Reaction of cis-[Mo2(OAc)2(CH3CN) 6][BF4]2 with NP-Et,Me (2-ethyl-3-methyl-1,8- naphthyridine) in acetonitrile provides trans-[Mo2(NP-Et,Me) 2(OAc)2(CH3CN)][BF4]2 (1). Partial protonation of 1 by HBF4·Et2O in acetonitrile leads to trans-[Mo2(NP-Et,Me)2(OAc)(CH 3CN)3][BF4]3 (2). In both compounds, NP-R ligands are arranged in a head-to-head (HH) fashion leaving one of the axial sites vacant. Substitution of acetonitriles by NP-Me (3-methyl-1,8- naphthyridine) in trans-[Mo2(NP-tz)2(OAc)(CH 3CN)2][BF4]3 provides trans-[Mo 2(NP-tz)2(OAc)(NP-Me)][BF4]3 (3) with retention of configuration. Fully solvated dimolybdenum(II) compound reacts with NP-NH2 to provide [Mo2(NP-NH2) 2(NP-NH)(CH3CN)2][BF4]3 (4) in which the NP-NH2 ligands are trans and arranged in a HH fashion. The deprotonated ligand (NP-NH-) binds the dimetal unit utilizing naphthyridine nitrogen and amido nitrogen. Treatment of [Mo 2(NP-tz)2(CH3CN)4][CF 3SO3]4 with bpym (2,2′-bipyrimidine) followed by crystallization in air provided an oxo complex [Mo 2(NP-tz)2(μ2-O)2(bpym) 2][CF3SO3]4 (5). Compounds 1-5 have been characterized by a variety of spectroscopic techniques and by X-ray crystallography. The reactivity pattern is rationalized based on ligand labilities and thermodynamic stabilities. © 2010 Elsevier B.V. All rights reserved.