Calcium or sodium atoms are added to selenium clusters in the reaction channel of a dual laser vaporization source to study the dependence of the product structures on the number and the valence of the metal atoms. Stabilities of product clusters are investigated by photofragmentation experiments. Several CaMSeN clusters show special stabilities for compositions that can be related to bulklike cuboid structures, while no pattern of geometrical stabilities is found for NaMSeN Clusters. Keeping a low sodium concentration in the reaction channel generates predominantly Na2SeN Clusters. They are deposited in a nitrogen matrix and investigated by Raman spectroscopy. A low-frequency Raman band is found which is consistent with calculated frequencies of selenium chains terminated at each end by one sodium atom and bent into horseshoe shapes by an attractive interaction between the two sodium atoms. Structural models for the metal/selenium clusters are discussed which are based on the idea of an electron transfer from the metal atoms to the selenium clusters according to the metal valences.