We present an analysis of the structural, energetic and spectral features associated with the different hydrogen bonded networks found in the first few acetylene-water clusters AW(n) (n = 1-4) from first principles calculations. Contrary to the predictions of an empirical interaction potential, acetylene is incorporated into a hydrogen bonded ring when it clusters with two or three water molecules. This structural pattern changes for n = 4 with the formation of a water tetramer interacting with acetylene. This structural transition from n = 3 to 4 is spectroscopically manifested by a qualitative change in the appearance of the infrared spectra of the corresponding global minima.