Raman and Infrared Spectra of the Dicyanamide Ion

Abstract

The dicyanamide or dicyanimide ion (NsaC-N-C=N)-is isoelectronic with carbon suboxide and therefore might exist + in a linear resonance form (N-=C=N=C=N-) having the same double bond array as the latter. A comparison of the infrared with Raman spectra should show at once whether this ion is linear or bent, since the linear form would have a center of symmetry and there would therefore be no coincidence in absorption between the two types of spectra.The IR spectrum of this ion has been investigated at the American Cyanamide Corporation laboratories [1], and since this work was completed, Kuhn and Mecke [2] have reported the IR spectra in the NaCI and KBr regions of a number of salts. Since quite low values for bending frequencies for nitrile compounds have been reported [4][5][6], and the Raman spectra of a solution of the sodium salt showed indications of a broad line at 170 cm -1, the infrared measurements were carried out to 100 cm-1 on the instrument at MIT built by Lord and Mc Cubbin [7].EXPERIMENT AL Sodium dicyanamide was the principal salt used in this investigation. Two samples were prepared: one from sodium cyanamide and cyanogen bromide according to the method of Madelung and Kern [8] and the other from zinc dicyanamide kindly supplied by the American Cyanamide Corporation. The spectra of the two samples were identical.Infrared spectra in the CaF 2, NaCI, and KBr regions were run on a Baird Associates Model A double-beam instrument using both nujol mulls and KBr pellets. For the spectra at frequencies below 425 cm-1 , the sodium dicyanamide was dispersed in polyethylene.

Pressure-Induced Polymerization of LiN(CN)2

“…Reckeweg et al reported this mode at 682 cm −1 , whereas Perkins observed this mode at 671 cm −1 for the Na salt. 21,40 We tentatively assign the ν 4 symmetric bending mode at 227 cm −1 on the basis of comparison of Raman intensity with our calculations. However, two additional bands are observed at 206 and 240 cm −1 , and calculations reveal that they both have character similar to that of ν 4 (symmetric bending).…”

“…The CN symmetric stretching mode (ν 2 ) was observed in the IR and the Raman at 944 and 943 cm −1 , respectively, and is in general agreement with our calculations and the previous study by Reckeweg et al 21 For the Na salt, the CN symmetric stretch was observed at 937 cm −1 (Raman) and 931 cm −1 (IR). 40 The CN asymmetric stretch (ν 8 ) was observed in the IR at 1346 cm −1 , but not observed in the Raman where it could possibly be obscured by the strong T 2g diamond phonon near 1333 cm −1 . The calculated frequency of the CN asymmetric stretching mode at 1422 cm −1 is significantly shifted from the observed position and the origin of this discrepancy is presently unclear.…”

“…This assignment is in agreement with our calculations (2235 cm −1 ) and comparable with the symmetric stretch of Na dicyanamide of 2225 cm −1 reported by Perkins. 40 The shift observed between Li and Na dicyanamides can be explained by differences in cations and through crystal structure effects. Our assignment is in contrast with Reckeweg et al, who reported the symmetric CN stretch at 2305 cm −1 ; the mode observed by Reckeweg et al at 2236 cm −1 was assigned to a combination of CN symmetric and asymmetric stretching modes.…”

“…Reckeweg et al 21 reported the CN asymmetric stretching mode at 2168 cm −1 , which is in agreement with this work, whereas this mode was observed at 2174 cm −1 for the Na analogue (Perkins). 40 For the isolated C 2v molecule, the symmetric (A 1 ) and asymmetric (B 2 ) CN stretching modes are active in both the Raman and IR. In the solid state, these modes are split into A g , A u , B g , and B u components, but the Raman and IR frequencies remain nearly coincident.…”

The Raman and infrared spectra of the dicyanoiodate (I) ion

“…However, several of the 18 post-transition elements have well-established binary cyanides, and the present work is concerned with the characterization of a complex cyanide of iodine, the dicyanoiodate ion [I(CN)J, which is derived from the binary cyanide, iodine cyanide, ICN. Apart from the dicyanamide ion [N(CN)2]-already referred to, the only other dicyano complex ions known are those of the transition metals, Cu(I), Ag (1) and Au (1). The [Ag(CN)J and [Au(CN)~]-ions are known to be linear in their solid potassium salt^,^" but unexpectedly the [Cu(CN)J ion is bent and three-coordinate in its solid potassium salt.…”