By using the semiempirical MO methods, we study the molecular shapes and molecular orbital interactions in $Zr(TPP)_2$, one of metal - porphyrin sandwich complexs which have drawn great attention in recent years because of the similarities in their spectroscopic properties with those of the bacteriochlorophyll dimer in the photosynthetic reaction center. The major factor which determines the degree of dome - shape is the ionic radius of central metal, and the strength of electrostatic repulsion between nitrogens on the two $TPP_2$ fragments decides the magnitude of twist angle in metal - porphyrin sandwich complexes. Energies of molecular orbitals in porphyrin monomer depend upon the electronegativity of substituents on the meso - carbon. The magnitude of $\pi-\pi$ interaction between the orbitals of two $TPP_2$ fragments depends upon the shape of $(TPP)_2$ fragment. The magnitude of $\pi-\pi$ interaction decides the ordering of molecular orbitals in metal - porphyrin sandwich complexs.
