Bridged macrocyclic transition metal complexes, a new type of semiconducting materials
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Bridged quasi-one-dimensional macrocyclic transition metal complexes linked by linear bridging ligands L containing delocalizable ir-electrons to form stacked arrangements [MacM(L)]n have been synthesized. As macrocycles Mac, e.g., phthalocyanine (Pc), tetrabenzoporphyrine (TBP), 1,2- and 2,3-naphthalocyanine (1,2- and 2,3-Nc), 2,3-tetranaphthoporphyrine (2,3TNP) and phenanthrenocyanine (Phc) have been used. Fe, Ru, Co, Rh, and others were taken as central metals and as bridging ligands, e.g., pyrazine (pyz), tetrazine (tz), diisocyanobenzene (dib), substituted diisocyanobenzenes, cyanide (CN~), and thiocyanate 1 (SCN-) (Fig. 1). The characterization of the bridged macrocyclic metal compounds was carried out by IR spectroscopy or thermogravimetric methods and in the case of the iron compounds by 57Fe-M6ssbauer spectroscopy. NMR studies to investigate the mechanism of the formation of the bridged metal complexes was described earlier with PcM(me4dib)2 and [PcM(me4dib)]«, M = Fe, Ru.2 For [PcFe(pyz)]n, a degree of polymerization of n > 20 was estimated by quantitative IR measurements of the end-group absorptions.3 In the case of [PcCotCN)^, the chain length was shown to be up to 40 units.4 The bridged complexes [MacM(L)]« prepared by us are hardly soluble in organic solvents. In order to obtain additional information about the molecular structure and the stability and also to improve the processibility of these materials, we also synthesized soluble oligomers, namely the tetra-tert-butylsubstituted phthalocyaninatoruthenium compounds J. Mater. Res., Vol. 6, No. 2, Feb 1991 http://journals.cambridge.org
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[(*-Bu)4PcRu(dib)J, and [(?-Bu)4PcRu(me4dib)l, by reacting f-Bu4PcRu with dib and me4dib, respectively.5 The (f-Bu)4PcRu is entirely soluble in acetone, chloroform, dichloromethane, and other organic solvents. It was dissolved in acetone and dib and me4dib was added and the mixture refluxed for 24 h. The resulting bridged complexes [(f-Bu)4PcRu(dib)]n and [(f-Bu)4PcRu(me4dib)]n are completely soluble in CHC13 even at room temperature. The characteristic shift of the I-N=C valence frequencies in the IR spectra indicate (see Table I) that oligomeric phthalocyanine complexes are formed. By measuring their 'H-NMR spectra it was possible to determine the structures as well as the chain length n of these two oligomers (see Fig. 2). The peripheral protons of the macrocycles of [(f-Bu)4PcRu(dib)X, and [(£-Bu)4PcRu(me4dib)]n show typical splitting patterns at low field, whereas the peaks for the protons of the axial coordinated ligands dib and me4dib are shifted to high field. The four positional isomeric complexes of (f-Bu)4PcRu are statistically distributed in the bridged oligomers. Thereby eight nonequivalent isoindole units with regard to their neighbors are formed, having protons which are expected to exhibit only slightly different chemical shifts. The proton signals of the two most exterior phthalocyanines appear farthest downfield. On the other hand, the peaks of the inner phthalocyanines are shi
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