Toward Heteronuclear Molecular Re(I)-Cu(II) Boxes: Structural, Luminescent, and Magnetic Properties

The bifunctional
ligands of isonicotinic acid (Py-4-COOH) and 4-pyrid-4-ylbenzoic
acid (Pybz-4-COOH) instead of polypyridines were therefore reacted
with (Re­(CO)4)3(C3N3S3) (C3N3S3 = cyanurate trianion),
resulting in the formation of two trinuclear [(Re­(CO)3)3(C3N3S3)­(Py-4-COOH)3] (1) and [(Re­(CO)3)3(C3N3S3)­(Pybz-4-COOH)3] (2), respectively. In the meantime, both complexes 1 and 2 are connected by three bifurcated hydrogen bonds between
their carboxylic acid moieties Py-4-COOH and Pybz-4-COOH to form the
supramolecular trigonal-prismatic and -antiprismatic structures, respectively.
It is noted that complex 1 can further react with copper­(II)
nitrate upon deprotonation to give nonanuclear [(Re­(CO)3)3(C3N3S3)­(Py-4-COO)3]2Cu3(H2O)9 (3), where two trinuclear [(Re­(CO)3)3(C3N3S3)­(Py-4-COO)3]
moieties are connected by three penta-coordinate copper­(II) ions,
each coordinating to two carboxylates and three water molecules, to
form the trigonal-prismatic structure. Surprisingly, addition of pyrazine
(pz) in the synthetic process of complex 3 resulted in
serendipitous isolation of a rare example of octadecanuclear {[(Re­(CO)3)3(C3N3S3)­(Py-4-COO)3]2Cu3(H2O)6(pz)2}2 (4), which can be regarded as a
dimer of complex 3, connected by two bridging pz ligands.
Interestingly, both complexes 3 and 4 are
heteronuclear molecular Re­(I)-Cu­(II) boxes, constructed by a complex-as-a-ligand
strategy. Furthermore, complexes 1 and 2 can exhibit respective low-energy luminescence at ca. 561 and 534 nm at room temperature upon photoexcitation, and complex 3 is found to display antiferromagnetic coupling of −127.68
and −134.70 cm–1, possibly due to multiple
hydrogen bonds inducing significant Cu­(II)···Cu­(II)
coupling.