Transition series electronic structure

Our focus is on the most comprehensively studied series, the monophosphides of the first-row transition metals, whose structures successively distort from NaCl-type (ScP) to TiAs-type (TiP), NiAs-type (VP), MnP-type (CrP, MnP, FeP, CoP), and NiP-type, forming stronger metal-metal and phosphorus-phosphorus bonding with greater electron count (Fig. 11) [63-65], The P atoms are six-coordinate, but... 

An important advantage of ECP basis sets is their ability to incorporate approximately the physical effects of relativistic core contraction and associated changes in screening on valence orbitals, by suitable adjustments of the radius of the effective core potential. Thus, the ECP valence atomic orbitals can approximately mimic those of a fully relativistic (spinor) atomic calculation, rather than the non-relativistic all-electron orbitals they are nominally serving to replace. The partial inclusion of relativistic effects is an important physical correction for heavier atoms, particularly of the second transition series and beyond. Thus, an ECP-like treatment of heavy atoms is necessary in the non-relativistic framework of standard electronic-structure packages, even if the reduction in number of... 

The structures of metal-complex dyes, which must exhibit a high degree of stability during synthesis and application, is limited to certain elements in the first transition series, notably copper, chromium, iron, cobalt and nickel. The remaining members of the transition series form relatively unstable chelated complexes. The following description of the influence of electronic structure, however, is applicable to all members of the series. 

As for the possible correlation between geometry and electronic structure, consider the variation of ionic radii with atomic number in the first row transition metal series If the points for Ca, Mn, and Zn are connected, i. e., for atoms with a spherically symmetrical distribution of d electrons, the ionic radii of the other atoms are smaller than interpolation would yield from the Ca-Mn-Zn line. The nonuniform distribution of d electrons around the nuclei is assumed to be the reason for this contraction of the ionic radii. The data available so far on the bond lengths for the vapor-phase dichlorides are seen in Fig. 8. 

Table II I4I, 149-162) consists of a summary of 9-factors, D values and hyperfine coupling constants observed for ions of the first transition series. A molecular orbital (MO) treatment of the metal ion and ligand orbitals has been discussed by Stevens 163) and Owen 164) to account for covalent bonding and resulting hyperfine structure from hgands of transition element ions. Expressions derived for g-factors and hyperfine coupling constants from a MO treatment allow an estimation of the amount of charge transfer of metal electrons to ligand orbitals. Owen 164) has given a MO treatment of Cr +, Ni++ and Cu++ assuming no t bonding.

In the present paper we demonstrated the feasibility of a semiempirical description of electronic structure and properties of the Werner TMCs on a series of examples. The main feature of the proposed approach was the careful following to the structural aspects of the theory in order to preclude the loss of its elements responsible for description of qualitative physical behavior of the objects under study, in our case of TMCs. If it is done the subsequent parameterization becomes sensible and successful solutions of two long lasting problems semi-empirical parameterization of transition metals complexes and of extending the MM description to these objects can be suggested. 

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