Clifton Woods

Synthesis and molecular structure of monomeric copper (II) acetates with 2-methylimidazole and 1, 2-dimethylimidazole

Abstract The complexes cis-bis(acetato)bis(2-methylimidazole)copper(II) (1), and cis-bis(acetato)bis(1,2-dimethylimidazole) copper(II) (2) have been prepared by the reaction of the appropriate imidazole derivative with copper(II) tetraacetate. The complexes have been characterized by analytical, magnetic, spectroscopic and crystallographic methods. Complex 1 crystallizes in the orthorhombic space group P212121 and has unit cell dimensions of a=7.5380(10), b=7.7100(10), c=26.310(5) A. Complex 2 crystallizes in the monoclinic space group P2/c and has unit cell dimensions of a=15.574(2), b=7.9520(10), c=14.752(2) A.

Synthesis, characterization and catecholase-mimetic activity of mononuclear copper(II) aspirinate complexes

Abstract Four mononuclear copper(II) complexes have been prepared by allowing copper(II) aspirinate to react with benzimidazole, 2-methylbenzimidazole, metronidazole or 2-methyl-5-nitrobenzimidazole ligands. Elemental analyses, UV-Vis, IR, EPR and magnet moment data are consistent with mononuclear square planar complexes that contain two aspirinate ligands and two N-containing ligands to give a CuO 2 N 2 chromophore. The benzimidazole, 2-methylbenzimidazole and metronidazole complexes catalyze the oxidation of catechol to o -quinone. This reaction was monitored spectrophotometrically by following the increase in intensity of the o -quinone band at 390 nm with time. Enzyme-mimetic activity of these copper complexes was determined and expressed as micromoles of substrate per mg catalyst per min. The activities were found to be 0.314 for the benzimidazole complex, 0.0998 for the 2-methylbenzimidazole complex, and 0.129 for the metronidazole complex. In the case of the 2-methyl- 5-nitrobenzimidazole complex the initial formation of o -quinone is very rapid; however, after 2–3 min the catalyst is poisoned and the concentration of o -quinone drops slightly and remains constant.

Preparation, structure and catecholase-mimetic activity of two mononuclear ferrocenecarboxylate copper(II) complexes

Abstract The complexes trans -bis(ferrocenecarboxylato)bis(pyridine)copper(II) ( 2 ) and trans -bis(ferrocenecarboxylato)-bis(imidazole)copper( II ) ( 3 ) have been prepared from the reaction of tetrakis(ferrocenecarboxylato)bis(tetra-hydrofuran)dicopper( II ) ( 1 ) and the appropriate base. trans -Bis(ferrocenecarboxylato)bis(pyridine)copper(II) crystallizes as two isomers — one in which the carboxylate group coordinates in a chelating mode ( 2a ) and one in which the carboxylate group coordinates as a monodentate ligand ( 2b ). Complex , 2a crystallizes in the monoclinic space group P 2 1 / c with a =14.761(5), b =5.922(2), c =15.913(6) A, β=102.69(3)°, V =1357.1(8) A, Z =2. The structure is compressed rhombic octahedral with four equatorial carboxylate oxygen atoms and two axial pyridine nitrogen atoms. The two CuO distances differ by approximately 0.2 A suggesting that the carboxylate function bonds in an approximate chelating mode. Complexes 2b and 3both crystallize in the triclinic space group P 1 with a =5.986(2), b =8.038(2), c =15.512(3) A, α=104.42(2), β=93.11(2), γ=99.95(2)°, V =708.1(3) A, Z =1, and a =7.475(3), b =9.296(3), c =10.090(3) A, α=111.05(2), β=92.38(4), γ=101.69(3)°, V =635.7(4) A 3 , Z =1 for 2b and 3 , respectively. The structures of 2b and 3 are best described as square planar with a CuN 2 O 2 core having remote, weakly interacting, carboxylate oxygen atoms from the carboxylate groups at 2.53 and 2.76 A from the copper atom for 2b and 3 , respectively. The catalytic activities of 1 , 2 and 3 toward the aerobic oxidation of catechol to o -quinone were determined. The activity of 2 is similar to that of 1 but much greater than that of 3 . These differences are described in terms of the proposed requirement that two proximate metal atoms are involved in the catalytic process and the possible dimerization of 2 and not 3 .

Mononuclear copper (II) salicylate imidazole complexes derived from copper (II) aspirinate. Crystallographic determination of three copper geometries in a unit cell

Abstract Complexes of the type Cu(Im)n(sal)2 (1,2,3) (where Im = imidazole, and sal = salicylate ion) have been prepared from the reaction of Im with tetrakis (aspirinato) dicopper (II) and were crystallographically and spectroscopically characterized. The three imidazole complexes 1 (n=2), 2 (n=5) and 3 (n=6) co-crystallize and each complex is found in the unit cell. Crystals that contained 1, 2 and 3 have unit cell parameters of a=12.772(5), b=13.078(4) and c=18.199(7) A, α=79.53(3), β=81.20(3) and γ=75.98(3)° and belong to the space group P l . In 1 the copper ion is coordinated in a trans arrangement by two imidazole nitrogen atoms and two carboxylate oxygen atoms from the salicylate ligands. The second carboxylate atoms form weak interactions with the copper ion. For complex 2 the copper ion is in a distorted square pyramidal environment of nitrogen atoms from five imidazole ligands. There are two salicylate counterions. Complex 3 exists as tetragonally distorted octahedral copper (II) cation with six coordinated imidazole ligands and two salicylate counterions.

Synthesis, spectroscopic and structural characterization of bis(acetato)tetrakis(imidazole)copper(II): a model complex for DNA binding

Abstract The complex bis(acetato)tetrakis(imidazole)copper(II), [Cu(Im)4(OAc)2] (2), has been prepared by the reaction of excess imidazole with Cu2(OAc)4. Complex 2 exhibits a magnetic moment of 1.88 BM, consistent with one unpaired electron and the formulation of the complex as a Cu(II) monomer. The frozen-solution ESR spectrum exhibits axial symmetry with g∥ and g⊥ values of 2.221 and 2.040, respectively, and A∥(Cu)=181×10−4 cm−1. The g⊥ signal and lowest-field component of the g∥ signal exhibit 14N super-hyperfine structure that consists of nine lines with A⊥(N)=15×10−4 and A∥(N)=10×10−4 cm−1. The ESR data are consistent with the tetragonally elongated chromophore CuN4···O2. Complex 2 crystallizes in the space group C2/c with a=13.187(2), b=8.591(1), c=17.644(2) A, β=104.13(1), V=1938.4(5) A3, Z=4, Dcalc=1.556 g/cm3. The relevance of complex 2 to DNA binding of copper(II) imidazole complexes is discussed.

Structure, physical and photophysical properties of platinum(II) complexes containing 7,8-benzoquinoline and various bis(diphenylphosphine) ligands

Abstract A series of platinum complexses. [Pt(7,8-bzq)(dppm)](PF6), [Pt(7,8-bzq)(dppe)](PF6) and [Pt(7,8-bzq)(dppp)](PF6), which vary only in the number of carbon atoms bridging two diphenyl phosphine ligands, have been synthesized and their structures have been determined by single crystal X-ray crystallography. Structural characteristics are as follows: [Pt(7,8-bzq)(dppm)](PF6), orthorhombic, Pbca, a = 17.427(4), b = 17.946(4), c = 22.262 A , Z = 8 ; [Pt(7,8-bzq)(dppe)](PF6), monoclinic, P2 1 /c, a = 11.519(2), b = 14.080(3), c = 21.804(4) A , Z = 4 ; [Pt(7,8-bzq)(dppp)](PF6), Pna2 1 , a = 20.216(4), b = 11.574(2), c = 15.739(3) A Z = 4 . The PPtP bite angle varies in the series from 72.1(5) to 84.55(2) to 91.57(10)° for [Pt(7,8-bzq)(dppm)]−, [Pt(7,8-bzq)(dppe)]− and [Pt(7,8-bzq)(dppp)]+, respectively. The absorption spectra are blue-shifted and the emission lifetimes at 77 K increase in the same order. Emission lifetime differences are shown to relate to the perturbation associated with the additional methylene groups.

Characterization and catecholase-mimetic behavior of imidazole adducts of copper(II) valproate. Crystal structure of the 2-methylimidazole adduct

Four mononuclear imidazole adducts of copper(II) valproate have been prepared and characterized with IR, UV—Vis, EPR spectroscopic techniques and fast atom bombardment mass spectrometry. The catecholase-mimetic catalytic activities of the complexes have been determined by monitoring the formation of o -quinone from catechol. The catalytic activities of the mononuclear complexes are lower than that of the dinuclear copper(II) valproate. The complexes with 2-methylimidazole and 1,2-dimethylimidazole show slightly lower activities that the imidazole and N -methylimidazole complexes. The structure of Cu(Val) 2 (2mIm) 2 (Val=valproate; 2mIm=2-methylimidazole) has been determined. The complex crystallizes in the P 2 1 / c space group with unit cell dimensions of a =9.309(1), b =12.456(2), c =12.560(2) A, β=99.84(1)°, V =1435.0(3) A 3 , Z =2.

Structure, physical, chemical and photophysical properties of Pt(bph) (CO)2, where bph is the biphenyl dianion

The complex Pt(bph) (CO)2 crystallizes in the space group Cmcm with a = 18.647(6), b = 9.566(2) and c = 6.4060(5) A. The geometry of the molecule is slightly distorted from square planar with a PtC(CO) bond distance of 1.98(2) A and a PtC(bph) bond distance of 2.04(2) A. The Pt(bph)(CO)2 complex serves as a precursor for the preparation of a wide variety of Pt(bph)X2 complexes, where X = monodentate ligands such as acetonitrile, pyridine, etc., and X2 = bidentate ligands such as bypyridine, 1,10-phenanthroline, etc. In the solid state, the complex exhibits a green color, but when ground with an alkali metal salt turns deep blue to purple. In CH2Cl2, the color disappears but optical transitions are observed at 271 nm (2.7 × 104 M−1 cm−1), 303 nm (1.1 × 104 M−1 cm−1) and 330 nm (5.5 × 103 M−1 cm−1). The complex is a weak emitter exhibiting a structured spectrum in CH2Cl2 at r.t. with maxima located at 562 and 594 nm and an emission lifetime of 3.1 μs when excited at 337 nm.

Synthesis, characterization, and oxidase activities of copper(II) complexes of the anticonvulsant drug valproate

Abstract The interaction of binuclear copper(II) complex of the anticonvulsant drug valproate, Cu 2 (valp) 4 ( 1 ), with metronidazole (mtnd) or 2-methyl-5-nitrobenzimidazole (2m5nbnz), have led to the isolation of two binuclear adducts of the type Cu 2 (valp) 4 (mtnd) 2 ( 2 ), and Cu 2 (valp) 4 (2m5nbnz) 2 ( 3 ), and one mononuclear adduct of the type Cu(valp) 2 (2m5nbnz) 2 ( 4 ). Spectral and magnetic data and preliminary X-ray measurements for complexes 2 and 3 are consistent with a binuclear structure as found for copper(II) tetracarboxylate adducts. The above data for complex 4 are consistent with a mononuclear square planar complex that contains two valproate ligands and two N-containing 2m5nbnz ligands to give essentially a trans -CuN 2 O 2 chromophore. The catalytic activities of the complexes toward the aerobic oxidation of 3,5-di-t-butycatechol to the corresponding o-benzoquinone and N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) to TMPD + were determined. The activities were found to be in the order 1 > 2 > 3 > 4 . The formation of a copper ion-semiquinone species in solution, which may be the catalytic intermediate that reacts directly with oxygen, was demonstrated spectrophotometrically.

Synthesis and studies of cis-Mo(CO)2(L–L′)2 and Mo(L–L′)3 complexes of 2-(phenylazo)pyridines (L–L′) and the crystal structures of Mo(CO)2(4-methyl-2-(phenylazo)pyridine)2 and Mo(4-methyl-2-(phenylazo)pyridine)3

Abstract The complexes cis -Mo(CO) 2 (X-2-(phenylazo)pyridine) 2 ( III ) and Mo(X-2-(phenylazo)pyridine) 3 ( IV ) (X=4-CH 3 O ( a ), 4-CH 3 ( b ), H ( c ), 4-Cl ( d ), 5-Br ( e ), 5-CF 3 ( f ), 6-CH 3 ( g )), cis -Mo(CO) 2 (2-(2-CH 3 -phenylazo)pyridine) 2 ( IIIh ), and Mo(2-(2-CH 3 -phenylazo)pyridine) 3 ( IVh ) have been synthesized and characterized by cyclic voltammetry, by visible and infrared spectroscopy, and by 1 H, 13 C, and 95 Mo NMR spectroscopy. Correlations among these data and correlations of the data with the Hammett σ parameter within each series of complexes were investigated. Initially, correlations were found only for the Hammett σ parameter with the first oxidation potential and with the first reduction potential for both the type III and type IV complexes and with the sum of the carbonyl stretching frequencies for the type III complexes. However, combining 95 Mo NMR linewidth and chemical shift data for this quadrupolar metal allowed separation of the nephelauxetic and spectrochemical effects and revealed a number of additional correlations. The X-ray crystal structures of cis -Mo(CO) 2 (4-CH 3 -2-(phenylazo)pyridine) 2 ( IIIb ) and Mo(4-CH 3 -2-(phenylazo)pyridine) 3 ( IVb ) also have been determined. In IIIb each CO is trans to a pyridyl nitrogen of a 2-(phenylazo)pyridine ligand. In IVb each pyridyl nitrogen is trans to an azo nitrogen, yielding the facial isomer of the complex.