Electronic structure of a paramagnetic {MNO}6 complex: MnNO 5,5-tropocoronand

Journal Article

Using density functional theory (OLYP/STO-TZP) calculations, we have investigated the electronic structure of [Mn(5,5-tropocoronand)(NO)], a rare paramagnetic {MNO}6 complex. Experimental methods, including magnetic susceptibility measurements and high-field electron paramagnetic resonance spectroscopy, have not provided an unambiguous spin state assignment for this complex. In other respects, however, the compound was fully characterized, including by means of single-crystal X-ray structure determination. The optimized S = 1 OLYP geometry reproduced all key aspects of the trigonal-bipyramidal molecular structure, including a short Mn-N(O) distance (∼1.7 Å;) and an essentially linear MnNO angle. In contrast, the S = O and S = 2 optimized structures disagreed with the crystal structure in critical respects. Moreover, three different exchange-correlation functionals (OLYP, B3LYP, and B3LYP) indicated an S = 1 ground state by a clear margin of energy. An examination of the Kohn-Sham MOs of this state indicated a primarily d xz2/dyz2dxy1dx2-z21 electronic configuration, where the z axis is identified with the nearly linear MnNO axis. The y2 orbital is formally unoccupied in this state, interacting, as it does, head-on with two tropocoronand nitrogens lying along the y axis, the pseudo-3-fold axis of the trigonal bipyramid. The doubly occupied dxz and dyz orbitais are in actuality dπ(Fe)-π(NO)-based π-bonding molecular orbitais, the a and ß "components" of which are significantly offset spatially. This offset results in excess minority spin density on the NO unit. Thus, the OLYP/TZP atomic spin populations are Mn, 2.85; N(O), -0.52; and O, -0.35. © 2010 American Chemical Society.

Full Text

Duke Authors

Cited Authors

  • Tangen, E; Conradie, J; Franz, K; Friedle, S; Telser, J; Lippard, SJ; Ghosh, A

Published Date

  • 2010

Published In

Volume / Issue

  • 49 / 6

Start / End Page

  • 2701 - 2705

PubMed ID

  • 20166686

International Standard Serial Number (ISSN)

  • 0020-1669

Digital Object Identifier (DOI)

  • 10.1021/ic901860x