Margaret Goodgame

Steric and electronic effects in complexes of cadmium halides with substituted pyridines

Abstract ESR spectra at X- and Q-band frequencies are reported for manganese(II) ions doped into the halide-bridged polymeric complexes CdL 2 X 2 (L = pyridine or substituted pyridine, X = Cl or Br). Zerofield splitting parameters D and λ (= E/D ) are obtained. The D values, which give a measure of axial distortion, are influenced by both steric and electronic factors. In general, D values are high when the pyridine ligand is a good σ-donor, and low when it is a poor σ-donor, while steric hindrance by the substituent reduces the D value. Values of λ depend on the position of the substituent. The similarity of Cd(4-hydroxypyridine) 2 Cl 2 to the other complexes suggests that it is N-bonded.

Preparation and spectroscopic studies of the complexes of diacetamide with meta(II) perchlorates

Abstract The preparations of complexes formed by diacetamide (DA) with metal(II) perchlorates in 1:4 and 1:2 stoichiometry are reported. The ESR spectra, at both X- and Q-band, of Mn(II) ions doped in all these complexes and also those of 1:3 stoichiometry are reported, and the zero-field splitting parameters D and λ (= E / D ) are deduced. Very small values of D observed for complexes M(DA) 3 (ClO 4 ) 2 (M ue5fb Fe, Co, Ni) are consistent with an MO 6 2+ chromophore. The corresponding Zn and Cd complexes have distinctly higher D values. The identical values of D and λ, observed for all complexes with 1:4 stoichiometry, suggest identical structures and the X-ray powder patterns of these complexes also show marked resemblances. Considerably higher values of λ for M[(DA) 2 (H 2 O) 2 ](ClO 4 ) 2 (Mue5fbCo, Zn) show appreciable distortion. IR spectra distinguish coordinated from hydrogen bonded diacetamide.

Metal complexes of virus inhibitors. Part II. [1]. Coordination properties of 2-α-methoxybenzylbenzimidazole (= L) and x-ray crystal structure of CoL2I2·acetone·2H2O

Abstract Complexes are described of cobalt(II) and nickel(II) salts with the title ligand (=L). The X-ray crystal structure of [CoL2I2]·acetone·2H2O shows the ligand to be chelating to give distorted cis-octahedral geometry. In other complexes the ligand is monodentate through the imidazole nitrogen and an infrared spectral criterion to distinguish these modes of coordination is described. Some of the complexes bind strongly to carbonyl groups, especially of amides. It is suggested that similar binding to proteins may be important in the mode of anti-viral activity.

Metal complexes of the virus-inhibitor 3,4-dihydro-1-phenyl-1H-[1,4]-oxazino [4,3-a] benzimidazole

Abstract Complexes of the title ligand with cobalt(II) and nickel(II) salts have been prepared and characterised. The complexes are readily formed in solvents such as ethanol and acetone, with coordination taking place through the imidazole nitrogen (N 10). Electronic and infrared spectra and magnetic properties are reported for the complexes, which are mostly tetrahedral with ML 2 X 2 stoichiometry.

Chain polymeric complexes of some first-series transition-metal ions with N,N,N′,N′-tetra-acetyl-1,4-diaminobutane

The preparations are reported of the compounds [M(TADB)(H 2 O) 2 ](ClO 4 ) 2 (where TADB= N , N , N ′, N ′-tetra-acetyl-1,4-diaminobutane, and M=Mn, Co, Ni and Zn), and also of the analogous tetrafluoroborate salts with M=Mn, Co, Cu and Zn, and the complex Cu(TADB)(ClO 4 ) 2 . Crystals of [Zn(TADB)(H 2 O) 2 ](ClO 4 ) 2 are monoclinic, P 2 1 / n , with a =7.3735(2), b =12.4954(5), c =12.0313(5) A, β =100.581(4)°, and Z =2. Each zinc centre is coordinated to two trans -disposed aqua ligands and two chelating diacetamide units, one from each of two different TADB ligands, which, in turn bridge neighbouring zinc centres so as to generate cationic polymeric chains. X-ray powder diffraction studies show that, except for the copper(II) compounds, the other complexes are isostructural with the zinc complex. X-band EPR spectral results for the manganese(II) complexes and for samples of the other compounds ‘doped’ with small amounts of manganese(II) are also given.

An ESR study of manganese(II) ions in complexes of diacetamide

Abstract ESR spectra at both X- and Q-band are reported for Mn(II) ions doped at a nominal 1% in the lattices of [M(DA) 2 (H 2 O) 2 ]X 2 (M = Mg, Co and Ni; X = Cl or Br), [Mg(DA) 2 (H 2 O) 2 ](NO 3 ) 2 , [Co(DA) 4 (H 2 O) 2 ]Br 2 , M(DA) 2 Cl 2 (M = Mg, Co and Ni) and M(DA) 2 (NO 3 ) 2 (M = Co and Zn). The zero-field splitting parameters D and λ (= E/D ) are deduced. The observed values of D and λ for all the hydrated complexes are consistent with an MO 6 2+ chromophore, suggesting the coordination of water molecules. Higher values of D are observed for M(DA) 2 Cl 2 (M = Mg, Co and Ni) than for the hydrated analogues. The positive sign of D , deduced for the first time from the hyperfine spacing at Q-band, suggests the trans -coordination of chloride ions and very high λ values indicate considerable inplane distortion.

Ligand dependence of the polymeric structure for CdLCl2 (L= substituted pyridine)

Abstract Compounds of the type CdLX2 (L = substituted pyridine, X = halide) have been studied by ESR spectra of the manganese-doped complexes, and shown to have the double-stranded polymeric structure found for CdimidazoleCl2. There appear to be steric constraints on the formation of this structure, and no compounds of this type could be made with 3,5- disubstituted pyridines. Zero-field splitting parameters are reported for the complexes.

Electron spin resonance spectra of manganese(II) ions in the double-stranded chain polymers CdLX2(L = pyridine or methylpyridine; X = Cl or Br)

E.s.r. spectra at X and Q band are reported for manganese(II) ions doped into CdLX2(L = pyridine or 3- or 4-methylpyridine; X = Cl or Br). The zero-field splitting parameters D and λ(=E/D) are obtained. For the chlorides D is in the range –0.0576 to –0.0631 cm–1, with λ= 0.04 ± 0.01, while for the bromides |D|=ca. 0.185 cm–1, with λ= 0.07 ± 0.01. These figures support the proposed double-stranded polymeric structure, which may readily be identified from the form of the spectrum.

Manganese(II) ions as stereochemical probes in reactions of zinc halides with pyrazine

Pyrazine is shown to form complexes [Zn(pyz)2X2](pyz = pyrazine, X = Cl or Br) as well as the previously known [Zn(pyz)X2]. E.s.r. spectra of these compounds doped with manganese(II) ions show the stereochemistry to be polymeric with pyrazine bridges, and the doping technique permits identification of the complexes even in mixtures.

Zero-field splitting of manganese(II) ions in polymeric MN2X4(M = Cd or Zn, X = halogen) co-ordination

E.s.r. spectra at X and Q band are reported for manganese(II) ions doped into the halide-bridged polymers Cd(py)2X2(X = Cl or Br), Cd(4Me-py)2Cl2, Cd(pyz)X2(X = Cl, Br, or I), and Zn(pyz)Cl2·0.5H2O (py = pyridine, 4Me-py = 4-methylpyridine, pyz = pyrazine). Zero-field splitting parameters D and λ(=E/D) are obtained. For all the complexes λ is close to zero, while D is in the range 0.11–0.14 cm –1for the chlorides, and ca. 0.3 cm–1 for the bromides. The distortion from octahedral geometry is therefore less than in related MnN4X2 complexes.