Coordination chemistry of N-aminopropyl pendant arm derivatives of mixed N/S-, and N/S/O-donor macrocycles, and construction of selective fluorimetric chemosensors for heavy metal ions

The coordination chemistry of the N-aminopropyl pendant arm derivatives (L1c-4c) of the mixed donor macrocyclic ligands [12]aneNS2O, [12]aneNS3, [12]aneN2SO, and [15]aneNS2O2(L1a-4a) towards Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II) in aqueous solution has been investigated. The protonation and stability constants with the aforementioned metal ions were determined potentiometrically and compared, where possible, with those of the unfunctionalised macrocycles. The measured values show that Hg(II) and Cu(II) in water have the highest affinity for all ligands considered, with the N-aminopropyl pendant arm weakly coordinating the metal centres. Crystals suitable for X-ray diffraction analysis were grown for the perchlorate salt (H2L1c)(ClO4)2.dmf, and for the 1 : 1 complexes [Cd(L3a)(NO3)2](1), [Cu(L4a)dmf](ClO4)2(2), [Zn(L1c)(ClO4)]ClO4(3), [Cd(L1c)(NO3)]NO3(4), and [Hg(L2c)](ClO4)2(5). Their structures show the macrocyclic ligands adopting a folded conformation, which for the 12-membered systems can be either [2424] or [3333] depending on the nature of the metal ion. L1c-4c were also functionalised at the primary amino pendant group with different fluorogenic subunits. In particular the N-dansylamidopropyl (Lnd, n= 1-4), and the N-(9-anthracenylmethyl)aminopropyl (Lne, n= 1, 2, 4, ) pendant arm derivatives of L1a-4a were synthesised and their optical responses to the above mentioned metal ions were investigated in MeCN/H2O (4 : 1 v/v) solutions.     

Co-ordination chemistry of amino pendant arm derivatives of 1,4,7-triazacyclononane

The binding properties of 1,4,7-triazacyclononane ([9]aneN3) to metal cations can be adapted through sequential functionalisation of the secondary amines with aminoethyl or aminopropyl pendant arms to generate ligands with increasing numbers of donor atoms. The new amino functionalised pendant arm derivative of 1,4,7-triazacyclononane ([9]aneN3), L1, has been synthesised and its salt [H2L1]Cl2 characterised by X-ray diffraction. The protonation constants of the ligands L1-L4 having one, two or three aminoethyl or three aminopropyl pendant arms, respectively, on the [9]aneN3 framework, and the thermodynamic stabilities of their mononuclear complexes with CuII and ZnII have been investigated by potentiometric measurements in aqueous solutions. In order to discern the protonation sites of ligands L1-L4, 1H NMR spectroscopic studies were performed in D2O as a function of pH. While the stability constants of the CuII complexes increase on going from L1 to L2 and then decrease on going from L2 to L3 and L4, those for ZnII complexes increase from L1 to L3 and then decrease for L4. The X-ray crystal structures of the complexes [Cu(L1)(Br)]Br, [Zn(L1)(NO3)]NO3, [Cu(L2)](ClO4)2, [Ni(L2)(MeCN)](BF4)2, [Zn(L4)](BF4)2.MeCN and [Mn(L4)](NO3)2.1/2H2O have been determined. In both [Cu(L1)(Br)]Br and [Zn(L1)(NO3)]NO3 the metal ion is five co-ordinate and bound by four N-donors of the macrocyclic ligand and by one of the two counter-anions. The crystal structures of [Cu(L2)](ClO4)2 and [Ni(L2)(MeCN)](BF4)2 show the metal centre in slightly distorted square-based pyramidal and octahedral geometry, respectively, with a MeCN molecule completing the co-ordination sphere around NiII in the latter. In both [Zn(L4)](BF4)2.MeCN and [Mn(L4)](NO3)2.1/2H2O the metal ion is bound by all six N-donors of the macrocyclic ligand in a distorted octahedral geometry. Interestingly, and in agreement with the solution studies and with the marked preference of CuII to assume a square-based pyramidal geometry with these types of ligands, the reaction of L4 with one equivalent of Cu(BF4)2.4H2O in MeOH at room temperature yields a square-based pyramidal five co-ordinate CuII complex [Cu(L6)](BF4)2 where one of the three propylamino pendant arms of the starting ligand has been cleaved to give L6.     

Structural and EPR studies on single-crystal and polycrystalline samples of copper(II) and cobalt(II) complexes with N2S2-based macrocyclic ligands

The properties of Cu(II) and Co(II) complexes with oxygen- or nitrogen-containing macrocycles have been extensively studied; however, less attention has been paid to the study of complexes containing sulfur atoms in the first coordination sphere. Herein we present the interaction between these two metal ions and two macrocyclic ligands with N2S2 donor sets. Cu(II) and Co(II) complexes with the pyridine-containing 14-membered macrocycles 3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L) and 7-(9-anthracenylmethyl)-3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L1) have been synthesized. The X-ray structural analysis of {[Co(ClO4)(H2O)(L)][Co(H2O)2(L)]}(ClO4)3 shows two different metal sites in octahedral coordination. The EPR spectra of powdered samples of this compound are typical of distorted six-coordinated Co(II) ions in a high-spin (S=3/2) configuration, with the ground state being S=1/2 (g1=5.20, g2=3.20, g3=1.95). The EPR spectrum of [Cu(ClO4)(L)](ClO4) was simulated assuming an axial g tensor (g1=g2=2.043, g3=2.145), while that of [Cu(ClO4)(L1)](ClO4) slightly differs from an axial symmetry (g1=2.025, g2=2.060, g3=2.155). These results are compatible with a Cu(II) ion in square-pyramidal coordination with N2S2 as basal ligands. Single-crystal EPR experiment performed on [Cu(ClO4)(L1)](ClO4) allowed determining the eigenvalues of the molecular g tensor associated with the copper site, as well as the two possible orientations for the tensor. On the basis of symmetry arguments, an assignment in which the eigenvectors are nearly along the Cu(II)-ligand bonds is chosen.     

Tuning the selectivity/specificity of fluorescent metal ion sensors based on N2S2 pyridine-containing macrocyclic ligands by changing the fluorogenic subunit: spectrofluorimetric and metal ion binding studies

Two new fluorescent chemosensors for metal ions have been synthesized and characterized, and their photophysical properties have been explored; they are the macrocycles 5-(2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L5) and 5-(5-chloro-8-hydroxyquinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L6). Both systems have a pyridyl-thioether-containing 12-membered macrocycle as a binding site. The coordination properties of these two ligands toward CuII, ZnII, CdII, HgII, and PbII have been studied in MeCN/H2O (1:1 v/v) and MeCN solutions and in the solid state. The stoichiometry of the species formed at 25 degrees C have been determined from absorption, fluorescence, and potentiometric titrations. The complexes [CuL5](ClO4)(2).1/2MeCN, [ZnL5(H2O)](ClO4)2, [HgL5(MeCN)](ClO4)2, [PbL5(ClO4)2], [Cu3(5-Cl-8-HDQH-1)(L6H-1)2](ClO4)(3).7.5H2O (HDQ=hydroxyquinoline), and [Cu(L6)2](BF4)(2).2MeNO2 have also been characterized by X-ray crystallography. A specific CHEF-type response of L5 and L6 to the presence of ZnII and CdII, respectively, has been observed at about pH 7.0 in MeCN/H2O (1:1 v/v) solutions.     

Dinuclear zinc(II) complexes of tetraiminodiphenol macrocycles and their interactions with carboxylate anions and amino acids. Photoluminescence, equilibria, and structure

The reaction equilibria [H(4)L](2+) + Zn(OAc)(2) right harpoon over left harpoon [Zn(H(2)L)](2+) + 2HOAc (K(1)) and [Zn(H(2)L)](2+) + Zn(OAc)(2) right harpoon over left harpoon [Zn(2)L](2+) + 2HOAc (K(2)), involving zinc acetate and the perchlorate salts of the tetraiminodiphenol macrocycles [H(4)L(1)(-)(3)](ClO(4))(2), the lateral (CH(2))(n)() chains of which vary between n = 2 and n = 4, have been studied by spectrophotometric and spectrofluorimetric titrations in acetonitrile. The photoluminescence behavior of the complexes [Zn(2)L(1)](ClO(4))(2), [Zn(2)L(2)(H(2)O)(2)](ClO(4))(2), [Zn(2)L(2)(mu-O(2)CR)](ClO(4)) (R = CH(3), C(6)H(5), p-CH(3)C(6)H(4), p-OCH(3)C(6)H(4), p-ClC(6)H(4), p-NO(2)C(6)H(4)), and [Zn(2)L(3)(mu-OAc)](ClO(4)) have been investigated. The X-ray crystal structures of the complexes [Zn(2)L(2)(H(2)O)(2)](ClO(4))(2), [Zn(2)L(3)(mu-OAc)](ClO(4)), and [Zn(2)L(2)(mu-OBz)(OBz)(H(3)O)](ClO(4)) have been determined. The complex [Zn(2)L(2)(mu-OBz)(OBz)(H(3)O)](ClO(4)) in which the coordinated water molecule is present as the hydronium ion (H(3)O(+)) on deprotonation gives rise to the neutral dibenzoate-bridged compound [Zn(2)L(2)(mu-OBz)(2)].H(2)O. The equilibrium constants (K) for the reaction [Zn(2)L(2)(H(2)O)(2)](2+) + A(-) right harpoon over left harpoon [Zn(2)L(2)A](+) + 2H(2)O (K), where A(-) = acetate, benzoate, or the carboxylate moiety of the amino acids glycine, l-alanine, l-histidine, l-valine, and l-proline, have been determined spectrofluorimetrically in aqueous solution (pH 6-7) at room temperature. The binding constants (K) evaluated for these systems vary in the range (1-8) x 10(5).     

Homo- and heteropolynuclear Ni2+ and Cu2+ complexes of polytopic ligands, consisting of a tren unit substituted with three 12-membered tetraazamacrocycles

Two new polytopic ligands L1 and L2 have been synthesized. They consist of a central tren unit to which three 1,4,7,10-tetraazacyclododecane rings are attached via an ethylene and a trimethylene bridge, respectively. The complexation properties of L1 and L2 towards Cu(2+) and Ni(2+) were studied by potentiometric pH titration, UV-Vis, EPR spectroscopy and kinetic techniques. As a comparison, the Cu(2+) and Ni(2+) complexes with L3 (1-(N-methyl-2-aminoethyl-1,4,7,10-tetraazacyclododecane)) were also investigated. The crystal structures of [CuL3H(H(2)O)](ClO(4))(3) and [NiL3Cl](ClO(4)) were solved and show that the side chain in its protonated form is not involved in coordination, whereas deprotonated it binds to the metal ion. The thermodynamically stable 3:1 complexes of L1 or L2 have a metal ion in the three macrocyclic units. However, when three equivalents of Cu(2+) are added to L1 or L2 the metal ion first binds to the tren unit and only then to the macrocycles. The kinetics of the different steps of complexation have been studied and a mechanism is proposed.     

Dinuclear, tetranuclear and polymeric complexes in copper(II) perchlorate/pyridine-2,6-diamidoxime chemistry: synthetic, structural and magnetic studies

The initial use of pyridine-2,6-diamidoxime (pdamoH(2)) in metal cluster and polymer chemistry is described. Depending on the reaction conditions employed, the Cu(ClO(4))(2)·6H(2)O/pdamoH(2) system has provided access to the dinuclear compound [Cu(2)(pdamoH)(2)(ClO(4))(2)(MeOH)(2)] (1), the chain-like polymer [Cu(2)(pdamoH)(2)](n)(ClO(4))(2n) (2) and to the tetranuclear cluster [Cu(4)(pdamo)(2)(pdamoH)(2)](ClO(4))(2) (3). Single-crystal, X-ray crystallography reveals different coordination modes for the pdamoH(-) ligand in each compound, providing the first evidence for the flexibility and versatility of the anionic forms of pdamoH(2). Variable-temperature magnetic susceptibility studies indicate very strong antiferromagnetic coupling in the three complexes, attributable to the double oximato bridges which link the Cu(II) spin carriers.     

Monopicolinate cyclen and cyclam derivatives for stable copper(II) complexation

The syntheses of a new 1,4,7,10-tetraazacyclododecane (cyclen) derivative bearing a picolinate pendant arm (HL1), and its 1,4,8,11-tetraazacyclotetradecane (cyclam) analogue HL2, were achieved by using two different selective-protection methods involving the preparation of cyclen-bisaminal or phosphoryl cyclam derivatives. The acid-base properties of both compounds were investigated as well as their coordination chemistry, especially with Cu(2+), in aqueous solution and in solid state. The copper(II) complexes were synthesized, and the single crystal X-ray diffraction structures of compounds of formula [Cu(HL)](ClO(4))(2)·H(2)O (L = L1 or L2), [CuL1](ClO(4)) and [CuL2]Cl·2H(2)O, were determined. These studies revealed that protonation of the complexes occurs on the carboxylate group of the picolinate moiety. Stability constants of the complexes were determined at 25.0 °C and ionic strength 0.10 M in KNO(3) using potentiometric titrations. Both ligands form complexes with Cu(2+) that are thermodynamically very stable. Additionally, both HL1 and HL2 exhibit an important selectivity for Cu(2+) over Zn(2+). The kinetic inertness in acidic medium of both complexes of Cu(2+) was evaluated by spectrophotometry revealing that [CuL2](+) is much more inert than [CuL1](+). The determined half-life values also demonstrate the very high kinetic inertness of [CuL2](+) when compared to a list of copper(II) complexes of other macrocyclic ligands. The coordination geometry of the copper center in the complexes was established in aqueous solution from UV-visible and electron paramagnetic resonance (EPR) spectroscopy, showing that the solution structures of both complexes are in excellent agreement with those of crystallographic data. Cyclic voltammetry experiments point to a good stability of the complexes with respect to metal ion dissociation upon reduction of the metal ion to Cu(+) at about neutral pH. Our results revealed that the cyclam-based ligand HL2 is a very attractive receptor for copper(II), presenting a fast complexation process, a high kinetic inertness, and important thermodynamic and electrochemical stability.     

Fluorometric chemosensors. Interaction of toxic heavy metal ions Pb(II), Cd(II), and Hg(II) with novel mixed-donor phenanthroline-containing macrocycles: spectrofluorometric,conductometric, and crystallographic studies

The macrocycles L(1)-L(3) incorporating N(2)S(3)-, N(2)S(2)O-, and N(2)S(2)-donor sets, respectively, and containing the 1,10-phenanthroline unit interact in acetonitrile solution with heavy metal ions such as Pb(II), Cd(II), and Hg(II) to give 1:1 ML, 1:2 ML(2), and 2:1 M(2)L complex species, which specifically modulate the photochemical properties of the ligands. The stoichiometry of the complex species formed during spectrofluorometric titrations and their formation constants in MeCN at 25 degrees C were determined from fluorescence vs M(II)/L molar ratio data. The complexes [Pb(L(1))][ClO(4)](2).(1)/(2)H(2)O (1), [Pb(L(2))][ClO(4)](2).MeNO(2) (1a), [Pb(L(3))(2)][ClO(4)](2).2MeCN (1b), and [Cd(L(3))][NO(3)](2) (2b) were also characterized by X-ray diffraction studies. The conformation adopted by L(1)-L(3) in these species reveals the aliphatic portion of the rings folded over the plane containing the heteroaromatic moiety with the ligands trying to encapsulate the metal center within their cavity. In 1, 1a, and 2b the metal ion completes the coordination sphere by interacting with counteranion units and solvent molecules. On the contrary, the 1:2 complex 1b shows Pb(II) sandwiched between two symmetry-related molecules of L(3) reaching an overall [4N + 4S] eight-coordination.     

Reversible anion exchanges between the layered organic-inorganic hybridized architectures: syntheses and structures of manganese(II) and copper(II) complexes containing novel tripodal ligands

Six noninterpenetrating organic-inorganic hybridized coordination complexes, [Mn(3)(2)(H(2)O)(2)](ClO(4))(2).2 H(2)O (5), [Mn(3)(2)(H(2)O)(2)](NO(3))(2) (6), [Mn(3)(2)(N(3))(2)].2 H(2)O (7), [Cu(3)(2)(H(2)O)(2)](ClO(4))(2) (8), [Mn(4)(2)(H(2)O)(SO(4))].CH(3)OH.5 H(2)O (9) and [Mn(4)(2)](ClO(4))(2) (10) were obtained through self-assembly of novel tripodal ligands, 1,3,5-tris(1-imidazolyl)benzene (3) and 1,3-bis(1-imidazolyl)-5-(imidazol-1-ylmethyl)benzene (4) with the corresponding metal salts, respectively. Their structures were determined by X-ray crystallography. The results of structural analysis of complexes 5, 6, 7, and 8 with rigid ligand 3 indicate that their structures are mainly dependant on the nature of the organic ligand and geometric need of the metal ions, but not influenced greatly by the anions and metal ions. While in complexes 9 and 10, which contain the flexible ligand 4, the counteranion plays an important role in the formation of the frameworks. Entirely different structures of complexes 5 and 10 indicate that the organic ligands greatly affect the structures of assemblies. Furthermore, in complexes 5 and 6, the counteranions located between the cationic layers can be exchanged by other anions. Reversible anion exchanges between complexes 5 and 6 without destruction of the frameworks demonstrate that 5 and 6 can act as cationic layered materials for anion exchange, as determined by IR spectroscopy, elemental analyses, and X-ray powder diffraction.     

Metal complexes with a new N(4)O(3) amine pendant-armed macrocyclic ligand: synthesis, characterization, crystal structures, and fluorescence studies

The synthesis of a new oxaaza macrocyclic ligand, L, derived from O(1),O(7)-bis(2-formylphenyl)-1,4,7-trioxaheptane and tren containing an amine terminal pendant arm, and its metal complexation with alkaline earth (M = Ca(2+), Sr(2+), Ba(2+)), transition (M = Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+)), post-transition (M = Pb(2+)), and Y(3+) and lanthanide (M = La(3+), Er(3+)) metal ions are reported. Crystal structures of [H(2)L](ClO(4))(2).3H(2)O, [PbL](ClO(4))(2), and [ZnLCl](ClO(4)).H(2)O are also reported. In the [PbL] complex, the metal ion is located inside the macrocyclic cavity coordinated by all N(4)O(3) donor atoms while, in the [ZnLCl] complex, the metal ion is encapsulated only by the nitrogen atoms present in the ligand. pi-pi interactions in the [H(2)L](ClO(4))(2).3H(2)O and [PbL](ClO(4))(2) structures are observed. Protonation and Zn(2+), Cd(2+), and Cu(2+) complexation were studied by means of potentiometric, UV-vis, and fluorescent emission measurements. The 10-fold fluorescence emission increase observed in the pH range 7-9 in the presence of Zn(2+) leads to L as a good sensor for this biological metal in water solution.     

Coordination chemistry of a new cofacial binucleating macropolycycle derived from 1,4,7-triazacyclononane

We have prepared and characterized a new phenol-based compartmental ligand (H(2)L) incorporating 1,4,7-triazacyclononane ([9]aneN(3)), and we have investigated its coordination behavior with Cu(II), Zn(II), Cd(II), and Pb(II). The protonation constants of the ligand and the thermodynamic stabilities of the 1:1 and 2:1 (metal/ligand) complexes with these metal ions have been investigated by means of potentiometric measurements in aqueous solutions. The mononuclear [M(L)] complexes show remarkably high stability suggesting that, along with the large number of nitrogen donors available for metal binding, deprotonated phenolic functions are also involved in binding the metal ion. The mononuclear complexes [M(L)] show a marked tendency to add a second metal ion to afford binuclear species. The formation of complexes [M(2)(H(2)L)](4+) occurs at neutral or slightly acidic pH and is generally followed by metal-assisted deprotonation of the phenolic groups to give [M(2)(HL)](3+) and [M(2)(L)](2+) in weakly basic solutions. The complexation properties of H(2)L have also been investigated in the solid state. Crystals suitable for X-ray structural analysis were obtained for the binuclear complexes [Cu(2)(L)](BF(4))(2).(1)/(2)MeCN (1), [Zn(2)(HL)](ClO(4))(3).(1)/(2)MeCN (2), and [Pb(2)(L)](ClO(4))(2).2MeCN (4). In 1 and 2, the phenolate O-donors do not bridge the two metal centers, which are, therefore, segregated each within an N(5)O-donor compartment. However, in the case of the binuclear complex [Pb(2)(L)](ClO(4))(2).2MeCN (4), the two Pb(II) centers are bridged by the phenolate oxygen atoms with each metal ion sited within an N(5)O(2)-donor compartment of L(2)(-), with a Pb.Pb distance of 3.9427(5) A.     

Diverse solid-state and solution structures within a series of hexaamine dicopper(II) complexes

Mono- and dicopper(II) complexes of a series of potentially bridging hexaamine ligands have been prepared and characterized in the solid state by X-ray crystallography. The crystal structures of the following Cu(II) complexes are reported: [Cu(HL3)](ClO4)(3), C11H31Cl3CuN6O12, monoclinic, P2(1)/n, a = 8.294(2) A, b = 18.364(3) A, c = 15.674(3) A, beta = 94.73(2) degrees, Z = 4; ([Cu2(L4)(CO3)](2))(ClO4)(4).4H2O, C40H100Cl4Cu4N12O26, triclinic, P1, a = 9.4888(8) A, b = 13.353(1) A, c = 15.329(1) A, alpha = 111.250(7) degrees, beta = 90.068(8) degrees, gamma = 105.081(8) degrees, Z = 1; [Cu2(L5)(OH2)(2)](ClO4)(4), C13H36Cl4Cu2N6O18, monoclinic, P2(1)/c, a = 7.225(2) A, b = 8.5555(5) A, c = 23.134(8) A, beta = 92.37(1) degrees, Z = 2; [Cu2(L6)(OH2)(2)](ClO4)(4).3H2O, C14H44Cl4Cu2N6O21, monoclinic, P2(1)/a, a = 15.204(5) A, b = 7.6810(7) A, c = 29.370(1) A, beta = 100.42(2) degrees, Z = 4. Solution spectroscopic properties of the bimetallic complexes indicate that significant conformational changes occur upon dissolution, and this has been probed with EPR spectroscopy and molecular mechanics calculations.     

A rational design for imidazolate-bridged linear trinuclear compounds from mononuclear copper(II) complexes with 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL): syntheses, structures, and magnetic properties of [Cu(L)(hfac)M(hfac)2Cu(hfac)(L)] (M = ZnII, CuII, MnII)

Two mononuclear copper(II) complexes with the unsymmetrical tridentate ligand 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL), [Cu(HL)(H2O)](ClO4)2.2H2O (1) and [Cu(HL)Cl2] (2), have been prepared and characterized. The X-ray analysis of 2 revealed that the copper(II) ion assumes a pentacoordinated square pyramidal geometry with an N3Cl2 donor set. When 1 and 2 are treated with an equimolecular amount of potassium hydroxide, the deprotonation of the imidazole moiety promotes a self-assembled process, by coordination of the imidazolate nitrogen atom to a Cu(II) center of an adjacent unit, leading to the polynuclear complexes [[Cu(L)(H2O)](ClO4)]n (3) and [[Cu(L)Cl].2H2O]n (4). Variable-temperature magnetic data are well reproduced for one-dimensional infinite regular chain systems with J = -60.3 cm(-1) and g = 2.02 for 3 and J = -69.5 cm(-1) and g = 2.06, for 4. When 1 is used as a "ligand complex" for [M(hfac)2] (M = Cu(II), Ni(II), Mn(II), Zn(II)) in a basic medium, only the imidazolate-bridged trinuclear complexes [Cu(L)(hfac)M(hfac)2Cu(hfac)(L)] (M = Zn(II), Cu(II)) (5, 6) can be isolated. Nevertheless, the analogous complex containing Mn(II) as the central metal (7) can be prepared from the precursor [Cu(HL)Cl2] (2). All the trinuclear complexes are isostructural. The structures of 5 and 6 have been solved by X-ray crystallographic methods and consist of well-isolated molecules with Ci symmetry, the center of symmetry being located at the central metal. Thus, the copper(II) fragments are in trans positions, leading to a linear conformation. The magnetic susceptibility data (2-300 K), which reveal the occurrence of antiferromagnetic interactions between copper(II) ions and the central metal, were quantitatively analyzed for symmetrical three-spin systems to give the coupling parameters JCuCu = -37.2 and JCuMn = -3.7 cm(-1) with D = +/-0.4 cm(-1) for 6 and 7, respectively. These magnetic behaviors are compared with those for analogous systems and discussed on the basis of a localized-orbital model of exchange interactions.     

Selenadiazolopyridine: a synthon for supramolecular assembly and complexes with metallophilic interactions

The synthesis and characterization of the complexes of Cu(I), Ag(I), Cu(II), and Co(II) ions with 1,2,5-selenadiazolopyridine (psd) is reported. The following complexes have been prepared: [Cu(2)(psd)(3)(CH(3)CN)(2)](2+)2(PF(6)(-)); [(CuCl)(2)(psd)(3)]; [Cu(2)(psd)(6)](2+)2(ClO(4))(-); [Ag(2)(psd)(2)](2+)2(NO(3))(-); [Ag(2)(psd)(2)](2+)2(CF(3)COO)(-); [Cu(psd)(2)(H(2)O)(3)](2+)2(ClO(4))(-)·(psd)(2); [Cu(psd)(4)(H(2)O)](2+)2(ClO(4))(-)·(CHCl(3)); [Cu(psd)(2)(H(2)O)(3)](2+)2(NO(3))(-)·(H(2)O)·(psd)(2), and [Co(psd)(2)(H(2)O)(4)](2+)2(ClO(4))(-)·(psd)(2). The electronic structure of ligand psd, in particular the bond order of Se-N bonds, has been probed by X-ray diffraction, (77)Se NMR, and computational studies. A detailed analysis of the crystal structures of the ligand and the complexes revealed interesting supramolecular assembly. The assembly was further facilitated by the presence of neutral ligands for some complexes (Cu(II) and Co(II)). The molecular structure of the ligand showed that it was present as a dimer in the solid state where the monomers were linked by strong secondary bonding Se···N interactions. The crystal structures of Cu(I) and Ag(I) complexes revealed the dinuclear nature with characteristic metallophilic interactions [M···M] (M = Cu, Ag), while the Cu(II) and Co(II) complexes were mononuclear. The presence of M···M interactions has been further probed by Atoms in Molecules (AIM) calculations. The paramagnetic Cu(II) and Co(II) complexes have been characterized by UV-vis, ESI spectroscopy, and room temperature magnetic measurements.     

Anion binding by metallo-receptors of 5,5'-dicarbamate-2,2'-bipyridine ligands

Three 5,5'-dicarbamate-2,2'-bipyridine ligands (L = L(1)-L(3)) bearing ethyl, isopropyl or tert-butyl terminals, respectively, on the carbamate substituents were synthesized. Reaction of the ligands L with the transition metal ions M = Fe(2+), Cu(2+), Zn(2+) or Ru(2+) gave the complexes ML(n)X(2)·xG (1-12, n = 1-3; X = Cl, NO(3), ClO(4), BF(4), PF(6), ?SO(4); G = Et(2)O, DMSO, CH(3)OH, H(2)O), of which [Fe(L(2))(3)???SO(4)]·8.5H(2)O (2), [Fe(L(1))(3)???(BF(4))(2)]·2CH(3)OH (7), [Fe(L(2))(3)???(Et(2)O)(2)](BF(4))(2)·2CH(3)OH (8), [ZnCl(2)(L(1))][ZnCl(2)(L(1))(DMSO)]·2DMSO (9), [Zn(L(1))(3)???(NO(3))(2)]·2H(2)O (10), [Zn(L(2))(3)???(ClO(4))(Et(2)O)]ClO(4)·Et(2)O·2CH(3)OH·1.5H(2)O (11), and [Cu(L(1))(2)(DMSO)](ClO(4))(2)·2DMSO (12) were elucidated by single-crystal X-ray crystallography. In the complexes ML(n)X(2)·xG the metal ion is coordinated by n = 1, 2 or 3 chelating bipyridine moieties (with other anionic or solvent ligands for n = 1 and 2) depending on the transition metal and reaction conditions. Interestingly, the carbamate functionalities are involved in hydrogen bonding with various guests (anions or solvents), especially in the tris(chelate) complexes which feature the well-organized C(3)-clefts for effective guest inclusion. Moreover, the anion binding behavior of the pre-organized tris(chelate) complexes was investigated in solution by fluorescence titration using the emissive [RuL(3)](2+) moiety as a probe. The results show that fluorescent recognition of anion in solution can be achieved by the Ru(II) complexes which exhibit good selectivities for SO(4)(2-).     

Synthesis, structures and properties of Cu(II) and Mn(II) complexes with 1,10-phenanthroline-2-carboxylic acid and 2,2'-bipyridine ligands

Four new 2,2'-bipyridine and 1,10-phenanthroline complexes, namely [Mn(phenca)(2)]·(H(2)O)(2) (1), [Cu(4)(phen)(4)(OH-)(4)(H(2)O)(2)](DMF)(4)(ClO(4)-)(4)(H(2)O) (2), [Cu(2)(2,2-bipy)(2)(C(2)O(4)2-)(H(2)O)(2)(NO(3))(2)] (3) and [Cu(2,2-bipy)(2)(ClO(4)-)](ClO(4)-) (4) (2,2'-bpy = 2,2'-bipyridine, Hphenca = 1,10-phenanthroline-2-carboxylic acid) have been synthesized by a hydrothermal reaction. The products were characterized by elemental analysis, infrared spectroscopy and X-ray crystal diffraction. While strong hydrogen bonds play central roles in the formation of the 3D structure, the combined influence of the weak interactions such as π···π interactions is also evident in the structures. A preliminary investigation on the ion exchange properties of the complexes is presented.     

Color tuning of a nickel complex with a novel N2S2 pyridine-containing macrocyclic ligand

The novel pyridine-containing 14-membered macrocycle 3,11-dithia-7,17-diazabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L), which contains an N2S2 donor set, was synthesized, and its protonation behavior was studied by absorption titration with CH3SO3H. The reaction of L with Pd(II) was studied spectroscopically, and the square-planar complex [Pd(L)](BF4) was isolated and characterized. The reactions between L and NiX2 x 6 H2O (X = BF4, ClO4) in ethanol or acetonitrile afforded the octahedral complexes [Ni(CH3CN)(H2O)(L)](X)2 and [Ni(H2O)2(L)](X)2, respectively. The square-planar complexes [Ni(L)](X)2 were obtained by heating these octahedral complexes. Spectrophotometric titrations of [Ni(L)](BF4)2 were performed with neutral and negatively charged ligands. The color of nitromethane solutions of this square-planar complex turns from red to cyan, purple, blue, yellow-green, and pink following addition of halides, acetonitrile, water, pyridine, and 2,2'-bipyridine, respectively. X-ray structural analyses were carried out on the {[Ni(ClO4)(H2O)(L)][Ni(H2O)2(L)]}(ClO4)3, [Ni(CH3CN)(H2O)(L)](ClO4)2, [{Ni(L)}2(mu-Cl)2](ClO4)2, and [{Ni(L)}2(mu-Br)2]Br2 x 2 CH3NO2 complexes.     

Helical-chain copper(II) complexes and a cyclic tetranuclear copper(II) complex with single syn-anti carboxylate bridges and ferromagnetic exchange interactions

Tridentate Schiff-base carboxylate-containing ligands, derived from the condensation of 2-imidazolecarboxaldehyde with the amino acids beta-alanine (H2L1) and 2-aminobenzoic acid (H2L5) and the condensation of 2-pyridinecarboxaldehyde with beta-alanine (HL2), D,L-3-aminobutyric acid (HL3), and 4-aminobutyric acid (HL4), react with copper(II) perchlorate to give rise to the helical-chain complexes [[Cu(mu-HL1)(H2O)](ClO4)]n (1), [[Cu(mu-L2)(H2O)](ClO4).2H2O]n (2), and [[Cu(mu-L3)(H2O)](ClO4).2H2O]n (3), the tetranuclear complex [[Cu(mu-L4)(H2O)](ClO4)]4 (4), and the mononuclear complex [Cu(HL5)(H2O)](ClO4).1/2H2O (5). The reaction of copper(II) chloride with H2L1 leads not to a syn-anti carboxylate-bridged compound but to the chloride-bridged dinuclear complex [Cu(HL1)(mu-Cl)]2 (6). The structures of these complexes have been solved by X-ray crystallography. In complexes 1-4, roughly square-pyramidal copper(II) ions are sequentially bridged by syn-anti carboxylate groups. Copper(II) ions exhibit CuN2O3 coordination environments with the three donor atoms of the ligand and one oxygen atom belonging to the carboxylate group of an adjacent molecule occupying the basal positions and an oxygen atom (from a water molecule in the case of compounds 1-3 and from a perchlorate anion in 4) coordinated in the apical position. Therefore, carboxylate groups are mutually cis oriented and each syn-anti carboxylate group bridges two copper(II) ions in basal-basal positions with Cu...Cu distances ranging from 4.541 A for 4 to 5.186 A for 2. In complex 5, the water molecule occupies an equatorial position in the distorted octahedral environment of the copper(II) ion and the Cu-O carboxylate distances in axial positions are very large (>2.78 A). Therefore, this complex can be considered as mononuclear. Complex 6 exhibits a dinuclear parallel planar structure with Ci symmetry. Copper(II) ions display a square-pyramidal coordination geometry (tau = 0.06) for the N2OCl2 donor set, where the basal coordination sites are occupied by one of the bridging chlorine atoms and the three donor atoms of the tridentate ligand and the apical site is occupied by the remaining bridging chlorine atom. Magnetic susceptibility measurements indicate that complexes 1-4 exhibit weak ferromagnetic interactions whereas a weak antiferromagnetic coupling has been established for 6. The magnetic behavior can be satisfactorily explained on the basis of the structural data for these and related complexes.     

Synthesis,structure, and DNA cleavage activity of new trinuclear Zn(3) and Zn(2)Cu complexes of a chiral macrocycle: structural correlation with the active center of P1 nuclease

New homo trinuclear Zn(II) complexes [Zn(3)L(1)(micro-OAc)](ClO(4))(2).3CHCl(3).H(2)O, 1, and [Zn(3)L(1)(micro-OAc)].ClO(4).PF(6).5CH(3)OH.H(2)O, 2, and hetero trinuclear complex [Zn(2)CuL(1)(micro-OAc)](ClO(4))(2).3CHCl(3).H(2)O,3, of optically active hexaaza triphenolic macrocycle H(3)L(1) were synthesized and crystallographically characterized. The cation [Zn(3)L(1)(micro-OAc)](+) structure of 1 and 2 closely resembles the trinuclear Zn(II) active site of P1 nuclease. The distorted tetrahedral geometry of Zn3 was successfully reproduced at Cu1 in complex 3. The complexes 2 and 3 cleave CT DNA at 37 and 50 degrees C.