Hyperfine interactions in aqueous solution of Cr3+:: an ab initio molecular dynamics study

We performed an ab initio molecular dynamics simulation of the paramagnetic transition metal ion Cr3+ in aqueous solution. Isotropic hyperfine coupling constants between the electron spin of the chromium ion and nuclear spins of all water molecules have been determined for instantaneous snapshots extracted from the trajectory. The coupling constant of first sphere oxygen, A(iso)(O-17(I)) = 1.9 +/- 0.3 MHz, is independent on Cr-O-I distance but increases with the tilt angle for the water molecule approaching 180 degrees. First sphere hydrogen spins have A(iso)(H-1(I)) = 2.1 +/- 0.2 MHz which decreases with increasing tilt angle and shows a Cr-H-I distance dependence. The hyperfine coupling constants for second sphere O-17 is negative and an order of magnitude smaller (-0.20 +/- 0.02 MHz) compared to first sphere.