Comment on the paper by R. Sankar, R. Muralidharan, C.M. Rahgavan, R. Mohan Kumar, R. Jayavel, “Synthesis, growth, and characterization of nonlinear optical material L-arginine iodate crystal”, Materials Letters 62(1), 133–136 (2008) A.M. Petrosyan ⁎ Molecule Structure Research Center, NAS of Armenia, 26 Azatutyan Avenue, 0014 Yerevan, Armenia Received 6 December 2007; accepted 26 February 2008 Available online 4 March 2008 Abstract It is shown that the crystal L-arginine diiodate (L-Arg·2HIO 3 ) in contrary to the statement of the authors of the title paper has not been prepared and grown by the authors for the first time. Respective references are specified. © 2008 Elsevier B.V. All rights reserved. Keywords: Nonlinear optical crystals; L-arginine iodates The title attracted my attention because L-arginine iodate (L-Arg·HIO 3 ) was prepared by Monaco et al. [1] in the form of non-crystallizing fine powder. However, from the Abstract I learned that the authors in fact synthesized, grew and investigated L-arginine diiodate (L-Arg· 2HIO 3 ) and I was surprised that the authors declared that this crystal was grown by them for the first time. Acquaintance with the text of the paper caused even more questions. 1) In the Introduction the authors write: “L-arginine iodate, L-arginine formate, and L-arginine glutamate were formed as extremely fine powders (10) . The aim of the present work was to grow large-sized single crystals of L-Arg-2HIO 3 from its aqueous solution…”. It is not clear from where the authors know that in addition to L-arginine iodate also L-arginine diiodate exists and it can be grown as large-sized crystals. 2) In Fig. 1 the picture of as-grown L-Arg·2HIO 3 is shown, and in Fig. 2 the morphology of the same crystal is shown. However, the ratio of linear sizes of the crystals in Figs. 1 and 2 mismatch with each other. 3) In Section 5.1 crystallographic data are provided. How- ever, the calculated value 2.509 g/cm 3 can not be obtained from the provided crystallographic data (molecular weight = 426.88 g, Z =4, V = 1383.04 Å 3 ). The calculated value leading from these data is 2.049 g/cm 3 . 4) In Section 5.2 the authors mention the group COO - , which is characteristic for L-Arg + cation and COOH group, which is characteristic for L-Arg 2+ cation. Then they write that it is difficult to determine with certainty the presence or absence of water molecules on the basis of the IR spectrum alone. After that it is not clear how the authors found that the composition of the crystal is L-Arg·2HIO 3 , i.e., anhydrous and with 1:2 ratio. 5) In the Conclusion, the authors write that the density of the grown crystals is evaluated to be 2.409 g/cc from crystal- lographic data and verified by experimental method. How- ever, this value is in agreement neither with 2.509 g/cm 3 nor with 2.049 g/cm 3 . It is possible to assume that there is a misprint, especially in case of taking into account the fact that there are other misprints in the article. For example, in the Introduction it should be 1 pm/V instead of 41 pm/V and 15 J/cm 2 instead of 415 J/cm 2 . By analogy it is possible to assume that there is a misprint also in the value of molecular weight and it should be 526.88 g/mol instead of 426.88 g. Available online at www.sciencedirect.com Materials Letters 62 (2008) 3305 – 3306 www.elsevier.com/locate/matlet DOI of original article: doi:10.1016/j.matlet.2007.04.107. ⁎ Tel.: +374 10 285139; fax: +374 10 282267. E-mail address: apetros@msrc.am. 0167-577X/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2008.02.066