AbstractDiazadiene metal tetracarbonyls, DAD M(CO)4, (M = Cr, Mo, W; DAD = R-N = CH-CH = NR with aliphatic and aromatic substituents R) show equidistribution of one labelled CO when synthesized from fac-DAD M(CO)3(CH3CN) as a consequence of intramolecular CO site exchange. The structures of two Mo-complexes (1: R = iso-propyl; 2: R = 2,6-diisopropylphenyl) with DAD's of different bulkiness have been solved by X-ray methods. From the infrared solution spectra, including those of isotopically labelled (13CO, C18O) compounds, all of the force constants k1, k2, ktt, kcc and kcc have been calculated independently. The ratios of interaction force constants deviate sharply from Cotton-Kraihanzel assumptions, perhaps because of the substantial deviation of the iraws-pair of CO groups from linearity (1: 154.5°, 2: 147.9°). The solid state N-Mo, Mo-C and C - O bond lengths are neither in agreement with the generally accepted picture for donor/acceptor influences nor with typical IR data and force constant interpretations. (2 with higher v(CO) and k1, k2 has the longer CO bonds and shorter Mo-C bonds than 1.) The force constant sets have been used to calculate CO frequencies for over 60 labelled compounds with good accuracy (Δv < 2 cm-1).
The Raman spectra of Bis(hexamethylenetetramine)-iodine(I) and -bromine(I) perchlorates