Theoretical characterization of the sulfilimine bond: Double or single?

Using quantum mechanical calculations in combination with AIM and NBO analyses, we investigate the properties of the sulfilimine bond, which has been recently detected in collagen IV [Vanacore et al., Science 325 (2009) 1230]. Contrary to the general belief that this is a double bond, –NS<, our analysis of the wavefunction of a model compound indicates it being a coordinate covalent (dative) single bond, –N ← S<, with a strong polarization towards nitrogen.