We present a combined experimental and quantum chemical study of gas-phase group 9 metal
nitrosyl complexes, M(NO)n
+
(M = Co, Rh, Ir). Experimental infrared photodissociation spectra
of mass-selected ion-molecule complexes are presented in the region 1600 cm-1
– 2000 cm-1 which
includes the NO stretch. These are interpreted by comparison with the simulated spectra of
energetically low-lying structures calculated using density functional theory. A mix of linear and
non-linear ligand binding is observed, often within the same complex and clear evidence of
coordination shell closing is observed at n = 4 for Co(NO)n
+
and Ir(NO)n
+
. Calculations of
Rh(NO)n
+
complexes suggest additional low-lying five-coordinate structures. In all cases, once a
second coordination shell is occupied, new spectral features appear which are assigned to (NO)2
dimer moieties. Further evidence of such motifs comes from differences in the spectra recorded in
the dissociation channels corresponding to single and double ligand loss.
