On the Interaction between Deprotonated Cytosine [C (−H) ] − and Ba 2+ : Infrared Multiphoton Spectroscopy and Dynamics

Gas‐phase interactions between Ba 2+ and deprotonated cytosine (C (−H) ) were studied in [C (−H) Ba] + and [C (−H) BaC] + complexes by IRMPD spectroscopy coupled to tandem mass‐spectrometry in combination with DFT calculations. For the [C (−H) BaC] + complex only one [C (−H) KAN1O−Ba‐C anti ] + isomer was found, although the presence of another structure cannot be excluded. This isomer features a central tetracoordinated Ba 2+ that simultaneously interacts with keto‐amino [C (−H) ] − deprotonated on N1 and neutral keto‐amino C. Both moieties are in different planes as a consequence of an additional NH…O=C hydrogen bond between C and [C (−H) ] − . A sequential IRMPD dynamics is observed in this complex. For the [C (−H) Ba] + complex produced by electrospray ionization two isomers ([C (−H) KAN1OBa] + and [C (−H) KAN3OBa] + ) were identified, in which Ba 2+ interacts simultaneously with the C=O group and the N1 or N3 atom of the keto‐amino [C (−H) ] − , respectively. A comparison with the related [C (−H) Pb] + complex (J. Y. Salpin et al., Chem. Phys. Chem . 2014 , 15, 2959–2971) is also presented.