Low-temperature STM observations of the low-coverage chemisorption behavior of iodobenzene on Cu(110) are presented at two annealing temperatures. When a random distribution of isolated iodobenzene molecules deposited at T < 100 K is annealed to approximately 170 K, the undissociated molecules assemble into chainlike clusters composed of identical subunits. An STM tip-induced dissociation reaction is used to determine that the individual units in the chains are composed of pairs of iodobenzene molecules. A model is proposed in which iodine atoms on each member of the pair are directed toward one another. The driving force for the formation of such clusters is suggested to be the dispersion interactions between the polarizable iodobenzene molecules.