Three-dimensional geometry, transition structure

Fig. 3. Fe(CO)4 cross section of the Jahn-Teller surface around a tetrahedral geometry (Td), which has a triply degenerate singlet electronic state. The surface is a two-dimensional cross section through the three-dimensional Jahn-Teller surface. There are four equivalent C2v minima connected via four equivalent Cs transition structures. The CASSCF CFeC angles are given to the left. Further C2v minima and Cs transition structures exist in the remaining orthogonal coordinate.

Some of the first metal complexes of squaric acid were synthesized by West and Niu(12). These complexes contained divalent transition metal ions such as Mn(II), Fe(II), Co(II), Ni(II), and trivalent metals such as Al(III), Fe(III), an Cr(III). The divalent metal complexes were initially assumed to have structure , but X-ray structural studies show that these metals form a three dimensional polymer network 5 with squaric acid(13). The trivalent complexes, however, are belived to have a dimeric structure 6, with uncoordinated oxygens (hereafter referred to as the diketosquarate derivatives) (12, 14, 15). In both the divalent and trivalent metal complexes, the geometry about the metal is octahedral (or approximately octahedral), which is the preferred geometry for these metal ions. 

Computer Model A three-dimensional finite element was developed using ANSYS software. Two elements were selected to represent the geometry 3-D 10-node tetrahedral structural solid element and 8-node structural shell element. The tetrahedral element is defined by 10 nodes having three transition degrees of freedom at each node. The shell element is defined by 8 nodes having three transitional and three rotational degrees of freedom at each node. The tetrahedral element was used to represent the verte-... 

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