Chemical Equilibrium between Metalloporphyrins (MTPP and M(o-Cl)TPP) and Basic Ligands(L). (M = $Zn^{2+],\;Cu^{2+},\;Ni^{2+}$: TPP = tetraphenylporphyrin, (o-Cl)TPP = tetrakis (ortho-chlorophenyl)porphyrin: L = imidazole, pyridine, 1-methylimidazole, 2,6-