Cobalt-59 NMR and X-ray diffraction studies of hydrated and dehydrated (+/-)-tris(ethylenediamine) cobalt(III) chloride

Cobalt-59 NMR experiments have been carried out on single-crystal and polycrystalline (powder) samples of (+/-)-tris(ethylenediamine)cobalt(III) chloride trihydrate, (+/-)-Co(en)(3)]Cl(3) x 3H(2)O, and of its dehydrate. In addition, the X-ray crystal structure of the dehydrated sample has been determined. X-ray diffraction measurements confirm a long-held assumption that dehydration has only minor effects on the structure of the Co(en)(3)](3+) cation. Nevertheless, these small differences have a detectable effect on the 59Co nuclear magnetic resonance properties of these compounds; in particular, the nuclear quadrupole coupling constant, C(Q). Straightforward identification of the c-axis for large single crystals of (+/-)-Co(en)(3)]Cl(3).3H(2)O and of its dehydrate allowed us to obtain single-crystal 59 Co NMR data by orienting the crystals in an MAS rotor. Data collected on single crystals and polycrystalline samples indicate that C(Q)=-3.05+/-0.05 and -2.80+/-0.05 MHz for the hydrated and dehydrated samples, respectively; the signs have been assigned on the basis of a point charge model. The chemical shift tensor principal components were also determined: for the hydrated sample, delta(perpendicular)=7281+/-2 ppm, delta(parallel)=7004+/-4 ppm and delta(iso)=7189 ppm; for the dehydrated sample, delta(perpendicular)=7288+/-2 ppm, delta(parallel)=7008+/-4 ppm and delta(iso)=7195 ppm. The electric field gradient and chemical shift tensors are axially symmetric, as required by crystal symmetry.