Spirocyclic Sulfur and Selenium Ligands as Molecular Rigid Rods in Coordination of Transition Metal Centers

A set of analogous chalcogen-containing spirocycles, 2,6-dithiaspiro[3.3]heptane, 2,6-diselenaspiro[3.3]heptane,
and 2-thia-6-selenaspiro[3.3]heptane [E2C5H8, E = S (1), Se (2), and S/Se (3)], has been prepared and fully
characterized by spectroscopic methods and by X-ray diffraction. The structural characterization of 2 was presented
by us earlier, while the crystal structures of 1 and 3 are reported here for the first time. Molecules 1−3 are built
around the central tetrahedral carbon atom and therefore are nonplanar. The E···E separation ranges from 4.690(1) Å in 1 to 4.906(1) Å in 2. Molecule 3 has statistically mixed positions of sulfur and selenium atoms in the solid
state with all geometric characteristics being intermediate between those of 1 and 2. Compounds 2 and 3 have
been tested as molecular rigid rod ligands in coordination reactions with transition metal complexes such as Cu(hfac)2 (4), cis-Co(hfac)2·2H2O (5), and cis-Ni(hfac)2·2H2O (6) (hfac = hexafluoroacetylacetonate). Several coordination
products built of two building blocks, M(hfac)2 (M = Cu, Co, and Ni) and Se2C5H8 (2), have been prepared in
crystalline form and structurally characterized. The copper-based product (7) is comprised of the oligomeric units
{[Cu(hfac)2]3·2μ2-Se2C5H8-Se,Se‘} built on the axial Cu···Se interactions averaged at 2.909 Å. These units are
further assembled into 1D polymeric chains via intermolecular Cu···F contacts at 2.829 Å. The SSeC5H8 (3) ligand
was also used in the reaction with Cu(hfac)2 to afford an analogue of 7, namely {[Cu(hfac)2]3·2μ2-SSeC5H8-S,Se}
(8). Complex 8 exhibits statistically mixed positions of the donor sulfur and selenium atoms to give an average
axial Cu···S/Se contact at 2.892 Å. In contrast to the copper complexes of composition 3:2, the stoichiometries of
the isolated cobalt and nickel products are 1:1, [M(hfac)2·Se2C5H8] (M = Co (9) and Ni (10)). Complexes 9 and
10 exhibit 1D polymer structures having alternating metal units cis-M(hfac)2 and ligands 2 with intermolecuar M···Se separations of 2.6046(8) and 2.5523(16) Å, respectively. In all products 7−10 the initial cis or trans geometry
of M(hfac)2 complexes is preserved and the spiro[3.3]heptane ligands act as bidentate linkers bridging transition
metal centers via both donor ends. The magnetic properties of this series of new CuII, CoII, and NiII complexes
have been tested by variable-temperature magnetic susceptibility measurements.