Busch Systems

Vol. 107. Multielement Detection Systems for Spectrochemical Analysis. By Kenneth W. Busch and Marianna A. Busch... 

Im and Busch, using the optical activity method, have also made a study of the exchange of the propylenediaminetetraacetate complexes of Co(III) and Co(II) (CoPY and CoPY ). This system can be treated by the McKay equation. Optical rotation data was obtained at temperatures between 80 and 100°C and various pH s between 2.0 and 7.0. This was again found to be consistent with exchange via two pathways k and k )... 

Selected other metal ion systems. There have been a number of investigations of the reduction of iron macrocyclic ligand complexes. In one such study, the Fe(n) complex [FeL(CH3CN)2]2+ [where L = (292)] was shown to exhibit three reduction waves in acetonitrile (Rakowski Busch, 1973). Controlled-potential electrolysis at the first reduction plateau (—1.2 V) led to isolation of [FeL]+ for which the esr spectrum is typical of a low-spin Fe(i) system. The quasi-reversible Fe(i)/Fe(n) couple occurs at —0.69 V versus Ag/AgN03. 

The location of the induced unsaturation in the macrocyclic system is metal-ion dependent. This is illustrated by the examples given in Figure 8.2. In the Fe(n) complex, the imine functions form as conjugated pairs (Dabrowiak, Lovecchio, Goedken Busch, 1972 Goedken Busch, 1972) - such a-diimine species have long been known to have a special affinity for Fe(ii). In contrast, Ni(n) promotes formation of a product in which the respective imine functions are in electronically isolated positions (Curtis, 1968 1974). 

The formation of diimine systems by Schiff -base-type condensation of suitable aldehydes and primary amines has been widely applied. Those reported are mostly strong field systems and their relevance to the spin crossover field is generally in systems of the kind [Fe(diimine)2(NCS)2]. The effect of the incorporation of substituents likely to hinder coordination has been studied. Robinson and Busch noted a fundamental difference at room temperature in the electronic properties of the [Fe N6]2+ derivatives of 2-pyridi-nalmethylhydrazone and 2-pyridinal-dimethylhydrazone, those of the former being low spin and those of the latter high spin [49]. The temperature-dependence of the magnetism of the latter complex was not reported but may well be of interest. However, spin crossover [Fe(diimine)3]2+ systems have been characterised for systems where the incorporation of appropriate substituents has reduced the ligand field. 

These techniques were first employed3052 in 1969 to prepare [NiraL(MeCN)2]3+ (L = cyclam, r c- (5,14)-meso-(5,12) - Me6[14]aneN4 and corresponding 4,11 and 4,13 dienes). An extensive study of the electrochemical behaviour of nickeltetraazamacrocyclic systems has been carried out by Busch and co-workers.3056 Cocolios and Kadish investigated the redox behaviour of nickel(III) porphyrins.3028... 

Several points are to be noted. Firstly, pores and changes of sample dimension have been observed at and near interdiffusion zones [R. Busch, V. Ruth (1991)]. Pore formation is witness to a certain point defect supersaturation and indicates that sinks and sources for point defects are not sufficiently effective to maintain local defect equilibrium. Secondly, it is not necessary to assume a vacancy mechanism for atomic motion in order to invoke a Kirkendall effect. Finally, external observers would still see a marker movement (markers connected by lattice planes) in spite of bA = bB (no Kirkendall effect) if Vm depends on composition. The consequences of a variable molar volume for the determination of diffusion coefficients in binary systems have been thoroughly discussed (F. Sauer, V. Freise (1962) C. Wagner (1969) H. Schmalzried (1981)]. 

Virtually all types of metal ions have been complexed with macrocyclic ligands.2-7 Complexes of transition metal ions have been studied extensively with tetraaza macrocycles (Chapter 21.2). Porphyrin and porphyrin-related complexes are of course notoriously present in biological systems and have been receiving considerable investigative attention (Chapter 22).8 Macrocyclic ligands derived from the Schiffbase and template-assisted condensation reactions of Curtis and Busch also figure prominantly with transition metal ions.6,7 The chemistry of these ions has been more recently expanded into the realm of polyaza, polynucleating and polycyclic systems.9 Transition metal complexes with thioether and phosphorus donor macrocycles are also known.2... 

A three-site system for peptide synthesis around a cobalt(III) complex has been studied. Instead of a quadridentate ligand as used in the above experiments, Wu and Busch chose the tridentate ligand diethylenetriamine. The formation of dipeptide and tetrapeptide complexes is shown in Scheme 92.360 The ester carbonyl group in the 0-bonded amide intermediate (127) cannot be activated by coordination because it cannot reach the metal ion. Isomerization to the jV-bonded amide complex (128) occurs with base and enables coordination and therefore activation of the ester carbonyl group. 

Daryle H. Busch Lawrence, Kansas A Sampling of Multi-receptor Supramolecular Systems and Beginnings in the Chemistry of Orderly Entanglements... 

Busch M, Schmidt J, Rothen SA, Leist C, Sonnleitner B, Verpoorte S (1996) Proc 2nd Int Symp Miniaturized Total Analysis Systems (TAS96), 19-22 Nov 1996, Basel, (Analytical Methods and Instrumentation, Special Issue 1996, Widmer HM, Verpoorte E, Barnard S (eds), p 120... 

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