Copper(II) complexes with pyrazolyl-substituted nitronyl and imino nitroxides

• Published in: Polyhedron Vol. 27; no. 2; pp. 739 - 749
• Main Authors: Tretyakov, Eugene V., Tolstikov, Svyatoslav E., Gorelik, Elena V., Fedin, Matvey V., Romanenko, Galina V., Bogomyakov, Artem S., Ovcharenko, Victor I.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 06-02-2008
• Subjects: Copper complexes; Imino nitroxides; Nitronyl nitroxides; Pyrazoles; Pyrazoles; Imino nitroxides; Nitronyl nitroxides; Copper complexes
• ISSN: 0277-5387
• DOI: 10.1016/j.poly.2007.11.003

Reactions of Cu
2(OAc)
4(H
2O)
2 with pyrazolyl-substituted nitronyl and imino nitroxides lead to tetra- and dinuclear copper(II) heterospin complexes, which tend to form polymer ribbons and layers in solids due to intermolecular H-bonding. In the case of pyrazole esters, the reaction with Cu
2(OAc)
4(H
2O)
2 causes cleavage of the ester bond and transformation of the starting nitroxides into the corresponding dianion.
It was established that the reactions of pyrazol-3-yl-substituted nitronyl nitroxide (
HL
1) and pyrazol-3-yl-substituted imino nitroxide (
HL
3) with Cu(II) acetate lead to self-assembly of the Cu
4(OH)
2(OAc)
4(DMF)
2(L
1)
2 tetranuclear and Cu
2(OAc)
2(H
2O)
2(L
3)
2 dinuclear complexes, respectively. The reaction of Cu(II) acetate with 5-ethoxycarbonyl-pyrazol-3-yl-substituted nitronyl nitroxide (
HL
2) gave unexpected solid Cu
2(H
2O)
2(L
6)
2
·
2DMF, in which
L
6 is a deprotonated 5-carboxy-pyrazol-3-yl-substituted nitronyl nitroxide, formed as a result of cleavage of an ester bond in the starting
HL
2. A similar transformation of the paramagnetic ligand was observed in the reaction of Cu(II) acetate with 5-ethoxycarbonyl-pyrazol-3-yl-substituted imino nitroxide (
HL
4). It led to the formation of Cu
2(DMF)
2(L
7)
2, where
L
7 is deprotonated 2-(5-carboxy-1
H-pyrazol-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1
H-imidazole 3-oxide. An X-ray diffraction study indicated that in Cu
4(OH)
2(OAc)
4(DMF)
2(L
1)
2 and Cu
2(OAc)
2(H
2O)
2(L
3)
2, the
L
1 and
L
3 paramagnetic ligands perform the bridging cyclic tridentate function, while in Cu
2(H
2O)
2(L
6)
2
·
2DMF and Cu
2(DMF)
2(L
7)
2, the paramagnetic
L
6 and diamagnetic
L
7 are bridging bicyclic tetradentate ligands. The magnetic behavior of complexes with coordinated nitronyl nitroxide – Cu
4(OH)
2(OAc)
4(DMF)
2(L
1)
2 and Cu
2(H
2O)
2(L
6)
2
·
2DMF is dictated by the dominant antiferromagnetic exchange interactions, which is confirmed by quantum-chemical data. The magnetic susceptibility of Cu
2(OAc)
2(H
2O)
2(L
3)
2 reflects the competition between the antiferromagnetic and ferromagnetic components, of which the latter is due to electron coupling in the Cu(II)
←
N=C–N
∸
O exchange channels. EPR data confirm the results received from static magnetic measurements for multispin solids.