Comments on the paper: Crystal growth and comparison of vibrational and thermal properties of semi-organic nonlinear optical materials

Gunasekaran et al (Pramana J. Phys. 75 683-690 (2010)) report to have grown the nonlinear optical crystals urea thiourea mercuric chloride (UTHC) and urea thiourea mercuric sulphate (UTHS). We argue that UTHC and UTHS are dubious crystals and are not what the authors propose.