The interaction between R 3 SnCl, (R 3 Sn) 2 O, R 2 SnO or R 2 SnCl 2 acceptors (R=Me, n Bu or Ph) and the two novel β-diketone proligands (LH=1,3-diphenyl-4-R 4 (C O)-pyrazol-5-one: L 1 H, R 4 =Ph; L 2 H, R 4 =Me) yields complexes [SnR 3 (L)(H 2 O)] (R=Me or n Bu, L=L 1 or L 2 ), [SnPh 3 (L)] and [SnR 2 (L) 2 ] (L=L 1 or L 2 ). The phenyl substituent on position 3 induces instability of the triorganotin derivatives in solution with the formation of SnR 2 (L) 2 and SnR 4 compounds. Moreover, diorganotin derivatives partially dissociate in solution yielding [SnR 2 (L)(solvent)] 2 + species. When compared with the related 3-methyl species, the crystal structure of (1,3-diphenyl-4-benzoyl-pyrazolon-5-ato)triphenyltin(IV) is not modified by the 3-phenyl substitution. The chemical instability generated by the Ph in position 3 is greater than in positions 1 and 4. In addition, the Ph in position 3 of the pyrazole influences the solution behavior of the free neutral 4-acyl-5-pyrazolones stabilizing a novel amino-diketo tautomeric form.