International Journal of Mass Spectrometry and Ion Processes, I 17 (1992) 47- 63 Elsevier Science Publishers B.V., Amsterdam 47 Positive ion chemistry of gaseous boric and polyboric acids* Marina Attind”, Fulvio Cacace”, Felice Grandinettib, Giorgio Occhiuccib and Andreina Ricci” “University of Rome “La Sapienza”. 00185 Rome (Italy) bIstituro di Chimica Nucleare del CNR, Monlerotondo Stazione, 00016 Rome (Italy) (First received 6 December 1991; in final form 12 February 1992) ABSTRACT The positive ion chemistry of H,BO, has been studied by chemical ionization (CI) and Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. From the results of equilibrium and “bracketing” experiments, the gas-phase basicity (GPB) and the proton affinity (PA) of H,BO, are estimated to be 167.8 f 0.5 and 176 + 2 kcal mol-’ respectively. The latter value is in fair agreement with the PA of 181.2 kcalmol-’ from MO SCF calculations at the MP3/6-3lG**//6-31G* + ZPVE (6-3lG*) level of theory. The PA of HBO, calculated at the MP4(SDTQ)/6-31G**//6-31G* + ZPVE (6-3IG*) level is 181.2 kcal mol-’ , which falls within the interval set by ICR “bracketing” experiments. The H,BO: ion undergoes condensation with H, BO, yielding protonated polyboric acids containing up to seven B atoms belonging to three different classes, (H,+,B,O,+,)H+, (H,B,O,)H+ and (H,_,B,O,_,)H+, formed via sequences established by FT-ICR experiments involving isolation of the ionic reactants by multiple resonance. The structures of the polyions observed are discussed and compared to those of the correspond- ing anions, also observed in the gas phase, and of the few anions whose structures have been established in crystalline borates. The fast isotope exchange with H,‘80 undergone by H,BO: suggests that the H,BO,+ ion observed in the CI spectra of H,BO, may contain a tetrahedrally coordinated B atom, as present in many borate and polyborate anions. The reactions of H,BO, and/or of H,BO: with MeOH and HCOOH, yielding protonated esters, respectively anhydrides, of boric and polyboric acids are surveyed. Keywords: boric acid; chemical ionization; gas-phase basicity; ICR, proton affinity. INTRODUCTION In contrast with the numerous studies on boric and polyboric acids and anions in the solid state and in solution [ 1,2a], their gas-phase ion chemistry is largely unexplored. In fact, mass spectrometric studies have been focused on analytical aspects, i.e. the determination of the isotopic composition of boron from the “B/“B ratio measured in Na,BOl and BO; ions [3-61, analysis of traces of boron in metals and alloys based on the formation of BO; ions [7], Correspondence to: F. Cacace, University of Rome “La Sapienza”, 00185, Rome, Italy. * Dedicated to Professor Charles H. DePuy on the occasion of his 65th birthday. 0168-I 176/92/$05.00 0 1992 Elsevier Science Publishers B.V. AI1 rights reserved.