Search

The use of methylalanine in manganese/calcium chemistry has led to the synthesis and characterization of the first manganese/calcium amino acid containing polynuclear clusters.

Ligand design remains key to the synthesis of coordination compounds possessing specific topologies, nuclearities and symmetries that direct targeted physical properties. N,O-chelates based on ethanolamine have been particularly prolific in constructing a variety of paramagnetic 3d transition metal complexes with fascinating magnetic properties. Here, we show that combining three ethanolamine moieties within the same organic framework in the form of the pro-ligand 1,3,5-tri(2-hydroxyethyl)-1,3,5-triazacyclohexane (LH3) leads to the formation of two highly unusual Mn wheels. Reaction of Mn(NO3)2·6H2O with LH3 in basic methanolic solutions leads to the formation of [MnIII12MnII4(μ3-O)6(μ-OH)4(μ3-OMe)2(μ-OMe)2(L)4(LH)2(H2O)10](NO3)6(OH)2 (1) and [MnIII10(μ3-O)4(μ-OH)4(μ-OMe)4(L)4(H2O)4](NO3)2 (2), the only difference in the synthesis being the ratio of metal:ligand employed. The structure of the former describes two offset [MnIII6MnII2] square wheels, linked through a common centre, and the latter a single [MnIII10] wheel twisted at its centre, such that the top half is orientated perpendicular to the bottom half. In both cases the L3−/LH2− ligands dictate the orientation of the Jahn-Teller axes of the MnIII ions which lie perpendicular to the triazacyclohexane plane. Direct current magnetic susceptibility and magnetisation data reveal the presence of competing exchange interactions in 1 and strong antiferromagnetic interactions in 2. Given the simplicity of the reactions employed and the paucity of previous work, the formation of these two compounds suggests that LH3 will prove to be a profitable ligand for the synthesis of a multitude of novel 3d transition metal complexes., CJM and TGT thank the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “First Call for H.F.R.I. Research Projects to support Faculty members and Researchers and the procurement of high-cost research equipment grant” (Project Number: 400). EKB thanks the EPSRC for financial support under grant reference numbers EP/I03255X/1 and EP/I031421/1. GL and ME thank the Ministerio de Ciencia e Innovación (RTI2018-094909-J-I00) and CSIC (PIE 201960E002).

Employment of H3L2 (=2-(β-naphthalideneamino)-2-hydroxyethyl-1-propanol) in manganese–lanthanide cluster chemistry has led to the isolation of two new isostructural tetrametallic [MnIII2MnIVLnIII] complexes (Ln = Gd, Dy), with the Dy analogue displaying temperature and frequency dependent out-of-phase signals, thus indicating possible single molecule magnetism behaviour.

The use of H3L (= 2-(β-naphthalideneamino)-2-hydroxymethyl-1-propanol) in mixed-metal manganese-lanthanide carboxylate cluster chemistry has led to the isolation of two new dodecametallic heteronuclear isostructural [Mn6(III)Ln6(III)] complexes (Ln = Gd, Dy), with the Dy analogue displaying temperature and frequency dependent out-of-phase signals suggesting possible single molecule magnetism behaviour.

Employment of H3L (= 2-(β-naphthalideneamino)-2-hydroxymethyl-1-propanol) in mixed-metal manganese-lanthanide cluster chemistry has led to the isolation of five new octametallic heteronuclear isostructural [MnIII6LnIII2] complexes. More specifically, the reaction of Mn(ClO4)2·6H2O with H3L and the corresponding lanthanide nitrate in MeCN in the presence of a base, NEt3, yielded four complexes with the general formula [MnIII6LnIII2O2(OH)2(H2O)2(HL)6(NO3)6]·6MeCN·0.5H2O (Ln: Gd, 1·6MeCN·0.5H2O; Tb, 2·6MeCN·0.5H2O; Dy, 3·6MeCN·0.5H2O; Er, 4·6MeCN·0.5H2O). Furthermore, the YIII analogue, [MnIII6YIII2O2(OH)2(H2O)2(HL)6(NO3)6]·6MeCN·0.5H2O (5·6MeCN·0.5H2O), was also synthesized in the same manner. All five clusters describe a central rod-like topology consisting of four face-sharing defective cubane metallic units, forming a planar hexametallic [MnIII4LnIII2] core, which is further capped by two MnIII ions. Dc magnetic susceptibility studies in the 5–300 K range for complexes 1–5 reveal the presence of dominant antiferromagnetic exchange interactions within the metallic clusters, while ac magnetic susceptibility measurements show temperature and frequency dependent out-of-phase signals for the DyIII analogue (3·6MeCN·0.5H2O), suggesting potential single molecule magnetism character. Furthermore, the YIII analogue yielded a diamagnetic ground-state for the [MnIII6] core, thus proving that the SMM character displayed by 3·6MeCN·0.5H2O is due to the presence of the DyIII centres.