This paper summarizes the first part of a systematic study of the small nitride molecules and simple dinitrogen complexes of the lanthanide metals except promethium. Simple nitrides of the general formulas LnN and (LnN)(2) have been identified for Ln = Ce, Pr, Nd, Sm, Eu, and Gd; LnN(2) has been identified for Ln = Ce, Pr, Nd, and Sm. Several dinitrogen complexes of the type Ln(N-2), Ln(NN), Ln(NN)(2), and Ln(NN)(x) have also been observed in matrix infrared investigations. The tendency of the identified nitrides to complex dinitrogen is readily determined from experimental data, which provide frequencies for observed fundamentals both before and after dinitrogen complexation. Several reaction pathways to formation of the small nitrides have been explored. The favored pathway to the (LnN)(2) molecule involves reduction of N-2 by two Ln metal atoms concurrent with complete scission of the N=N triple bond.