Ligand-driven nuclearity: the unusual case of luminescent Cu(I) and Ag(I) polynuclear systems with 3,5-dimethyl-4-sulfonate pyrazolates

In the last decade, great attention has been devoted to the synthesis and structural characterization of coinage metals luminescent compounds [1]. Among the others, oligonuclear pyrazolate-based compounds, [M(pz*)]x (M = Cu, Ag, Au; pz* = generic substituted pyrazolate ligand; x = 3, 4) often showed high photoluminescence performances together with attractive structure-properties relations [2]. In these systems, the metal centers are kept in close proximity so that significant metallophilic interactions raise. In particular, coinage metals compounds with 3,5-dimethyl pyrazolates (dmpz*) habitually organize in cyclic [M(dmpz*)]3 trimers, whose outstanding photophysical properties are strictly connected to Cu∙∙∙Cu intermolecular interactions originating from supramolecular stacking [3]. Herein we describe the synthesis of 3,5-dimethyl-4-sulfonate pyrazole ligands (HdmpzSO3M'; M' = Li, Na, K, Rb) and the corresponding Cu(I) and Ag(I) derivatives. With M' = Na, depending on the experimental conditions employed it has been possible to isolate three stable Cu(I) compounds which differ for their water content, namely [Cu(dmpzSO3Na)]∙1.5H2O (Cu/Na1), [Cu(dmpzSO3Na)]∙H2O (Cu/Na2) and [Cu(dmpzSO3Na)] (Cu/Na3). An XRPD performed on Cu/Na2 surprisingly revealed that differently from what is usually observed (see above), in our systems the metal centers are disposed in zig-zag chains, held together by the 3D motif imposed by the SO3Na group and water molecules. Compounds Cu/Na1, Cu/Na2 and Cu/Na3 show notable photoluminescent behavior when irradiated with UV light (λexc = 284-310 nm), with a bathochromic shift of λmax of emission when increasing the water content (λmax being 469 (Cu/Na3), 544 (Cu/Na2) and 565 nm (Cu/Na1), respectively). Additionally, high absolute quantum yields (up to 0.50) and high Stokes’ shift (Δ = 1.67-2.10 eV) are measured in the solid state. References 1) Hsu, C.-W.; Lin, C.-C.; Chung, M.-W. ; Chi, Y. ; Lee, G.-H. ; Chou, P.-T. ; Chang, C.-H. ; Chen, P.- Y., J. Am. Chem. Soc. 2011, 133, 12085-12099. 2) Rasika Dias, H. V.; Diyabalanage, H. V. K.; Eldabaja, M. G.; Elbjeirami, O.; Rawashdeh-Omary, M. A.; Omary, M. A. ; J. Am. Chem. Soc. 2005, 127, 7489-7501. 3) Ni, W.-X.; Li, M.; Zheng, J.; Zhan, S.-Z.; Qiu, Y.-M.; Ng, S. W.; Li, D., Angew. Chem. Int. Ed. 2013, 52, 13472-13476.