Mixed-valence copper(i,ii) complexes with 4-(1H-pyrazol-1-yl)-6-R-pyrimidines: from ionic structures to coordination polymers

Abstract

Two pyrimidine-based ligands, 4-(3,5-diphenyl-1H-pyrazol-1-yl)-6-(morpholino)pyrimidine () and 4-(3,5-diphenyl-1H-pyrazol-1-yl)-6-phenoxypyrimidine (), and a series of mixed-valence copper(i,ii) halide complexes, [Cu(L(2))2Br]2[Cu2Br4] (), [Cu(L(2))2Cl][CuCl2] (), and [Cu2L(3)Br3]n (), have been synthesized. The complex [Cu(L(2))2Br]2[Cu2Br4] was prepared by the reaction of with CuBr2 in a 1 : 1 molar ratio in MeCN. Its chlorido-analogue, the complex [Cu(L(2))2Cl][CuCl2], was synthesized by the reaction between , CuCl2 and CuCl in a 2 : 1 : 1 molar ratio in MeCN. The ligand acts as a chelating one. In the structures of the complexes [Cu(L(2))2Br]2[Cu2Br4] and [Cu(L(2))2Cl][CuCl2] the Cu(2+) ion is in the cationic part of the complex whereas the Cu(+) ion is located in the anionic part. The best way to synthesize the mixed-valence 1D coordination polymer [Cu2L(3)Br3]n is to react CuBr2 with in a 2 : 1 molar ratio in the MeCN/CHCl3 mixture on heating. In the structure of [Cu2L(3)Br3]n the ligand shows chelating/bridging tridentate coordination. This is the first example of the tridentate coordination of 4-(1H-pyrazol-1-yl)-6-R-pyrimidines. The striking difference between the coordination behavior of and (chelating bidentate vs. chelating/bridging coordination) is related with the possibility of rotation of the 6-phenoxy group around the C-O bond which makes the N(1) pyrimidine atom less sterically hindered, enabling it to participate in metal ion binding. Importantly, all copper ions in [Cu2L(3)Br3]n show similar tetrahedral environments, CuNBr3 and CuN2Br2, which is extremely rare for mixed-valence copper(i,ii) compounds. The ligands and show blue emission which is quenched upon their coordination to copper ions. The 1D coordination polymer [Cu2L(3)Br3]n shows high thermal stability and unusual solvent-occlusion properties. The role of the substituents favoring the formation of the mixed-valence copper(i,ii) complexes with 4-(1H-pyrazol-1-yl)-6-R-pyrimidines is discussed.

Crystal structure of 4-(pyrazin-2-yl)morpholine

“…pyridine (Dahlgren et al, 2012;Horton et al, 2012;Huth et al, 2007;Klauschenz et al, 1994;Li et al, 2014, Reck et al, 1992 or pyrimidine (Cheprakova et al, 2014;García et al, 2009;Gorbunov et al, 2013;Hansen & Geffken, 2012;Vinogradova et al, 2016). For pyrazine as the heterocycle, however, (to the best of our knowledge and after conducting a database search, see x4) the present work constitutes the first structural report even though the title compound itself has been known since 1969 (Abe et al, 1969).…”

“…The orientation of the morpholine ring, in its typical chair conformation, relative to the aromatic plane can be either more or less in plane (e.g. Vinogradova et al, 2016), tilted around the N-C bond (e.g. Li et al, 2014), bent away from the aromatic plane (e.g.…”

Synthesis and Study of Photothermal Properties of a Mixed-Valence Nanocluster CuI/CuII with Strong near-Infrared Optical Absorption Supported by 4-tert-Butylcalix[4]arene Ligand

“…38 It is important to point out that the four-coordinated Cu I ions often favor tetrahedral geometry. 29,39,40 Every Calix4 ligand binds with five copper atoms, including one Cu I and four Cu II atoms, with Cu I O Calix4 distances in the range of 1.921(4)−1.959(4) Å and Cu II O Calix4 distances in the range of 1.925 (6)−1.949(5) Å (Figure 2b).…”

“…We assigned the three four-coordinated copper ions with square-planar geometry as mono-valence and the six five-coordinated copper ions with square pyramid geometry as bivalence . It is important to point out that the four-coordinated Cu I ions often favor tetrahedral geometry. ,, Every Calix4 ligand binds with five copper atoms, including one Cu I and four Cu II atoms, with Cu I O Calix4 distances in the range of 1.921(4)–1.959(4) Å and Cu II O Calix4 distances in the range of 1.925 (6)–1.949(5) Å (Figure b).…”

N^N^C-Cyclometalated rhodium(iii) complexes with isomeric pyrimidine-based ligands: unveiling the impact of isomerism on structural motifs, luminescence and cytotoxicity

“…HL 2,5 and HL 2,6 belong to pyrazolyl-pyrimidine ligands 23,69–76 and contain the pyrazolyl group at the position 4 of the pyrimidine ring. Aided by the N 3 pyrimidinic atom, this group forms the N^N-chelating site of the ligand molecule.…”