Structurally
variable organochalcogen clusters containing palladium(II)
and nickel(II) ions were assembled starting from the salicylidene-substituted
dichalcogenides (Y–C6H4–NCH–C6H4–OH)2 ({HLY}2, where Y = Se or Te), and palladium or nickel acetate. The
tetrameric palladium clusters contain reduced chalcogenolato ligands
{Y–C6H4–NCH–C6H4–O)}2– ({L′Y}2–, where Y = Se or Te), while the initially
formed trimeric nickel clusters contain the intact, coordinated dichalcogenides.
The palladium clusters have a general formula of [Pd4(L′Y)4] and represent the first examples of palladium
complexes where both a gyrobifastigial and a pseudocubane arrangement
of the central Pd4Y4 unit could be established
with the same ligand, only depending on the solvents used for crystallization.
Reduced density gradient (RDG) considerations based on density functional
theory calculations suggest that the commonly referred to stabilizing
chalcogen–palladium or palladium–palladium interactions
for the two geometric arrangements are weak van der Waals contacts
resulting from the contact of two nonbinding lone pairs. In the case
of the pseudocubane arrangement, a repulsive steric effect, which
is indicated by RDG analysis, is clearly supported by the cuplike
distortions detected in the solid-state structure of the compound.
In contrast to the reactions with palladium acetate, where the dichalcogenides
were cleaved, during similar reactions with nickel acetate, the dichalcogenides
remained intact and trimeric clusters of the composition [Ni-μ2-κ2-(Ni{κ5-LY}2)2-μ2-(OAc)2]
(Y = Se, Te) were formed. Air oxidation and hydrolysis of [Ni-μ2-κ2-(Ni{κ5-LTe}2)2-μ2-(OAc)2]
gave a rare example of a hexanuclear nickel cluster of the composition
[Ni2-κ5-(Ni4-κ6-μ6-{(L′Te
2O3)(L′TeO2)2}2)-μ2-(H2O)2], which is composed of a well-defined
framework consisting of tellurinic anhydride and tellurinate units,
which proves the comparably higher oxidation sensitivity of the trinickel
dichalcogenide complexes. Electron spray ionization mass spectrometry
spectra of both the palladium and nickel clusters indicate that they
show fluctional behavior with varying nuclearity in solution and can
adopt multiple charge states especially because of the noninnocence
of the chalcogen-based ligands. The complexes were fully characterized
by spectroscopic methods, elemental analyses, and X-ray diffraction.