Syntheses and characterization of anti-inflammatory dinuclear and mononuclear zinc indomethacin complexes. Crystal structures of [Zn2(indomethacin)4(L)2] (L = N,N-dimethylacetamide, pyridine, 1-methyl-2-pyrrolidinone) and [Zn(indomethacin)2(L1)2] (L1 = ethanol, methanol)

The syntheses and spectral and structural characterizations of Zn(II) indomethacin [1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1H-indole-3-acetic acid = IndoH] complexes, as different solvent adducts, have been studied. The complexes are unusual in that both monomeric and dimeric complexes are formed and that this is the first example of the same carboxylato ligand binding via both carboxylate oxygen atoms in monomeric and dimeric Zn(II) complexes. The crystal structures of Zn-Indo complexes with N,N-dimethylacetamide (DMA), pyridine (Py), 1-methyl-2-pyrrolidinone (NMP), EtOH, and MeOH as solvent ligands, [Zn2(Indo)4(DMA)2].2DMA, 1, [Zn2(Indo)4(Py)2].2H2O, 2b, [Zn2(Indo)4(NMP)2], 3, cis-[Zn(Indo)2(EtOH)2], 4, and cis-[Zn(Indo)2(MeOH)2], 5, were determined. Complexes 1, 2b, and 3 crystallize in the triclinic space group P1 (No. 2): a = 13.628(2) A, b = 17.462(2) A, c = 11.078(1) A, alpha = 99.49(1) degrees, beta = 108.13(1) degrees, gamma = 110.10(1) degrees for 1; a = 13.347(3) A, b = 16.499(5) A, c = 10.857(1) A, alpha = 99.48(2) degrees, beta = 108.25(2) degrees, gamma = 106.24(2) degrees for 2; a = 14.143(3) A, b = 14.521(2) A, c = 11.558(2) A, alpha = 109.07(1) degrees, beta = 90.80(2) degrees, gamma = 116.40(1) degrees for 3. The three complexes exhibit dinuclear paddle-wheel structures with a Zn...Zn distance of 2.9686(6) A, Zn-ORCOO distances of 2.035(2)-2.060(2) A, and a Zn-ODMA distance of 1.989(2) A in 1, a Zn...Zn distance of 2.969(1) A, Zn-ORCOO distances of 2.020(3)-2.049(3) A, and a Zn-NPy distance of 2.036(3) A in 2, and a Zn...Zn distance of 2.934(1) A, Zn-ORCOO distances of 2.009(3)-2.051(3) A, and a Zn-ONMP distance of 1.986(3) A in 3. In these cases, the zinc ions are offset along the z direction such that the L-Zn...Zn-L moiety is nonlinear, unlike the Cu analogues. Each Zn has a square-pyramidal geometry bridged by four carboxylato ligands in the basal plane with the solvent ligands containing an O- or N-donor atom at the apex. Complexes 4 and 5 are isostructural, with space group C2/c (No. 15). For 4, a = 30.080(2) A, b = 5.3638(6) A, c = 24.739(2) A, beta = 90.342(7) degrees, and for 5, a = 29.419(2) A, b = 5.320(2) A, c = 24.461(2) A, beta = 90.840(4) degrees. The Zn resides on a 2-fold axis and the complexes have a distorted cis octahedral structure with Zn-ORCOO bond lengths of 2.183(3) and 2.169(3) A, a Zn-OEtOH bond length of 2.015(3) A in 4, Zn-ORCOO bond lengths of 2.195(2) and 2.151(2) A, and a Zn-OMeOH bond length of 2.022(3) A in 5.     

Determination of the structures of antiinflammatory copper(II) dimers of indomethacin by multiple-scattering analyses of X-ray absorption fine structure data

Copper K-edge X-ray absorption spectroscopic (XAS) measurements were recorded for the veterinary antiinflammatory Cu(II) complexes of indomethacin (1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1H-indole-3-acetic acid = IndoH), of the general formula [Cu(2)(Indo)(4)L(2)] (L = N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methylpyrrolidone (NMP), and water), and [Cu(2)(OAc)(4)(OH(2))(2)] at room temperature and 10 K. The bond lengths and bridging O-C-O angles of the dimeric Cu(II) cage (Cu(2)O(10)C(8)) obtained from the multiple-scattering (MS) fitting of the X-ray absorption fine structure (XAFS) using a centrosymmetric model of [Cu(2)(Indo)(4)(DMF)(2)] gave Cu.Cu = 2.62(2) A, mean Cu-O(Ac) = 1.95(2) A, Cu-O(L) = 2.15(2) A, bridging O-C-O = 125(1) degrees, Cu displacement from plane 0.19 A compared with the XRD data Cu.Cu = 2.630(1) A, mean Cu-O(Ac) = 1.959 A, Cu-O(L) = 2.143(5) A, bridging O-C-O angles = 123.2(5) degrees, Cu displacement from plane 0.20 A. The excellent agreement between the XAFS- and XRD-derived data allowed the structures of related [Cu(2)(Indo)(4)L(2)] (L = DMA, NMP) complexes to be determined. All display a similar Cu(2)O(10)C(8) coordination geometry, which is independent of the nature of the axial ligand. While XAFS analysis of [Cu(2)(Indo)(4)(OH(2))(2)] and [Cu(2)(OAc)(4)(OH(2))(2)] indicates a coordination geometry similar to that of [Cu(2)(Indo)(4)L(2)] (L = DMF, DMA, NMP), removal of symmetry restraints in the MS model is required to obtain axial bond lengths comparable to those derived in the XRD structures of the acetate complex. For the Indo complex, the fitted bond lengths with the lower symmetry model give a mean Cu-L(OH2) bond distance within experimental errors of the value for [Cu(2)(Indo)(4)(DMSO)(2)] (2.16(2) A) (XRD). The difficulty in refining the Cu-O(OH2) distance of [Cu(2)(OAc)(4)(OH(2))(2)] and [Cu(2)(Indo)(4)(OH(2))(2)] using a centrosymmetric MS model is attributed to a symmetry reduction due to hydrogen-bonding effects characteristic of the aqua adducts, as is observed in the XRD structure of the acetate complex.     

Correlation of infrared spectra of zinc(II) carboxylates with their structures

The correlation of the infrared spectra of zinc(II) carboxylates with their structures was investigated in the paper. The complexes with different modes of the carboxylate binding, from chelating, through bridging (syn-syn, syn-anti, monatomic), ionic to monodentate were used for the study, namely [Zn(C6H5CHCHCOO)2(H2O)2] (I) with chelating carboxylate group (C6H5CHCHCOO=cinnamate), [Zn2(C6H5COO)4(pap)2] (II) with syn-syn bridging carboxylate (C6H5COO=benzoate; pap=papaverine), [Zn(C6H5CHCHCOO)2(mpcm)]n (III) with syn-anti carboxylate bridge (mpcm=methyl-3-pyridylcarbamate), [Zn(C5H4NCOO)2(H2O)4] (IV) with ionic carboxylate group (C5H4NCOO=nicotinate), [Zn(C6H5COO)2(pcb)2]n (V) with monodentate carboxylate coordination (pcb=3-pyridylcarbinol) and [Zn3(C6H5COO)6(nia)2] (VI) with syn-syn and monatomic carboxylate bridges (nia=nicotinamide). First, the mode of the carboxylate binding was assigned from the infrared spectra using the magnitude of the separation between the carboxylate stretches, Deltaexp=nuas(COO-)-nus(COO-). Then the values Deltaexp were compared with those calculated from structural data of the carboxylate anion (Deltacalc). The conclusions about the carboxylate binding which resulted from the Delta values, were confronted with the crystal structure of the complexes. The limitations and recommendations were formulated to assign the mode of the carboxylate binding from the infrared spectra. The dependence of the Deltaexp values on the magnitudes of Zn-O-C angles in bidentate carboxylate coordination was observed.     

Selective recognition of configurational substates of zinc cyclam by carboxylates: implications for the design and mechanism of action of anti-HIV agents

The interaction of metal cyclams with carboxylate groups is thought to play an important role in their binding to the CXCR4 chemokine receptor and in their anti-HIV activity. Here we report the synthesis of acetate, phthalate, perchlorate and chloride complexes of Zn(II) cyclam (1,4,8,11-tetraazacyclotetradecane). The X-ray crystal structures of [Zn(cyclam)(phthalate)](n)(CH(3)OH)(2n) and [Zn(cyclam)(H(2)O)(2)](OAc)(2) contain octahedral Zn(II) centres. Phthalate acts as a bridging ligand in the former complex, binding through monodentate carboxylate groups, and giving rise to infinite chains in the lattice together with extensive hydrogen bonding between carboxylate donor oxygen atoms and amine and methanol acceptor atoms. The uncoordinated acetate groups and the aqua ligand in the acetate complex are also involved in a rich network of hydrogen bonds and this may account for the unusually long Zn[bond]O distance (2.27 A). In both crystalline complexes, the macrocycle adopts the trans-III (S,S,R,R) configuration. 1D (1)H NMR spectra of all four complexes have been fully assigned by a combination of 2D [(1)H, (1)H] COSY and TOCSY, and [(1)H, (13)C] and [(1 )H, (15)N] HSQC NMR data. In aqueous solution, the stable trans-III configuration found in the solid-state equilibrates slowly (hours at 298 K) with trans-I (R,S,R,S) and cis-V (R,R,R,R) configurations. The trans-III configuration is predominant in aqueous solution for both the chloride and perchlorate complexes, but for the acetate and phthalate complexes, the cis-V configuration dominates. Carboxylate groups appear to stabilize the cis-V configuration in solution through Zn(II) coordination and hydrogen bonding. Titration of the chloride Zn(II)-cyclam complex with acetate confirmed that carboxylates strongly induce formation of the cis-V configuration. This implies that carboxylates can exert a strong influence over configurational selectivity. Cyclam NH hydrogen bonding is prevalent both in the solid state and in solution, and is relevant to the anti-HIV activity of Zn(II) and other metal cyclam complexes and to their ability to recognize the CXCR4 transmembrane co-receptor.     

Crystal structures and spectroscopic properties of zinc(II) ternary complexes of vitamin L, H' and their isomer m-aminobenzoic acid with bipyridine

The crystal structures of the three Zn(II) complexes, [Zn(bpy)(o-AB)2] (1) (bpy=2,2'-bipyridine, o-AB=o-aminobenzoic acid=Vitamin L), [Zn(bpy)(m-AB)Cl]2 (2) (m-AB=m-aminobenzoic acid), [Zn(bpy)(p-AB)Cl]*p-AB*H2O (3) (p-AB=p-aminobenzoic acid=Vitamin H'), have been determined and the basic coordination geometries and architectures organized by hydrogen-bonds and pi-pi interactions also characterized. The substitute amine group at ortho-, meta-, and para-position of AB plays an important role to produce completely different coordination motif of these complexes, further, in all complexes, aromatic amines are not coordinated to Zn(II) atom. While two different types of coordination modes of the carboxylate O atoms are present in these complexes: one mode consists of the usual Zn-O bond lengths (2.009(2)-2.251(2) A) in complex 1, 2 and 3; another consists of a very long Zn-O bond lengths (2.422(2) A) in complex 1. Each of the complexes has the characteristic UV absorption bands around 250-310 nm region, and the intense fluorescence band at near 325 nm.     

On the unprecedented level of dinitrogen activation in the calix[4]arene complex of Nb(III)

The calix[4]arene niobium(III) complex ([L]Nb-N=N-Nb[L] where [L] = p-tert-butylcalix[4]arene), reported to bind N(2) in a μ(2)-linear dimeric capacity and to activate the N(2) triple bond to 1.39 ?, corresponding to the longest N(2) bond known in the end-on coordination mode, was subjected to a computational investigation involving both density functional and wavefunction based methods to establish the basis for the unprecedented level of activation. Replacement of the calix[4]arene ligand with hydroxide or methoxide ligands reveals that the organic backbone structure of the calix[4]arene ligand exerts negligible electronic influence over the metal centre, serving only to geometrically constrain the coordinating phenoxide groups. A fragment bonding analysis shows that metal-to-dinitrogen π* backbonding is the principal Nb-N interaction, providing a strong electronic basis for analogy with other well-characterised three- and four-coordinate complexes which bind N(2) end-on. While the calculated structure of the metallacalix[4]arene unit is reproduced with high accuracy, as is also the Nb-Nb separation, the calculated equilibrium geometry of the complex under a variety of conditions consistently indicates against a 1.39 ? activation of the N(2) bond. Instead, the calculated N-N distances fall within the range 1.26-1.30 ?, a result concordant with closely related three- and four-coordinate μ(2)-N(2) complexes as well as predictions derived from trends in N-N stretching frequency for a number of crystallographically characterized linear N(2) activators. A number of potential causes for this bond length discrepancy are explored.     

Synthetic, structural, electrochemical and solvent extraction studies of neutral trinuclear Co(II), Ni(II), Cu(II) and Zn(II) metallocycles and tetrahedral tetranuclear Fe(III) species incorporating 1,4-aryl-linked bis-beta-diketonato ligands

Uncharged complexes, formulated as trimeric metallocycles of type [M3(L(1))3(Py)6] (where M = cobalt(II), nickel(II) and zinc(II) and L(1) is the doubly deprotonated form of a 1,4-phenylene linked bis-beta-diketone ligand of type 1,4-bis(RC(O)CH2C(O))C6H4 (R = t-Bu)) have been synthesised, adding to related, previously reported complexes of these metals with L(1) (R = Ph) and copper(ii) with L(1) (R = Me, Et, Pr, t-Bu, Ph). New lipophilic ligand derivatives with R = hexyl, octyl or nonyl were also prepared for use in solvent extraction experiments. The X-ray structures of H2L(1) (R = t-Bu) and of its trinuclear (triangular) nickel(II) complex [Ni3(L(1))3(Py)6].3.5Py (R = t-Bu) are also presented. Electrochemical studies of H2L(1), [Co3(L(1))3(Py)6], [Ni3(L(1))3(Py)6], [Cu3(L(1))3], [Zn3(L(1))3(Py)6] and [Fe4(L(1))6] (all with R = t-Bu) show that oxidative processes for the complexes are predominantly irreversible, but several examples of quasireversible behaviour also occur and support the assignment of an anodic process, seen between +1.0 and +1.6 V, as involving metal-centred oxidations. The reduction behaviour for the respective metal complexes is not simple, being irreversible in most cases. Solvent extraction studies (water/chloroform) involving the systematic variation of the metal, bis-beta-diketone and heterocyclic base concentrations have been performed for cobalt(II) and zinc(II) using a radiotracer technique in order to probe the stoichiometries of the respective extracted species. Significant extraction synergism was observed when 4-ethylpyridine was also present with the bis-beta-diketone ligand in the chloroform phase. Competitive extraction studies demonstrated a clear uptake preference for copper(II) over cobalt(II), nickel(II), zinc(II) and cadmium(II).     

Complexation of molybdenum(V) with glycolic acid: an unusual orientation of glycolato ligand in {Mo2O4}2+ complexes

(PyH)5[Mo(V)OCl4(H2O)]3Cl2 and (PyH)n[Mo(V)OBr4]n reacted with glycolic acid (H2glyc) or its half-neutralized ion (Hglyc(-)) to afford a series of novel glycolato complexes based on the {Mo(V)2O4}2+ structural core: (PyH)3[Mo2O4Cl4(Hglyc)]. (1)/ 2CH 3CN (1), (PyH) 3[Mo 2O 4Br 4(Hglyc)].Pr(i)OH(2), (PyH)2[Mo2O4(glyc) 2Py 2] (3), (PyH) 4[Mo 4O 8Cl 4(glyc) 2].2EtOH (4), and [Mo 4O 8(glyc) 2Py 4] (5) (Py = pyridine, C 5H 5N; PyH(+) = pyridinium cation, C 5H 5NH (+) and glyc (2-) = a doubly ionized glycolate, (-)OCH 2COO (-)). The compounds were fully characterized by X-ray crystallography and infrared spectroscopy. The Hglyc (-) ion binds to the {Mo 2O 4} (2+) core through a carboxylate end in a bidentate bridging manner, whereas the glyc (2-) ion adopts a chelating bidentate coordination through a deprotonated hydroxyl group and a monodentate carboxylate. The orientations of glyc (2-) ions in 3- 5 are such that the alkoxyl oxygen atoms occupy the sites opposite the multiply bonded oxides. {(C6H5) 4P}[Mo(VI)O 2(glyc)(Hglyc)] ( 6), an oxidized complex, features a reversed orientation of the glyc(2-) ion. The theoretical DFT calculations on the [Mo(V)2O4(glyc) 2Py 2](2-) and [Mo(VI)O2(glyc)2](2-) ions confirm that binding of glycolate with the alkoxyl oxygen to the site opposite the MoO bond is energetically more favorable in {Mo(V)2O4}(2+) species, whereas a reversed orientation of the ligand is preferred in Mo(VI) complexes. An explanation based on the orbital analysis is put forward.     

Neutral (bis-beta-diketonato) iron(III), cobalt(II), nickel(II), copper(II) and zinc(II) metallocycles: structural, electrochemical and solvent extraction studies

Neutral dimeric metallocyclic complexes of type [M(2)(L(1))(2)B(n)] (where M = cobalt(II), nickel(II) and zinc(II), L(1) is the doubly deprotonated form of a 1,3-aryl linked bis-beta-diketone ligand of type 1,3-bis(RC(O)CH(2)C(O))C(6)H(4) (R=Me, n-Pr, t-Bu) and B is pyridine (Py) or 4-ethylpyridine (EtPy)) have been synthesised, adding to similar complexes already reported for copper(II). New lipophilic ligand derivatives with R = octyl or nonyl were also prepared for use in solvent extraction experiments. Structural, electrochemical and solvent extraction investigations of selected metal complex systems from the above series are reported, with the X-ray structures of [Co(2)(L(1))(2)(Py)(4)] x 2.25CHCl(3) x 0.5H(2)O (R=Pr), [Co(2)(L(1))(2)(EtPy)(4)] (R=t-Bu), [Ni(2)(L(1))(2)(EtPy)(4)] (R=t-Bu), [Zn(2)(L(1))(2)(EtPy)(2)] (R=Me) and [Zn(2)(L(1))(2)(EtPy)(4)] (R=t-Bu) being presented. The electrochemistry of H(2)L(1) (R=t-Bu) and of [Fe(2)(L(1))(3)], [Co(2)(L(1))(2)(Py)(4)], [Ni(2)(L(1))(2)(Py)(4)], [Cu(2)(L(1))(2)] and [Zn(2)(L(1))(2)(Py)(2)] has been examined. Oxidative processes for the complexes are dominantly irreversible, but several examples of quasireversible behaviour were observed and support the assignment of an anodic process, seen between +1.0 and +1.6 V, as a metal-centred oxidation. The reduction processes for the respective metal complexes are not simple, and irreversible in most cases. Solvent extraction studies (water/chloroform) involving variable concentrations of metal, bis-beta-diketone and heterocyclic base have been performed for cobalt(II) and zinc(II) using a radiotracer technique to probe the stoichiometries of the extracted species in each case. Synergism was observed when 4-ethylpyridine was added to the bis-beta-diketone ligand in the chloroform phase. Competitive extraction studies show a clear uptake preference for copper(II) over cobalt(II), nickel(II), zinc(II) and cadmium(II).     

Diastereopure Fe(II) and Zn(II) complexes derived from a tridentate N,N',N-bis(methyl-L-prolinate)-substituted pyridine ligand

A series of mononuclear iron(II) and zinc(II) complexes of the new chiral Py(ProMe)2 ligand (Py(ProMe)2 = 2,6-bis[[(S)-2-(methyloxycarbonyl)-1-pyrrolidinyl]methyl]pyridine) have been prepared. The molecular geometry in the solid state (X-ray crystal structures) of the complexes [FeCl2(Py(ProMe)2)] (1), [ZnCl2(Py(ProMe)2)] (2), [Fe(OTf)2(Py(ProMe)2)] (3), [Fe(Py(ProMe)2)(OH2)2](OTf)2 (4), and [Zn(OTf)(Py(ProMe)2)](OTf) (5) are reported. They all show a meridional NN'N coordination of the Py(ProMe)2 ligand. The bis-chloride derivatives 1 and 2 represent neutral isostructural five-coordinated complexes with a distorted geometry around the metal center. Unusual seven-coordinate iron(II) complexes 3 and 4 having a pentagonal bipyramidal geometry were obtained using weakly coordinating triflate anions. The reaction of Zn(OTf)2 with the Py(ProMe)2 ligand afforded complex 5 with a distorted octahedral geometry around the zinc center. All complexes were formed as single diastereoisomers. In the case of complexes 3-5, the oxygen atoms of both carbonyl groups of the ligand are also coordinated to the metal. The stereochemistry of the coordinated tertiary amine donors in complexes 3-5 is of opposite configuration as in complexes 1 and 2 as a result of the planar penta-coordination of the ligand Py(ProMe)2. Complexes 1, 2, and 5 have an overall -configuration at their metal center, while the Fe(II) ion in complexes 3 and 4 has the opposite delta-configuration (crystal structures and CD measurements). The magnetic moments of iron complexes 1, 3, and 4 correspond to that of high-spin d6 Fe(II) complexes. The solution structures of complexes 1-5 were characterized by means of UV-vis, IR, conductivity, and CD measurements and their electrochemical behavior. These studies showed that the coordination environment of 1 and 2 observed in the solid state is maintained in solution. In coordinating solvents, the triflate anion (3, 5) or water (4) co-ligands of complexes 3-5 are replaced by solvent molecules with retention of the original pentagonal bipyramidal and octahedral geometry, respectively.     

Synthesis,characterization and anticancer studies of bis-(N-methyl-1-phenyldithiocarbamato) Cu(II), Zn(II), and Pt(II) complexes: single crystal X-ray structure of the copper complex

Abstract

Cu(II), Pt(II), and Zn(II) complexes of N-methyl-1-phenyldithiocarbamate were synthesized and characterized by FTIR, NMR, UV-visible spectroscopy and elemental analysis. The complexes were formulated as [Cu(L)₂], [Zn(L)₂] and [Pt(L)₂] (where L?=?N-methyl-1-phenyldithio­carbamate) in which two molecules of the ligands coordinate to the metal ions in a bidentate chelating fashion. This is confirmed by elemental analysis and the presence of strong single bands at 952, 951, and 955?cm^?1 for Cu(II), Pt(II), and Zn(II) complexes, respectively, in the FTIR spectra. The electronic spectra of Pt(II) and Cu(II) complexes are consistent with four-coordinate square planar geometry. Single crystal X-ray of [Cu(N-mpDTC)₂] confirmed square planar structural arrangement (CuS₄) in which the ligands are asymmetrically bonded to the Cu(II) ion building a centrosymmetric monomer entity. The S-Cu-S bite angle is 77.95° (3) whereas the intramolecular N–C bond length is 1.318 Å and trans S1¹-Cu-S1?=?S2¹-Cu-S2 is 180°, which are consistent with reported copper thiolates in square planar environment. In vitro antiproliferative activity of the complexes against three human cancer cell lines showed that the zinc complex has better activity compared to Cu and Pt complexes, with IC₅₀ values of 14.28, 22.74 and 20.10?μM against TK10, UACC62, and MC7 cell lines, respectively.     

Formation of a unique zinc carbamate by CO2 fixation: implications for the reactivity of tetra-azamacrocycle ligated Zn(II) complexes

The macrocyclic ligand [13]aneN 4 ( L1, 1,4,7,10-tetra-azacyclotridecane) was reacted with Zn(II) perchlorate and CO 2 in an alkaline methanol solution. It was found that, by means of subtle changes in reaction conditions, two types of complexes can be obtained: (a) the mu 3 carbonate complex 1, {[Zn( L1)] 3(mu 3-CO 3)}(ClO 4) 4, rhombohedral crystals, space group R3 c, with pentacoordinate zinc in a trigonal bipyramidal enviroment, and (b) an unprecedenced dimeric Zn(II) carbamate structure, 2, [Zn( L2)] 2(ClO 4) 2, monoclinic crystals, space group P2 1/ n. The ligand L2 (4-carboxyl-1,4,7,10-tetra-azacyclotridecane) is a carbamate derivative of L1, obtained by transformation of a hydrogen atom of one of the NH moieties into carbamate by means of CO 2 uptake. In compound 2, the distorted tetrahedral Zn(II) coordinates to the carbamate moiety in a monodentate manner. Most notably, carbamate formation can occur upon reaction of CO 2 with the [Zn L1] (2+) complex, which implicates that a Zn-N linkage is cleaved upon attack of CO 2. Since complexes of tetra-azamacrocycles and Zn(II) are routinely applied for enzyme model studies, this finding implies that the Zn-azamacrocycle moiety generally should no longer be considered to play always only an innocent role in reactions. Rather, its reactivity has to be taken into account in respective investigations. In the presence of water, 2 is transformed readily into carbonate 1. Both compounds have been additionally characterized by solid-state NMR and infrared spectroscopy. A thorough comparison of 1 with related azamacrocycle ligated zinc(II) carbonates as well as a discussion of plausible reaction paths for the formation of 2 are given. Furthermore, the infrared absorptions of the carbamate moiety have been assigned by calculating the vibrational modes of the carbamate complex using DFT methods and the vibrational spectroscopy calculation program package SNF.     

Synthesis,crystal structures,and superoxide dismutase activity of two isostructural copper(II)–zinc(II) complexes derived from N,N′-bis(4-methoxysalicylidene)cyclohexane-1,2-diamine

Two new isostructural copper(II)–zinc(II) complexes, [CuZnLBr₂] (1) and [CuZnLCl₂] (2) (H₂L = N,N′-bis(4-methoxysalicylidene)cyclohexane-1,2-diamine), have been synthesized and characterized by elemental analyses, infrared spectroscopy, and single-crystal X-ray diffraction. Both complexes crystallize in the P-1 space group. The Cu in each complex is four-coordinate square planar with two imines and two phenolates of L. The Zn in each complex is four-coordinate tetrahedral with two phenolates of L and two halides (Br for 1 and Cl for 2). The superoxide dismutase (SOD) activity of the complexes indicates that both complexes are rudimentary models for SOD.     

The pressure tunning Raman and IR spectral studies on the multinuclear metal carbyne complexes

The Raman and infrared (IR) spectra of four tungsten metal carbyne complexes I, II, IV and V [Cl(CO)2(L)W[triple bond]CC6H4[triple bond](C[triple bond]CC6H4)n[triple bond]N[triple bond]C[triple bond]]2M (L = TMEDA, n = 0, M = PdI2 or ReCl(CO)3; L = DPPE, n = 1, M = PdI2 or ReCl(CO)3) were studied at high external pressure. Their pressure-induced phase transitions were observed near 20kbar (complexes I), 15 kbar (complexes II), 25 kbar (complex IV) and 30 kbar (complex V). The pressure-induced phase transition likely is first order in complex I and the pressure-induced phase transitions of complexes II, IV and V are mostly second order. The pressure sensitivities d nu/dp of nu(W[triple bond]C) are high in the low-pressure phase area and very low in the high-pressure phase area due to the pressure strengthening pi back-bonding from metal W to pi* orbital of C[triple bond]O in fragment Cl(CO)2(L)W[triple bond]C. The pressure strengthening metal pi back-bonding from metal Re or Pd to pi* orbital of C[triple bond]O or C[triple bond]N also happened to both of central metal centers of NCPd(I2)CN in complex I and NCReCl(CO)3CN in complex II.     

Mononuclear Ni(III) complexes [NiIII(L)(P(C6H3-3-SiMe3-2-S)3)]0/1- (L = thiolate, selenolate, CH2CN, Cl, PPh3): relevance to the nickel site of [NiFe] hydrogenases

The stable mononuclear Ni(III)-thiolate complexes [NiIII(L)(P(C6H3-3-SiMe3-2-S)3)]- (L = SePh (2), Cl (3), SEt (4), 2-S-C4H3S (5), CH2CN (7)) were isolated and characterized by UV-vis, EPR, IR, SQUID, CV, 1H NMR, and single-crystal X-ray diffraction. The increased basicity (electronic density) of the nickel center of complexes [NiIII(L)(P(C6H3-3-SiMe3-2-S)3)]- modulated by the monodentate ligand L and the substituted groups of the phenylthiolate rings promotes the stability and reactivity. In contrast to the irreversible reduction at -1.17 V (vs Cp2Fe/Cp2Fe+) for complex 3, the cyclic voltammograms of complexes [NiIII(SePh)(P(o-C6H4S)3)]-, 2, 4, and 7 display reversible NiIII/II redox processes with E(1/2) = -1.20, -1.26, -1.32, and -1.34 V (vs Cp2Fe/Cp2Fe+), respectively. Compared to complex 2 containing a phenylselenolate-coordinated ligand, complex 4 with a stronger electron-donating ethylthiolate coordinated to the Ni(III) promotes dechlorination of CH2Cl2 to yield complex 3 (kobs = (6.01 +/- 0.03) x 10-4 s-1 for conversion of complex 4 into 3 vs kobs = (4.78 +/- 0.02) x 10-5 s-1 for conversion of complex 2 into 3). Interestingly, addition of CH3CN into complex 3 in the presence of sodium hydride yielded the stable Ni(III)-cyanomethanide complex 7 with a NiIII-CH2CN bond distance of 2.037(3) A. The NiIII-SEt bond length of 2.273(1) A in complex 4 is at the upper end of the 2.12-2.28 A range for the NiIII-S bond lengths of the oxidized-form [NiFe] hydrogenases. In contrast to the inertness of complexes 3 and 7 under CO atmosphere, carbon monoxide triggers the reductive elimination of the monodentate chalcogenolate ligand of complexes 2, 4, and 5 to produce the trigonal bipyramidal complex [NiII(CO)(P(C6H3-3-SiMe3-2-S)3]- (6).     

Aluminum and zinc complexes based on an amino-bis(pyrazolyl) ligand: synthesis, structures, and use in MMA and lactide polymerization

The coordination chemistry of bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl]amine (1, LH) with aluminum- and zinc-alkyls has been studied. Reaction of 1 with AlR3 affords the adducts [LH] x AlR3 (R = Me, 2; Et, 3), which undergo alkane elimination upon heating to yield the amido complexes [L]AlR2 (R = Me, 4; Et, 5). Reaction of LiO(iPrO)C=CMe2 with 2 proceeds via N-H deprotonation to give Li[L]AlMe3 (6), while the former enolate adds to 4 to generate [Me2C=C(OiPr)OLi] x [L]AlMe2 (7). Similarly, the 1:1 reaction of ZnEt2 with 1 gives [LH] x ZnEt2 (9), which is transformed into [L]ZnEt (10) upon heating. When an excess of ZnEt2 was used in the latter reaction, the bimetallic complex [L]ZnEt x ZnEt2 (11) was isolated beside 10. Performing the same reaction in the presence of O2 traces yielded selectively the dinuclear ethyl-ethoxide complex [L]Zn2Et2(mu-OEt) (12), which was alternatively prepared from the reaction of 10 and ZnEt(OEt). Zinc chloride complexes [LH] x ZnRCl (R = Et, 13; p-CH3C6H4CH2, 14) and [L]ZnCl (15) were prepared in high yields following similar strategies. Ethyl abstraction from 10 with B(C6F5)3 yields [L]Zn+EtB(C6F5)3- (16). All complexes have been characterized by multinuclear nuclear magnetic resonance (NMR), elemental analysis, and single-crystal X-ray diffraction studies for four-coordinate Al complexes 2, 4, and 6 and Zn complexes 9-12 and 14. Aluminate species 6 and 7 initiate the polymerization of methyl methacrylate, and the monomer conversions are improved in the presence of neutral complexes 2 or 4, respectively; however, these methyl methacrylate (MMA) polymerizations are uncontrolled. Polymerization of rac-lactide takes place at 20 degrees C in the presence of zinc ethoxide complex 12 to yield atactic polymers with controlled molecular masses and relatively narrow polydispersities.     

Mono- and Dinuclear Transition Metal Complexes of the Hexadentate Ligand Tris(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane (L)

The hexadentate, pendant arm macrocycle 1,4,7-tris(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane (H(3)L) has been synthesized and isolated as its trihydrochloride, H(3)L.3HCl, or sodium salt, Na(3)L, and its coordination chemistry with first-row transition metals has been studied. Mononuclear complexes of the type [LM(III)] (M = Ga (1), In (2), V (3), Cr (4), Mn (5), Fe,Co (6)) have been isolated as have the one-electron-oxidized forms [LM]PF(6) (M = V(IV) (3a), Mn(IV) (5a)). The crystal structure of 6 has been determined by single-crystal X-ray crystallography. Complex 6 crystallizes in the orthorhombic space group Iba2, with cell constants a = 14.206(8) ?, b = 22.53(1) ?, c = 26.07(1) ?, V = 8344.0(3) ?(3), and Z = 8. The cobalt(III) ion is in a distorted octahedral fac-N(3)S(3) donor set. The reaction of L with divalent metal chlorides in a 1:2 ratio in methanol affords the homodinuclear complexes [LM(II)(2)Cl] (M = Mn (7), Co (8), Ni (9), Zn (10), Cd (11)) where one metal is six- (N(3)MS(3)) and the other is four-coordinate (S(3)MCl); the two polyhedra are linked by three &mgr;(2)-thiolato bridges. Heterodinuclear complexes of the type [LM(1)M(2)Cl] have been obtained from [LM(2)Cl] species by abstraction of the four-coordinate metal ion and replacement by a different metal ion. The complexes [LZn(II)M(II)Cl] (M = Fe (12), Co (13), Ni (14)), [LNi(II)M(II)Cl] (M = Co (15), Zn (16)), and [LMn(II)M(II)Cl] (M = Fe (17), Co (18), Ni (19), Zn (20), Cd (21), Hg (22)) have been isolated as solid materials. The crystal structure of 14 has been determined by X-ray crystallography. Complex 14 crystallizes in the orthorhombic space group P2(1)2(1)2(1), with cell constants a = 15.45(1) ?, b = 17.77(1) ?, c = 17.58(1) ?, V = 4826.5(4) ?(3), and Z = 4. The linkage isomers 14 and 16 show characteristic electronic spectra for octahedrally and tetrahedrally coordinated Ni(II), respectively. The electronic structures of new complexes have been investigated by UV-vis spectroscopy; their magnetochemistry and electrochemistry are reported.     

Structures and redox reactivities of copper complexes of (2-pyridyl)alkylamine ligands. Effects of the alkyl linker chain length

Ligand effects on the structures and redox reactivities of copper complexes have been examined using (2-pyridyl)alkylamine derivatives as the supporting ligands, where particular attention has been focused on the effects of the alkyl linker chain length connecting the tertiary amine nitrogen atom and the pyridine nucleus: N[bond]CH(2)[bond]Py (Pym) vs N[bond]CH(2)CH(2)[bond]Py (Pye). X-ray crystallographic analysis of the copper(I) complex of tridentate ligand (Phe)L(Pym2) [N,N-di(2-pyridylmethyl)-2-phenylethylamine] (complex 1) has demonstrated that it possesses a trigonal pyramidal geometry in which a d[bond]pi interaction with an eta(1)-binding mode exists between the metal ion and one of the ortho carbons of the phenyl ring of the ligand side arm (phenethyl). The result shows sharp contrast to the d[bond]pi interaction with an eta(2)-binding mode existing in the copper(I) complex of (Phe)L(Pye2) [N,N-di[2-(2-pyridyl)ethyl]-2-phenethylamine] (complex 2). Such a d-pi interaction has been shown to affect the stability of the copper(I) complex in CH(2)Cl(2). Oxygenation of copper(I) complex 1 supported by (Phe)L(Pym2) produces a bis(mu-oxo)dicopper(III) complex, also being in sharp contrast to the case of the copper(I) complex 2 with ligand (Phe)L(Pye2), which preferentially affords a (micro-eta(2):eta(2)-peroxo)dicopper(II) complex in the reaction with O(2). Such an effect of the alkyl linker chain length of the metal binding site has also been found to operate in the RSSR (disulfide)/2RS(-) (thiolate) redox system. Namely, ligand (S2,R)L(Pym1) (di[2-[(alkyl)(2-pyridinylmethyl)amino]ethyl] disulfide) with the methylene linker group (Pym) induced the reductive disulfide bond cleavage in the reaction with copper(I) ion to give a bis(micro-thiolato)dicopper(II) complex, while the ligand with the ethylene linker group (Pye), (S2,Bn)L(Pye1) (di[2-[(benzyl)(2-(2-pyridinyl)ethyl)amino]ethyl] disulfide), gave a disulfide-dicopper(I) complex. These ligand effects in the Cu(2)[bond]O(2) and Cu(2)[bond]S(2) systems have been discussed by taking into account the difference in electron-donor ability of the pyridine nucleus between the Pym and Pye ligand systems.     

Synthesis, crystal structure, EPR spectra of Cu2+ doped [Zn(methylisonicotinate)2(H2O)4]·(sac)2 single crystal

The tetraaquabis(methylisonicotinate)zinc(II) disaccharinate [hereafter, [Zn(mein)2(H2O)4]·(sac)2], complex has been synthesized and characterized by spectroscopic IR, EPR and X-ray diffraction technique. The octahedral Zn(II) ion, which rides on a crystallographic centre of symmetry, is coordinated by two monodentate mein ligands through the ring nitrogen and four aqua ligands to form discrete [Zn(mein)2(H2O)4] unit, which captures two saccharinate ions in up and down positions, each through intermolecular hydrogen bonds. The magnetic environments of Cu2+ doped [Zn(mein)2(H2O)4]·(sac)2 complex have been identified by electron paramagnetic resonance (EPR) technique. EPR spectra of Cu2+ doped [Zn(mein)2(H2O)4]·(sac)2 single crystals have been studied between 113 and 300 K in three mutually perpendicular planes. The calculated results of the Cu2+ doped [Zn(mein)2(H2O)4]·(sac)2 indicate that Cu2+ ion contains two different complexes and each complexes are located in different chemical environments and each environment contains two magnetically inequivalent Cu2+ sites in distinct orientations occupying substitutional positions in the lattice. The vibrational spectra of this compound were discussed in relation to other compounds containing methyl isonicotinate and saccharinate complexes. The assignments of the observed bands were discussed.     

Synthesis and studies on metal coordination with a novel carboxyamide ligand

Novel complexes of Co(II), Ni(II), Cu(II) and Pd(II) with the new ligand [N,N'-bis(2-carboxy-1-oxo-phenelenyl)ethylenediamine] (H2L) have been synthesized and characterized on the basis of elemental analyses, magnetic susceptibility, thermal, infrared, electronic, 1H NMR and EPR spectral studies. Infrared and 1H NMR spectra show that H2L acts as a binegative tetradentate ligand. Coordination occurs through deprotonated carboxylate oxygens and nondeprotonated amido nitrogens in all the complexes. Electronic spectral studies and magnetic moment values suggest N2O2 coordination around each metal centre with strong field square planar chromophores. The probable structures of the complexes have been assigned on the basis of spectral studies. The complex formation between M(II) [M(II) = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)] and (L2-) has also been studied potentiometrically in 75% aqueous DMF at 25 degrees C in 0.1 M NaClO4. The stability constants were found to follow the order: Mn(II) < Co(II) < Ni(II) < Cu(II) > Zn(II).