A mass spectrometric investigation of clusters formed by sodium cations and pentacyanonitrosylferrate(2−) anions in the gas phase, and an exploration of structures of some of the clusters using Density Functional Theory

Approximately 50 new cationic and anionic aggregates of general formula [Nax(NP)y]z (NP2−=pentacyanonitrosylferrate(2−), nitroprusside, [Fe(CN)5(NO)]2−) have been observed mass spectrometrically by electrospraying a methanolic solution of Na2(NP)·2H2O, with ion identification using Fourier-transform ion cyclotron resonance, and/or a quadrupole ion trap. Several families of ions have been observed in which the m/z values are the same but the values of z differ between family members. The distribution of species is compared with those of PPh4+-containing analogs, reported earlier and augmented here. Density Functional Theory has been used to determine structures and relative energies (after inclusion of zero-point and dispersion energies) of aggregates with y=1 or 2. In general, isomeric structures occur, but in none of the optimized structures was bonding of Na+ to the oxygen or nitrogen atoms of the nitrosyl group of NP2− observed. A terminal Na+ could be associated with as many as three nitrogen atoms from cyanide ligands, while a bridging Na+ could be associated with up to six such nitrogen atoms. Association of Na+ with two or three nitrogen atoms in a chelating manner was found to result in significant Fe–C–N and C–Fe–C angle bending. On the basis of these structures, and the bonding motifs within them, possible structures of ions with larger values of y are discussed.