Unusual Coordination Mode Research Articles

Atypical fluoroquinolone gold(III) chelates as potential anticancer agents: Relevance of DNA and protein interactions for their mechanism of action

Quinolones are known for their antimicrobial and antitumor activities. Gold(III) compounds constitute an emerging class of biologically active substances, of special interest as potential anticancer agents. In this work three gold(III) complexes of the fluoroquinolones antimicrobial agents norfloxacin (NOR), levofloxacin (LEVO) and sparfloxacin (SPAR) were prepared and characterized with physicochemical and spectroscopic techniques. In these complexes, NOR, LEVO and SPAR act as bidentate neutral ligands bound to gold(III) through the nitrogen atoms of the piperazine ring, which is an unusual mode of coordination for this class of compounds. Two chloride ions occupy the remaining coordination sites.The cytotoxic activity of the fluoroquinolones and their gold(III) complexes was tested against the A20 (murine lymphoma), B16-F10 (murine melanoma) and K562 (human myeloid leukemia) tumor cell lines as well as the L919 (murine lung fibroblasts) and MCR-5 (human lung fibroblasts) normal cells lines. All complexes were more active than their corresponding free ligands. Complex [AuCl2(LEVO)]Cl was selected for DNA fragmentation and cell cycle analysis.Spectroscopic titration with calf-thymus DNA (CT DNA) showed that the complexes can bind weakly to CT DNA, probably by an external contact (electrostatic or groove binding). The complexes exhibit good binding propensity to bovine serum albumin (BSA) having relatively high binding constant values.

Non-Centrosymmetric Coordination Polymer with a Highly Hindered Octahedral Copper Center Bridged by Mandelate

A novel chiral coordination polymer, [Cu(C(6)H(5)CH(OH)COO)(μ-C(6)H(5)CH(OH)COO)] (1-L and 1-D), was synthesized through a reaction of copper acetate with L-mandelic acid at room temperature. Although previously reported copper mandelate prepared by hydrothermal reaction was a centrosymmetric coordination polymer because of the racemization of mandelic acid, the current coordination polymer shows noncentrosymmetry and a completely different structure from that previously reported. The X-ray crystallography for 1-L revealed that the copper center of the compound showed a highly distorted octahedral structure bridged by a chiral mandelate ligand in the unusual coordination mode to construct a one-dimensional (1D) zigzag chain structure. These 1D chains interdigitated each other to give a layered structure as a result of the formation of multiple aromatic interactions and hydrogen bonds between hydroxyl and carboxylate moieties at mandelate ligands. The coordination polymer 1-L belongs to the noncentrosymmetric space group of C2 to show piezoelectric properties and second harmonic generation (SHG) activity.

Synthesis and structures of a pentanuclear Al(iii) phosphonate cage, an In(iii) phosphonate polymer, and coordination compounds of the corresponding phosphonate ester with GaI3 and InCl3

A cationic, pentanuclear aluminium phosphonate cage, [L(4)Al(5)Cl(6)(THF)(6)]Cl, 1, supported by (phthalimidomethyl) phosphonate, (L), has been synthesized and characterized. This polynuclear cage features the phosphonate ligand in an unusual coordination mode, supporting five aluminium atoms in two different environments. In comparison, the aqueous reaction of LH(2) with In(ClO(4))(3) afforded [{(LH)In(H(2)O)}(H(2)O)(2)(ClO(4))](n), 2, an indium(III) phosphonate coordination polymer, that has been crystallographically characterized. Reactions of the corresponding phosphonate ester, diethyl (phthalimidomethyl) phosphonate, (L'), with GaI(3) and InCl(3) afforded the simple coordination complexes, [L'·GaI(3)], 3, and [L'·InCl(3)(THF)], 4.

Four novel alkaline-earth metal coordination polymers with networks controlled by the diverse coordination modes of amino-sulfonate ligand: Synthesis, crystal structures and luminescent properties

Four novel alkaline-earth metal coordination polymers based on 4,4′-diamino-2,2′-stilbenedisulfonic acid ligand (H2dsd), namely, [Mg(dsd)(H2O)4]n (1), {[Ca(dsd)(H2O)2]·H2O}n (2), {[Sr(dsd)(H2O)6]·H2O}n (3), [Ba(dsd)(H2O)2]n (4), were synthesized under hydrothermal conditions and structurally characterized by elemental analysis, IR, single-crystal X-ray diffraction and thermogravimetric analysis. These complexes exhibit various polymeric networks due to the diverse coordination modes of dsd2−. Complexes 1 and 3 display a 1D zigzag chain structure with dsd2− group as a μ-bis(monodentate) ligand (denoted as μ2-η1η1 ligand). Complex 2 is a 1D ribbon chain coordination polymer in which dsd2− shows the μ3-η1η2η1 coordination mode, and complex 4 is a 2D coordination polymer in which dsd2− presents the unusual μ4-η1η2η1η1 coordination mode. The present four complexes exhibit different fluorescent emissions in the solid state at room temperature.

Characterization of [Pd(pap)(NHC)I2]n (n = +1, 0, −1; pap = phenylazopyridine; NHC = N-heterocyclic carbene): Unusual coordination mode of pap and non-innocent behavior of NHC

The compounds [Pd(pap)(NHC)I2], 1 and 2 (pap=Phenylazopyridine, NHC=1,3-di-n-butyl-benzimidazolin-2-ylidene, 1 and NHC=1-n-butyl-3-isopropyl-benzimidazolin-2-ylidene, 2) were synthesized from the respective 1,3-disubstituted benzimidazolium salts and [Pd(pap)] precursor in the presence of a base. Crystallographic characterization of 1 shows an unusual coordination mode of pap, with the ligand coordinating to the Pd(II) center only through the pyridine nitrogen atom in an η1-N fashion. Both the nitrogen atoms of the azo group remain uncoordinated to the metal center. Cyclic voltammetry of 1 and 2 shows two oxidation and two reduction steps. A combination of UV–Vis and EPR spectroelectrochemistry is used to show that the reduction steps are pap based, proving its known non-innocent character. Investigation of the first oxidation step points to an electron removal from a predominantly NHC based orbital, thus showing the potential non-innocent nature of these ligands. These results can provide new mechanistic insights into the use of Pd–NHC catalysts for cross-coupling reactions, where oxidative addition is one of the deciding steps for catalysis.

Magnetic Ordering in Three-Dimensional Metal–Organic Frameworks Based on Carboxylate Bridged Square-Grid Layers

Three isomorphous metal-organic frameworks of formula [M(ppdc)(H(2)O)(2)](n) [M = Mn(II), Fe(II), and Co(II)] were synthesized from sodium p-phenylenediacrylic (Na(2)ppdc). Crystallographic studies revealed that the compounds are layer-pillared 3D frameworks in which the square-grid M(II) layers with single carboxylate bridges are interlinked by long organic spacers with large interlayer separations of about 13 Å. Magnetic investigations indicated that they all display intralayer antiferromagnetic interactions through the carboxylate bridges in the unusual skew-skew coordination mode but the bulk behaviors are quite different. The Co(II) compound, like most compounds containing similar M-O-C-O-M layers, shows no 3D magnetic ordering down to 2 K, while the Mn(II) and Fe(II) compounds exhibit spin-canted ordering, behaving as a weak ferromagnet (T(C) = 3.8 K) and a metamagnet (T(N) = 3.8 K, H(c) = 650 Oe), respectively. Spin-canted ordering is still a rarity in this series of materials. Magnetostructural comparisons with analogous compounds indicate that the occurrence of spin-canted ordering can be related to the uncommon skew-skew and anti-anti coordination modes of carboxylate bridges, which induce stronger antiferromagnetic interactions than the common syn-anti mode.

Syntheses and X‐ray Crystal Structures of Organoantimony Diazides

Antimony(III) complexes of the general type LSbF(2) (3: L(1) =[tBuC(NiPr)(2)]; 4: L(2) =[tBuC(NDipp)(2) , Dipp=2,6-iPr(2)C(6)H(3)) and LSb(N(3))(2) (6: L(1); 7: L(2)) were prepared in high yields and characterized by elemental analyses, NMR and IR spectroscopy and single-crystal X-ray diffraction. Moreover, the solid-state structures of [L(2)SbF(2)][L(2)Li] (5), [L(2) AlH(2)] (1), and [L'H][L'K(thf)(3)] (2; L'=HC(NDipp)(2)) are described, in which the Li (5) and K atoms (2) adopt rather unusual coordination modes.

A Click Fluorophore Sensor that Can Distinguish CuII and HgII via Selective Anion‐Induced Demetallation

A cyclam-based fluorescent sensor featuring a novel triazole pendant arm has been synthesised using click chemistry. The sensor is highly responsive to both Cu(II) and Hg(II) in neutral aqueous solution and displays excellent selectivity in the presence of various competing metal ions in 50-fold excess. The addition of specific anions such as I(-) and S(2)O(3)(2-) causes a complete revival of fluorescence only in the case of Hg(II), providing a simple and effective method for distinguishing solutions containing Cu(II), Hg(II) or a mixture of both ions, even in doped seawater samples. X-ray crystal structures of both the Hg(II) sensor complex and a model Cu(II) complex show that pendant triazole coordination occurs through the central nitrogen atom (N2), providing to the best of our knowledge the first reported examples of this unusual coordination mode in macrocycles. Fluorescence, mass spectrometry and (1)H NMR experiments reveal that the mechanism of anion-induced fluorescence revival involves either displacement of pendant coordination or complete removal of the Hg(II) from the macrocycle, depending on the anion.

Structural and magnetic properties of three novel complexes with the versatile ligand 5-methyl-1,2,4-triazolo[1,5-a]pyrimidin-7(4H)-one

Conventional reactions of the versatile multidentate ligand 5-methyl-1,2,4-triazolo[1,5-a]pyrimidin-7(4H)-one (HmtpO) with metallic(II) salts lead to three novel multidimensional complexes [Cu(HmtpO)(2)(H(2)O)(3)](ClO(4))(2)·H(2)O (1), {[Cu(HmtpO)(2)(H(2)O)(2)](ClO(4))(2)·2HmtpO}(n) (2) and {[Co(HmtpO)(H(2)O)(3)](ClO(4))(2)·2H(2)O}(n) (3). In each compound, the triazolopyrimidine ligand shows a different and unusual coordination mode, giving rise to structures with diverse topologies and dimensionality. Compound 1 is a monomeric complex, in which HmtpO shows both N3-monodentate and N1,O71-bidentate modes. 2 is a bidimensional framework with the ligand showing a N3,O71 bidentate-bridging mode. The structure of 3 consists of 1D chains, in which HmtpO displays a N1,N3,O71-tridentate-bridging mode. It should be noted that these coordination modes of the HmtpO ligand are unique in the case of compounds 2 and 3. On the other hand, the magnetic properties of the polynuclear complexes 2 and 3 have been studied showing weak ferromagnetic and antiferromagnetic behaviour, respectively.

Utilization of IR spectral detailed analysis for coordination mode determination in novel Zn–cyclen–aminoacid complexes

The infrared spectra, elemental and thermal (TG/DTG and DTA) analyses of novel [Zn(cyclen-κ 4N 1,4,7,10)(HGly-κ 2O,O′)](ClO 4) 2 ( 1), and [Zn 2(cyclen-κ 4N 1,4,7,10) 2(μ-S-Ala-κ 2N,O)](ClO 4) 3·2H 2O ( 2) complexes (cyclen – 1,4,7,10-tetraazacyclododecane) were recorded and analyzed in the relation to their structural peculiarities. IR spectral data indicate both mono- or bidentate coordination mode of a carboxylate group in the prepared complexes (at pH ≈ 9). The results indicate unusual bidentate carboxylate coordination mode (in complex ( 1)) toward to Zn 2+–cyclen unit. Therefore the crystal structure determination of the crystalline complex [Zn(cyclen-κ 4N 1,4,7,10)(NO 3-κ 2O,O′)](NO 3) was attached in order to support the coordination mode assignment in complex ( 1).

Synthesis, Structure, and DNA Cleavage Properties of Copper(II) Complexes of 1,4,7-Triazacyclononane Ligands Featuring Pairs of Guanidine Pendants

Two new ligands, L(1) and L(2), have been prepared via N-functionalization of 1,4,7-triazacyclononane (tacn) with pairs of ethyl- or propyl-guanidine pendants, respectively. The X-ray crystal structure of [CuL(1)](ClO4)2 (C1) isolated from basic solution (pH 9) indicates that a secondary amine nitrogen from each guanidine pendants coordinates to the copper(II) center in addition to the nitrogen atoms in the tacn macrocycle, resulting in a five-coordinate complex with intermediate square-pyramidal/trigonal bipyramidal geometry. The guanidines adopt an unusual coordination mode in that their amine nitrogen nearest to the tacn macrocycle binds to the copper(II) center, forming very stable five-membered chelate rings. A spectrophotometric pH titration established the pK(app) for the deprotonation and coordination of each guanidine group to be 3.98 and 5.72, and revealed that [CuL(1)](2+) is the only detectable species present in solution above pH ∼ 8. The solution speciation of the CuL(2) complex (C2) is more complex, with at least 5 deprotonation steps over the pH range 4-12.5, and mononuclear and binuclear complexes coexisting. Analysis of the spectrophotometric data provided apparent deprotonation constants, and suggests that solutions at pH ∼ 7.5 contain the maximum proportion of polynuclear complexes. Complex C1 exhibits virtually no cleavage activity toward the model phosphate diesters, bis(p-nitrophenyl)phosphate (BNPP) and 2-hydroxypropyl-p-nitrophenyl phosphate (HPNPP), while C2 exhibits moderate activity. For C2, the respective kobs values measured at pH 7.0 (7.24 (± 0.08) × 10(-5) s(-1) (BNPP at 50 °C) and 3.2 (± 0.3) × 10(-5) s(-1) (HPNPP at 25 °C)) are 40- and 10-times faster than [Cu(tacn)(OH2)2](2+) complex. Both complexes cleave supercoiled pBR 322 plasmid DNA, indicating that the guanidine pendants of [CuL(1)](2+) may have been displaced from the copper coordination sphere to allow for DNA binding and subsequent cleavage. The rate of DNA cleavage by C2 is twice that measured for [Cu(tacn)(OH2)2](2+), suggesting some degree of cooperativity between the copper center and guanidinium pendants in the hydrolysis of the phosphate ester linkages of DNA. A predominantly hydrolytic cleavage mechanism was confirmed through experiments performed either in the presence of various radical scavengers or under anaerobic conditions.

Coordination behavior of three geometric isomers of indole-based S-benzyldithiocarbazone ligands towards nickel, zinc and cadmium divalent ions

Three indolyl-imine ligands have been synthesized through the condensation of S-benzyldithiocarbazate with indole-2-carbaldehyde, indole-3-carbaldehyde and indole-7-carbaldehyde. Treatment of these Schiff bases with acetate salts of Ni(II), Zn(II) and Cd(II) in ethanol yielded a series of complexes of 2:1 type (ligand/metal ratio) in which the ligands coordinated to the metal ions as monoanionic NS bidentate chelates. While the 2-imineindole and 3-imineindole formed the expected five-membered chelate rings, the X-ray crystal structure of [Cd(HL3)(py)2], (HL3=the mono-deprotonated 7-imineindole), revealed an unusual mode of coordination, namely formation of four-membered rings with the metal atom. Reaction of the 7-imineindole with the metal ions in the presence of potassium hydroxide produced complexes of the type [M(L3)(H2O)] in which the Schiff base acts as a dianionic NNS tridentate ligand.

Enhanced Anion Binding from Unusual Coordination Modes of Bis(thiourea) Ligands in Platinum Group Metal Complexes

Treatment of a range of bis(thiourea) ligands with inert organometallic transition-metal ions gives a number of novel complexes that exhibit unusual ligand binding modes and significantly enhanced anion binding ability. The ruthenium(II) complex [Ru(η(6)-p-cymene)(κS,S',N-L(3)-H)](+) (2b) possesses juxtaposed four- and seven-membered chelate rings and binds anions as both 1:1 and 2:1 host guest complexes. The pyridyl bis(thiourea) complex [Ru(η(6)-p-cymeme)(κS,S',N(py)-L(4))](2+) (4) binds anions in both 1:1 and 1:2 species, whereas the free ligand is ineffective because of intramolecular NH⋅⋅⋅N hydrogen bonding. Novel palladium(II) complexes with nine- and ten-membered chelate rings are also reported.

Reactivity of [1],[1]Disilamolybdenocenophane toward Zerovalent Platinum Complexes

The results of studies of the reactivity of strained [1],[1]disilamolybdenocenophane toward zerovalent platinum complexes are reported. Whereas [Pt(PEt(3))(3)] underwent clean insertion into both Si-C(ispo) bonds of the twofold-bridged molybdenocene, the reaction with the tricyclohexylphosphine analogue is considerably more complex. Thus, treatment of the molybdenum compound with 2 equiv of [Pt(PCy(3))(2)] results in a trinuclear cluster. To gain insight into the mechanistic aspects, the reaction was performed in a 1:1 stoichiometry. Multinuclear NMR spectroscopy revealed the presence of different species in solution. Two constitutional isomers were identified by X-ray diffraction analyses, one presumably depicting an intermediate in the formation of the trinuclear cluster. The predominant isomer in solution was identified as the product of C-H oxidative addition to the platinum phosphine fragment. Its solid-state structure displays an unusual coordination mode of platinum, and structural parameters suggest the formulation as the sigma-complex of a Mo-Si bond.

A double helical dicopper(II) complex with biacetyl bis(benzoylhydrazone)

A dinuclear double helicate of copper(II) with the Schiff base biacetyl bis(benzoylhydrazone) (H 2babh) is reported. The solid state physical properties of the dicopper(II) species are compared with that of its mononuclear precursor. The O,N,N,O-donor babh 2− shows an unusual bridging coordination mode in [Cu 2(μ-babh) 2]. Each metal center in the complex is in very similar tetrahedrally distorted square-planar N 2O 2 coordination sphere assembled by the two halves of the two babh 2−. To accommodate the metal centers, two halves of each ligand are twisted along the (CH 3)C–C(CH 3) bond.

Stabilization of Unusual Substrate Coordination Modes in Dinuclear Macrocyclic Complexes

The steric protection offered by the macrobinucleating hexaazaditiophenolateligand (L) allows for the preparation of the first stable dinuclear nickel(II) borohydride bridged complex, which reacts rapidly with elemental sulphur producing a tetranuclear nickel(II) complex [{(L)Ni2}2(μ-S6)]2+ bearing a helical μ4-hexa- sulfide ligand. The [(L)CoII 2]2+ fragment have been able to trap a monomethyl orthomolybdate in the binding pocket. Unusual coordination modes of substrate in dinuclear macrocyclic compounds was demonstrated.

Assembly of 3D Metal-Organic Framework Based on Heterobimetallic Cu-K Unit and Oxalate Linkage

A novel heterobimetallic Cu-K coordination polymer [Cu(ox) 2 K 2 ( μ 3 -H 2 O) 2 ] n (ox = oxalate dianion) was synthesized under mild condition and characterized by single-crystal X-ray diffraction. Its X-ray crystal structure shows that the new coordination polymer belongs to a triclinic system, P-1 space group. The crystallographic data are: a = 6.938(2) Å, b = 8.703(3) Å, c = 9.022(3)Å, α = 108.250(4)°, β = 99.957(4)°, γ = 97.188(4)°. In this complex, it has a three-dimensional structure containing 2D K 2 (ox) 2+ n sheet and 1D Cu(ox) 2 2− n zigzag chain. Interestingly, the ox ligand adopts unusual coordination modes, which have not observed in its coordination chemistry.

A Novel Hydrogen-Bonded 3D Network with Unusual Coordination Mode

通讯作者地址: Yang, SY (通讯作者), Xiamen Univ, Dept Chem, Coll Chem & Chem Engn, Xiamen 361005, Peoples R China 地址: 1. Xiamen Univ, Dept Chem, Coll Chem & Chem Engn, Xiamen 361005, Peoples R China 2. W Anhui Univ, Dept Chem, Luan 237012, Peoples R China 电子邮件地址: syyang@xmu.edu.cn

Structure and decomposition of [HFe(CO) 4(B 2H 5)], a revised behavior of an old uncharacterized complex

The protonation reaction of the anionic complex [Fe(CO) 4B 2H 5]− gives a product which decomposes easily at −120 °C yielding [Fe(CO) 5] and B 2H 6 as reported by Coffy and Shore (J. Organomet. Chem. C27 (1990) 7394). In this work we have theoretically revised the understanding of this protonation using B3PW91/6-311+G** and B3P86/6-311+G** levels of theory. We found an unusual mode of coordination of B 2H 6 to the iron centre. The most stable structure exhibits a Fe–(μ-H)–B–(μ-H)–B five-membered ring which undergoes an isomerisation leading to the intermediate which displays an unusual interaction between [Fe(CO) 4] and B 2H 6 via (μ 3-H) binding. Atom-in-molecule (AIM) theory data indicate the presence of weak interactions between iron and boron atoms which are partially responsible of the facile decomposition of the formed complex. We consider that the decomposition pathway can occur in two steps; the first one gives [Fe(CO) 4] and B 2H 6 (the aim of this work) followed by second one where [Fe(CO) 4] undergoes a transformation to give [Fe(CO) 5], this step remaining ambiguous up to today. Parameters such as solvent effect, solvent interaction and spin split were considered to provide with reliable results about decomposition mechanism.

Binuclear Uranium(VI) Complexes with a “Pacman” Expanded Porphyrin: Computational Evidence for Highly Unusual Bis-Actinyl Structures

On the basis of uranyl complexes reacting with a polypyrrolic ligand (H(4)L), we explored structures and reaction energies of a series of new binuclear uranium(VI) complexes using relativistic density functional theory. Full geometry optimizations on [(UO(2))(2)(L)], in which two uranyl groups were initially placed into the pacman ligand cavity, led to two minimum-energy structures. These complexes with cation-cation interactions (CCI) exhibit unusual coordination modes of uranyls: one is a T-shaped (T) skeleton formed by two linear uranyls {O(exo)=U(2)=O(endo)-->U(1)(=O(exo))(2)}, and another is a butterfly-like (B) unit with one linear uranyl coordinating side-by-side to a second cis-uranyl. The CCI in T was confirmed by the calculated longest distance and lowest stretching vibrational frequency of U(2)=O(endo) among the four U=O bonds. Isomer B is more stable than T, for which experimental tetrameric analogues are known. The formation of B and T complexes from the mononuclear [(UO(2))(H(2)L)(thf)] (M) was found to be endothermic. The further protonation and dehydration of B and T are thermodynamically favorable. As a possible product, we have found a trianglelike binuclear uranium(VI) complex having a O=U=O=U=O unit.