Ni+(C2H2), ion-molecule complexes are produced by laser vaporization in a pulsed nozzle source. These ions are mass analyzed and size-selected with a reflectron time-of-flight spectrometer. Infrared excitation with a pulsed OPO/OPA laser induces photodissociation of these complexes that proceeds by sequential loss Of C2H2 molecules. IR resonance-enhanced photodissociation (IR-REPD) spectra are measured in the C-H stretch region for Ni+(C2H2), complexes (n = 3-6). The C-H stretch vibrations are shifted to lower frequencies than those in free acetylene, consistent with the formation of metal cation pi-complexes. At the cluster sizes of n = 5 and larger, new bands are measured attributed to surface acetylene molecules. Additional redshifted bands at n = 5 and beyond are assigned to an intracluster cyclization reaction, forming pi-bonded cyclobutadiene.