The dinitrogen (N) chemistry of lanthanides remains less developed compared to the d-block metals and lanthanide-promoted N functionalization chemistry in well-defined lanthanide complexes remains elusive. Here we report the synthesis and characterization (SQUID, EPR, DFT, X-Ray) of the siloxide supported heterobimetallic (Tm/K) complexes [{KTm(OSi(OBu))}(μ-η : η-N)] (1) and [K{Tm(OSi(OBu))}(μ-η : η-N)] (2). Complex 2 provides a rare example of a metal complex of the triply reduced N radical. The structure of 2 differs from the few previously reported N complexes as it presents two Tm and three K cations binding the N radical, facilitating N functionalization. Notably, the KTm-bound N moiety reacts with excess H to form NHCl in 18 % yield, and with MeOTf at room temperature to yield the dimethyl hydrazido complex [K{Tm(OSi(OBu))}(μ-(CH)NN(CH))] (3). Protonolysis of 3 yields MeHN-NMeH ⋅ 2HCl in 18 % yield.