The Schiff base compound 2,2'-{[(2-aminoethyl)imino]bis[2,1-ethanediyl-nitriloethylidyne]}bis-2-hydroxy-benzoic acid (H4L) as a proligand was prepared in situ. This proligand has three potential coordination pockets which make it possible to accommodate from one to three metal ions allowing for the possible formation of mono-, di-, and trinuclear complexes. Reaction of in situ prepared H4L with Dy(NO3)(3)center dot 5H(2)O resulted in the formation of a mononuclear complex [Dy(H3L)(2)](NO3)center dot(EtOH)center dot 8(H2O) (1), which shows SMM behavior. In contrast, reaction of in situ prepared H4L with Mn(ClO4)(2)center dot 6H(2)O and Dy(NO3)(3)center dot 5H(2)O in the presence of a base resulted in a trinuclear mixed 3d-4f complex (NHEt3)(2)[Dy{Mn(L)}(2)](ClO4)center dot 2(H2O) (2). At low temperatures, compound 2 is a weak ferromagnet. Thus, the SMM behavior of compound 1 can be switched off by incorporating two Mn(II) ions in close proximity either side of the Dy(III). This quenching behavior is ascribed to the presence of the weak ferromagnetic interactions between the Mn(II) and Dy(III) ions, which at T > 2 K act as a fluctuating field causing the reversal of magnetization on the dysprosium ion. Mass spectrometric ion signals related to compounds 1 and 2 were both detected in positive and negative ion modes via electrospray ionization mass spectrometry. Hydrogen/deuterium exchange (HDX) reactions with ND3 were performed in a FT-ICR Penning-trap mass spectrometer.