Tetrazine-Bridged Phthalocyaninato Metal Complexes: A new Class Of Intrinsic Semiconductors
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ABSTRACT Stacked transition metal macrocycles [MacM(L)]n with M e.g. Fe, Ru, Os, Co, Rh and Mac = phthalocyanine (Pc) 1,2- or 2,3-naphthalocyanine (1,2-, 2,3-Nc) have been synthesized by us. The bridging ligands (L) are e.g. pyrazine (pyz) or s-tetrazine (tz). In general, these complexes [MacM(L)]n are insoluble in organic solvents, however, soluble oligomers [R4 PcM(L)]n can be prepared using metallomacrocycles RnPcM, R = t-bu, et, OR, M = Fe, Ru, which are substituted in the peripheric positions. A systematic investigation of the influence of the bridging ligands on the semiconducting properties in [MacM(L)]n reveal, that changing L, e.g from dabco over pyz to tz leads to a steady increase of the semiconducting properties without external oxidative doping. Powder conductivities in the order of 0. 1 S/cm can be reached by using s-tetrazine, 3,6-dimethyl-s-tetrazine (me2tz) and others, e.g. fumnarodinitrile as the bridging ligands. The intrinsic conductivities are a result of the low oxidation potential of tz and me 2 tz and due to the low lying LUMO in the corresponding bridged systems [MacM(tz)]n. The electrical and physical properties, especially the UV and the M6olbauer spectra for the tetrazine-bridged macrocyclic metal complexes are discussed in respect to intrinsic semiconducting properties of these compounds.
Stacked transitionmetalmacrocycles [MacM(L)]n can be obtained by the so-called "shish kebab" approach in which the transition metallomacrocycles (MacM) are linked together by bidentate bridging ligands (L). [MacM(L)]n with transition metals e.g. Fe, Ru, Os, Co, Rh in various oxidation states have been synthesized by us [1]. As macrocycles (Mac), not only phthalocyanine (Pc), tetrabenzoporphyrine (TBP), but also macrocycles containing more extended ir-systems like 1,2- or 2,3-naphthalocyanine (1,2-, 2,3-Nc) or phenanthrenocyanine (Phc) are used [1]. The bridging ligands (L) are bifunctional organic donor molecules, e.g. pyrazine (pyz), s-tetrazine (tz), for metals in the oxidation state +2, or e.g. cyanide (CN-), thiocyanate (SCN-) or azide (N 3 -) for transition metals in the oxidation state +3 [la]. In general, these complexes [MacM(L)]n are insoluble in organic solvents, however, soluble oligomers [RxPcM(L)]n were prepared using metallomacrocycles R4 PcM and R8PcM, R = t-bu, et, OR', (R' = C5 - CI 0), M = Fe, Ru, which are substituted in the peripheric positions (Fig. 1). 233 Mat. Res. Soc. Symp. Proc. Vol. 328. 0,1994 Materials Research Society
Figure 1.
Schematic structure of bridged macrocyclic transition metal complexes
M
M
L
L
M
L
M
L-
M = Fe2+, Fe3+, Co2+, Co3+, Ru2+, Mn2+, Mn3+, Cr3
L=N
N,
N
N , CN 0
NC, CN-
J =
Pc2-, R4Pc2-, R8Pc2-, 1,2-Nc 2-, 2.3-Nc 2-, TBP'-
We report about a systematic investigation of the influence of the bridging ligand on the conductivity of the bridged phthalocyaninato and 2,3-naphthalocyaninatotransition metal complexes. As bridging ligand dabco, pyrazine (pyz), 1,4-diisocyanobenzene (dib), tetrazine (tz) and its derivatives e.g. 3,6-dimethyl-s-te
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