Effect of N,N,N′-trimethylpiperazinium (TMP+) cations on magnetic properties and dimerization of fullerenes in the (TMP+)(CoIIporphyrin)(C60−) salts

Abstract

New salts of fullerene C60•− radical anions with N,N,N′-trimethylpiperazinium cations (TMP+) containing neutral cobalt(II) porphyrin molecules: {(TMP+)⋅CoIIOEP}⋅(C60•−)⋅2C6H4Cl2⋅C6H5CN (1) and (TMP+)3{CoIITMPP⋅(C60−)}2(C60•−) ⋅C6H4Cl2⋅C6H5CN (2) have been obtained (OEP and TMPP are octaethyl- or tetrakis(4-methoxyphenyl)porphyrins, respectively). In these salts the C60•− radical anions or the TMP+ cations with free nitrogen atom can coordinate to cobalt(II) porphyrins and form Co-C(C60−) or Co-N(TMP+) bonds. The properties of these salts and the possibility of fullerene dimerization depend on type of bonds formed. For example, TMP+ cations in 1 form coordination (TMP+)⋅CoIIOEP assemblies preserving free non-bonded C60•− radical anions. They are effectively coupled with S = 1/2 spins localized on CoIIOEP (Weiss temperature is −27 K and decrease of magnetic moment of 1 is observed below 150 K). Previously the {(MDABCO+)⋅CoIITMPP}2⋅(C60−)2⋅(C6H4Cl2)2.5⋅(C6H5CN)1.5 salt was obtained in which doubly-bonded (C60−)2 dimers were found. In contrast to this salt, TMP+ cations in 2 preserved uncoordinated allowing the formation of the Co-C(C60−) bond of 2.273(3) Å length in the diamagnetic σ-bonded CoIITMPP⋅(C60−) anions. In coordinated state, fullerene anions cannot dimerize in 2 in spite of that their mutual arrangement and short interfullerene distances are favorable for such dimerization. Thus, variation of cations in the (Cation+)(CoIIporphytin)(C60−) salts drastically affects their properties and allows one to control dimerization of fullerene anions.