The infrared spectra of the isomeric complexes [Co(DH)2(py)(NCS)] and [Co(DH)2(py)(SCN)] (DH ˭ dimethylglyoximate anion, py ˭ pyridine) and their py-15N-, py-d5- and15NCS-labelled derivatives have been determined. Band assignments are based on the shifts incurred by labelling and on previous labelling studies applied to the complexes [Co(DH)2(py)X] (X ˭ CH3, Cl, Br, I).vCo-N(py) occurs at 464 cm−1in both complexes with an additional band at 450 cm−1in the isothiocyanate complex, whilevCo-N(DH) appears at 513 cm−1in both complexes.vCo-NCS occurs at 377 cm−1in the isothiocyanate complex whilevCo-SCN appears at 356 cm−1in the thiocyanate complex.