Ln2O3 under hydrothermal conditions, and characterized via elemental analysis, infrared spectroscopy, thermogravimetric analysis, single-crystal X-ray diffraction, and powder X-ray diffraction. The compounds 1–6 are isostructural and have a 1D layer architecture; the layers are linked by hydrogen bonding and π–π stacking interactions to form a 3D supramolecular framework. Hirshfeld surfaces and the luminescence properties of these complexes were also investigated. The 3-D Hirshfeld surfaces and 2-D fingerprint plots show that the main interactions are the O⋯H/H⋯O intermolecular interactions. Finely, preliminary emission experiments have been carried out on the compounds 3 and 5.

International audience

International audience; H2cb‐te2pa, a cross‐bridged cyclam functionalized by two picolinate arms, was used for the formation of an incredible inert In(III) chelate. For the first time a bifunctional analogue of H2cb‐te2pa was prepared by C‐functionalization to keep its coordination properties intact. However, this strategy leads to the formation of two diastereoisomers, as evidenced and studied by NMR experiments and DFT calculations. Kinetic studies proved nevertheless that both isomers of the complex are equally inert; they were therefore used without distinction for their covalent grafting on polystyrene beads. The so‐called metal‐encoded beads were tested for Imaging Mass Cytometry. The detection of 115In allows the generation of images with high quality, proving the great potential of the bifunctional [In(cb‐te2pa)]+ derivatives for single‐cell analysis by mass cytometry.; H2cb-te2pa, un cyclam renforcé fonctionnalisé par deux bras picolinate, a été utilisé pour la formation d'un chélate d’indium(III) incroyablement inerte. Pour la première fois, un analogue bifonctionnel de H2cb-te2pa a été préparé par C-fonctionnalisation pour conserver ses propriétés de coordination intactes. Cependant, cette stratégie conduit à la formation de deux diastéréoisomères, comme en témoignent les expériences de RMN et les calculs de DFT. Les études cinétiques ont néanmoins prouvé que les deux isomères du complexe étaient également inertes; ils ont donc été utilisés sans distinction pour leur greffage covalent sur des billes de polystyrène. Les billes obtenues ont été testées pour l’imagerie par cytométrie de masse. La détection de l’115In permet de générer des images de haute qualité, prouvant ainsi le potentiel des dérivés bifonctionnels [In (cb-te2pa)]+ pour l'analyse monocellulaire par cytométrie de masse.

[Abstract] We report a detailed study of the photophysical properties of EuIII and TbIII complexes with two ligands based on a 3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane platform containing either four pyridine-2yl-methyl (L1) or four hydroxyethyl (L2) pendant arms. The [TbL1]3+ and [TbL2]3+ complexes present moderate luminescence quantum yields upon excitation through the ligand bands (ϕH2O = 7.4 and 21%, respectively). The [EuL2]3+ complex displays a relatively low quantum yield in H2O (ϕH2O = 1.6%) that increases considerably in D2O (ϕD2O = 5.3%), which highlights the strong quenching effect of the four ligand O–H oscillators. The emission spectrum of [EuL1]3+ is rather unusual in that it shows a relatively high intensity of the 5D0 → 7F5,6 transitions, which appears to be also related to the distorted D4d symmetry of the coordination polyhedron. Surprisingly, the quantum yield of the [EuL1]3+ complex is very low (ϕH2O = 0.10%), considering the good protection of the EuIII coordination environment offered by the ligand. Cyclic voltammograms recorded from aqueous solutions of [EuL1]3+ display a reversible curve with a half-wave potential of −620 mV (versus Ag/AgCl), while [EuL2]3+ presents a reduction peak at more negative potential (−1040 mV). Thus, the L1 ligand provides a rather good stabilisation of divalent Eu compared to the L2 analogue, suggesting that the presence of a low-lying ligand-to-metal charge-transfer (LMCT) state might be responsible for the low quantum yield determined for [EuL1]3+. A density functional theory (DFT) study provides very similar energies for the ligand-centered excited singlet (1ππ*) and triplet (3ππ*) states of [EuL1]3+ and [EuL2]3+. The energy of the 9LMCT state of [EuL1]3+ was estimated to be 20 760 cm−1 by using all-electron relativistic calculations based on the DKH2 approach, a value that decreases to 15 940 cm−1 upon geometry relaxation. Ministerio de Economía y Competitividad; CTQ2016-76756-P Xunta de Galicia; ED431B 2017/59 Xunta de Galicia; ED431D 2017/01

The GdIII-complexes of DO3A-acetophenone and ortho- or para- hydroxyacetophenone ligands have been investigated to assess the effect of the presence of a phenol group on the relaxivity and on the water exchange rate of these potential MRI contrast agents. H-Bonding between the ortho-phenol(ate) groups and the water molecules involved in the dissociative exchange mechanism is shown to speed up the water exchange rate by stabilizing the eight-coordinate transition state.

We present two novel octadentate cyclen-based ligands bearing one (L

[Abstract] The GdIII-complexes of DO3A-acetophenone and ortho- or para- hydroxyacetophenone ligands have been investigated to assess the effect of the presence of a phenol group on the relaxivity and on the water exchange rate of these potential MRI contrast agents. H-Bonding between the ortho-phenol(ate) groups and the water molecules involved in the dissociative exchange mechanism is shown to speed up the water exchange rate by stabilizing the eight-coordinate transition state. This work was carried out under the EU COST Action CA15209 "European Network on NMR Relaxometry". The authors thank Centro de Supercomputación de Galicia (CESGA) for providing the computer facilities

[Abstract] We report a pentadentate ligand containing a 2,2′-azanediyldiacetic acid moiety functionalized with a picolinate group at the nitrogen atom (H3paada), as well as a lipophylic derivative functionalized with a dodecyloxy group at position 4 of the pyridyl ring (H3C12Opaada). The protonation constants of the paada3− ligand and the stability constant of the Mn(II) complex were determined using a combination of potentiometric and spectrophotometric titrations (25 °C, 0.15 M NaCl). A detailed relaxometric characterisation was accomplished by recording 1H Nuclear Magnetic Relaxation Dispersion (NMRD) profiles and 17O chemical shifts and relaxation rates. These studies provide detailed information on the microscopic parameters that control their efficiency as relaxation agents in vitro. For the sake of completeness and to facilitate comparison, we also characterised the related [Mn(nta)]− complex (nta = nitrilotriacetate). Both the [Mn(paada)]− and [Mn(nta)]− complexes turned out to contain two inner-sphere water molecules in aqueous solution. The exchange rate of these coordinated water molecules was slower in [Mn(paada)]− (k298ex = 90 × 107 s−1) than in [Mn(nta)]− (k298ex = 280 × 107 s−1). The complexes were also characterised using both DFT (TPSSh/def2–TZVP) and ab initio CAS(5,5) calculations. The lipophylic [Mn(C12Opaada)]− complex forms micelles in solution characterised by a critical micellar concentration (cmc) of 0.31 ± 0.01 mM. This complex also forms a rather strong adduct with Bovine Serum Albumin (BSA) with an association constant of 5.5 × 104 M−1 at 25 °C. The enthalpy and entropy changes obtained for the formation of the adduct indicate that the binding event is driven by hydrophobic interactions. Authors R. P.-P., I. B., E. I., C. P.-I. and D. E.-G. thank Ministerio de Economía y Competitividad (CTQ2016-76756-P) and Xunta de Galicia (ED431B 2017/59 and ED431D 2017/01) for generous financial support and Centro de Supercomputación of Galicia (CESGA) for providing the computer facilities. R. P.-P. thanks Ministerio de Economía y Competitividad for a PhD FPI grant (BES-2014-068399) and a fellowship for a short term stay in Alessandria (EEBB-I-18-13075). R. U.-V. thanks Xunta de Galicia for a PhD grant (ED481A-2018/314). M.B. and F.C. are grateful to Università del Piemonte Orientale for financial support (Ricerca locale 2016). This work was carried out within the framework of the COST CA15209 Action “European Network on NMR Relaxometry” Xunta de Galicia; ED431B 2017/59 Xunta de Galicia; ED431D 2017/01 Xunta de Galicia; ED481A-2018/314

[Abstract] A new family of carboranyl phosphine-iminophosphorane ligands was prepared and characterized. The new ligands present a carboranyl group directly attached to the iminophosphorane nitrogen atom through a cage carbon atom (C-carboranyl derivatives L1–L3) or through the B3 boron atom (B-carboranyl derivatives L4 and L5), and the phosphine group on a side chain derived from the diphosphine dppm, i.e. with a two-atom spacer between the P and N donor atoms. The non-carboranyl analogue L6, with a biphenyl group on the nitrogen atom, was also synthesized for comparison. These potential (P, N) ligands were used to obtain palladium complexes (Pd1–Pd6) and, thus, study how the different inductive effect of the carboranyl substituents can modify the coordinating ability of the nitrogen atom. The structural analysis of the complexes revealed two different coordination modes for the ligands: the (P, N) chelate coordination and the unexpected P-terminal coordination, which is not observed for non-carboranyl phosphine-iminophosphoranes. These unexpected structural differences led us to perform DFT calculations on the ligands and metal complexes. The calculations show that the final coordination modes depend on the balance between the electronic and steric properties of the particular carboranyl group. This work was supported by Xunta de Galicia (Spain) (grant no. 10PXIB209285PR) Xunta de Galicia; 10PXIB209285PR

We report a detailed study of the structure of the [Bi(DO3A)] complex both in the solid state and in solution. The X-ray crystal structure of [Bi(DO3A)] evidences the octa-coordination of the Bi(iii) ion, which is directly coordinated to the four nitrogen atoms of the cyclen unit and three oxygen atoms of the carboxylate groups. The octa-coordination is completed by an oxygen atom of a neighboring carboxylate group, which bridges Bi(iii) ions thanks to μ2-η1:η1 coordination, resulting in the formation of a coordination polymer. The Bi(iii) ion presents a twisted-square antiprismatic (TSAP) coordination geometry associated with the Δ(δδδδ)/Λ(λλλλ) enantiomeric pair. A computational DFT study indicates that the 6s2 lone pair of Bi(iii) is stereochemically active in [Bi(DO3A)] and most of the cyclen-based complexes reported in the literature. Depending on the spatial arrangement of the donor atoms of the ligand the lone pair points in different directions, so that Bi(iii) can easily accommodate different coordination environments. In solution the [Bi(DO3A)] complex exists as a monomeric complex, as demonstrated by DOSY measurements. The stability constant of the [Bi(DO3A)] complex, determined by using batch spectrophotometric titrations, was found to be rather high (log K = 26.85(5)). The complex presents characteristic absorption in the UV spectrum at 299 nm (ε = 8770 M-1 cm-1) that was attributed to the Bi(iii)-centered 6p ← 6s band on the basis of TDDFT calculations. Spectrophotometric titrations reveal weak binding of different anions to the [Bi(DO3A)] complex, with association constants of K11 = 3.55(8), 3.09(7), 6.2(1) and 2.19(5) for Cl-, Br-, I- and N3-, respectively.

We present a novel family of polyhalide salts of Bi(III) with the general formula [Dim]

International audience; We report a detailed characterization of lanthanide complexes with two azaligands based on the pyclen macrocycle containing two picolinate and one acetate pendant arms. The two picolinate arms are attached to either opposite (L3) or adjacent (L4) amine nitrogen atoms of the macrocyclic platform. The X-ray structures of the Yb3+ complexes show nine coordination of the ligand to the metal ion, a situation that is also observed for EuL4 in the solid state. The EuL3 complex forms centrosymmetric dimers in the solid state joined by μ2-η1:η1 carboxylate groups, which results in 10-coordinate Eu3+ ions. The emission spectra of EuL3 measured in H2O and D2O solution reveal the presence of a hydration equilibrium involving a nine-coordinate species lacking inner-sphere water molecules and a monohydrated 10-coordinate species. The Eu3+ complexes present modest emission quantum yields in buffered aqueous solution (Φ = 16 and 22% for EuL3 and EuL4, 0.1 M tris buffer, pH 7.4), while the corresponding Tb3+ complexes present very high emission quantum yields under the same conditions (∼90%). 1H NMR studies show that the complexes of L3 present a fluxional behavior in D2O solution, while those of L4 are more rigid. The analysis of the Yb3+-induced NMR shifts of YbL4 indicates that the complex presents a structure in solution similar to that observed in the solid state. The Gd3+ complexes present very high thermodynamic stability constants (log KGdL = 23.56(2) and 23.44(2) for GdL3 and GdL4, respectively). The corresponding pGd values (pGd = −log[Gd3+]free with cL = 1 × 10–5 M and cGd = 1 × 10–6 at pH 7.4) of 20.69 (GdL3) and 21.83 (GdL4) are higher than that of Gd(dota)− (pGd = 19.21). The Gd3+ complexes also show remarkable inertness with respect to their proton-assisted dissociation, with dissociation half-life times of 50 min (GdL3) and 20 h (GdL4) in 1 M HCl.; Deux ligands azamacrocycliques à base de picolinate et d'acétate dans un rapport (2: 1) L3 et L4 et différemment distribué présentent des propriétés très intéressantes en tant que chélateurs pour les ions lanthanides (III), notamment une stabilité thermodynamique élevée, une cinétique de complexation rapide, une cinétique de dissociation lente ainsi qu’un des rendements quantiques d’émission très élevés, en particulier dans le cas des complexes Tb3 +.

International audience; The release of uranyl(VI) is a hazardous environmental issue, with limited ways to monitor accumulation in situ. Here, we present a method for the detection of uranyl(VI) ions through the utilization of a unique fluorescence energy transfer process to europium(III). Our system displays the first example of a “turn‐on” europium(III) emission process with a small, water‐soluble lanthanide complex triggered by uranyl(VI) ions.

We report a detailed characterization of the thermodynamic stability and dissociation kinetics of Gd3+ complexes with DO3A derivatives containing a (methylethylcarbamoylmethylamino)acetic acid (L1), (methylpropylcarbamoylmethylamino)acetic acid (L2), 2-dimethylamino-N-ethylacetamide (L3), or 2-dimethylamino-N-propylacetamide (L4) group attached to the fourth nitrogen atom of the macrocyclic unit. These ligands are model systems of Ca2+- and Zn2+-responsive contrast agents (CA) for application in magnetic resonance imaging (MRI). The results of the potentiometric studies (I = 0.15 M NaCl) provide stability constants with log KGdL values in the range 13.9–14.8. The complex speciation in solution was found to be quite complicated due to the formation of protonated species at low pH, hydroxido complexes at high pH, and stable dinuclear complexes in the case of L1,2. At neutral pH significant fractions of the complexes are protonated at the amine group of the amide side chain (log KGdL×H = 7.2–8.1). These ligands form rather weak complexes with Mg2+ and Ca2+ but very stable complexes with Cu2+ (log KCuL = 20.4–22.3) and Zn2+ (log KZnL = 15.5–17.6). Structural studies using a combination of 1H NMR and luminescence spectroscopy show that the amide group of the ligand is coordinated to the metal ion at pH ∼8.5, while protonation of the amine group provokes the decoordination of the amide O atom and a concomitant increase in the hydration number and proton relaxivity. The dissociation of the complexes occurs mainly through a rather efficient proton-assisted pathway, which results in kinetic inertness comparable to that of nonmacrocyclic ligands such as DTPA rather than DOTA-like complexes.

[Abstract] We report a series of Cu(II) and Zn(II) complexes with different ligands containing a dipicolyl unit functionalized with urea groups that may contain or not a phenylboronic acid function. These complexes were designed for the recognition of phosphorylated anions through coordination to themetal ion reinforced by hydrogen bonds involving the anion and NHgroups of urea. The complexes were isolated and several adducts with pyrophosphate were characterized using X-ray diffraction measurements. Coordination of one of the urea nitrogen atoms to themetal ion promoted the hydrolysis of the ligands containing 1,3-diphenylurea units, while ligands bearing 1-ethyl-3-phenylurea groups did not hydrolyze significantly at room temperature. Spectrophotometric titrations, combined with 1H and 31P NMR studies, were used in investigating the binding of phosphate, pyrophosphate (PPi), and nucleoside 50-polyphosphates (AMP, ADP, ATP, CMP, and UMP). The association constants determined in aqueous solution (pH 7.0, 0.1MMOPS) point to a stronger association with PPi, ADP, and ATP as compared with the anions containing a single phosphate unit. The [CuL4]2+ complex shows important selectivity for pyrophosphate (PPi) over ADP and ATP. Galicia. Consellería de Cultura, Educación e Ordenación Universitaria; EM 2012/088

[Abstract] Two synthetic approaches—temperature variation and anion templation—allowed for the selective formation of a [2]catenane ([2]C4+) or a trefoil knot (TK6+), or for the enhanced formation of a Solomon link (SL8+), all from a simple set of starting materials (Zn(II) acetate, diformylpyridine (DFP) and a diamino-2,2′-bipyridine (DAB)) in mixed aqueous solutions. The catenane formed exclusively at 90 °C in a 1 : 1 mixed solvent of D2O and MeOD. In the presence of bromide ion as template, TK6+ formed exclusively at 50 °C in the same solvent. In the solid state, TK6+ hosts two bromide ions in its central cavity by forming six Csp2–H hydrogen bonds. In D2O, TK6+, which was originally prepared as a trifluoroacetate (TFA) salt, was found to exchange two TFA counterions for two monovalent anions of different sizes and shapes, which lodged within the knot's central cavity. In contrast to bromide, the larger triflate anion (CF3SO3−) promoted the formation of SL8+, which was characterized by 1H NMR spectroscopy and mass spectrometry. Two dimensional heteronuclear 19F-1H-HOSEY NMR experiments detected CH⋯F interactions inside the cavity of SL8+. Thus, the product distribution of this dynamic link forming system is sensitive to temperature and the size and shape of the anion template, and one of the products, TK6+, is capable of binding a variety of monovalent anions in D2O with high affinity (with log β2 values of 4 to 6 being typical).

The immobilization of molecular switches within materials can give rise to new bulk properties that are useful for a variety of applications. Here, we report the synthesis and characterization of covalent organic polymers composed of cyclotriphosphazene core moieties linked together by redox-switchable viologen units. The polymers are isolated as non-porous, micro- and nano-sized spherical particles whose constituent viologens allow access to three distinct redox states: dicationic, radical-cationic and neutral. With viologens in their dicationic state, the particles were used for magic printing, gaseous ammonia sensing, and efficient oxoanion capture. With viologens in any oxidation state, the polymers were capable of capturing 200 to 380% of their weight of iodine vapor. Iodine capture within all of the viologen-based polymers was fast, requiring minutes, as compared to capture by previously reported polymers, which requires hours. With viologens in their neutral state, the polymers exhibited the highest iodine loadings reported to date. Upon one and two-electron reduction, the polymers partially or completely lost their cationic character and, concomitantly, their anion removal capability.

The displacement of water molecule(s) from the inner coordination sphere of [Gd(DTTA-Me)(H2O)2]- (DTTA = ethylenetriamine NNN?N? tetraacetate) by fluoride has been studied by multinuclear NMR relaxation (1H 17O 19F) and DFT calculations. Fluoride anions can replace only one of the coordinated water molecules. The thermodynamic stability constant (KGdLF298 0 = 11.6 ± 0.3) and thermodynamic parameters characterizing the formation of [Gd(DTTA-Me)(H2O)F]2- were determined (?H0 = +6.3 ± 0.1 kJ mol-1; ?S0 = +41.5 ± 3.4 J mol-1 K-1; ?V0 = +4.5 ± 1.2 cm3 mol-1). Fluoride binding causes a marked acceleration of the water exchange which is seven times faster for [Gd(DTTA-Me)(H2O)F]2- (kex1 298 = 177 ×106 s-1) than for [Gd(DTTA-Me)(H2O)2]- (kex2 298 = 24.6 × 106 s-1). Water exchange on both compounds is faster than formation of the fluoride complex. The analysis of the Gd-Owater distances electron density and electron localization function (ELF) at the bond critical points using DFT calculations reveals that F- binding weakens the Gd-Owater bonds thereby facilitating the departure of the coordinated water molecule following a dissociative mechanism. The water exchange on both Gd(DTTA-Me) complexes follow dissociative reaction pathways as shown by the positive activation volumes ?V? = +8 ± 2 cm3 mol-1 and +15 ± 4 cm3 mol-1 for the bis aqua complex and the monofluoro complex respectively.

[Abstract] Concentration, temperature and/or solvent polarity control the speciation on the metal-directed self-assembly of a ditopic pyridyl ligand L with cis-protected Pd(II) metal centers. This results into a controllable dynamic system, involving a [Pd2L2]6+ metallacycle and a [Pd4L4]12+ ring-in-ring complex. Ministerio de Economía y Competitividad; CTQ-201341097-P Xunta de Galicia; EM2014/056

Three topologically non-trivial cadmium(ii)-based complexes-Cd-[2]C, Cd-TK and Cd-SL-were simultaneously self-assembled in a dynamic library, individually isolated and fully characterized using solid-state, gas-phase and solution-phase techniques. Post-synthetic modifications, including reduction and transmetalation, were subsequently achieved. Imine bond reduction followed by demetallation led to the isolation of the corresponding organic molecules [2]C, TK and SL. Transmetalation of Cd-TK and Cd-SL with the zinc(ii) cation resulted in isolation of the corresponding zinc(ii)-containing complexes Zn-TK and Zn-SL.

We report a series of ligands containing pentadentate 6,6′-((methylazanediyl)bis(methylene))dipicolinic acid binding units that form mono- (H2dpama), di- (mX(H2dpama)2), and trinuclear (mX(H2dpama)3) complexes with Mn2+ containing two coordinated water molecules per metal ion, which results in pentagonal bipyramidal coordination around the metal ions. In contrast, the hexadentate ligand 6,6′-((ethane-1,2-diylbis(azanediyl))bis(methylene))dipicolinic acid (H2bcpe) forms a complex with distorted octahedral coordination around Mn2+ that lacks coordinated water molecules. The protonation constants of the ligands and the stability constants of the Mn2+, Cu2+, and Zn2+ complexes were determined using potentiometric and spectrophotometric titrations in 0.15 M NaCl. The pentadentate dpama2– ligand and the di- and trinucleating mX(dpama)24– and mX(dpama)36– ligands provide metal complexes with stabilities that are very similar to that of the complex with the hexadentate ligand bcpe2–, with log β101 values in the range 10.1–11.6. Cyclic voltammetry experiments on aqueous solutions of the [Mn(bcpe)] complex reveal a quasireversible system with a half-wave potential of +595 mV versus Ag/AgCl. However, [Mn(dpama)] did not suffer oxidation in the range 0.0–1.0 V, revealing a higher resistance toward oxidation. A detailed 1H NMRD and 17O NMR study provided insight into the parameters that govern the relaxivity for these systems. The exchange rate of the coordinated water molecules in [Mn(dpama)] is relatively fast, kex298 = (3.06 ± 0.16) × 108 s–1. The trinuclear [mX(Mn(dpama)(H2O)2)3] complex was found to bind human serum albumin with an association constant of 1286 ± 55 M–1 and a relaxivity of the adduct of 45.2 ± 0.6 mM–1 s–1 at 310 K and 20 MHz.

International audience; A series of Gd(3+) complexes exhibiting a relaxometric response to zwitterionic amino acid neurotransmitters was synthesized. The design concept involves ditopic interactions 1) between a positively charged and coordinatively unsaturated Gd(3+) chelate and the carboxylate group of the neurotransmitters and 2) between an azacrown ether appended to the chelate and the amino group of the neurotransmitters. The chelates differ in the nature and length of the linker connecting the cyclen-type macrocycle that binds the Ln(3+) ion and the crown ether. The complexes are monohydrated, but they exhibit high proton relaxivities (up to 7.7 mM(-1) s(-1) at 60 MHz, 310 K) due to slow molecular tumbling. The formation of ternary complexes with neurotransmitters was monitored by (1) H relaxometric titrations of the Gd(3+) complexes and by luminescence measurements on the Eu(3+) and Tb(3+) analogues at pH 7.4. The remarkable relaxivity decrease (≈80 %) observed on neurotransmitter binding is related to the decrease in the hydration number, as evidenced by luminescence lifetime measurements on the Eu(3+) complexes. These complexes show affinity for amino acid neurotransmitters in the millimolar range, which can be suited to imaging concentrations of synaptically released neurotransmitters. They display good selectivity over non-amino acid neurotransmitters (acetylcholine, serotonin, and noradrenaline) and hydrogenphosphate, but selectivity over hydrogencarbonate was not achieved.

We present a theoretical investigation of Gd-Owater bonds in different complexes relevant as contrast agents in magnetic resonance imaging (MRI). The analysis of the Ln-Owater distances, electron density (ρBCP), and electron localization function (ELF) at the bond critical points of [Ln(DOTA)(H2O)](-) and [Ln(DTPA-BMA)(H2O)] indicates that the strength of the Ln-Owater bonds follows the order DTPA-BMADOTA (M isomer)DOTA (m isomer). The ELF values decrease along the 4f period as the Ln-Owater bonds get shorter, in line with the labile capping bond phenomenon. Extension of these calculations to other Gd(3+) complexes allowed us to correlate the experimentally observed water exchange rates and the calculated ρBCP and ELF values. The water exchange reaction becomes faster as the Gd-Owater bonds are weakened, which is reflected in longer bond distances and lower values of ρBCP and ELF. DKH2 calculations show that the two coordinated water molecules may also have significantly different (17)O hyperfine coupling constants (HFCCs).

We reported a quantum mechanical study of the complexes formed between Sm 3+ and the bisphosphonate ligand pamidronate in aqueous solution. According to available experimental p K a values pamidronate was expected to exist in aqueous solution, at physiologically relevant pH, in its di- and tri-protonated forms (denoted by H 3 L and H 2 L). The most stable structures of the ligands and Sm 3+ complexes were found by using a detailed analysis of the conformational space with semiempirical and DFT methods. The results showed that both H 2 L and H 3 L bisphosphonates acted as a tridentate ligands in their complexes with Sm 3+ . The addition of explicit water molecules to the coordination sphere of the metal not only gave different coordination numbers for H 2 L and H 3 L complexes (CN=9 and 10), but also provided different trends in stabilization energies. The results highlighted the importance of considering not only an explicit first coordination shell, but also a second hydration shell, for an adequate description of this type of complexes in aqueous solution.

International audience; We report the synthesis of two azaligands based on the pyclen macrocyclic platform containing two picolinate and one acetate pendant arms. The two ligands differ in the relative positions of the pendant functions, which are arranged either in a symmetrical (L3) or nonsymmetrical (L4) fashion. The complexation properties of the ligands toward natY3+ and 90Y3+ were investigated to assess their potential as chelating units for radiopharmaceutical applications. The X-ray structures of the YL3 and YL4 complexes show nonadentate binding of the ligand to the metal ions. A multinuclear 1H, 13C, and 89Y NMR study shows that the complexes present a structure in solution similar to that observed in the solid state. The two complexes present very high thermodynamic stability constants (log KYL = 23.36(2) and 23.07(2) for YL3 and YL4, respectively). The complexes also show a remarkable inertness with respect to their proton-assisted dissociation, especially YL4. 90Y radiolabeling was proved to be efficient under mild conditions. The 90YL3 and 90YL4 radiochelates were found to be more stable than 90Y(DOTA).

The oxygen-evolving complex (OEC) is the native enzyme that catalyzes the oxidation of water in natural photosynthesis. Two new classes of manganese cluster complexes of formula Ba2Mn2L12(H3L1)2(CH3OH)4 1 and Mn4L26Cl2 2 were prepared (H4L1 = N,N&prime, (ethane-1,2-diyl)bis(2-hydroxybenzamide), L2 = methyl picolinimidate) and characterized by standard techniques including microanalysis, IR spectroscopy, ESI spectrometry, and magnetic susceptibility measurements. X-ray diffraction studies of these complexes revealed (i) a box-type structure for 1 formed by two redox-active manganese(III) ions and two barium(II) ions connected by two bridging bisamido-bisphenoxy ligand molecules, and (ii) a planar-diamond array for Mn4N6 cluster 2 where the picolinimidates act as chelating ligands through the two nitrogen atoms. The ability of 1 and 2 to split water has been studied by means of water photolysis experiments. In these experiments, the oxygen evolution was measured in aqueous media in the presence of p-benzoquinone (acting as the hydrogen acceptor), the reduction of which was followed by UV-spectroscopy. The relevant photolytic activity found for 1 is in contrast to the inactivity of 2 in the photolytic experiments. This different behavior is discussed on the basis of the structure of the biomimetic models and the proposed reaction mechanism for this process supported by DFT calculations.

Copper(II) complexes with the potentially tridentate Schiff bases N-[(3-ethoxy-2-hydroxyphenyl)methylidene]-N′-tosylbenzene-1,2-diamine (H2L1) and N-[(2-hydroxynaphthanyl)methylidene]-N′-tosylbenzene-1,2-diamine (H2L2) have been synthesized by electrochemical oxidation of the metal in an electrochemical cell containing a solution of the corresponding ligand in acetonitrile. Adducts of these compounds with 2,2′-bipyridine (2,2′-bpy), 4,4′-bipyridine (4,4′-bpy) or 1,10-phenanthroline (phen) were also obtained. The complexes have been characterized by microanalysis, mass spectrometry, EPR, IR and UV-Vis spectroscopies, as well as DFT calculations. The ligand H2L1 and the compounds [CuL1(H2O)]·H2O (1), [Cu2L12(4,4′-bpy)] (3), [CuL1(phen)] (4), [CuL2(2,2′-bpy)] (6), and [Cu2L22(4,4′-bpy)3] (7) have also been characterized by X-ray diffraction. The copper compounds 1, 4 and 6 are mononuclear with a square planar geometry around the metal for 1 and square pyramidal for 4 and 6. However, 3 and 7 are dinuclear complexes with a 4,4′-bpy ligand bridging two copper atoms with square planar (3) or square pyramidal (7) coordination. The supramolecular structures were studied by means of Hirshfeld surface analysis. The adducts of phen and 2,2′-bpy exhibit enhanced DNA cleavage ability compared to the [CuL(H2O)] complexes (L = L1 or L2), while the binuclear entities formed by 4,4′-bpy coordination present reduced nuclease efficiency.

Herein we report a detailed investigation of the solid state and solution structures of lanthanide(III) complexes with the 18-membered pyridinophane ligand containing acetamide pendant arms TPPTAM (TPPTAM = 2,2',2″-(3,7,11-triaza-1,5,9(2,6)-tripyridinacyclododecaphane-3,7,11-triyl)triacetamide). The ligand crystallizes in the form of a clathrated hydrate, where the clathrated water molecule establishes hydrogen-bonding interactions with the amide NH groups and two N atoms of the macrocycle. The X-ray structures of 13 different Ln(3+) complexes obtained as the nitrate salts (Ln(3+) = La(3+)-Yb(3+), except Pm(3+)) have been determined. Additionally, the X-ray structure of the La(3+) complex obtained as the triflate salt was also obtained. In all cases the ligand provides 9-fold coordination to the Ln(3+) ion, ten coordination being completed by an oxygen atom of a coordinated water molecule or a nitrate or triflate anion. The bond distances of the metal coordination environment show a quadratic change along the lanthanide series, as expected for isostructural series of Ln(3+) complexes. Luminescence lifetime measurements obtained from solutions of the Eu(3+) and Tb(3+) complexes in H2O and D2O point to the presence of a water molecule coordinated to the metal ion in aqueous solutions. The analysis of the Ln(3+)-induced paramagnetic shifts indicates that the complexes are ten-coordinated throughout the lanthanide series from Ce(3+) to Yb(3+), and that the solution structure is very similar to the structures observed in the solid state. The complexes of the light Ln(3+) ions are fluxional due to a fast Δ(λλλλλλ) ↔ Λ(δδδδδδ) interconversion that involves the inversion of the macrocyclic ligand and the rotation of the acetamide pendant arms. The complexes of the small Ln(3+) ions are considerably more rigid, the activation free energy determined from VT (1)H NMR for the Lu(3+) complex being ΔG(⧧)298 = 72.4 ± 5.1 kJ mol(-1).

International audience; A versatile and efficient bisaminal template approach for the synthesis of cyclam and [13]aneN4 (homocyclen) bifunctional chelating agents (BCAs) bearing a hydroxyethyl function as a C-appended group is presented. The synthesis is rapid (two steps/one week) and does not require fastidious protection–deprotection steps or chromatographic purification. Another reactional route and alternative work-up give access to their oxo-cyclam and oxo-homocyclen analogues. The procedure consists of the cyclization of the preorganized tetraamine 1,4,8,11-tetraazaundecane, in its cis-butanedione-bisaminal form, with an α,β-unsaturated lactone to provide the tetracyclic oxo-intermediate whose bisaminal bridge can be easily removed and/or its amide function reduced under mild conditions. Furthermore, the synthetic route was successfully applied to the synthesis of teta and trita BCAs analogues starting from the linear tetraamine 1,4,7,10-tetraazadecane. Additionally, the appended alcohol functions of various cyclam and homocyclen based ligands were converted into their ethylamine functions following a very convenient procedure. Finally, preliminary analytical and complexation studies highlight that the supplementary hydroxyethyl C-appended chain has only a low impact on the acid–base behaviour and copper(II) or zinc(II) coordination properties of the macrocycle.

The synthesis of a new nonacoordinating ligand based on an AMPED (6-amino-6-methylperhydro-1,4-diazepine) scaffold functionalized by three picolinate (6-carboxy-2-methylpyridine) arms is described. Coordination of lanthanide cations (Ln = Eu and Tb) was investigated by spectrophotometric titrations monitored by UV-Vis absorption and steady-state emission spectroscopy, showing the formation of [LnL] complexes in aqueous solutions. The corresponding Eu and Tb complexes were isolated and characterized, and their spectroscopic properties (luminescence quantum yields, excited state lifetimes) were determined in buffered water (TRIS/HCl, pH 7.4) and compared to the data reported in the literature for related systems. DFT modelling of the complexes showed the picolinate arms to be perfectly wrapped around the Ln(3+) cations, affording an excellent shielding of the metal as confirmed by the determination of the hydration number of q = 0 for both complexes. The high resolution emission spectrum was used to determine the radiative lifetime of Eu in the complex (τrad = 3.05 ms) and the metal-centred luminescence quantum yield (0.20). The modest 0.10 overall luminescence quantum yield of the Eu complex is a consequence of an energy transfer with medium efficiency (0.50) and a low metal centred luminescence efficiency attributed in part to the presence of numerous NH and CH bonds in close proximity to the metal centre.

Stereoisomerization and the unprecedented phenomenon of metal translocation in the absence of redox processes were probed in two inherently chiral bimetallic [2]catenanes by using a combination of variable-temperature 1H NMR and CD spectroscopies, X-ray crystallography, and DFT calculations.

A previous report demonstrated that EuDO3A could be used as an NMR shift reagent for imaging extracellular lactate produced by cancer cells using CEST imaging. In this work, a series of heptadentate macrocyclic YbDO3A-trisamide complexes with δ-chiral carbons in the three pendant side-arms were examined as shift reagents for lactate detection. High resolution 1H NMR spectra and DFT calculations provided evidence for the formation of stereoselective lactate·YbDO3A-trisamide complexes each with a different CEST signature. This stereoselectivity allowed discrimination of d- versus l-lactate by both high-resolution NMR and CEST. This work demonstrates that lanthanide-based paramagnetic shift reagents can be designed to detect important metabolites by CEST MRI selectively.

[Abstract] Gadolinium(III) complexes with pH-dependent relaxivities have been proposed as responsive magnetic resonance imaging (MRI) contrast agents (CA) for mapping of pH value in living subjects. The latter is clinically relevant because hypoxia-induced reduction of interstitial pH (acidosis) is a hallmark of tumor progression and resistance against chemotherapy. In order to obtain versatile building blocks for integration of a pH-responsive MRI-CA functionality into larger molecular assemblies, such as bioconjugates, micelles or nanoparticles, we equipped the structural motif GdDO3A-ethylene(arylsulfonic acid) with additional carboxylic acid moieties in the aromatic para-position. Two novel compounds were characterized concerning their pH-dependent relaxivity as well as by 17O NMR and 1H NMRD, augmented by determination of luminescence lifetimes of the respective Eu(III) complexes and structural modelling by density functional theory (TPSSh/LCRECP/6-31G(d)). Unexpected involvement of the peripheral carboxylates into metal ion complexation effected self-assembly of the lanthanide(III) complexes, resulting in dimeric species comprising two lanthanide ions, two symmetrically bridging ligands, and one coordinated water molecule per Gd(III) (q = 1). These structures are stable even at low concentrations and in presence of competing anions like phosphate. The pH-sensitive sulfonamide moieties are not involved into Gd(III) coordination, resulting in virtually constant relaxivities of r1 = 6.7 mM−1 s−1 (298 K, 20 MHz) over the biologically relevant pH range (4 to 9). Since further functionalisation on the peripheral carboxylates would effectively inhibit dimer formation, the compounds are nonetheless suited for the initially envisaged field of application. Lorenzo Tei sincerely acknowledges the Alexander von Humboldt Foundation (AvH) for a Research fellowship. The authors also thank Dr. Claudio Cassino for the help in acquisition of 1H NMR DOSY spectra, and the Deutsche Forschungsgemeinschaft (CRC 824) for support

The Ni2+ complexes with hexadentate ligands containing two 6 methylpicolinamide groups linked by ethane-1,2 diamine (H2dedpam) or cyclohexane-1,2 diamine (H2chxdedpam) spacers were investigated as potential contrast agents in magnetic resonance imaging (MRI). The properties of the complexes were compared to those of the analogues containing 6 methylpicolinate units (dedpa2 and chxdedpa2 ). The X ray structure of the [Ni(H2dedpam)]2+ complex reveals a six-coordinated metal ion with a distorted octahedral environment. The protonation constants of the dedpa2 and H2dedpam ligands and the stability constants of their Ni2+ complexes were determined using pH-potentiometry and spectrophotometric titrations (25 ºC, 0.15 M NaCl). The [Ni(dedpa)] complex (logKNiL = 20.88(1)) was found to be considerably more stable than the corresponding amide derivative [Ni(H2dedpam)]2+ (logKNiL = 14.29(2)). However, the amide derivative [Ni(H2chxdedpam)]2+ was found to be considerably more inert with respect to proton-assisted dissociation than the carboxylate derivative [Ni(chxdedpa)]. A detailed 1H NMR and DFT study was conducted to assign the 1H NMR spectra of the [Ni(chxdedpa)] and [Ni(H2chxdedpam)]2+ complexes. The observed 1H NMR paramagnetic shifts were found to be dominated by the Fermi contact contribution. The amide resonances of [Ni(H2chxdedpam)]2+ at 91.5 and 22.2 ppm were found to provide sizeable chemical exchange staturation transfer effect, paving the way for the development of NiCEST agents based on these rigid non-macrocyclic platforms.

Thanks to a smart regiospecific N-functionalization, a pyclen based ligand bearing one picolinate and two acetate arms organized in a dissymmetric manner was synthesized for Y

We report two novel macrocyclic ligands based on the 1,4-DO2AM platform (1,4-DO2AM = 2,2'-(1,4,7,10-tetraazacyclododecane-1,4-diyl)diacetamide) and containing two benzyl groups attached either to the nitrogen atoms of the macrocyclic unit (1,4-BzDO2AM) or to the amide pendant arms (1,4-DO2AMBz). The protonation constants of the ligands and the stability constants of their Mn

[Abstract] A series of mono‐, di‐, and trinuclear complexes of Eu and Tb was designed to study the influence of the number of Ln emitting centers on the luminescence properties of discrete polynuclear complexes. The complexes are based on a cyclen scaffold, functionalized by two picolinic acid pendant arms. These coordinating units are separated by a 1,3‐dimethylbenzene spacer for the dinuclear complex and a 1,3,5‐trimethylbenzene bridge in the case of the trinuclear complex. The synthesis and characterization of the ligands are presented, together with the preparation and spectroscopic characterization of the complexes. The luminescence properties of the complexes were determined by UV/Vis absorption spectroscopy and steady‐state and time‐resolved luminescence spectroscopy in buffered aqueous solutions. Comparison of the electronic absorption spectra showed that the absorption properties can almost be considered as extensive parameters within experimental error, as expected for electronically non‐conjugated systems. A small drop of both the excited state luminescence lifetimes and the luminescence quantum yields was observed for the trinuclear complexes in the case of Tb. To understand this behavior, theoretical HF (Hartree–Fock) calculations were performed for the three complexes. Models indicate that the average intermetallic distance in the dinuclear complex is almost the same as in the trinuclear one, disfavoring a possible distance dependence of the observed phenomena. Francia. Agence Nationale de la Recherche; ANR P2N 2012

A series of transition metal complexes [ML(1)] (H2L(1) = 1,4,10-trioxa-7,13-diazacyclopentadecane-N,N'-diacetic acid, M = Co, Ni, Cu, or Zn) have been prepared and characterized. The X-ray structures of the [CoL(1)] and [CuL(1)] complexes reveal that the metal ions are seven-coordinated with a distorted pentagonal bipyramidal coordination. The five donor atoms of the macrocycle define the pentagonal plane of the bipyramid, while two oxygen atoms of the carboxylate groups coordinate apically. The [NiL(1)] complex presents a very distorted structure with long Ni-O distances involving two oxygen atoms of the crown moiety [2.544(3) Å]. This distortion is related to the Jahn-Teller effect that is expected to operate in d(8) pentagonal bipyramidal complexes. The spectroscopic characterization of the [ZnL(1)] and [CuL(1)] complexes using NMR and EPR and the theoretical calculation of the (13)C NMR shifts and g- and A-tensors using DFT confirm that these complexes retain the pentagonal bipyramidal coordination in aqueous solution. The stability trend of the [ML(1)] complexes (Co(2+)Ni(2+)Cu(2+)Zn(2+)), which is in contradiction with the Irving-Williams order, has been analyzed using DFT calculations (TPSSh functional). The free energy values calculated in the gas phase for [CoL(1)](g) + [M(H2O)6](2+)(g) → [ML(1)](g) + [Co(H2O)6](2+)(g) (M = Ni, Cu, Zn) reproduce fairly well the stability trend observed experimentally, the agreement being improved significantly upon inclusion of solvent effects. Our results indicate that the pentagonal bipyramidal coordination is particularly unfavorable for Ni(2+), and thus preorganized ligands that favor this geometry such as L(1) are selective for Co(2+) over Ni(2+) cations.

The stability constants of complexes of the macrocyclic ligand do3a-pic4– (H4do3a-pic = 2,2′,2″-{10-[(6-carboxypyridin-2-yl)methyl]-1,4,7,10-tetraazacyclododecane-1,4,7-triyl}triacetic acid) with several divalent metal ions (Pb2+, Cd2+, Zn2+, Cu2+, Ca2+, and Mg2+) have been determined by using pH-potentiometric titrations (I = 0.1 M KCl, 25 °C). The stability of these complexes follows the trend Cu2+ > Cd2+ ≈ Pb2+ ≈ Zn2+ >> Ca2+ >> Mg2+. A particularly high stability constant has been determined for the Cu2+ complex [log KCuL = 23.20(4)]. Analysis of the titration curves indicate the presence of protonated forms of the complexes in solution, with protonation constants of log KM(HxL) = 6.9–2.0 (x = 1, 2, or 3). The structure of the complexes in solution has been investigated by using 1H and 13C NMR spectroscopy and DFT calculations performed in aqueous solution at the TPSSh/6-31G(d) level. In the case of the Pb2+ and Cd2+ complexes, relativistic effects were considered with the use of relativistic effective core potentials. Calculations show that the complexes with the largest metal ions (Pb2+ and Ca2+) are nine-coordinate, with their coordination polyhedra being best described as capped twisted square antiprisms. The Cd2+ and Mg2+ complexes are seven-coordinate, with the metal ions being bound to the four nitrogen atoms of the cyclen unit and the three acetate pendant arms. Finally, in the Cu2+ and Zn2+ complexes, the metal ions are six-coordinated, with the metal ions being asymmetrically placed inside the macrocyclic cavity of the ligand, and the coordination polyhedra can be described as an octahedron and a trigonal prism, respectively.

The previously reported organic solid-state fluorophore 7-(3,4-dimethoxyphenyl)-2-ethoxy-4-phenyl-1,8-naphthyridine-3-carbonitrile 1 was found to spontaneously self-organize into diverse 1D crystalline nanostructures by choosing appropriate liquid phase self-assembly conditions. Experimental results, as well as DFT quantum calculations (at the M06-2X/6-31+G(d) level), shed light on the aggregation mechanism. This was found in good agreement with molecules being primarily joined together through intermolecular alignment caused by electrostatic interactions, as well as minimization of the steric repulsions. This alignment provokes the preferential growth of the crystalline materials into 1D aggregates, as well as the observed fluorescence of the material in the solid state. Luminescent nanowires, nanodendrons, and nanodendrimers, obtained following this spontaneous liquid phase self-assembly, have shown a versatile fluorescent behavior. Here, the obtained nanostructured materials showed a blue-shifted emiss...

The molecular structures of Li2[Ni(tmdta)]·5H2O (1a, tmdta = trimethylenediaminetetraacetate), {C(NH2)3}2[Ni(tmdta)]·6H2O (1b), and {Ni(H2O)6}[Ni(tmdta)]·2H2O (2a) have been determined. The central trimethylenediamine chelate ring shows half-chair (hc) geometries in 1a and 1b, while a twist-boat (tb) conformation is encountered in 2a. The coexistence of tb and hc forms in the solid state prompted us to elucidate the existence of a tb ⇌ hc equilibrium in aqueous solution. Evaluation of the data from solid state vibrational spectra (Raman and IR) for the hc and tb forms showed excellent agreement with simulated spectra obtained with DFT computations (TPSSh/TZVP). This outstanding matching between theory and experiment enabled us to build composite spectra with varying hc:tb ratios. Comparison of these results with Raman and IR spectra recorded for [Ni(tmdta)](2-) in aqueous solution revealed that simulated Raman and IR spectra with a hc:tb ratio = 2:3 match the solution spectra in an accurate way. This equilibrium ratio enabled us to compute (13)C NMR sifts for the paramagnetic solution spectrum of [Ni(tmdta)](2-) based on the relative contributions by hc and tb fractions. This leads to computed shifts that agree closely with the experimental ones. Also, the kinetics of the skeleton dynamics could be estimated quantitatively by temperature-dependent (13)C NMR spectroscopic measurements. An interesting effect encountered for the very first time here concerns a drastic intensity difference of the 10Dq band ((3)A2g → (3)T2g(F) transition) in solid state electronic spectra of tb vs hc isomers, where the intensity of this band in the case of the hc form is much lower than that of the tb conformer and thus more similar to the case of the usual Ni(II) chromophore in octahedral environment. The equilibrium constants for complex formation and protonation of Ni(II)-tmdta at low pH have been estimated by pH-dependent UV-vis titration experiments. Correlation of these data with those of Ni(II)-edta and related 3d M(II) edta and tmdta complexes allow important conclusions on the consequences resulting from extending the central diamine ring in the ligand by one methylene group in terms of both complex and protolytic stability for edta vs tmdta complexes.