176 Mn3 triangles full IC

176 Mn3 triangles full IC - Inorg. Chem. 1997, 36,...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Synthesis and Magnetic Properties of Six New Trinuclear Oxo-Centered Manganese Complexes of General Formula [Mn 3 O(X-benzoato) 6 L 3 ](X ) 2-F, 2-Cl, 2-Br, 3-F, 3-Cl, 3-Br; L ) Pyridine or Water) and Crystal Structures of the 2-F, 3-Cl, and 3-Br Complexes Joan Ribas,* ,1a Belen Albela, 1a Helen Stoeckli-Evans, 1b and George Christou 1c Departament de Quı´mica Inorga `nica, Universitat de Barcelona, Diagonal, 647, 08028-Barcelona, Spain, Institut de Chimie, Universite ´ de Neucha ˆtel, Avenue de Bellevaux 51, CH-2000 Neucha ˆtel, Switzerland, and Department of Chemistry, Indiana University, Bloomington, Indiana 47405-4001 Recei V ed October 18, 1996 X The reaction of N- n -Bu 4 MnO 4 or NaMnO 4 with appropriate reagents in ethanol - pyridine leads to the high-yield formation of new mixed-valence trinuclear oxo-centered Mn III,III,II complexes of general formulation [Mn 3 O(X- benzoato) 6 L 3 ]( 1 ,X ) 2-fluoro, L ) pyridine; 2 ) 2-chloro, L ) pyridine; 3 ) 2-bromo, L ) pyridine; 4 ) 3-fluoro, L ) 2 pyridine + 1H 2 O; 5 ) 3-chloro, L ) 2 pyridine + 2 O; 6 ) 3-bromo, L ) 2 pyridine + 2 O). The crystal structures of 1 , 5 ,and 6 were determined. Complex 1 crystallizes in the monoclinic system, space group C 2/ c with a ) 15.774(2) Å, b ) 17.269(2) Å, c ) 21.411(2) Å, â ) 91.11(1) ° Z ) 4. Complex 5 crystallizes in the monoclinic system, space group P 2 1 / n with a ) 15.172(2) Å, b ) 17.603(2) Å, c ) 21.996(3) Å, â ) 106.300(10), and Z ) 4. Complex 6 crystallizes in the monoclinic system, space group P 2 1 / n with a ) 15.533(3) Å, b ) 17.884(2) Å, c ) 21.997(4) Å, â ) 106.95(1) ° Z ) 4. The three complexes are neutral and possess an oxo-centered Mn 3 O unit with peripheral ligands provided by bridging carboxylate and terminal pyridine or H 2 O groups. Each manganese ion is distorted octahedral, and consideration of overall charge necessitates a mixed-valence Mn II Mn III 2 description. In 1, the presence of a C 2 axis through the central O atom and one of the manganese atoms (Mn II ) and the absence of imposed symmetry elements in 5 and 6 (they have the two Mn III with a terminal pyridine group and the Mn II with a H 2 O terminal molecule) suggest a trapped-valence situation in all three cases. The Mn II is assigned on the basis of its longer metal - ligand distances. Variable- temperature magnetic susceptibility studies were performed on 1 - 6 in the temperature range 2 - 300 K. Satisfactory fits to the observed susceptibility data were obtained by assuming isotropic magnetic exchange interactions and using the appropriate spin Hamiltonian and susceptibility equation. The derived J and J* exchange parameters are all relatively small in magnitude, | J | < 10 cm - 1 . J characterizes the Mn II ‚‚‚ Mn III interactions and J* the Mn III ‚‚‚ Mn III interaction. Magnetization measurements at 2 K up to 50 kG indicate the variability of the ground state: S ) 3 / 2 for 2 and 3 ; S ) 1 / 2 for 1 , 4 5 ;and S ) 3 / 2 , 1 / 2 for 6 . X-band EPR spectra measured from 4 K to room temperature on polycrystalline samples of 1 - 6 show highly significant differences when the ground state is 3 / 2 or 1 / 2 .F o r S ) 3 / 2 complexes ( 2 and 3 ), there is a transition centered at g 4, which decreases in intensity with increasing temperature. For
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 9

176 Mn3 triangles full IC - Inorg. Chem. 1997, 36,...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online