The soln. structure of the two intimate ion pairs present in soln. for [PtMe(h2-olefin)(a-diimine)]BF4 compds. (1-3, shown as I.BF4, R = Ph, 4-MeC6H4, 4-CF3C6H4) their relative abundance and the consequent thermodn. equil. parameters were detd. by a quant. detection of H...F interionic dipolar interactions in the 19F,1H-HOESY NMR spectra. The tetrafluoroborate anion predominantly occupies the lower position relative to central chelate ring of I, being syn- to the R substituent of the alkene ligand (pseudo-cis, PC position). The possible reasons of domination of PC position of the anion are discussed with data of DFT and mixed quantum mechanics/mol. mechanics (QM/MM) calcns. for 1-3 and previously investigated I, R = Me (4). [on SciFinder (R)]