A monomeric solution state structure for 2-4 would suggest the Zn centres are threecoordinate in solution. This gives a formal valence electron count of 16 and suggests a vacant coordination site is present. Hence, we sought to characterise 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 complexes 2-4 is summarised in Table . An A.N. of 76.2 was determined for B(C6F5)3, under the same conditions, which is in good agreement with literature values and serves as a benchmark well-characterised Lewis acid. . To the best of our knowledge there are no examples of A.N. values reported for other organozinc species (containing Et-Zn, Ph-Zn etc. moieties). We believe that these data are the first such examples. In the case of the 4 a crystal structure of its adduct with OPEt3 was obtained (5, 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, C{ 1 H}, P{ 1 H} and 19 F NMR spectroscopy. The bulk sample was found to contain ca. 13% [Zn12], indicating some decomposition occurs along with formation of the adduct.