Synergistic effect between metal coordination and hydrogen bonding in phosphate and halide recognition

Synergism of primary and secondary interactions in a crystalline hydrogen peroxide complex with tin

Despite the significance of H2O2-metal adducts in catalysis, materials science and biotechnology, the nature of the interactions between H2O2 and metal cations remains elusive and debatable. This is primarily due to the extremely weak coordinating ability of H2O2, which poses challenges in characterizing and understanding the specific nature of these interactions. Herein, we present an approach to obtain H2O2-metal complexes that employs neat H2O2 as both solvent and ligand. SnCl4 effectively binds H2O2, forming a SnCl4(H2O2)2 complex, as confirmed by 119Sn and 17O NMR spectroscopy. Crystalline adducts, SnCl4(H2O2)2·H2O2·18-crown-6 and 2[SnCl4(H2O2)(H2O)]·18-crown-6, are isolated and characterized by X-ray diffraction, providing the complete characterization of the hydrogen bonding of H2O2 ligands including geometric parameters and energy values. DFT analysis reveals the synergy between a coordinative bond of H2O2 with metal cation and its hydrogen bonding with a second coordination sphere. This synergism of primary and secondary interactions might be a key to understanding H2O2 reactivity in biological systems.

The crystal structure of 6-amino-2-carboxypyridin-1-ium bromide, C6H7BrN2O2

C6H7BrN2O2, monoclinic, C2/c (no. 15), a = 23.7470(19) Å, b = 5.4355(4) Å, c = 15.3336(11) Å, β = 127.291(2)°, V = 1574.6(2) Å3, Z = 8, R gt(F) = 0.0292, wR ref(F 2) = 0.0756, T = 150(2) K.

Chain Entropy Beats Hydrogen Bonds to Unfold and Thread Dialcohol Phosphates inside Cyanostar Macrocycles To Form [3]Pseudorotaxanes

The recognition of substituted phosphates underpins many processes including DNA binding, enantioselective catalysis, and recently template-directed rotaxane synthesis. Beyond ATP and a few commercial substrates, however, little is known about how substituents effect organophosphate recognition. Here, we examined alcohol substituents and their impact on recognition by cyanostar macrocycles. The organophosphates were disubstituted by alcohols of various chain lengths, dipropanol, dihexanol, and didecanol phosphate, each accessed using modular solid-phases syntheses. Based on the known size-selective binding of phosphates by π-stacked dimers of cyanostars, threaded [3]pseudorotaxanes were anticipated. While seen with butyl substituents, pseudorotaxane formation was disrupted by competitive OH···O- hydrogen bonding between both terminal hydroxyls and the anionic phosphate unit. Crystallography also showed formation of a backfolded propanol conformation resulting in an 8-membered ring and a perched cyanostar assembly. Motivated by established entropic penalties accompanying ring formation, we reinstated [3]pseudorotaxanes by extending the size of the substituent to hexanol and decanol. Chain entropy overcomes the enthalpically favored OH···O- contacts to favor random-coil conformations required for seamless, high-fidelity threading of dihexanol and didecanol phosphates inside cyanostars. These studies highlight how chain length and functional groups on phosphate's substituents can be powerful design tools to regulate binding and control assembly formation during phosphate recognition.

Crystal structure of bis(6-aminopyridine-2-carboxylato-κ2 O,N)-copper(II), C12H10O6N4Cu

C12H10O6N4Cu, monoclinic, P21/c (no. 14), a = 3.7015(2) Å, b = 7.3920(4) Å, c = 21.3535(12) Å, β = 91.060(5)°, Z = 2, V = 584.16(6) Å3, R gt(F) = 0.0319, wR ref(F2) = 0.0769, T = 293 K.

X-Ray Structural Studies of Small-Bite Ligands on Large Cations – Lanthanide(III) Ions and Dimethylphosphate

Reactions of lanthanide chlorides or trifluoracetates (tfa) or picrates with trimethylphosphate alone in the first two cases or trimethylphosphate plus 1,10-phenanthroline or 2,2′;6′,2′′-terpyridine in the third, result in the formation of crystalline products containing dimethylphosphate (dmp–). Single crystal X-ray structural characterisation of these materials has shown that the stoichiometrically simple Ln(dmp)3 species obtained with chloride reactants and the lighter lanthanides are polymeric and commonly dimorphic, while the stoichiometrically more variable mixed dmp/tfa complexes have structures closely related to one phase of the Ln(dmp)3 family, and the presence of picrate and aza-aromatic ligands enables the isolation of Y and Lu derivatives containing binuclear species. In all, the dmp– ligands adopt exclusively the κ1O;κ1O′ bridging mode, the overall results indicating that this should apply to the complete lanthanide series.

Bis(ethanol-κO)-bis(6-aminopicolinato-κ2N,O)magnesium(II), C16H22O6N4Mg

C16H22O6N4Mg, triclinic, P1̄ (no. 2), a = 7.3165(15) Å, b = 8.2660(17) Å, c = 8.7599(18) Å, α = 71.60(3)°, β = 77.07(3)°, γ = 64.19(3)°, V = 450.2(2) Å3, Z = 1, Rgt(F) = 0.0513, wRref(F2) = 0.1335, T = 293(2) K.

Mononuclear Cu(ii) and Zn(ii) complexes with a simple diamine ligand: synthesis, structure, phosphodiester binding and DNA cleavage studies

Mononuclear Cu(ii) and Zn(ii) complexes with simple 1,2-diaminocylohexane were synthesized. They interact with phosphodiesters and CT-DNA. Cu(ii) complex with ascorbate efficiently cleaves supercoiled DNA up to Form III at 25 µM under oxidative pathway.

Discrete and polymeric cobalt organophosphates: isolation of a 3-D cobalt phosphate framework exhibiting selective CO2 capture

Auxiliary ligand assisted control over the structural diversity has been achieved in the case of cobalt(ii) organophosphates.

Catalytic zinc complexes for phosphate diester hydrolysis

Creating efficient artificial catalysts that can compete with biocatalysis has been an enduring challenge which has yet to be met. Reported herein is the synthesis and characterization of a series of zinc complexes designed to catalyze the hydrolysis of phosphate diesters. By introducing a hydrated aldehyde into the ligand we achieve turnover for DNA-like substrates which, combined with ligand methylation, increases reactivity by two orders of magnitude. In contrast to current orthodoxy and mechanistic explanations, we propose a mechanism where the nucleophile is not coordinated to the metal ion, but involves a tautomer with a more effective Lewis acid and more reactive nucleophile. This data suggests a new strategy for creating more efficient metal ion based catalysts, and highlights a possible mode of action for metalloenzymes.

One-step synthesis of α/β cyano-aqua cobinamides from vitamin B12 with Zn(II) or Cu(II) salts in methanol

This short communication describes the screening of various metal salts for the preparation of cyano-aqua cobinamides from vitamin B12 in methanol. ZnCl2 and Cu(NO3)2·3H2O have been identified as most active for this purpose and represent useful alternatives to the widely applied Ce(III) method that requires excess cyanide.

The combination of transition metal ions and hydrogen-bonding interactions

This feature article presents an overview of the types of hydrogen bonding interactions involving metal complexes and their functional effects. It shows with recent examples why hydrogen bonds have become a crucial functional and structural element in modern inorganic chemistry. The relevance of this combination in tackling current chemistry challenges such as energy production and the development of new materials and more effective catalysts, sensors and medicines is illustrated.

Evidence of anion-induced dimerization of a squaramide-based host in protic solvents

The combination of squaramide units with tetraalkylammonium groups leads two hosts that bind distinctively dianions in water-ethanol mixtures. The formation of complexes of 2:1 stoichiometry with host was supported by ITC, fluorescence, and (1)H NMR data.

Metal-mediated transport of electrons across molecular films

Electron transfer (ET) to a redox probe in solution across the self-assembled monolayers (SAMs) of a tris-(2-pyridylmethyl)amine-based ligand on gold electrodes is greatly enhanced by Cu-binding.

Hydrogen Bonding Cavities Regulating Redox Behavior and Binding of Metal-Bound Ligands

Binding of 3,5-di-tert-butyl-1,2-benzochatechol (H2DTBC) at Zn(II) complexes of a tetradentate, tripodal ligand L is significantly enhanced (36-4.6 x 10(4) fold), and its reduction potential shifted (90-270 mV) to more positive values by introducing one to three amino hydrogen bond donors. The structure of one of the [(L)Zn(DTBC)] complexes is reported and shows intramolecular N-H...O hydrogen bonding between the ligand-based amino group and the Zn(II)-bound chatecholate, which provides an explanation for the observed behavior.

A synthetic receptor for phosphocholine esters

A bifunctional Zn-salen modified cavitand, reminiscent of the enzyme phospholipase C, shows high efficiency and synergic effect in the binding of the phospholipid DOPC.

Multiple Hydrogen Bonds Tuning Guest/Host Excited-State Proton Transfer Reaction: Its Application in Molecular Recognition

A molecular recognition concept exploiting multiple-hydrogen-bond fine-tuned excited-state proton-transfer (ESPT) was conveyed using 3,4,5,6-tetrahydrobis(pyrido[3,2-g]indolo)[2,3-a:3',2'-j]acridine (1a). The catalytic type 1a/carboxylic acids hydrogen-bonding (HB) complexes undergo ultrafast ESPT, resulting in an anomalously large Stokes shifted tautomer emission (lambdamax approximately 600 nm). Albeit forming a quadruple HB complex, ESPT is prohibited in the noncatalytic-type 1a/urea complexes (lambdamax approximately 430 nm). The HB configuration tuning ESPT properties lead to a feasible design for sensing multiple-HB-site analytes of biological interest.

The affinity of phosphates to zinc(ii) complexes can be increased with hydrogen bond donors

Amino H-bond donors adjacent to a zinc(II) centre increase the affinity of phosphates to the zinc(II) centre.

Monomeric, Tetrameric, and Polymeric Copper Di-tert-butyl Phosphate Complexes Containing Pyridine Ancillary Ligands,

The reaction of di-tert-butyl phosphate (((t)BuO)(2)P(O)(OH), dtbp-H) with copper acetate in the presence of pyridine (py) and 2,4,6-trimethylpyridine (collidine) has been investigated. Copper acetate reacts with dtbp-H in a reaction medium containing pyridine, DMSO, THF, and CH(3)OH to yield a one-dimensional polymeric complex [Cu(dtbp)(2)(py)(2)(mu-OH(2))](n) (1) as blue hollow crystalline tubes. The copper atoms in 1 are octahedral and are surrounded by two terminal phosphate ligands, two pyridine molecules, and two bridging water molecules. The mu-OH(2) ligands that are present along the elongated Jahn-Teller axis are responsible for the formation of the one-dimensional polymeric structure. Recrystallization of 1 in a DMSO/THF/CH(3)OH mixture results in the reorganization of the polymer and its conversion to a more stable tetranuclear copper cluster [Cu(4)(mu(3)-OH)(2)(dtbp)(6)(py)(2)] (2) in about 60% yield. The molecular structure of 2 is made up of a tetranuclear core [Cu(4)(mu(3)-OH)(2)] which is surrounded by six bidentate bridging dtbp ligands. While two of the copper atoms are pentacoordinate with a tbp geometry, the other two copper atoms exhibit a pseudooctahedral geometry with five normal Cu-O bonds and an elongated Cu-O linkage. The pentacoordinate copper centers bear an axial pyridine ligand. The short Cu.Cu nonbonded distances in the tetranuclear core of 2 lead to magnetic ordering at low temperature with an antiferromagnetic coupling at approximately 20 K (J(P) = -44 cm(-1), J(c) = -66 cm(-1), g = 2.25, and rho = 0.8%). When the reaction between di-tert-butyl phosphate (dtbp-H) and copper acetate was carried out in the presence of collidine, large dark-blue crystals of monomeric copper complex [Cu(dtbp)(2)(collidine)(2)] (3) formed as the only product. A single-crystal X-ray diffraction study of 3 reveals a slightly distorted square-planar geometry around the copper atom. Thermogravimetric analysis of 1-3 revealed a facile decomposition of the coordinated ligands and dtbp to produce a copper phosphate material around 500 degrees C. An independent solid-state thermolysis of all the three complexes in bulk at 500-510 degrees C for 2 days produced copper pyrophosphate Cu(2)P(2)O(7) along with small quantities of Cu(PO(3))(2) as revealed by DR-UV spectroscopic and PXRD studies.

O–H Bond elongation in co-ordinated water through intramolecular PO⋯H–O bonding. ‘Snap-shots’ in phosphate ester hydrolysis

Molecular structure of [Cu(dtbp)2(phen)(OH2)] (dtbp-H = di-tert-butylphosphate, phen = 1,10-phenanthroline), determined at 293, 203 and 93 K, provides useful snap-shots of O-H bond activation of a metal-bound water, which is aided by an intramolecular P=O...H-O hydrogen bonding interaction.