Thus, two pairs Cu1 and Cu2 are equivalent and four coordinate tetrahedral,
while the Cu3 pairs are structurally similar to each other but
different from Cu1 and Cu2 and are five coordinate trigonal bipyramidal
involving one nitrogen, two sulfur and Cu1–Cu3–Cu2 bridge
bonding. The six copper atoms form a distorted octahedron and the
eight surfaces of the octahedron are capped by six uninegative eptu
ligands. The average Cu–N and Cu–S distances of 2.01 and 2.250 Å,
respectively, are comparable to those reported for four coordinate
copper(I) complexes [24]. The computed average Cu–N and Cu–S
distances of 2.056 and 2.356 Å, respectively, are very close to the
observed crystal data. The shorter N(1)–C(2) distance (1.28 Å)
and longer carbon–sulfur distance (2.23 Å), as compared to those
found in the ligand (Heptu), shows delocalization of charge within
the chelate ring. The literature shows that Cu–Cu distances bridged
by sulfur atoms in this class of complexes range widely from 2.616
to 3.306 Å, suggesting that they are strongly influenced by the
characteristics of the ligand and the nuclearity of the complex. It
is observed that the Cu–Cu distance in complex 2, (Table 3)
together with the Cu–S–Cu bridging moieties are longer than those
bridged by the copper ion. The Cu Cu distances in the hexanuclear
units of the [Cu6(eptu)6] octahedron (2) are in the 3.596–3.629 Å
range, whereas the Cu Cu distances in the triangular [l-S–Cu3–
Cu1] and [l-S–Cu3–Cu2] units are in the 3.133–3.255 Å range for
the triangle formed by Cu1Cu3Cu2. The structure of complex
2 is stabilized by C–H S hydrogen bonding, leading to the formation
of a paddle-wheel like structure (Fig. 5).