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

Abstract

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.Keywords: crystal growth; urea thiourea mercuric chloride; urea thiourea mercuric sulphate. CommentDuring the course of a literature survey of metal compounds containing both thiourea and urea ligands, the title paper by Gunasekaran et al [1] reporting on growth of so called urea thiourea mercuric chloride (UTHC) and urea thiourea mercuric sulphate (UTHS) crystals attracted our attention. For formulating these crystals, the authors did not take into consideration the known chemistry of Hg(II) towards thiourea

Comments on the paper “Growth and characterization of semi-organic nonlinear optical crystal: urea thiourea cadmium sulfate”

“…[5], while the 1:3 compound [Cd(tu) 3 (SO 4 )] crystallizes in the centrosymmetric triclinic space group Pī having unit cell parameters a = 8.77(2), b = 9.05(2), c = 9.83(1) Å , a = 91.3(2)°, b = 111.9(1)°, c = 95.5(2)° [6]. Although these data appear the closest to the cell reported (without any esd values) in the title paper, UTCS should be declared as a dubious crystal in view of (1) the absence of structure refinement details, (2) non-reporting of any chemical composition, and (3) claim of using equimolar ratios of CdSO 4 and tu for crystal growth. For a dubious crystal (UTCS), studies such as thermal analysis and NLO property are meaningless and hence are not commented.…”

“…Based on the IR spectrum, it can be concluded that the name 'urea thiourea cadmium sulfate' is inappropriate for the UTCS crystal. The same criterion namely the absence of the C=O vibration was used as evidence to prove the dubious nature of five other improperly characterized compounds (Table 1) claimed to contain both urea and thiourea [2][3][4].…”