Alkaloids as Ligands. 1. Synthesis and Characterization of Three Cobalt(II) Pseudohalide Compounds Containing L-sparteine

The alkaloid l-sparteine (sp) combines with cobalt(II) cyanate, thiocyanate, and selenocyanate to form pseudotetrahedral, N-bonded four-coordinate complexes of the type Co(sp)(NCX) ₂ (X = O, S, or Se). Their electronic spectra indicate that Co(Sp)(NCSe) ₂ is nearly tetrahedral whereas Co(sp)(NCO) ₂ and Co(Sp)(NCS) ₂ ·1/2H ₂ O are more severely distorted from tetrahedral geometry. This distortion is observed in the low-symmetry splitting of the ν ₂ and ν ₃ ligand field transitions which is ca. twice as large in the isocyanate and isothiocyanate complexes as in the isoselenocyanate complex which exhibits a splitting of ca. 2000 cm ^-1 for ν ₂ and 1000 cm ^-1 for ν ₃ . Apparently the isoselenocyanate complex maintains a nearly regular tetrahedral geometry by changing the conformation of the A ring of l-sparteine from the chair to the boat conformation. Pseudohalide stretching and bending modes are identified and found to be similar to those of other complexes containing nitrogen-coordinated pseudohalides. For the isocyanate, isothiocyanate, and isoselenocyanate compounds cobalt-tertiary nitrogen stretching frequencies are 465, 498, and 473 cm ^-1 , respectively. Below 400 cm ^-1 two cobalt-pseudohalide nitrogen stretching bands for each compound are identified.