An ab initio computational study of the properties of weakly bound hydrogen-bonded dimers of HKrCl and the small molecules N-2, CO, and HF was undertaken at the MP2/6-311++G(2d,2p) level of theory. These complexes, the linear N-2.HKrCl and OC.HKrCl dimers, and the nonlinear HF.HKrCl dimer, were found to have large blue shifts of the H-Kr stretching frequency, accompanied by a decrease in the infrared intensity of the stretching mode and compression of the H-Kr bond. We examine the charge density reorganization within the HKrCl molecule on complexation and offer an explanation for these unusual vibrational results. (C) 2003 American Institute of Physics.