The thulium complex of 1,4,7,10-tetrakis{[N-(1H-imidazol-2-yl)carbamoyl]methyl}-1,4,7,10-tetraazacyclododecane (dotami) as a ParaCEST contrast agent

1,4,7,10-Tetrakis{[N-(1H-imidazol-2-yl)carbamoyl]methyl}-1,4,7,10-tetraazacyclododecane (dotami), a tetra(1H-imidazol-2-yl) derivative of the well-studied octadentate 1,4,7,10-tetrakis[(carbamoyl)methyl]-1,4,7,10-tetraazacyclododecane (dotam) ligand, was synthesized by reaction of 1,4,7,10-tetraazacyclododecane with N-(1H-imidazol-2-yl)chloroacetamide in high yield. Its tricationic thulium complex was isolated as a water-soluble chloride salt. The detection of the mildly acidic amide and amine protons by direct proton NMR in aqueous solution was unsuccessful, but such exchangeable protons could be detected via their chemical exchange-dependent saturation transfer (CEST) effect. The observed CEST effect was distinctly different from that found for respective dotam complexes and is, therefore, ascribed to exchangeable protons associated with the imidazole substituent.     

A new tris(2-furyl) substituted pyrazolylborate ligand and its zinc complex chemistry

The new ligand hydrotris(3-(2′-furyl)-5-methylpyrazolyl)borate (Tp^Fu,Me) was prepared by the usual procedure. With zinc salts, it forms the Tp^Fu,MeZn-X complexes (X = Cl, Br, I, NCS, CH₃COO, CF₃COO). With zinc perchlorate, the bis-ligand complex Zn(Tp^Fu,Me)₂ is formed preferrably, but by carefully controlling the reaction conditions, the “enzyme model” Tp^Fu,MeZn-OH could be obtained. The latter models carbonic anhydrase by inserting CO₂ and CS₂ in methanol producing Tp^Fu,MeZn-OCOOMe and Tp^Fu,MeZn-SCSOMe. It models hydrolases by the hydrolytic cleavage of tris(p-nitrophenyl)phosphate and γ-thiobutyrolactone. It does not hydrolyse trifluoroacetamide, but instead deprotonates it, yielding Tp^Fu,MeZn-NHCOCF₃.     

Dinuclear macrocyclic polyamine zinc(II) complexes linked with flexible spacers: synthesis, characterization, and DNA cleavage

Dinuclear macrocyclic polyamine zinc(II) complexes, which have two cyclen groups linked by flexible spacers, have been synthesized as DNA cleavage agents. The structures of these new dinuclear complexes are consistent with the data obtained from elemental analysis, MS and ¹H NMR spectroscopy. The catalytic activity of these dinuclear complexes on DNA cleavage was studied. The results showed that the dinuclear zinc(II) complexes can catalyze the cleavage of supercoiled DNA (pUC 19 plasmid DNA) (Form I) under physiological conditions to produce selectively nicked DNA (Form II).     

Nickel(II)-, cobalt(II)-, copper(II)-, and zinc(II)-phthalate and 1-methylimidazole coordination compounds: synthesis, crystal structures and magnetic properties

Three new coordination polymers [M(Pht)(1-MeIm)₂]_n (where M=Cu (1), Zn (2), Co (3); Pht²⁻=dianion of o-phthalic acid; 1-MeIm=1-methylimidazole) and two compounds [M(1-MeIm)₆](HPht)₂ · 2H₂O (M=Co (4), Ni (5)) have been synthesized and characterized by X-ray crystallography. The structures of 1-3 (2 is isostructural to 3) consist of [M(1-MeIm)₂] building units connected by 1,6-bridging phthalate ions to form infinite chains. In complex 1, each copper(II) center adopts a square coordination mode of N₂O₂ type by two O atoms from different phthalate ions and two N atoms of 1-MeIm, whereas in 3 two independent metal atoms are tetrahedrally (N₂O₂) coordinated to a pair of Pht ligands and a pair of 1-MeIm molecules. There are only van der Waals interactions between the chains in 1, while the three-dimensional network in 3 is assembled by C-H?O contacts. In contrast to polymers 1-3 the structures of 4 and 5 (complexes are also isostructural) are made up of the [M(1-MeIm)₆]²⁺ cation, two hydrogen phthalate anions (HPht⁻) and two H₂O solvate molecules. The coordination around each metal(II) atom is octahedral with six nitrogen atoms of 1-MeIm. Extended hydrogen bonding networks embracing the solvate water molecules and a phthalate residue as well as the weak C-H?O interactions stabilize the three-dimensional structures. Magnetic studies clearly show that the magnetic ions do not interact with each other. Furthermore, in compound 4 we have another example of a highly anisotropic Co²⁺ ion with a rhombic g-tensor and large zero-field-splitting. The complexes were also characterized by IR and ¹H NMR spectroscopy, thermogravimetric analysis, and all data are discussed in the terms of known structures.     

Structural, magnetic, electrochemical, catalytic, DNA binding and cleavage studies of new macrocyclic binuclear copper(II) complexes

The macrocyclic symmetrical and a series of unsymmetrical binuclear copper(II) complexes have been synthesized by using mononuclear complex [CuL] [3,3′-((1E,7E)-3,6-dioxa-2,7-diazaocta-1,7-diene-1,8-diyl)bis(3-formyl-5-methyl-2-diolato)copper(II)]. Another compartment of the [CuL] have been condensed with various diamines like 1,2-bis(aminooxy)ethane (L¹), 1,2-diamino ethane(L^2a), 1,3-diamino propane(L^2b), 1,4-diamino butane(L^2c), 1,2-diamino benzene(L^2d), 1,8-diamino naphthalene(L^2e) and characterized by elemental, spectroscopic, and X-ray crystallographic methods. The influence of the coordination geometry and the ring size of the binucleating ligands on the electronic, redox, magnetic, catecholase activity, DNA binding and cleavage properties have been studied. The molecular structures of the symmetrical binuclear complex [Cu₂L¹(H₂O)₂](ClO₄)₂ (1) and unsymmetrical binuclear complex [Cu₂L^2b(ClO₄)(H₂O)]ClO₄ (2b) were determined by X-ray crystallography. Both of them were discrete binuclear species in which each Cu(II) ions are in distorted square pyramid. The Cu?Cu distances vary from 3.0308 (2b) to 3.0361 Å (1). Electrochemical studies evidenced that two quasi-reversible one electron-transfer reduction waves −0.91 to −1.01 V, −1.26 to −1.55 V) for binuclear complexes are obtained in the cathodic region. Cryomagnetic investigation of the binuclear complexes reveals a weak antiferromagnetic spin exchange interaction between the Cu(II) ions within the complexes (−2J = 104.4-127.5 cm⁻¹). The initial rate (V_in) for the oxidation of 3,5-di-tert-butylcatechol to o-quinone by the binuclear Cu(II)complexes are in the range 3.6 × 10⁻⁵ to 7.3 × 10⁻⁵ Ms⁻¹. The binuclear Cu(II) complexes are avid binders to calf thymus DNA. The complexes display significant oxidative cleavage of circular plasmid pBR322 DNA in the presence of mercaptoethanol using the singlet oxygen as a reactive species. The aromatic diamine condensed macrocyclic ligands of copper(II) complexes display better DNA interaction and significant chemical nuclease activity than the aliphatic diamine condensed macrocyclic Cu(II) complexes.     

Synthesis, characterisation of a complex of Cu(II) with a multidentate macrocyclic ligand and its interactions with anions

A macrocyclic ligand possessing a donor set of {N₃S₂} synthesised via Cs⁺-templation, 4-(pyridin-2-ylmethyl)-1,7-dithia-4,10-diazacyclododecane (L) and its Cu(II) complex, [CuL(NCMe)]²⁺ (6), are described. This Cu(II) complex interacts with a range of anions, F⁻, Cl⁻, Br⁻, I⁻, HCOO⁻, AcO⁻, CO₃²⁻, NO₃⁻, C₂O₄²⁻, H₂PO₄⁻, SCN⁻, CN⁻, BF₄⁻. Of the investigated anions, I⁻, SCN⁻, and CN⁻, show strong interaction with the Cu(II) centre as indicated by their spectral variations. The iodide particularly demonstrates distinct change in colour. This change originates from a newly appeared band at 471 nm upon iodide binding, which arises from the ligand (I⁻) to Cu(II) charge transfer (LMCT) in the iodide-substituted Cu(II) complex, [CuLI]⁺ (7). All organic compounds are characterised by NMR spectroscopy and/or microanalysis. The identities of the two Cu(II) complexes are confirmed by using microanalysis and the complex 6 is crystallographically analysed.     

Solution properties of the nickel(II,III) and copper(II,III) complexes of trans-dioxocyclam (trans-dioxocyclam=5,12-dioxo-1,4,8,11-tetraazacyclotetradecane) and the X-ray crystal structure of the N-rac-isomer of the nickel(II) complex

The crystal and molecular structures of the N-rac-isomer of the nickel(II) complex of 14-membered amide-containing macrocycle [NiL¹] · 4H₂O (H₂L¹=5,12-dioxo-1,4,8,11-tetraazacyclotetradecane) have been determined. Two deprotonated amide and two amine donors co-ordinate to the nickel(II) in nearly square planar manner with Ni-N_amine bonds longer than Ni-N_amide ones (1.930 vs. 1.898 Å). Water molecules do not co-ordinate and form hydrogen bond bridges between macrocyclic units in the crystal lattice. The analysis of ¹H NMR data confirmed that the solid-state conformation of the macrocycle in N-rac[NiL¹] is retained in aqueous solution though equilibrated with some amount of N-meso isomer. The comparison of the spectroscopic characteristics of the M(II) and M(III) complexes and the redox potentials of M(III/II) couples (M=Ni and Cu) for ML¹ with those for ML²(H₂L²=5,7-dioxo-1,4,8,11-tetraazacyclotetradecane) revealed a rather small influence of the trans- vs. cis-arrangement of amide donors in co-ordination spheres of the metal ions.     

Self-assembled synthesis, characterization and antimicrobial activity of zinc(II) salicylaldimine complexes

One-pot metal promoted reactions between salicylaldehyde and 4-methyl-1,3-phenylenediamine in the presence of metal salts acting as template agents yield zinc(II) salicylaldimine complexes containing N,N′-bis(salicylidene)-4-methyl-1,3-phenylenediamine (H₂L) as a result of the [2 + 1] Schiff base condensation. The complexes of formula [Zn(HL)Cl(H₂O)₂] · C₂H₅OH and [Zn(H₂L)₂Cl(NO₃)(H₂O)] · CH₃OH were characterized as powder solids and in solution by spectroscopic methods (IR, ¹H and ¹³C NMR, FAB-MS, ESI-MS, UV-Vis), thermogravimetric and elemental analysis, potentiometry, and tested for antimicrobial activity against Staphylococcusaureus in a minimum inhibitory concentration (MIC) experiment. In these two powder solid species, the salicylaldimine, formed in a self-assembly process, acts in two different coordination modes: as monodeprotonated bidentate chelator with an N,O donor set or as a neutral monodentate using exclusively oxygen as the donor atom without involving the nitrogen atoms in the coordination. However, crystals of these two complexes are isomorphous, with 1:2 metal:ligand stoichiometry, and display the latter, relatively rare coordination pattern. In solution, the presence of a 1:1 complex of monodeprotonated state is only detected. The complexes exhibit antimicrobial activity against S.aureus.     

The structure of the 11-coordinate barium complex of the pendant-donor macrocycle 1,4,7,10-tetrakis(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane: an analysis of the coordination numbers of barium(II) in its complexes

The crystal structure of [Ba(DOTAM)Cl]₂(ClO₄)₂ · 2.7H₂O, is reported, where DOTAM is 1,4,7,10-tetrakis(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane [triclinic, space group, , a=937.6(2), b=1050.4(2), c=1476.6(3) pm, α=110.41(2), β=97.48(2), γ=97.75(2)°, Z=2, R=0.0423]. The structure consists of a dimer held together by four oxygen atoms bridging between the two Ba atoms. Each Ba is 11-coordinate, coordinated to four nitrogens from the macrocyclic ring, and four oxygens from the four pendant amide groups of DOTAM. In addition, each Ba has a coordinated chloride ion, as well as two bridging amide oxygens from the other member of the dimer. An analysis of the coordination numbers (CN) of Ba(II) complexes is presented. It is found that the CN of Ba(II) complexes ranges from 3 to 12, and is most commonly 9 with unidentate ligands. Higher coordination numbers of 10 and above are promoted by either polydentate ligands of denticity greater than six, or the presence of several ligands such as nitrate or acetate that form four-membered chelate rings. Lower coordination numbers of seven and below are promoted by increasingly large substitutents attached directly to the donor atoms of the ligand.     

A novel tetranuclear lanthanide(III)-copper(II) complex of the macrocyclic oxamide [PrCu3] (macrocyclic oxamide = 1,4,8,11-tetraazacyclotradecanne-2,3-dione): synthesis, structure and magnetism

A novel tetranuclear lanthanide(III)-copper(II) complex of macrocyclic oxamide, [Pr(CuL)₃(H₂O)₂](SCN)₃ · 1.5H₂O (L = 1,4,8,11-tatraazacyclotradecanne-2,3-dione) (1), has been synthesized, structurally characterized and preliminary investigated by magnetic studies. The structure of the title complex consists of a cationic PrCu₃ core, noncoordinated monovalent SCN⁻ anions and H₂O molecules; the packing diagram shows open channels formed through intermolecular weak interactions. The temperature-dependent magnetic susceptibilities were analyzed by an approximate treatment being enlightened by Matsumoto et al. leading to J = −1.62 × 10⁻² cm⁻¹, Δ = 3.12 cm⁻¹, g_Cu = 2.13, respectively.     

Synthesis, crystal structures, antimicrobial properties and enzyme inhibition studies of zinc(II) complexes of thiones

Zinc(II) complexes of thiones having the general formula [ZnL₂Cl₂] where L = N-methylthiourea (Metu), N,N′-dimethylthiourea (Dmtu), tetramethylthiourea (Tmtu), N,N′-diethylthiourea (Detu), and diazinane-2-thione (Diaz), were prepared by reacting ZnCl₂ with the corresponding thiones. They were characterized by elemental analysis, IR and NMR spectroscopy and two of them {[(Tmtu)₂ZnCl₂] (1) and [(Diaz)₂ZnCl₂] (2)} using X-ray crystallography. The spectral data suggests that the coordination of thiones to zinc(II) occurs through the sulfur atom as indicated by an up field shift in the CS resonance of thiones in ¹³C NMR and downfield shift in N-H resonance in ¹H NMR. The crystal structures of the complexes show a tetrahedral coordination environment around the zinc atoms with the bond angles ranging from 99.33(5)° to 116.81(7)°. Antimicrobial activities of the complexes were evaluated by minimum inhibitory concentration and the results showed that the complexes exhibited significant activities against gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa) and yeasts (Candida albicans, Saccharomyces cerevisiae). However, moderate activity was observed against molds (Aspergillus niger, Penicillium citrinum). The complexes were also tested for inhibition activity against an enzyme, Alkaline Phosphatase EC 3.1.3.1 and were found to be active inhibitors.     

Synthesis of {15-benzyloxy-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene}nickel(II) perchlorate and its analogs, and their catalytic behavior in reductive debromination of 1-bromo-4-tert-butylbenzene

New nickel(II) complexes with macrocyclic ligands bearing benzyloxy [(5), (9)], 2-methylbenzyloxy (7), 3-methylbenzyloxy (8), and hydroxy (6) groups on the pyridine ring have been synthesized. Structures of the hydroxy substituted macrocyclic ligand (L-OH·3HCl·H₂O), and the benzyloxy substituted ligand (L-OBn·3HCl) and its nickel(II) complex (5), as well as an analogous Ni(II) complex (8), have been revealed by X-ray crystallography. Their catalytic capabilities in the reductive debromination of 1-bromo-4-tert-butylbenzene have been elucidated, which has revealed that the pyridine ring can be a suitable position for the introduction of functional groups while maintaining the catalytic capabilities of the nickel(II) complexes.     

Three zinc(II) complexes constructed from aromatic dicarboxylate and 1,4-bis((2-(pyridin-2-yl)-1H-imidazol-1-yl)methyl)benzene: Syntheses, crystal structures and luminescent properties

To investigate the effect of organic anions on the coordination frameworks, we synthesized three new complexes, namely, Zn(DPA)(bpimb)_0.5(H₂O) (1), Zn(BDC)(bpimb)_0.5 (2) and Zn₂(SDBA)₂(bpimb)·H₂O (3) (H₂DPA = diphenic acid; H₂BDC = isophthalic acid; H₂SDBA = 4,4′-dicarboxybiphenylsulfone), which were obtained by the reactions of 1,4-bis((2-(pyridin-2-yl)-1H-imidazol-1-yl)methyl)benzene (bpimb) as main ligand, and several aromatic polycarboxylate as organic anions with Zn(NO₃)₂·6H₂O. Single-crystal structure analysis shows that complex 1 is a one-dimensional chain structure, which is further interlinked into a higher-dimensional supramolecular framework by hydrogen-bonding interactions. In 2, BDC bridge Zn(II) atoms to give dimeric units, which are further linked by bpimb ligands to form sql nets. In 3, SDBA ligands and bpimb ligands connect Zn(II) ions into catenane-like two-dimensional layers. These catenane-like two-dimensional layers stack in an ABAB fashion to form a 3D supramolecular network. The distinct structures indicate three kinds of carboxylic ligands with different lengths and angles play fundamental roles in the formation of the final products. In addition, the luminescence measurements reveal that three complexes exhibit strong fluorescent emissions in the solid state at room temperature.     

Chiral recognition by the copper(II) complex of 6-deoxy-6-N-(2-methylaminopyridine)-β-cyclodextrin

A modified β-cyclodextrin bearing a 2-aminomethylpyridine binding site for copper(II) (6-deoxy-6-[N-(2-methylamino)pyridine)]-β-cyclodextrin, CDampy was synthesized by C₆-monofunctionalization. The acid-base properties of the new ligand in aqueous solution were investigated by potentiometry and calorimetry, and its conformations as a function of pH were studied by NMR and circular dichroism (c.d.). The formation of binary copper(II) complexes was studied by potentiometry, EPR, and c.d. The copper(II) complex was used as chiral selector for the HPLC enantiomeric separation of underivatized aromatic amino acids. Enantioselectivity in the overall stability constants of the ternary complexes with D- or L-Trp was detected by potentiometry, whereas the complexes of the Ala enantiomers did not show any difference in stability. These results were consistent with a preferred cis coordination of the amino group of the ligand and of the amino acid in the ternary complexes (“cis effect”), which leads to the inclusion of the aromatic side chain of D-Trp, but not of that of L-Trp. In Trp-containing ternary complexes, the two enantiomers showed differences in the fluorescence lifetime distribution, consistent with only one conformer of D-Trp and two conformers of L-Trp, and the latter were found to be more accessible to fluorescence quenching by acrylamide and KI. Chirality 9:341–349, 1997. © 1997 Wiley-Liss, Inc.     

Synthesis of a novel 'smart' bifunctional chelating agent 1-(2-[beta,D-galactopyranosyloxy]ethyl)-7-(1-carboxy-3-[4-aminophenyl]propyl)-4,10-bis(carboxymethyl)-1,4,7,10-tetraazacyclododecane (Gal-PA-DO3A-NH2) and its Gd(III) complex

A new synthetic pathway to 1-(2-[beta,D-galactopyranosyloxy]ethyl)-7-(1-carboxy-3-[4-aminophenyl]propyl)-4,10-bis(carboxymethyl)-1,4,7,10-tetraazacyclododecane (Gal-PA-DO3A-NH2) and 1-(2-[beta,D-galactopyranosyloxy]ethyl)-4,7,10-tris(carboxymethyl)-1, 4,7,10-tetraazacyclododecane (Gal-DO3A) chelating agents was developed involving full hydroxyl- and carboxyl-group protection in precursors to product. Two sequences of cyclen-N-functionalisation were subsequently investigated, one successfully, towards synthesis of the novel 'smart' bifunctional Gal-PA-DO3A-NH2 chelate. The longitudinal proton relaxivities of the neutral [Gd-(Gal-PA-DO3A-NH2)] and [Gd-(Gal-DO3A)] complexes were increased by 28% and 37% in the presence of beta-galactosidase, respectively.     

Syntheses, structures and photoluminescent properties of two zinc(II) coordination polymers based on aromatic polycarboxylate and 1,4-bis(imidazol-1-ylmethyl)benzene

Hydrothermal reaction of Zn(NO₃)₂·6H₂O with benzene-1,2,3-tricarboxylic acid (H₃BTC) or 5-bromoisophthalic acid (H₂BIPA) in the presence of 1,4-bis(imidazol-1-ylmethyl)benzene (bix) produced two novel coordination polymers [Zn₂(OH)(BTC) (bix)]·H₂O (1) and Zn(BIPA)(bix) (2), which were characterized by single-crystal X-ray diffraction, elemental analysis, IR and thermoanalysis. Complex 1 is a novel example of the 2D (3,4)-connected nets with (4²·6)(4²·6³·8) topology. In 2, the BIPA and bix ligands linked the Zn(II) atoms into a deeply corrugated 2D sheet. The corrugated 2D sheets polycatenate each other in a parallel manner yielding a rare 2D → 3D parallel polycatenation net. Thermal and luminescent properties of two complexes have also been investigated.     

Copper(II) complexes of new pentadentate bis(benzimidazolyl)-dithioether ligands: synthesis, structure, spectra and redox properties

Copper(II) complexes of a series of linear pentadentate ligands containing two benzimidazoles, two thioether sulfurs and a amine nitrogen, viz. N,N^′-bis{4^′-(2″-benzimidazolyl)(methyl)-3^′-thiabutyl}amine(L¹), N,N^′-bis{4^′-(2″-benzimidazolyl)(methyl)-3^′-thiabutyl}N-methylamine (L²), 2,6-bis{4^′-(2″-benzimidazolyl)(methyl)-3^′-thiabutyl}pyridine(L³), N,N^′-bis{4^′-(2″-benzimidazolyl)-2^′-thiabutyl}amine (L⁴), N,N^′-bis{4^′-(2″-benzimidazolyl)-2^′-thiabutyl}N-methylamine (L⁵) and 2,6-bis{4^′-(2″-benzimidazolyl)-2^′-thiabutyl}-3pyridine (L⁶) have been isolated and characterized by electronic absorption and EPR spectroscopy and cyclic and differential pulse voltammetry. Of these complexes, [Cu(L¹)](BF₄)₂ (1) and [Cu(L²)](BF₄)₂ (4) have been structurally characterized by X-ray crystallography. The coordination geometries around copper(II) in 1 and 4 are described as trigonal bipyramidal distorted square based pyramidal geometry (TBDSBP). The distorted CuN₃S basal plane in them is comprised of amine nitrogen, one thioether sulphur and two benzimidazole nitrogens and the other thioether sulfur is axially coordinated. The ligand field spectra of all the complexes are consistent with a mostly square-based geometry in solution. The EPR spectra of complexes [Cu(L¹)](BF₄)₂ (1), [Cu(L¹)](NO₃)₂ (2), [Cu(L²)](BF₄)₂ (4) and [Cu(L³)](ClO₄)₂ (6) are consistent with two species indicating the dissociation/disproportionation of the complex species in solution. All the complexes exhibit an intense CT band in the range 305-395 nm and show a quasireversible to irreversible Cu^II/Cu^I redox process with relatively positive E_1/2 values, which are consistent with the presence of two-coordinated thioether groups. The addition of N-methylimidazole (mim) replaces the coordinated thioether ligands in solution, as revealed from the negative shift (222-403 mV) in the Cu^II/Cu^I redox potential. The present study reveals that the effect of incorporating an amine nitrogen donor into CuN₂S₂ complexes is to generate an axial copper(II)-thioether coordination and also to enforce lesser trigonality on the copper(II) coordination geometry.     

A fluorescent ligand rationally designed to be selective for zinc(II) over larger metal ions. The structures of the zinc(II) and cadmium(II) complexes of N,N-bis(2-methylquinoline)-2-(2-aminoethyl)pyridine

The metal ion coordinating properties of the ligands N,N-bis(2-methylquinoline)-2-(2-aminoethyl)pyridine (DQPEA) and N,N-bis(2-methylquinoline)-2-(2-aminomethyl)pyridine (DQPMA) are presented. DQPEA and DQPMA differ only in that DQPEA forms six-membered chelate rings that involve the pyridyl group, whereas DQPMA forms analogous five-membered chelate rings.These two ligands illustrate the application of a ligand design principle, which states that increase of chelate ring size in a ligand will result in increase in selectivity for smaller relative to larger metal ions. The formation constants (log K₁) of DQPEA and DQPMA with Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) are reported. As expected from the applied ligand design principle, small metal ions such as Ni(II) and Zn(II) show increases in log K₁ with DQPEA (six-membered chelate ring) relative to DQPMA (five-membered chelate ring), while large metal ions such as Cd(II) and Pb(II) show decreases in log K₁ when the chelate ring increases in size. In order to further understand the steric origin of the destabilization of complexes of metal ions of differing sizes by the six-membered chelate ring of DQPEA, the structures of [Zn(DQPEA)H₂O](ClO₄)₂ (1) [triclinic, , a = 9.2906(10), b = 10.3943(10), c = 17.3880(18) Å, α = 82.748(7)°, β = 88.519(7)°, γ = 66.957(6)°, Z = 4, R = 0.073] and [Cd(DQPEA)(NO₃)₂] (2) [monoclinic, C2/c, a = 22.160(3), b = 15.9444(18), c = 16.6962(18) Å, β = 119.780(3)°, Z = 8, R = 0.0425] are reported. The Zn in (1) is five-coordinate, with a water molecule completing the coordination sphere. The Cd(II) in (2) is six-coordinate, with two unidentate nitrates coordinated to the Cd. It is found that the bonds to the quinaldine nitrogens in the DQPEA complexes are considerably stretched as compared to those of analogous TPyA (tri(pyridylmethyl)amine) complexes, which effect is attributed to the greater steric crowding in the DQPEA complexes. The structures are analyzed for indications of the origins of the destabilization of the complex of the large Cd(II) ion relative to the smaller Zn(II) ion. A possible cause is the greater distortion of the six-membered chelate ring in (2) than in (1), as evidenced by torsion angles that are further away from the ideal values in (2) than in (1). Fluorescence properties of the DQPMA and DQPEA complexes of Zn(II) and Cd(II) are reported. It is found that the DQPEA complex of Zn(II) has increased fluorescence intensity compared to the DQPMA complex, while for the Cd(II) complex the opposite is found. This is related to the greater strain in the six-membered chelate ring of the Cd(II) DQPEA complex as compared to the Zn(II) complex, with resulting poorer overlap in the Cd-N bond, and hence greater ability to quench the fluorescence in the Cd(II) complex.     

Synthesis, structures, and magnetic properties of dicopper(II) and dinickel(II) complexes with a new bis(macrocycle), 7,7-(2-hydoxypropane-1,3-diyl)bis{3,7,11,17-tetraazabicyclo[11.3.1]- heptadeca-1(17),13,15-triene}

A new bis(macrocycle) ligand, 7,7^′-(2-hydoxypropane-1,3-diyl)-bis{3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene} (HL), and its dicopper(II) ([Cu₂(HL)Cl₂](NO₃)₂ · 4H₂O (4a), [Cu₂(HL)I₂]I₂ · H₂O (4b)) and dinickel(II) ([Ni₂(L)(OH₂)](ClO₄)₃ (5a), [Ni₂(L)(OH₂)]I₃ · 2H₂O (5b), [Ni₂(L)N₃](N₃)₂ · 7H₂O (5c)) complexes have been synthesized. The alkoxide bridged face-to-face structure of the dinickel(II) complex 5c has been revealed by X-ray crystallography, as well as the “half-opened clamshell” form of the bis(macrocyclic) dicopper(II) complex 4b. Variable temperature magnetic susceptibility studies have indicated that there exists intramolecular antiferromagnetic coupling (J=−33.8 cm⁻¹ (5a), −32.5 cm⁻¹ (5b), and −29.7 cm⁻¹ (5c)) between the two nickel(II) ions in the nickel(II) complexes.     

First example of ruthenium-azoimine-chloranilates: synthesis, structure, spectra and electrochemistry of ruthenium(II) 1-alkyl-2-(arylazo)imidazole chloranilates, and correlation of electronic properties with ZINDO calculation

Ag⁺-assisted dechlorination of blue cis-trans-cis Ru(R-aai-R^′)₂Cl₂ followed by the reaction with chloranilic acid (H₂CA) in presence of Et₃N gives a neutral mononuclear violet complex [Ru(R-aai-R^′)₂(CA)]. [R-aai-R^′=p-R-C₆H₄-NN-C₃H₂-NN-1-R^′, abbreviated as N,N^′ chelator, where N(imidazole) and N(azo) represent N and N^′, respectively; R=H (a), Me (b), Cl (c) and R^′=Me (4), Et (5), CH₂Ph (6)]. The structure in one case, [Ru(Cl-aai-Et)₂(CA)] has been established by X-ray diffraction study. The π-π stacking and H-bonding network give a supramolecular ladder. All the complexes exhibit strong intense MLCT transition in the visible region and weak broad bands in higher wavelength (>700 nm). Visible transition (580-595 nm) shows negative solvatochromic effect. The cyclic voltammograms show two quasi-reversible to irreversible couples at positive to SCE and are due to CA⁻/CA²⁻ (1.2-1.4 V) and Ru(III)/Ru(II) (1.6-1.8 V) redox processes. Three couples negative to SCE are assigned to CA²⁻/CA³⁻ (−0.2 to −0.3 V) and azo reductions (−0.5 to −0.7, −0.8 to −0.9 V) of the chelated R-aai-R^′. The molecular orbital calculation (ZINDO/1, ZINDO/S) supports the spectral feature and electrochemical properties of the complexes.