Novel Mixed-Valence Manganese Cluster with Two Distinct Mn₃(II/III/II) and Mn₃(III/II/III) Trinuclear Units in a Pseudocubane-like Arrangement

Abstract

The reaction between Mn(ClO 4) 2 and di-(2-pyridyl)-ketone in the presence of the sodium salt of propanediol as a base in MeOH leads to the formation of a hexanuclear manganese cluster. This cluster has been characterized by the formula [Mn(II) 3Mn(III) 3O(OH)(CH 3pdol) 3(Hpdol) 3(pdol)](ClO 4) 4 ( 1). Molecular conductance measurements of a 10 (-3) M solution of compound 1 in CH 3CN, DMSO, or DMF give Lambda m = 529, 135, or 245 muS/cm, respectively, which suggests a 1:4 cation/anion electrolyte. The crystal structure of hexanuclear manganese cluster 1 consists of two distinct trinuclear units with a pseudocubane-like arrangement. The trinuclear units show two different valence distributions, Mn(II)/Mn(III)/Mn(II) and Mn(III)/Mn(II)/Mn(III). Additional features of interest for the compound include the fact that (a) two of the Mn(III) ions show a Jahn-Teller elongation, whereas the third ion shows a Jahn-Teller compression; (b) one bridge between Mn(III) atoms is an oxo (O (2-)) ion, whereas the bridge between Mn(II) and Mn(III) is a hydroxyl (OH (-)) group; and (c) the di-(2-pyridyl)-ketone ligand that is methanolyzed to methyl-Hpdol and R 2pdol (R = CH 3, H) acts in three different modes: methyl-pdol(-1), Hpdol(-1), and pdol(-2). For magnetic behavior, the general Hamiltonian formalism considers that (a) all of the interactions inside the two "cubanes" between Mn(II) and Mn(III) ions are equal to the J 1 constant, those between Mn(II) ions are equal to the J 2 constant, and those between the Mn(III) ions are equal to the J 3 constant and (b) the interaction between the two cubanes is equal to the J 4 constant. The fitting results are J 1 = J 2 = 0.7 cm (-1), J 3 approximately 0.0, J 4 = -6.2 cm (-1), and g = 2.0 (fixed). According to these results, the ground state is S = 1/2, and the next excited states are S = 3/2 and 5/2 at 0.7 and 1.8 cm (-1), respectively. The EPR spectra prove that the spin ground state at a low temperature is not purely S = 1/2 but is populated with the S = 3/2 state, which is in accordance with the susceptibility and magnetization measurements.

Synthesis and characterization of homo- and heterovalent tetra- hexa- hepta- and decanuclear manganese clusters using pyridyl functionalized β-diketone, carboxylate and triethanolamine ligands

“…The six manganese sites lie in a near planar arrangement. Topological similarites can be drawn with hexanuclear clusters reported by Dimitrakopoulou et al 18 and Chakov et al 19 which have oxidation state distributions of Mn II 3 Mn III 3 and Mn III 6 respectively. In 2 the eight dppdligands that stabilize the core adopt two different modes of bonding.…”

Computational studies of the magneto-structural correlations in a manganese dimer with Jahn–Teller distortions

“…12,13 Ferromagnetic coupling has been reported for dimers with both Mn III centres in JT compressed coordination environments. 11,15,16 Literature examples containing both Jahn-Teller elongated and compressed octahedra in the same compound are rare, [17][18][19][20][21][22][23][24][25][26][27] with few reports of discrete complexes possessing both types of distortion. 17,18 As such, the effect of having both elongation and compression distortions on the magnetic exchange between two Mn III centres has not yet been determined.…”

“…11,15,16 Literature examples containing both Jahn-Teller elongated and compressed octahedra in the same compound are rare, [17][18][19][20][21][22][23][24][25][26][27] with few reports of discrete complexes possessing both types of distortion. 17,18 As such, the effect of having both elongation and compression distortions on the magnetic exchange between two Mn III centres has not yet been determined. Among our group's work on derivatised salicylaldoximes, [28][29][30][31][32][33][34] the crystal structure of a complex featuring two manganese coordination centres in distorted octahedral environments: one elongated and the other compressed was obtained (Fig.…”

Structure and magnetism of decanuclear and octadecanuclear manganese(II/III) triethanolamine clusters

“…A brief search of the literature led us to find only one further example of J-T compression in a manganese cluster. 31 The outer three Mn II atoms are seven co-ordinate and display a capped trigonal prismatic geometry with an average bond length for Mn II -O of 2.24 A ˚and Mn II -N of 2.36 A ˚. In previous examples of di-and trivalent manganese, 14,23,26 iron 27a and cobalt 28a,b clusters containing only the M 7 disc-like core, the central M II atom has been six coordinate and surrounded by six m 3 oxygen atoms.…”