Alistair G. Bingham

Synthetic, spectroscopic, and X-ray crystallographic studies on binuclear copper(II) complexes with a tridentate NNS-bonding 2-formylpyridine thiosemicarbazone ligand. The characterization of both neutral and deprotonated co-ordinated ligand structures

The preparation of the complexes [(CuLX)2](HL = 2-formylpyridine thiosemicarbazone) from the interaction of HL with the appropriate copper salt (X = CH3COO, Cl, NO3, or ClO4) or by reaction of an HL–KX mixture with copper(II) acetate monohydrate (X = Br or I) is described. Dissolution of [{CuL(CH3COO)}2] in H2SO4 or HCl yields the protonated ligand complexes [{Cu(HL)(SO4)}2] and [{Cu(HL)Cl2}2]·2H2O respectively. The complexes have been characterized by a variety of spectroscopic techniques and the crystal and molecular structures of [{CuL(CH3COO)}2] and [{Cu(HL)(SO4)}2] determined by single-crystal X-ray diffraction techniques from diffractometer data. Crystals of [{CuL(CH3COO)}2] are triclinic, space group P, with a= 8.827(3), b= 8.813(3), c= 8.997(3)A, α= 117.49(2), β= 110.96(3), γ= 91.65(3)°, and Z= 1. Crystals of [{Cu(HL)(SO4)}2] are monoclinic, space group C2/c, with a= 14.751(3), b= 9.138(2), c= 17.468(4)A, β= 104.91(2)°, and Z= 4. After full-matrix least-squares refinement the final R value was 0.027 for both complexes (2 216 and 2 206 observed reflections were used respectively). Both complexes consist of discrete centrosymmetric dimers, the monomeric units being bridged by two acetato or sulphato ligands. The copper atoms have a distorted square-pyramidal co-ordination geometry with three donor atoms (NNS) coming from L or HL to form a tricyclic ligating system. The fourth donor atom (oxygen) comes from the bridging CH3COO– or SO42– ion. The fifth co-ordination position is occupied by a less strongly bound oxygen from the second bridging anion.

Interaction of benzo-1,3-thiazoline-2-thione and related ligands with copper(II) salts and the single-crystal X-ray structure of µ-[1,2-bis-(diphenylphosphino)ethane]-bis{(benzo-1,3-thiazole-2-thiolato-S)[1,2-bis(diphenylphosphinoethane]copper(I)}

A reinvestigation of the reaction of benzo-1,3-thiazoline-2-thione (HL1) with copper salts has shown, in contradiction to earlier reports, that only two compounds are formed, viz. [Cu(L1)] from aqueous ethanol and [Cu(HL1)2Cl] from absolute ethanol. The incorrect formulations arise from contamination of the copper(I) complexes with bis(benzo-1,3-thiazol-2-yl) disulphide (L1–L1). These findings are supported by the reaction of other heterocyclic thioamides and diphenyldithiophosphinic acid with copper(II) salts. The complex [Cu(L1)] reacts with the chelating phosphines 1,2-bis(diphenylphosphino)methane (dppm) and 1,2-bis(diphenylphosphino)ethane (dppe), to give [Cu(L1)(dppm)] and [Cu2(L1)2(dppe)3]. The crystal and molecular structure of [Cu2(L1)2(dppe)3] has been determined by X-ray diffraction techniques. The crystals of the complex are triclinic, space group P, with a= 17.334(3), b= 17.348(2), c= 20.110(2)A, α= 82.54(1), β= 120.73(1), γ= 123.86(1)°, and Z= 2. After full-matrix least-squares refinement the final R value was 0.096 for 3 317 reflections. The complex consists of a centrosymmetric dppe-bridged dimer. Each copper atom has a distorted tetrahedral geometry with one phosphorus from the bridging dppe, two phosphorus atoms from a chelating dppe, and the exocyclic sulphur atom from the anionic L1 ligand making up the co-ordination sphere.

The crystal structure of chlorotris(3-methylpyridine)copper(I), and its conversion into hexa-µ-chloro-tetrakis(3-methylpyridine)-µ4-oxo-tetracopper(II)

The crystal and molecular structure of [Cu(3Me-py)3Cl](3Me-py = 3-methylpyridine) has been determined by single-crystal X-ray diffraction techniques from diffractometer data. Crystals of the complex are rhombohedral, space group R3, with a= 14.384(2), c= 7.451 (2)A, and Z= 3. After full-matrix least-squares refinement the final R value was 0.048 for 765 observed reflections. The complex consists of monomeric units with the copper having a tetrahedral co-ordination geometry. The monomers are stacked in such a manner that infinite linear Cu–Cl ⋯ Cu chains are formed with a separation of 7.451(2)A between copper atoms. The complexes [CuL3X][L = py (pyridine), 2Me-py (2-methylpyridine), or 3Me-py, X = Cl; L = 3Me-py, X = Br] are readily oxidised to [Cu4X6OL4] species.

Small molecule analogues for the specific metal-binding site of lactoferrin. Part 2. Phenolato-complexes of copper(II) and the nature of the charge-transfer transition in the visible region

The preparation of the following compounds is described: cis-[CuL2L1][L = pentafluorophenolate (pfp), L1= ethylenediamine (en), NNN′N′-tetramethylethylenediamine (tmen), 2,9-dimethyl-1,10-phenanthroline (dmphen), or 2,2′-bipyridyl (bipy); L = pentachlorophenolate (pcp), L1= en or dmphen; L = 2,4,6-tri-iodophenolate (tip), L1= en, tmen, or dmphen; L = 2,4,6-tribromophenolate (tbp), L1= en, tmen, or dmphen; L = 2,6-di-iodo-4-nitrophenolate (dinp), L1= en, dmphen, or bipy], trans-[CuL2L22][L = pfp, L2= pyridine (py), imidazole (imH), or 4-dimethylaminopyridine (dmap); L = pcp, pentabromophenolate (pbp), or dinp, L2= py; L = 2,4,6-trichlorophenolate (tcp), L2= dmap; L = tbp; L2= py or imH; L = tip, L2= py or dmap], and [CuL2L3][L = pfp, L3= collidine (2,4,6-trimethylpyridine)(coll); L = pcp, L3= coll or NN-dimethylformamide (dmf); L = dinp, L3= coll or (dmf)2]. Spectroscopic studies show most cis-[CuL2L1] and trans-[CuL2L22] have tetragonal structures with axial bonding (sometimes weak) by the appropriate ortho-halogeno-groups or, if condensed, by bridging phenolato-groups. For cis-[CuL2(dmphen)] an out-of-plane arrangement towards distorted tetrahedral exists in solution. The complexes [Cu(pcp)2(coll)] and [Cu(pcp)2(dmf)] have low magnetic moments at room temperature, hence binuclear or polymeric structures with bridging phenolato-groups are suggested. All the compounds show a strong charge-transfer (c.t.) absorption in the range 400–550 nm, with an intensity about 1 200 dm3 mol–1 cm–1, and weaker d–d bands at ca. 750 nm. By studying the variation in the c.t. absorption energy for this extensive series of compounds, where (a) the phenolate is kept constant and the coligands are varied and (b) the phenolate is varied and the coligands are kept constant, it is concluded that the assignment of the c.t. transition is consistent with a partial transfer of an electron from the Pπ orbital on the phenolate oxygen to a dσ· copper orbital. The c.t. band energies of the complexes are dependent on the nature of the solvent (solvents with low ET values lowering the c.t. energy), the basicity and number of coligands and phenolato-groups, and the chelate effect (which raises the energy). From these considerations, and e.s.r. data, it is concluded that the copper sites in copper(II) lactoferrin have a CuN2O2O′2 donor set containing two cis tyrosines, one histidine, and one water in the equatorial plane and possibly one histidine and an oxygen-donor ligand (non-ionized phenol) along the axial direction.

The interaction of 1-methylimidazoline-2(3H)-thione with copper(II) salts

The interaction of 1-methylimidazoline-2(3H)-thione (HL1) with the appropriate copper(II) species in ethanol solution directly produces the blue mixed-valence complexes, [CuI10CuII2(L1)12(H2O)4]X2·yH2O (X = O2CMe or OH, y= 2; X = ClO4 or PF6, y= 0). With CuCl2·2H2O the product is dependent on the HL1 : Cu molar ratio. If HL1 was in excess, e.s.r. spectroscopy indicated the formation of a ‘CuIIS4’ species, viz. [Cu(HL1)4]2+, in solution. At a 3:1 (HL1:Cu) molar ratio (CuII added to HL1) the known copper(I) complex, [Cu2(HL1)4Cl2] is obtained. However, using a 1.5:1 (HL1:Cu) molar ratio, and with HL1 added to CuII, the product is a mixed-valence complex formulated as [Cu2(HL1)2Cl3]. These compounds, and others obtained with imidazolidine-2-thione (HL2) and 4,5-diphenylimidazoline-2(3H)-thione (HL3), have been characterized by spectroscopic techniques. In nitromethane solution HL1 reacts in the presence of copper to yield the chelate N-donor ligand, bis(1-methylimidazol-2-yl) sulphide (L4) in the dimeric complex [Cu2(L4)2Cl4].