Vibrational Spectrum and Structure of Metal-Cyanide Complexes in the Solid State. IV. K3Cu(CN)4

The polarized infrared spectrum of single crystals of K3Cu(CN)4 has been observed. The fundamental frequencies of Cu(CN)4—3 under point group Td have been assigned as 2094, 288, 324, 63, 2079, 364, 306, 74, and 250 cm—1. From these frequencies, valence force symmetry force constants were calculated. Both the CN and CuC stretching force constants were found to be quite low (16.2 and 1.3 md/A, respectively). The CuC force constant, along with Badger's rule, gives a CuC distance of 2.05 A, somewhat shorter than the single bond distance of 2.12 A, predicted from the tetrahedral radii.