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Magnetostructural Studies on Tetranuclear Manganese [Mn III 2 Mn II 2 ] Complexes of 9‐Hydroxyphenalenone with Weak π···π Interactions
Author(s) -
Dey Suman Kr,
Honecker Andreas,
Mitra Partha,
Mandal Swadhin K.,
Mukherjee Arindam
Publication year - 2012
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201200800
Subject(s) - chemistry , crystallography , manganese , triclinic crystal system , monoclinic crystal system , carboxylate , crystal structure , ion , ionic radius , magnetic susceptibility , stereochemistry , organic chemistry
Two mixed‐valent tetranuclear Mn II/III complexes of formula [Mn 4 (L) 4 (OAc) 2 (OMe) 4 ] · 2H 2 O ( 1 ) and [Mn 4 (L) 4 (OAc) 2 (OMe) 4 ] ( 2 ), in which HL = 9‐hydroxyphenalenone, were synthesized by a solvothermal method and magnetostructurally characterized. Complex 1 crystallizes in the monoclinic space group P 2 1 / c with a = 12.69 Å, b = 15.51 Å, c = 15.40 Å, β = 114.35° and Z = 2. Complex 2 crystallizes in the triclinic space group P $\bar {1}$ with a = 8.74 Å, b = 12.06 Å, c = 13.89 Å, α = 114.23° β = 102.16°, γ = 98.54° and Z = 1. Both 1 and 2 are products of the same reaction and have the same molecular formula except for the solvent of crystallization. X‐ray crystallographic studies show that 1 and 2 have six coordinated Mn II and Mn III ions and almost the same tetranuclear core, which resembles a rhomboidal “butterfly motif” except that the Mn III ions are at the “wing‐tip” and Mn II ions in the “body” positions. The Mn II/III ions that form the metal core in 1 and 2 have two μ 3 ‐O alkoxo and four μ 2 ‐O alkoxo bridges along with two carboxylate anions that bridge the Mn II and Mn III centres situated at the “body” and the “wing‐tip” positions. Complex 1 shows intermolecular π ··· π and C–H ··· π interactions. Detailed direct current (DC) magnetic susceptibility studies in the temperature range 2–300 K suggest that 1 and 2 are antiferromagnetically coupled. The exchange coupling constants and g values were estimated by theoretical fitting of the magnetic susceptibility data. We find that it is difficult to determine a model with three different coupling constants ( J 1 , J 2 , J 3 ) unambiguously from the magnetic susceptibility data. Nevertheless, the bonding parameters of the metal core for 1 and 2 suggest a simplification to two exchange coupling constants ( J bb and J wb ) with a reasonably good fit. In addition, the theoretical fitting of the magnetic data when correlated to the structure shows good agreement for complexes with similar cores in the literature and it appears that the exchange coupling constants correlate with the solid angle formed by the μ 3 ‐O (alk)oxo bonded to the Mn II/III ions.