Garry M. Mockler

Nickel(II) complexes of some quadridentate Schiff-base ligands-II. Infrared spectra

Abstract The infrared spectra (4000-200cm−1) of a series of nickel(II) complexes of Schiff bases formed by the condensation of 5-chloro-2-hydroxybenzophenone and some alkanediamines, H2N(CH2)nNH2 (n = 2–12), has been investigated. The nickel62 isotope substitution method has been used to help identify the metal sensitive vibrations.

BINUCLEAR COPPER(II) COMPLEXES CONTAINING PHENOLS AND CATECHOLS

The synthesis and characterisation of a series of binuclear copper(II) complexes of ligands formed by the condensation of substituted salicylaldehydes and 1,3-diamino-2-propanol (SalDplH3) and 1,5-diamino-3-pentanol (SalDpeH3) and their interaction with both phenols and catechols are reported. Spectroscopic and magnetic data suggest that the neutral phenols and catechols can bind to binuclear copper(II) complexes without actually coordinating to the copper atoms. The crystal and molecular structure of two binuclear copper(II) complexes have been solved. The μ-hydroxo bridged dicopper(II) complex of SalDpe3−, [Cu2SalDpe(OH)], C19H20O4N2Cu2, I, having the space group P-1 and cell dimensions, a = 8.475(3), b = 15.727, c = 6.999(2) A, α = 99.51(2), β = 92.84(3), γ = 77.66(2)° was solved for 1839 structure factors (I>3.0σ(I)) and Z = 2, R = 4.2, Rw = 4.3%. The compound consists of neutral molecules with an out-of-plane interaction from a copper in one binuclear unit to the hydroxo group of an adjoining molecule. The 4-ethylphenol adduct of the μ-(O,O′) phenylacetate bridged dicopper(II) complex of SalDplH3, [Cu2SalDpl(Phenac) (4-Ethylphenol)], C33H31N2O6Cu2, II, having the space group P-1 and cell dimensions, a = 11.872(2), b = 13.418(3), c = 11.046(2) A, α = 101.95(2), β = 103.65(1), γ = 113.35(1)° was solved for 3833 structure factors (I>3.0σ(I)) and Z = 2, R = 4.1, Rw = 4.3%. The 4-ethylphenol group is involved in a strong hydrogen bond to one of the phenolic oxygen donor atoms of the SalDpl3− ligand and a weaker hydrogen bond to the adjoining oxygen donor atom of the bridging phenylacetate ion. The other phenolic oxygen donor atom is involved in an out-of-plane interaction to one of the copper atoms.

Structures and Properties of the Copper(II) and Nickel(II) Complexes of NN′-bis[(2-hydroxy-5-methylphenyl)phenylmethylene]-4-azaheptane-1,7- Diamine and Related Compounds: Direct Comparison of D8 and D9 Analogues

The nickel(II), copper(II), and zinc(II) complexes of the quinquedentate ligands mbp and cbp, derived from the Schiff-base condensation of 3,3′-iminobis(propylamine) with 2-hydroxy-5-methylbenzophenone (mbp) and 5-chloro-2-hydroxybenzophenone (cbp), have been investigated by magnetic, spectroscopic, and X-ray crystallographic techniques and shown to be five-co-ordinate monomers, the Cu compounds having normal magnetic moments while the Ni complexes are high spin. The e.s.r. spectra of the Cu complexes show ligand hyperfine splitting for two of the three nitrogen donor atoms, in agreement with X-ray structural observations for [Cu(mbp)]. The metal environments are approximately distorted trigonal bipyramids, but the Cu complex has one elongated Cu-N bond, which suggests distorted square pyramidal geometry, and a weaker ligand-field than for the Ni complex. Failure to observe ligand hyperfine contribution by this nitrogen to the e.s.r. spectrum of [Cu(cbp)], in either frozen chloroform or solid solution in the (isomorphous) ZnII analogue, can be rationalised by the assumption that the Cu complex has essentially the same structure in the Zn lattice as in the pure Cu complex and in chloroform solution.Crystal structures for [Cu(mbp)] and [Ni(mbp)] were determined by the heavy-atom method from counter data, and refined by full-matrix least-squares: [Cu(mbp)], space group P, Z= 2, a= 10.073(2),b= 12.438(3), c= 13.080(3)A, α- 73.89(2), β= 67.54(1), γ= 86.99(2)°, R 6.3%. 2569 reflections; [Ni(mbp)], space group Pcnb, Z= 4. a= 16.927 (2), b= 24.232(2), c= 7.1562(7)A, α=β=γ= 90°, R 6.1%, 1271 reflections. The ZnII complex [Zn(cbp)] is isomorphous with [Cu(mbp)].

Model compounds for galactose oxidase: The crystal and molecular structure of dimeric (4-methylpyridine-N) (N-salicylidene-tyrosinato-O, N, O')copper(II)

Galactose oxidase is a type II copper protein that contains a square–pyramidal five-coordinate copper center and catalyzes the oxidation of primary alcohols to aldehydes with a concomitant reduction of molecular oxygen. Dimeric (4-methylpyridine-N)(N-salicylidene-tyrosinato-O, N, O′)copper(II), which contains two square–pyramidal five-coordinate copper centers and thus serves as a model for galactose oxidase, crystallizes in the monoclinic space group P21/c with a = 8.914(1) Å, b = 18.415(2) Å, c = 12.802(2) Å, β = 107.70(1)°. The dinuclear unit comprises two four-coordinate units each consisting of the tridentate Schiff base and 4-methylpyridine with a weaker out-of-plane link to the phenolic oxygen atom from the adjoining unit in a typical 4 + 1 distorted square–pyramidal geometry.

Magnetic, spectroscopic, and structural properties of bis[bromo-, chloro-, and nitrato-(N-n-butyl-5-chloro-α-phenyl-2-hydroxybenzylid-ene)aminato-µ-O-copper(II)]

The title compounds were prepared by the action of copper nitrate or halide on bis[N-n-butyl(5-chloro-α-phenyl-2-hydroxybenzylidene)aminato] copper(II) which in turn was obtained from the reaction of copper(II) acetate with the n-butylamine adduct of 5-chloro-2-hydroxybenzophenone. The magnetic susceptibilities of the chloride, bromide, and nitrate adducts were determined as a function of temperature, and are interpreted in terms of binuclear molecules with the copper atoms in a four-co-ordinated, approximately planar, ligand environment, and bridged by the phenolic oxygens of the organic ligand. The electronic and i.r. spectra and a full three-dimensional X-ray crystal and molecular structure determination on the bromo complex support these conclusions. The precise environment about the [graphic omitted] bridge in the bromo complex, and particularly the copper atoms, is in good agreement with that expected from the strength of antiferromagnetic interaction. All the complexes are believed to be four-co-ordinated, though the chlorine adduct is a dihydrate and the possibility of water co-ordination cannot be ruled out completely. A number of the i.r. peaks could be assigned unambiguously. E.s.r. spectra at 300 and 77 K of the binuclear complexes revealed only peaks due to the small trace of the monomeric parent complex remaining in these compounds.

Properties and Structures of the Five-Coordinated Copper(II) and High-Spin Nickel(II) Complexes of 3,3'-Dichloro-2,2'-(1,12-diphenyl-2,6,11-triazadodeca-1,11-diene-1,12-diyl)bisphenol

Crystals of acetato(methanethio1ato)-gamma-picolinemercury(II), MeSHg02CMe,C6H7N (1), are monoclinic, P21/a, a 16.617(9), b 7.271(3), c 20.476(2), beta = 113.31(5), Z 8. The structure resembles that of its pyridine analogue, being based on a polymeric (-Hg-SMe-)n chain with acetate and picoline groups coordinated at each mercury; a similar structure is found for EtSHg02CMe,C5H5N (2), monoclinic, P21/c, a 9.344(2), b 17.917(9), c 7.179(2) A, beta 106.24(3), Z 4. The structure of tetrachlorotetra(2-methylpropane-2-thiolato)di(gamma-picoline)tetramercury(11), (ButS)4CI4Hg4(C6H7N)2 (3), also resembles that of its pyridine analogue being based on an unusual tetranuclear grouping of mercury atoms linked by chloride and thiolate bridges. Crystals of (3) are monoclinic, P21/c a 12.334(7), b 17.468(9), c 9.999(5) A, beta 91.18(4), Z 2. Crystals of MeSHgBr (4) are monolinic, P21/c, a 7.770(9), b 7.500(5), c 7.945(10) A, beta 91.71(3), Z 4, and contain parallel chains (-Hg-SMe-)n with neighbouring chains linked by bridging bromine atoms into parallel sheets. Each bromine is triply bridging, being coordinated to two mercury atoms in one chain, and one mercury atom in an adjacent chain. The structure of MeSHgCl appears to be isomorphous.

Ether formation on the tridentate Schiff base ligands of copper(II) complexes

A series of copper(II) complexes, CuL·imidazole, where L2− are tridentate Schiff base ligands formed by condensation of salicylaldehyde with a series of amino acids, have been synthesized. Visible spectral data indicate that copper(II) in these complexes are five coordinate in the solid state and in solution. Electrospray mass spectrometry has been used to show how these complexes react in alcohol/NaOH solutions with and without the presence of d-galactose. In the absence of d-galactose where the amino acid in the ligand is serine, the alcohol group on the ligand is converted to its alkyl ether after sonication of the solution for up to 4 h. In the presence of d-galactose, an alkoxy group is added to the ligands except for the ligand containing serine after sonication of the solutions for up to 4 h. At the same time, d-galactose is oxidized to its aldehyde. Where the ligand contains methionine, oxygen is also added to the ligand, most likely to the thioether sulfur. Graphical Abstract

Model compounds for the type III site and the combined type II and type III sites in multicopper oxidases

A series of model complexes for the diamagnetic type III site in multicopper oxidases has been developed based on tridentate ligands formed from the Schiff base condensation of bifunctional primary amines with the monoximes ofβ-diketones. The complexes resulting when copper salts, CuX2, react with the resulting ligands, HL, have the general formula Cu2L2X2 and have a central core made up of the two copper atoms bridged by two oxime groups resulting in a six-membered Cu(ON)2Cu moiety. This grouping is strictly planar and has significant shortening of the N-O bond length along with lengthening of the C=N bond indicating a delocalization of theπ-electrons in the ring. The result is a copper(II) dimer which is diamagnetic at all measurable temperatures (< 400 K). Spectroscopic, magnetic and electrochemical properties of the series of compounds will be compared with those of the parent enzyme containing the type III dicopper site. A second series of model complexes for both the type III site and the newly reported structure of the joint type II and type III site in ascorbate oxidase (crystal structure reported at the 3rd International Conference on Bioinorganic Chemistry, Boston, Mass, July 24–28, 1989) is also discussed. These compounds are obtained when ligands, H3L, resulting from the condensation of derivatives of salicylaldehyde with 1,3-diamino-2-propanol, are reacted with copper carboxylates resulting in compounds of formula Cu2L (carb). The carboxylate bridging group can be displaced by other better donors, L’, such as pyrazole, or indoles to give compounds (Cu2LL’)+ which have bridging L’ groups. The properties of this series of compounds will be compared with those of the type III site. If the L’ ligand is suitably derivatized, i.e. 6-aminoindole, then by a Schiff base condensation with copper salicylaldehyde, compounds of formula (Cu2LL’)2Cu(sal)2 can be obtained, which are models for multicopper oxidases having both the type II and type III sites in the same molecule, as has been found in the recent crystal structure of ascorbate oxidase. Comparisons between these models and multicopper oxidases will be drawn.

FIVE CO-ORDINATE 2-METHYLPYRIDINE ADDUCTS OF BIS(SALICYLIDENEIMINATO)NICKEL(II) COMPLEXES

Abstract The interaction of 2-methylpyridine with nickel(II) complexes of a range of substituted salicylideneimines has been investigated. In each case 1:1 base adducts are produced but these are formed incompletely even when 2-methylpyridine is employed as solvent. The five co-ordinate base adducts as paramagnetic and, by combination of solution magnetic and spectral results, the respective formation constants have been calculated. Steric factors appear to be important in the promotion of five co-ordination in these complexes.