Electrospray mass spectrometry of trans-[Ru(NO)Cl(dpaH)(2)](2+) (dpaH=2,2 '-dipyridylamine) and 'caged NO', [RuCl3(NO)(H2O)(2)]: loss of HCl and NO from positive ions versus NO and Cl from negative ions

The positive ion electrospray mass spectrometry (ESI-MS) of trans-[Ru(NO)Cl )(dpaH)(2)]Cl. (dpaH = 2,2 ' -dipyridylamine), obtained from the carrier so lvent of H2O-CH3OH (50:50), revealed 1+ ions of the formulas [Ru-II(NO+)Cl( dpaH)(dpa)](+) (m/z = 508), [Ru-III Cl(dpaH)(dpa(-))](+) (m/z = 478), [Ru-I I(NO+)(dpa)(2)] + (m/z = 472), [Ru-III (dpa)(2)](+) (m/z = 442), originatin g from proton dissociation from the parent [Ru-II(NO+)Cl(dpaH)(2)](2+) ion with subsequent loss of NO (17.41% of dissociative events) or loss of HCl ( 82.6% of dissociative events). Further loss of NO from the m/z = 472 fragme nt yields the tn/Z = 442 fragment. Thus, ionization of the NH moiety of dpa H is a significant factor in controlling the net ionic charge in the gas ph ase, and allowing preferential dissociation of HCl in the fragmentation pro cesses. With NaCl added, an ion pair, {Na[Ru-II(NO)Cl(dpa)(2)]}(+) (m/z = 5 30; 532), is detectable. All these positive mass peaks that contain Ru carr y a signature 'handprint' of adjacent m/z peaks due to the isotopic distrib ution of Ru-104, Ru-102, Ru-101, Ru-99, Ru-98 and Ru-96 mass centered aroun d Ru-101 for each fragment, and have been matched to the theoretical isotop ic distribution for each set of peaks centered on the main isotope peak, Wh en the starting complex is allowed to undergo aquation for two weeks in H2O , loss of the axial Cl- is shown by the approximately 77% attenuation of th e [Ru-II(NO+)Cl(dpaH)(dpa)](+) ion, being replaced by the [Ru-II(NO+)(H2O)( dpa)(2)](+) (m/z = 490) as the most abundant high-mass species. Loss of H2O is observed to form [Ru-II(NO+)(dpa)(2)](+) + (m/z = 472). No positive ion mass spectral peaks were observed for RuCl3(NO)(H2O)(2), 'caged NO'. Negat ive ions were observed by proton dissociation forming [Ru-II(NO)Cl-3(H2O)(O H)](-) in the ionization chamber, detecting the parent 1 - ion at m/z = 274 , followed by the loss of NO as the main dissociative pathway that produces [(RuCl3)-Cl-III(H2O)(OH)] (m/z = 244). This species undergoes reductive el imination of a chlorine atom, forming [(RuCl2)-Cl-II(H2O)(OH)](-) (m/z = 20 8). The ease of the NO dissociation is increased for the negative ions, whi ch should be more able to stabilize a Ru-III product upon NO loss. (C) 2001 Elsevier Science B.V. All rights reserved.