Showing papers by "Jan Reedijk published in 2011"

Putting anion-π interactions into perspective.

Abstract: Supramolecular chemistry is a field of scientific exploration that probes the relationship between molecular structure and function. It is the chemistry of the noncovalent bond, which forms the basis of highly specific recognition, transport, and regulation events that actuate biological processes. The classic design principles of supramolecular chemistry include strong, directional interactions like hydrogen bonding, halogen bonding, and cation-π complexation, as well as less directional forces like ion pairing, π-π, solvophobic, and van der Waals potentials. In recent years, the anion-π interaction (an attractive force between an electron-deficient aromatic π system and an anion) has been recognized as a hitherto unexplored noncovalent bond, the nature of which has been interpreted through both experimental and theoretical investigations. The design of selective anion receptors and channels based on this interaction represent important advances in the field of supramolecular chemistry. The objectives of this Review are 1) to discuss current thinking on the nature of this interaction, 2) to survey key experimental work in which anion-π bonding is demonstrated, and 3) to provide insights into the directional nature of anion-π contact in X-ray crystal structures.

Anion‐π‐Wechselwirkungen ins rechte Licht gerückt

Abstract: Die supramolekulare Chemie ist ein Gebiet, das die Beziehung zwischen molekularer Struktur und molekularer Funktion erforscht. Es ist die Chemie der nichtkovalenten Bindung, die die Grundlage der spezifischen Erkennung und der Transport- und Regulationsvorgange bildet, die biologische Vorgange antreiben. Die klassischen Konstruktionsprinzipien der supramolekularen Chemie umfassen starke, gerichtete Wechselwirkungen wie Wasserstoffbrucken, Halogenbrucken und Kation-π-Komplexbildung, aber auch weniger gerichtete Krafte wie Ionenpaarung, π-π-, solvophobe und Van-der-Waals-Wechselwirkungen. In den letzten Jahren wurde auch die Anion-π-Wechselwirkung (eine anziehende Kraft zwischen einem elektronenarmen aromatischen System und einem Anion) als bis dahin unerforschte nichtkovalente Bindung erkannt, und ihre Natur wurde experimentell und theoretisch untersucht. Die Konstruktion selektiver Anionenrezeptoren und -kanale auf der Grundlage dieser Wechselwirkung war ein wichtiger Fortschritt auf dem Gebiet der supramolekularen Chemie. Ziele dieses Aufsatzes sind: 1) aktuelle Vorstellungen uber die Natur dieser Wechselwirkung zu diskutieren, 2) eine Ubersicht uber die wichtigsten experimentellen Arbeiten zu geben, in denen Anion-π-Bindung nachgewiesen wurden, und 3) Einblicke in die Richtungsabhangigkeit von Anion-π-Kontakten in Kristallstrukturen zu geben.

Trigonal propeller-shaped [MnIII3MIINa] complexes (M = Mn, Ca): structural and functional models for the dioxygen evolving centre of PSII

Abstract: Two new polynuclear heterometallic cluster complexes with [MnIII3MIINa] (M = Mn, Ca) core were synthesized using two in situ formed Schiff bases. The compounds were structurally characterized by single crystal X-ray analysis. The compound with [MnIIICaIINa] appeared to catalyse water oxidation which was followed by using Clark electrode and online mass spectrometry.

Calorimetric investigation of triazole-bridged Fe(II) spin-crossover one-dimensional materials: measuring the cooperativity.

Abstract: The relevance of abrupt magnetic and optical transitions exhibiting bistability in spin-crossover solids has been pointed out for their potential applications in optical or memory devices. In this respect, triazole-based one-dimensional coordination polymers are widely recognized as one of the most interesting systems. The measure of the interaction among spin-crossover centers at the origin of such cooperative behavior is of paramount importance and has so far been realized through modeling of spin-crossover curves derived mostly from magnetic measurements. Here, a new series of triazole-based one-dimensional coordination polymers of formula [Fe(Rtrz)(3)](A)(2)·xH(2)O with R = methoxyethyl and A = monovalent anion has been prepared that show complete and abrupt spin-crossover phenomenon as shown by magnetic measurements. The spin-crossover transition in these and related compounds is studied by differential scanning calorimetry, and the thermodynamic excess enthalpies and entropies associated with the phenomenon are derived systematically. Then the cooperative character of the spin-crossover in these materials is quantified by use of two widely used models, so-called Slichter and Drickamer and domain models. The same procedure is applied to spin-crossover curves of similar compounds available in the literature and for which calorimetric studies have been reported. The experimental thermodynamic figures, in particular the excess enthalpies, are shown to be clearly correlated to the output parameters of both models, thus providing a direct, experimental, quantitative measure of the cooperative character of the spin-crossover phenomenon.

Increased understanding of platinum anticancer chemistry

Abstract: The development of a few worldwide routinely used Pt(II) coordination compounds is described from a mechanistic point of view and related to the molecular aspects of Pt-DNA binding. Mechanistic knowledge developed from these studies is applied nowadays for the design and synthesis of new bifunctional and trifunctional compounds, aimed for use as improved anticancer drugs.

Mono- and Dinuclear Iron Complexes of Bis(1-methylimidazol-2-yl)ketone (bik): Structure, Magnetic Properties, and Catalytic Oxidation Studies

Abstract: The newly synthesized dinuclear complex [FeIII2(μ-OH)2(bik)4](NO3)4 (1) (bik, bis(1-methylimidazol-2-yl)ketone) shows rather short Fe···Fe (3.0723(6) A) and Fe–O distances (1.941(2)/1.949(2) A) com...

Synthesis, crystal structures and magnetic properties of dinuclear copper(II) compounds with NNO tridentate Schiff base ligands and bridging aliphatic diamine and aromatic diimine linkers

Abstract: The synthesis and the characterization of new dinuclear copper(II) compounds of general formula [(La–d)2Cu2(μ-N–N)](ClO4)2 (1–6) with either neutral aliphatic diamine (N–N = piperazine, pip) or aromatic diimine (N–N = 4,4′-bipyridine, 4,4′-bipy) linker are reported. The copper ligands L− (La− = (E)-2-((2-aminoethylimino)methyl)phenolate, Lb− = (E)-2-((2-aminopropylimino)methyl)-phenolate, Lc− = (E)-2-((2-aminoethylimino)methyl)4-nitrophenolate, Ld− = (E)-2-((2-aminoethylimino)methyl)4-methoxyphenolate) are NNO tridentate Schiff bases derived from the monocondensation of a substituted salicylaldehyde 5-G-salH (G = NO2, H, OMe) with ethylenediamine, en, or 1,3-propylenediamine, tn. The crystal structures of compounds [(La)2Cu2(MeOH)2(μ-4,4′-bipy)](ClO4)2 (1·2MeOH), [(Lb)2Cu2(MeOH)2(μ-4,4′-bipy)](ClO4)2 (2·2MeOH), [(Ld)2Cu2(μ-4,4′-bipy)](ClO4)2 (4), [(La)2Cu2(μ-pip)](ClO4)2 (5) and [(Lb)2Cu2(μ-pip)](ClO4)2 (6) have been determined, revealing the preferred (e-e)-chair conformation of the bridging piperazine in compounds 5 and 6. The presence of hydrogen-bond-mediated intermolecular interactions, that involve the methanol molecules, yields dimers of dinuclear units for 1·2MeOH, and infinite zig-zag chains for 2·2MeOH. The temperature dependences of the magnetic susceptibilities χM(T) for all compounds were measured, indicating the presence of antiferromagnetic Cu–Cu exchange. For the compounds 2–4 with 4,4′-bipy, the coupling constants J are around −1 cm−1, while in compound 1 no interaction could be detected. The compounds 5 and 6 with piperazine display higher Cu–Cu magnetic interactions through the σ-bonding backbone of the bridging molecule, with J around −8 cm−1, and the coupling is favoured by the (e-e)-chair conformation of the diamine ring. The non-aromatic, but shorter, linker piperazine gives rise to stronger Cu–Cu antiferromagnetic couplings than the aromatic, but longer, 4,4′-bipyridine. In the latter case, the rotation along the C–C bond between the two pyridyl rings and the consequent non co-planarity of the two copper coordination planes play an important role in determining the magnetic communication. EPR studies reveal that the dinuclear species are not stable in solution, yielding the solvated [(L)Cu(MeOH)]+ and the mononuclear [(L)Cu(N–N)]+ species; it appears that the limited solubility of the dinuclear compounds is responsible for their isolation in the solid state.

Counterion and Solvent Effects on the Primary Coordination Sphere of Copper(II) Bis(3,5‐dimethylpyrazol‐1‐yl)acetic Acid Coordination Compounds

Abstract: Four copper(II) coordination compounds with the neutral ligand bis(3,5-dimethylpyrazol-1-yl)acetic acid (Hbdmpza, C12H16N4O2) and its anionic form (bdmpza–), namely [Cu(Hbdmpza)2](HSO4)2 (1), [Cu(Hbdmpza)2]Cl2 (2), [Cu(bdmpza)2](CH3COOH)(H2O) (3), and [Cu(bdmpza)2][Cu2(O2CCH3)4] (4) have been synthesized starting from different metal salts. All the compounds have been fully characterized by physical and analytical methods. In addition, a single-crystal XRD analysis revealed the 3D structure of 1, which exhibits tridentate, vicinal N,N,O-coordination of two symmetry-related Hbdmpza ligands in an elongated octahedral arrangement with four equatorial nitrogen atoms and two axial oxygen atoms. The neutral carboxylic moiety acts as a hydrogen-bond donor to a HSO4– counterion. The two hydrogensulfates form a unique hydrogen-bonded pair (HSO4–)2 with very short O···O distances (2.59 A) bridged between adjacent [Cu(HL)2]2+ coordination units. Also a short O···O contact (2.54 A) is present between the C–OH and an O of a hydrogensulfate. A characteristic IR C=O vibration is observed at 1700 cm–1 for 1 and 2, whereas the νas(O2C) vibration is present at 1650 cm–1 for 3 and 4. These IR data strongly suggest the presence of Hbdmpza ligands in 1 and 2 and the deprotonated form bdmpza– in 3 and 4. A mononuclear coordination unit [CuL2], as proven for 1 by X-ray diffraction, is also proposed for the other compounds 2–4. In compound 4, an additional dinuclear [Cu2(O2CCH3)4] neutral coordination unit is present, as deduced from the vibration bands νas(O2C) at 1600 cm–1 and νs(O2C) at 1420 cm–1, which are typical of a carboxylate function, and from the two-species analysis of the χMT(T) curve of the magnetic susceptibility data (2J = –322 cm–1). Also, the EPR spectra recorded at different temperatures agree with this structure.

Tripodal bis(imidazole)-based ligands and their chelation to copper(II)

Abstract: Three new copper(II) compounds are described containing chelating bis(imidazole)-based ligands. Compound 1, [Cu2(L1)2(H2O)2][SiF6]2·10H2O, was obtained by reaction of [bis-(1H-imidazol-2-yl)-methyl]-pyridin-2-ylmethyl-amine (L1) with Cu(BF4)2·6H2O in a glass vessel for a few weeks. The single-crystal X-ray structure of 1 consists of dinuclear copper(II) units, formed through ligand sharing. The starting BF4− anion was replaced by the SiF62− in the crystal structure of 1. In the crystal lattice, a discrete (H2O)8 cluster forms an eight-membered ring and is linked through four shared water molecules with the other (H2O)8 cluster. Both water clusters show hydrogen-bonding interactions with the neighbouring SiF62− anion. To investigate the effect of the presence of a bridging ligand such as oxalate on the coordination chemistry of L1 and copper(II) ion, compound 2, [Cu2(L1)(H2O)2][Cu(C2O4)2(ClO4)2]·2H2O, was prepared by reaction of L1 and Cu(ClO4)2·6H2O in the presence of oxalic acid; the crystal structure is built from 4+ and 4− ions in the crystal lattice. Compound 3, [Cu(ClO4)(C2O4)(HL2)H2O]·2H2O, was formed from the reaction of ligand [bis-(1H-imidazol-2-yl)-methyl]-isopropyl-amine (L2) and Cu(ClO4)2·6H2O in the presence of oxalic acid. The isopropylamine group is not coordinated to the copper in this case, but protonated. In compound 3, a mononuclear copper(II) unit is present, built from a bidentate L2, a bidentate oxalate, a monodentate perchlorate and a water. Two copper coordination entities are doubly bridged through hydrogen bonds with twice the pathway [Cu–OC2O4–(Owater)–Cu] to form a dimeric-like species. Low-temperature magnetic susceptibility studies showed no interaction between copper(II) ions.

Selective Copper‐Mediated Halogenation of Aromatic Rings Under Mild Conditions

Abstract: A mild copper-mediated halogenation reaction of phenolic rings is reported. The reaction of bis(2-hydroxybenzyl)-1,3-diaminopropane (H2bhbd) with copper(II) chloride in acetonitrile generates linear trinuclear [Cu3(bhcbd)2Cl2](CH3CN), containing modified ligands, whose phenol moieties are selectively chlorinated at the 5-position. Under comparable experimental conditions with copper(II) bromide, bromination of the ligand is observed, albeit at a slower reaction rate. In the presence of trialkylorthoformates, which are used as dehydrating agents, a ring closure of the ligand is observed after removal of copper to yield a product with a six-membered ring. This product has been isolated and characterized by NMR spectroscopy and MS. Similarly, bromination of bis(2-hydroxybenzyl)-1,3-diiminopropane (H2bhbdi) occurs in the presence of copper(II) bromide, with concomitant formation of a linear trinuclear complex. Surprisingly, an asymmetric dinuclear copper(II) coordination compound without chlorination of the ligand is obtained when the related ligand bis(2-hydroxybenzyl)-1,3-diminopropane (H2bhbdi) reacts with copper(II) chloride.