BIS(DITHIOSQUARAMIDE) LIGANDS AND THEIR COMPLEXES WITH DIVALENT NICKEL: THERMOCHROMIC BEHAVIOUR AND UNANTICIPATED FORMATION OF 2:2 SPECIES

Abstract

Reaction of two equivalents of N-mono- or di-substituted 3-amino-4-(n-butoxy)-3-cyclobutene-1,2-diones with a 1,2-diaminoethane gave N-mono- or di-substituted 1,2-bis((2-amino-1-cyclobutene-3,4-dione)amino)-ethane derivatives (bis(squaramides)). Reaction of the bis(squaramides) with excess P₄S₁₀ gave the analogous tetrathio derivatives (bis(dithiosquaramides), LH₂) of formula (NR¹R²)C₄S₂(NHCH₂CH₂NH)-C₄S₂(NR¹R²) (R¹=n-Bu, R²=H; R¹=R²=Et, n-Bu). The new bis(dithiosquaramide) ligands were characterized by elemental analysis, IR, ¹H NMR, ¹³C NMR, electronic, and mass spectroscopic methods. The complexes of these ligands with nickel(II) were prepared, isolated and characterized. The isolated complexes are neutral 2:2 species of formula Ni₂L₂, as evidenced by results from mass spectrometry, and they exhibit thermochromic behaviour in pyridine solution. Additional spectroscopic data (IR, NMR) are consistent with the ligands being coordinated only through sulfur donor atoms and a structure for the complexes is proposed.