In this study, a new cobaltous-(hexamethylenetetramine) [meso-tetra(para-methoxyphenyl)porphyrin complex with the formula [CoII(TMPP)(HMTA)] (I) was synthesized. The molecular structure was confirmed in solution by 1H NMR spectroscopy and mass spectrometry methods, and the single crystal X-ray diffraction structure of (I) was determined at both room temperature and low temperature. This species was further characterized by infrared, UV-visible and fluorescence spectroscopies, magnetic susceptibility measurements and cyclic voltammetry. The chemical reactivity behavior was also assessed theoretically through Density Functional Theory (DFT) approach. Magnetic investigation indicates that the Co(II)-HMTA porphyrin (I) species at low temperature is a cobaltous low-spin (S~=~1/2) species while at high temperature complex (I) exhibits a spin-crossover low-spin (S~=~1/2) ↔ high-spin (S~=~3/2). The adsorption kinetic of the ``vat yellow 1 dye'' was carried out in aqueous solution at pH~=~6. The experimental results are better fitted using the pseudo second order model. Furthermore, complex (I) was tested as catalyst in the degradation of the vat yellow 1 dye using an aqueous H2O2 solution and by photodegradation under solar light.