Vibrational Spectrum and Structure of Metal-Cyanide Complexes in the Solid State. III. Hg(CN)2

Abstract

The infrared spectra of solid Hg(CN)₂ and the mono‐ and di‐substituted C¹³ and N¹⁵ species have been observed. The polarized spectrum of a single crystal of the normal species was also observed. The seven fundamental vibrations of the linear, symmetric Hg(CN)₂ molecule have been assigned at 2192, 415, 2193.5, 442, 276, 341, and ca 100 cm^—1. From the observed frequencies of the normal and isotopic species, force constants were calculated for two possible structures: N–C–Hg–C–N and C–N–Hg–N–C. It is shown that the latter structure gives unreasonably large values for the CN stretching force constant (> 20 md/A) and the CN, HgN interaction constant (∼2.4 md/A), while the former structure yields quite reasonable force constants, namely: Fcn=17.6, Fhgc=2.61, Fcn, c′n′=—0.1, Fhgc, hgc′=0.1, and Fhgc, cn=0.1 md/A. These results are presented as strong evidence that the cyanides are bound to the mercury through carbon atoms.