A series of molybdenum and tungsten nitrido, [M(N)(X)(diphos)₂], and imido complexes, [M(NH)(X)(diphos)₂)]Y, (M = Mo, W) with diphosphine coligands (diphos = dppe/depe), various trans ligands (X = N₃^-, Cl^-, NCCH₃) and different counterions (Y^- = Cl^-, BPh₄^-) is investigated. These compounds are studied by infrared and Raman spectroscopies; they are also studied with isotope-substitution and optical-absorption, as well as emission, spectroscopies. In the nitrido complexes with trans-azido and -chloro coligands, the metal−N stretch is found at about 980 cm^-1; upon protonation, it is lowered to about 920 cm^-1. The ¹A₁ → ¹E (n → π*) electronic transition is observed for [Mo(N)(N₃)(depe)₂] at 398 nm and shows a progression in the metal−N stretch of 810 cm^-1. The corresponding ³E → ¹A (π* → n) emission band is observed at 542 nm, exhibiting a progression in the metal−N stretch of 980 cm^-1. In the imido system [Mo(NH)(N₃)(depe)₂]BPh₄, the n → π* transition is shifted to lower energy (518 nm) and markedly decreases in intensity. In the trans-nitrile complex [Mo(N)(NCCH₃)(dppe)₂]BPh₄, the metal−N(nitrido) stretching frequency increases to 1016 cm^-1. The n → π* transition now is found at 450 nm, shifting to 525 nm upon protonation. Most importantly, the reduction of this nitrido trans-nitrile complex is drastically facilitated compared to its counterparts with anionic trans-ligands (E_p^red = −1.5 V vs Fc⁺/Fc). On the other hand, the basicity of the nitrido group is decreased (pK_a{[Mo(NH)(NCCH₃)(dppe)₂](BPh₄)₂} = 5). The implications of these findings with respect to the Chatt cycle are discussed.