Manganese 3d and 4s electron-density distribution in phthalocyaninatomanganese(II)

Abstract

A new analysis of the 116 K single-crystal X-ray diffraction data set of good accuracy on β-phthalocyaninatomanganese(II) has yielded individual 3d and 4s orbital populations on the manganese atom of significant accuracy and qualitative estimates of bonding electron density in the macrocycle ring. The manganese orbital populations (x and y along Mn–N vactors, z perpendicular to the square plane of co-ordinated nitrogen atoms) have been determined by a least-squares refinement procedure as dxy1.5(2), dxz0.6(2), dyz0.7(2), dz20.9(2), dx2–y20.1(2), and 4s2.0(3). Difference-Fourier syntheses indicate the aspherical nature of the valence charge density on the manganese atom, and the presence of bonding charge density in the ligand. In the later stages of the structural and orbital population analyses, allowance was made in the scattering model for overlap charge density by placing small spherical charges of variable population and radial extent between C–C and C–N atom pairs and in the Mn–N vectors. The present treatment of the data differs from the previous analysis in that refinement of atomic positional and thermal parameters has been based upon intensities (I), and all 2 265 observations with (sinθ)/λ⩽ 0.662 Å–1, rather than on structure factor amplitudes (|F|) and only the 1 608 reflections with I > 3σ(I). Full-matrix least-squares refinement on the basis of a spherical atom model yielded R 0.045, and bond lengths and angles of improved accuracy are reported. The atomic positional and thermal parameters thus obtained have been used to generate a set of ‘difference structure factors,’Fd, containing, principally, information about the valence charge density on the manganese atom. These Fd values have been analysed by least-squares refinement in terms of aspherical density arising from 3d and 4s orbital populations on the manganese atom. The present analysis has established that worthwhile information on chemical bonding in a molecule as large as a transition-metal macro-cycle can be obtained from a low-temperature X-ray data set of good quality, and acts a guide for a program to involve the collection of low-temperature data sets of excellent quality for this purpose.