Zwitterionic {Fe(i)Pc(−2)−}·(TMP+) assemblies comprising anionic iron(i) phthalocyanines and coordinating N,N,N′-trimethylpiperazinium cations

Abstract

{[Fe(I)Pc(−2)⁻]·(TMP⁺)}·0.5C₆H₁₄ (1) and {Co(I)Pc(−2)⁻}·(TMP⁺) (2) salts containing iron(I) and cobalt(I) phthalocyanine anions and N,N,N′-trimethylpiperazinium cations (TMP⁺) have been obtained as single crystals. The TMP⁺ cations coordinate to the iron(I) centers in 1 by free nitrogen atoms to form a weak N(TMP⁺)–Fe bond of 2.568(3) and 2.553(3) Å length at 150 and 105 K, respectively. This is the first zwitterionic assembly containing anions and cations in one neutral coordination {[Fe(I)Pc(−2)⁻]·(TMP⁺)} unit. The Fe(I)Pc(−2)⁻ anions manifest strongly asymmetric EPR signals in the spectrum of 1 which can be fitted well by four components at 298 K with g₁ = 2.1770, g₂ = 2.1681, g₃ = 2.1425 and g₄ = 2.0708. The signal is attributed to the low-spin (S = 1/2) Fe(I) with the d⁷ configuration. The EPR spectrum of 1 does not change qualitatively upon slow cooling from 298 down to 4 K. Quenching of the sample for seconds produces a different EPR spectrum at 4 K. This spectrum can be attributed to the frozen metastable state of Fe(I)Pc(−2)⁻ which exists only at low temperatures and transfers to the spectrum observed for the slowly cooled sample above 70 K. Salt 2 contains EPR silent cobalt(I) with the d⁸ configuration and in this case the TMP⁺ cations do not coordinate to the cobalt(I) atoms.