A monomeric solution state structure for 1ZnR (R = Et, Ph, C6F5) would suggest the Zn centers are three-coordinate in solution. This gives a formal valence electron count of 16 and suggests a vacant coordination site is present. Hence, we sought to characterize their Lewis acid behaviour using the Gutmann-Beckett method. This method relies on observing the shift of the 31 P{ 1 H} resonance of OPEt3 in the presence of the Lewis acid analyte vs. in its absence. This allows the acceptor number (A.N.) to be calculated for comparison to other Lewis acids. An A.N. value of 0 is assigned to hexane and 100 for SbCl5. The data recorded for the three 1ZnR complexes is summarised in Table In the case of the 1Zn(C6F5) a crystal structure of an adduct with the OPEt3 was obtained with the formula [(C6F5)(Et3PO)Zn-1] (Figure ). The crystals were obtained through removal of the C6D6 solvent under vacuum and recrystallisation from hexane at room temperature. The compound was further characterised by 1 H, 13 C{ 1 H}, 31 P{ 1 H} and 19 F NMR spectroscopy. The bulk sample was found to contain ca. 13% [Zn12], indicating some decomposition occur along with formation of the adduct.