3-Methyl-4-nitropyridine N-Oxide (POM) is an efficient nonlinear optical organic material having a high nonlinear coefficient and achieving the parametric emission process within the desired spectral range (1–2 μm). POM crystallizes in the orthorhombic class, space group P212121, and point group 222. It is a positive biaxial crystal. It melts at 136°C and the nonlinear coefficient is deff=10 pm/V[1]. This compound exhibits a negative-linear-compressibility (NLC) region as well as exceptionally large positive thermal expansion. The initial compression of the weak supramolecular network in the molecular POM crystal is analogous to the hydrostatic responses of the framework crystals with much stronger cohesion forces. 3-Methyl-4-nitropyridine N-Oxide is a commercial NLO material for pico- and femtosecond optics in the near-IR range[2].