Charge transfer adducts of rare earth 3,5-dinitrobenzoates with N,N,N′,N′-tetramethyl-p-phenylenediamine

•Rare earth dinitrobenzoates form adducts with N,N,N′,N′-tetramethylphenylenediamine.•Charge transfer determines supramolecular structures of the adducts.•Charge transfer results in significant paramagnetism of Y compounds.•Ln dinitrobenzoate polymers are formed in absence of tetramethylphenylenediamine.•Dysprosium complex manifests single molecule magnet properties.

Crystallization of products of an exchange reaction between LnCl3·6H2O and potassium 3,5-dinitrobenzoate from acetonitrile in the presence of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) and DMSO results in two types of charge transfer adducts: [Ln2(O2CC6H3(NO2)2)6(DMSO)4]·TMPD·2MeCN (type A) and [Ln2(O2CC6H3(NO2)2)6(DMSO)4]·3TMPD (type B). Type A adducts were isolated in pure form for Tb(1), Dy(2a), Ho(3a), Er(4a) and Y(5a), whereas type B adduct was isolated for Er (4b). Crystallization in the absence of TMPD gives coordination polymers, [Ln(O2CC6H3(NO2)2)3(DMSO)2]n (Ln = Tb (8), Dy (9)) and [Ln(O2CC6H3(NO2)2)3(DMSO)]n·nMeCN (Ln = Ho (10), Er (11), Y (12)). In the case of Sm and Gd, the [Ln(O2CC6H3(NO2)2)3(DMSO)2]n coordination polymers (Ln = Sm (6), Gd (7)) are formed even with a large excess of TMPD. In the case of Tb, the [Tb(O2CC6H3(NO2)2)3(DMSO)(H2O)]n·0.5nTMPD·1.5nDMSO·0.5nCH3CN polymer (13) was isolated in a small yield in the presence of excess TMPD. Due to charge transfer between TMPD molecules and [Ln2(O2CC6H3(NO2)2)6(DMSO)4] fragments, stacking interactions occur that determine the supramolecular structures of the compounds. Spectral studies of these compounds indicate that a charge transfer structure predominates over an ion radical structure; however, according to EPR studies, the charge transfer moieties in the compounds are significantly paramagnetic. The magnetic properties of 1, 2a, 3a and 4b complexes correspond to predominance of antiferromagnetic interactions in all cases. Complex 2a manifests SMM properties.

Graphical abstractBinuclear 3,5-dinitrobenzoates of lanthanides form stable charge transfer (CT) adducts with N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), [Ln2(O2CC6H3(NO2)2)6(DMSO)4]·TMPD·2MeCN and [Ln2(O2CC6H3(NO2)2)6(DMSO)4]·3TMPD (Ln = Tb, Dy, Ho, Er, Y). CT adds paramagnetic contribution to the compounds and determines their 3D-supramolecular structures. In the absence of TMPD coordination polymers [Ln(O2CC6H3(NO2)2)3(DMSO)2]n (Ln = Tb, Dy) and [Ln(O2CC6H3(NO2)2)3(DMSO)]n·nMeCN (Ln = Ho, Er, Y) are formed.Figure optionsDownload full-size imageDownload as PowerPoint slide