Electron deformation density in titanium diboride chemical bonding in TiB2

Titanium diboride, TiB2, crystallizes in the AlB2-type structure, hexagonal P6/mmm. The conventional, free atom crystal structure refinement led to R = 2.23%, and including extinction corrections to R = 1.58%. Multipole refinements with multipoles up to order four (hexadecapole) reduced the R value to 1.21 %. Difference density maps revealed charge deficiencies on the boron sites and broadbands of charge accumulations between the boron atoms indicating a graphitic B-delocalization of the boron sp(2) hybrid orbitals. (C) 2003 Published by Elsevier Inc.