Showing papers by "Jan Reedijk published in 2002"

Spin Transition Regime in New One-Dimensional Polymeric Iron(II) Compounds. Importance of the Water Content for the Thermal and Optical Properties

Abstract: A new series of polymeric chainlike materials exhibiting the spin crossover phenomenon has been synthesized in aqueous conditions using different iron(II) salts and 4-(formylamino)-1,2,4-triazole (fatrz). The magnetic and thermogravimetric behaviors of the compounds of general formula [Fe(fatrz) 3 ](A) 2 xH 2 O are presented for 1 (A = trifluoromethanesulfonate and x = 3), 2 (A = tetrafluoroborate and x = 2), 3 (A = p-tolylsulfonate and x = 3), and 4 (A = nitrate and x = 1). In 1, the high (S = 2) ↔ low (S = 0) spin transition of the iron(II) ions occurs sharply in the close vicinity of 0 °C. Reflectivity measurements show that this transition can be cycled and used as a temperature sensor. However, 1 loses water when warmed above 320 K, whereby its transitions become more gradual and shift to lower temperatures. Calorimetric parameters for the spin transition of 1 have been obtained and indicate a strongly cooperative phenomenon, with ΔH = 17.19 kJ mol -1 and ΔS = 64.26 J K -1 mol -1 in the warming mode. 2 has a more gradual transition in the range 265-285 K. 3 and 4 are low spin at room temperature and possess large apparent hysteresis due to a loss of water upon the first L - H spin change. The reabsorption of water in 3 makes it a possible reusable temperature threshold sensor. The prominent role of water molecules in the whole family of chainlike spin crossover materials is discussed.

Ligand‐Templated Four‐Metal Chains Dimerize into a Unique [CuII8] Cluster

Abstract: Within the context of what has been termed coordination supramolecular chemistry, remarkable progress has been made in the design and preparation of multidentate ligands capable of participating in complicated molecular structures upon complexation, in predetermined manners, with transition metals.[1] This approach is starting to take hold in the area of molecular magnetism. Thus, in recent years, a few important reports have appeared describing the formation of new magnetic transition metal clusters through the template action of specifically designed multinucleating ligands.[2] We have reported the synthesis of an O-pentadentate donor possessing a phenol and two -diketone units (H3L), which was conceived to direct the formation of chains

Formation, Structures, and Magnetic and EPR Spectroscopic Properties of Dicobalt(III)‐Dicopper(II) Complexes Featuring Heterotetranuclear Cations of a Puckered Cyclic Structure with Diethanolamine and Diethanolamine(2−) as Bridging Ligands

Abstract: The compounds [CuII2CoIII2(H2dea)2(dea)4]X2(Solv)n [X = Cl (1), Br (2), SCN (3), O2CMe (4), I (5); Solv = H2O or/and CH3OH, DMF, n = 1−4] were synthesised by the reaction of zero-valent copper with cobalt(II) salts in non-aqueous (CH3OH, DMF, DMSO) solutions of diethanolamine (H2dea) in air. Crystallographic investigations of 1−4 reveal that the complexes contain the centrosymmetric cation [Cu2Co2(H2dea)2(dea)4]2+ in which the four metal atoms are linked together by bridging oxygen atoms of the six ligand groups to form a parallelogram with the length of the short edge (Cu···Co) being ca. 2.83 A and a short diagonal distance (Cu···Cu) at approximately 3.23−3.29 A. The copper atom is five-coordinate with a square-pyramidal geometry; the geometry at the trivalent cobalt ion is almost octahedral. The tetranuclear units are further stabilized by intramolecular O−H···O and N−H···O hydrogen bonds. The hydrogen-bonded network that involves the OH and NH groups of the ligands, uncoordinated anions, and solvent molecules links the tetranuclear units together and results in the formation of extended two- and three-dimensional networks. Variable-temperature magnetic susceptibility measurements of 1−3 and 5 show no significant exchange coupling between the copper centres. The frozen-solution and solid-state EPR spectra at 77 K are characteristic of a triplet state with the hyperfine structure distinctly resolved in solution. On the assumption of noncoaxiality of the g and D tensors the spectra were interpreted with the zero-field-splitting parameters D = 0.0560(1) (2−5) and D = 0.0712(1), E= 0.0028(2) cm−1 (1). Dominant contributions to the observed EPR zero-field splitting are presumed to be dipole-dipole in origin. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Monofunctionally trans-Diammine Platinum(II)-Modified Peptide Nucleic Acid Oligomers: A New Generation of Potential Antisense Drugs

Abstract: A solid-phase approach is described that provides facile access to monofunctionally trans-PtII-modified PNA oligomers of arbitrary sequence for potential use both in antigene and antisense strategies. The approach includes the synthesis of a platinated building block 1 and its subsequent incorporation into three different PNA oligomers 5-7 by solid-phase synthesis. In a model cross-linking reaction one of the latter is found to recognize sequence-specifically a target oligonucleotide 8 and to cross-link to it. The resulting structure is the trans-PtII-cross-linked PNA/DNA duplex 9 as revealed by mass spectrometry in combination with a Maxam-Gilbert sequencing experiment.

Selective and reversible extraction of heavy metal-ions by mixed-donor crown ether-modified oxirane and thiirane resins

Abstract: Three mixed-donor crown ethers, [15]aneNO 2 S 2 , [12]aneNOS 2 and [15]aneN 2 O 2 S, have been coupled to the oxirane- and thiirane-containing copolymers of glycidyl methacrylate and ethylene glycol dimethacrylate p (GMA-O) and p (GMA-S) by nucleophilic ring-opening reactions of the epoxy and thiirane groups. The ligand concentrations on the modified p (GMA-O) resins varied from 0.77 to 1.13 mmol g −1 , the ligand concentrations on the modified p (GMA-S) resins were found to be much lower, ranging from 0.22 to 0.37 mmol g −1 resin. The resulting oxa-azathiacrown ether containing polymers showed interesting metal-ion affinities. In competitive experiments in the presence of a range of divalent (post) transition metal-ions p (GMA-O)-[15]aneNO 2 S 2 and p (GMA-O)-[12]aneNOS 2 exhibit a very high capacity and selectivity towards Ag + over a wide range of pH (from 1 to 6). Indeed, Ag + is the only extracted ion. In contrast, the Ag + affinity of p (GMA-O)-[15]aneN 2 O 2 S is much lower, due to the presence of only one rather than two thioether moieties. In this case the Ag + uptake is relatively low (0.17 mmol g −1 ) at pH 1.5 and relatively high (0.58 mmol g −1 ) at pH 5. The relative stabilities of the resin–metal-ion complexes have been determined by measuring log D ( D =distribution coefficient), which showed that the Ag + complexes are up to 100 times more stable than the corresponding complexes with other metal-ion species. Regeneration of metal-loaded polymers appeared to be possible with 2.0 M solutions of HNO 3 or H 2 SO 4 (in the case of Cu 2+ , Cd 2+ and Pb 2+ ), or with a 1.0 M (NH 2 ) 2 CS solution (in the case of Ag + ), respectively.

Unusual Coordination of the Rare Neutral Imine Tautomer of 9-Methyladenine Chelating in the N6,N7-Mode to Ruthenium(II) Complexes

Abstract: The coordination of the DNA model base 9-methyladenine (9-MeAde) to both complexes cis-[Ru(bpy)2Cl2] and α-[Ru(azpy)2(NO3)2] is reported. Structural characterisation using 2D NMR techniques and variable-temperature NMR studies between 25 and −55 °C show that in the compounds α-[Ru(azpy)2(9-MeAde)](PF6)2 (1) and cis-[Ru(bpy)2(9-MeAde)](PF6)2 (2), 9-MeAde is coordinated to the ruthenium ion in a chelating mode via its N7 and exocyclic N6 atoms. The NMR spectroscopic data unambiguously prove the occurrence of the rare imine tautomer of 9-MeAde in these complexes, which is clearly stabilised by the bidentate coordination of 9-MeAde in both complexes. Variable-temperature NMR spectra and 2D COSY data show that the H2 resonance of 9-MeAde in 1 and 2 appears as a doublet at low temperatures and shows a COSY cross peak to the NH1 resonance of 9-MeAde, which confirms the protonation at the N1 site. This protonated N1 site, together with an observed pKa of ca. 6.5 of compound 1 is in agreement with the presence of the imine tautomeric form of 9-MeAde. As the binding mode of 9-MeAde to both cis-[Ru(bpy)2] and α-[Ru(azpy)2] moieties is the same, this binding mode does not explain the earlier observed difference in cytotoxicity between cis-[Ru(bpy)2Cl2] and α-[Ru(azpy)2Cl2].

Electrochemical and Catalytic Properties of Novel Manganese(III) Complexes with Substituted 2‐(2′‐Hydroxyphenyl)oxazoline Ligands − X‐ray Structures of Tris[5‐methyl‐2‐(2′‐oxazolinyl)phenolato]manganese(III) and Tris[5‐chloro‐2‐(2′‐oxazolinyl)phenolato]manganese(III)

Abstract: A series of manganese complexes of the type MnL3 were synthesised and characterised, with HL being (substituted) 2-(2′-hydroxyphenyl)oxazoline ligands. The molecular structures of [Mn(5′-Mephox)3] and [Mn(5′-Clphox)3] reveal their meridional configuration with a significant Jahn−Teller distortion. The ligand substituents exert a significant influence on the redox and catalytic properties of the manganese complexes. Cyclic voltammetry experiments show that the electrochemically quasi-reversible MnII/MnIII and reversible MnIII/MnIV redox couples shift towards higher potentials with more electron-withdrawing substituents. The same trend applies for the oxidation of the manganese(IV) complexes. Electrolysis experiments monitored with UV/Vis and EPR spectroscopy revealed that the reduction of the manganese(III) complexes to manganese(II), and their oxidation to manganese(IV) are both chemically reversible, while subsequent oxidation of the manganese(IV) species was found to be irreversible. All complexes are active oxidation catalysts with dihydrogen peroxide as the oxidant. In the oxidation of styrene, up to 220 turnover numbers were obtained towards styrene oxide. The turnover numbers in the oxidation reactions as well as the selectivity in the oxidation of styrene and cis-stilbene are affected significantly by the substituents, but no clear correlation with the electrochemical properties was observed. The most striking substituent effect is the higher stability of [Mn(5′-NO2phox)3] compared to the other complexes during styrene oxidation with dihydrogen peroxide in methanol.

The First Case of Local cis versus trans Coordination as the Controlling Factor for the Overall Structure in Dinuclear Assemblies

Abstract: The preparation and structure of two dinuclear assemblies [M2(HL)2(py)4 ]( M II = Mn, Ni) with the phenol bis-‚-diketone H3L are presented. The octahedral N2O4 coordination environments around the metals are in cis and trans configuration for Mn and Ni, respectively, leading to structurally different assemblies. These results represent the first example where

Dinuclear Copper Complexes of N-(2-Hydroxybenzylidene or 5-Bromo-2-hydroxybenzylidene)-4,6-O-ethylidene-β-D-glucopyranosylamine: Coordination Variation and Structural Diversity

Abstract: Dinuclear Cu(II) complexes of N-(2-hydroxybenzylidene or 5-bromo-2-hydroxybenzylidene)-4,6-O-ethylidene-β-D-glucopyranosylamine with coordination variation and molecular and lattice structural variations are explored.

Manganese Oxidation Catalysts with 2-(2'-Hydroxyphenyl)oxazoline Ligands: Catalyst Intermediates and Degradation Products - Crystal Structure of Bis[{2,(2'-oxazolinyl)phenolato}bis(1-methylimidazole)manganese(III)] Perchlorate.

Abstract: Manganese complexes with phox ligands [Hphox = 2-(2′-hydroxyphenyl)oxazoline] act as oxidation catalysts with dihydrogen peroxide. Their catalytic efficiency is strongly affected by the presence of a base, such as 1-methylimidazole (1-Meim). The crystal structure of an Mn−phox complex with two axial 1-Meim ligands, [Mn(phox)2(1-Meim)2](ClO4), is reported. The [Mn(phox)2]+ and [Mn(phox)2(1-Meim)]+ species have been detected in catalytic reaction mixtures by electrospray mass spectrometry. In the catalytic oxidation of styrene, turnover numbers of 428 and 456 have been obtained for styrene oxide in the presence of [Mn(phox)3] and of [Mn(5′-NO2phox)3], respectively. During these reactions, catalyst degradation occurs, and is the main obstacle to obtaining higher turnover numbers. GC-MS analysis of the degradation products of [Mn(5′-Clphox)3] after catalytic reactions indicates that the oxazoline group is decomposed. The same decomposition products are also observed with electrospray mass spectrometry at higher ionisation potentials. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Redetermination of bis(2‐amino­pyrimidine)­bis(nitrato)copper(II)

Abstract: The crystal structure of the title compound, [Cu(NO3)2(C4H5N3)], at room temperature was reported earlier, but full results were not published. According to the present study at 193 K, the CuII atom occupies a special position at an inversion centre and has a distorted octahedral geometry. The basal plane is formed by two N atoms of two 2-amino­pyrimidine mol­ecules and two O atoms of two trans-oriented nitrate anions. The apical positions are occupied by the remaining O atoms of the chelating nitrate groups. The hydrogen bond, formed by an amino group and the uncoordinated pyrimidine N atom of a 2-amino­pyrimidine ligand of the neighbouring mol­ecule of the complex, gives rise to Watson–Crick-type pairwise aggregation of amino­pyrimidine ligands, thus creating infinite chains of mol­ecules of the complex stretching along the [10\overline 1] direction in the crystal. The chains are further interconnected into layers parallel to the x0z plane, due to additional hydrogen bonds involving the second H atom of the amino group of the 2-amino­pyrimidine ligand and the O atom of the nitrate anion of the neighbouring mol­ecule.

Oxa-aza Crown Ethers as Ligands for Mixed-Ligand Cisplatin Derivatives and Dinuclear Platinum Anticancer Drugs

Abstract: In the search for novel platinum anticancer drugs, cisplatin derivatives and dinuclear platinum complexes containing oxa-aza crown ether and oxa-diaza crown ether ligands have been prepared. The cisplatin derivatives cis[PtCl2(NH3)(1,4,7,10,13-pentaoxa-16-azacyclooctadecaneN)] (AO18) and cis-[PtCl2(NH3)(1,4,7,10-tetraoxa-13-azacyclopentadecane-N)] (AO15), and the dinuclear cationic platinum complexes [{trans-PtCl(NH3)2}2(μ-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-N,N′)](NO3)2 (DAO18) and [{trans-PtCl(NH3)2}2(μ-1,4,10-trioxa-7,13-diazacyclopentadecane-N,N′)](NO3)2 (DAO15) were investigated for their cytotoxic properties, cellular uptake and intracellular DNA binding in A2780 human ovarian cancer. The cisplatin derivative AO15 shows the highest cytotoxic activity, whereas the cationic dinuclear complexes DAO18 and DAO15 display a disappointing lack of biological activity at concentrations up to 100 μM. In the intracallular DNA platination experiments, the fifteen-membered rings were found to have a threefold higher intracellular DNA binding compared to their 1eight-membered analogues for the neutral cisplatin derivatives as well as for the cationic dinuclear complexes. The crown ether complex with the most effective binding to DNA, AO15, also shows the highest cytotoxicity against A2780 cancer cells. It is remarkable that, although AO15 binds more effectively to DNA than cisplatin, its cytotoxic effect is much lower. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Metal‐Ion Extraction by Immobilised Aza Crown Ethers

Abstract: The immobilisation of [15]aneNO(4), [15]aneN(2)O(3), and [18]aneN(2)O(4) onto the oxirane and thiirane containing copolymers p(GMA-O) and p(GMA-S) resulted in six aza crown ether containing polymers with interesting metal-ion affinities, The pendent hydroxy or thiol groups, originating from the polymeric backbones, appeared to play an important role in the observed metal-ion affinities. The metal-ion affinity of p(GMA-O)-[15]aneN(2)O(3) for a range of cations was found to decrease with decreasing ionic radius: Ag+ > Pb2+ > Cd2+ > Cu2+. The thiol-containing analogue of this polymer, p(GMA-S)-[15]aneN(2)O(3), showed a reversed Cd2+/Cu2+ selectivity. This illustrates the capability of pendent hydroxy groups to seriously reduce the stability of complexes of small cations compared to those of large cations. All the modified oxirane resins tested were found to be Ag+-selective in the presence of a range Of divalent (heavy) transition-metal ions. The difference in ring size between [15]aneN(2)O(3) and [18]aneN(2)O(4) was found to have a significant effect on the uptake values of Cu2+ and Zn2+, as these ions are too small to fit into the ligand cavity of [18]aneN(2)O(4). The uptake values for the larger Ag+ and Pb2+ were found to be similar for both resins, Loaded resins were successfully regenerated (with an efficiency of 99%) by treatment with 2.0 m acid solutions (Pb2+ and Cd2+) or with a 3.35 m NH3 + 2.0 m NH4NO3 solution (Ag+).

catena-Poly[[dicyanamido(5,5′-dimethyl-2,2′-bipyridine-κ2N,N′)copper(II)]-μ-dicyanamido-κ2N1:N5]

Abstract: In the crystal structure of the title compound, [Cu(C2N3)2(C12H12N2)]n, the CuII atom adopts a distorted square-pyramidal geometry, the basal plane of which is formed by two N atoms of the bi­pyridine ligand, one N atom of a bidentate dicyan­amide anion and one N atom of a monodentate dicyan­amide anion [Cu—N = 1.9760 (15)–2.0157 (15) A]. The apical position is occupied by an N atom of a bidentate dicyan­amide anion, located 2.2468 (16) A from the Cu atom, thus forming a one-dimensional polymeric chain.