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Structurally Different Dinuclear Copper(II) Complexes with the Same Triazolopyrimidine Bridging Ligand
Author(s) -
Haj Mohammad Abul,
Quirós Miguel,
Salas Juan M.,
Dobado José A.,
Molina José Molina,
Basallote Manuel G.,
Máñez M. Ángeles
Publication year - 2002
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200203)2002:4<811::aid-ejic811>3.0.co;2-9
Subject(s) - chemistry , crystallography , electron paramagnetic resonance , copper , dimer , ligand (biochemistry) , antiferromagnetism , crystal structure , metal , magnetic susceptibility , bridging ligand , electrochemistry , stereochemistry , nuclear magnetic resonance , biochemistry , receptor , organic chemistry , physics , electrode , condensed matter physics
Four binuclear copper(II) compounds with the anionic form of the ligand 4,5‐dihydro‐5‐oxo[1,2,4]triazolo[1,5‐ a ]pyrimidine (5tpO − ) have been isolated, their formulae being [Cu 2 (5tpO) 4 (H 2 O) 2 ]·2H 2 O ( 1 ), [Cu 2 (phen) 2 (5tpO) 2 (H 2 O) 2 ](NO 3 ) 2 ·4H 2 O ( 2 ), [Cu 2 (biim) 2 (5tpO) 2 (H 2 O)](ClO 4 ) 2 ·5.5H 2 O ( 3 ), and [Cu 2 (CH 3 CO 2 ) 2 (5tpO) 2 (H 2 O) 2 ] ( 4 ) (phen = 1,10‐phenanthroline, biim = bisimidazole). A related mononuclear complex, [Cu(phen) 2 (5HtpO) 2 ](NO 3 ) 2 ( 5 ), has also been prepared. The crystal structure of compounds 1−3 has been determined by X‐ray diffraction, showing their binuclear nature with four ( 1 ) or two ( 2 , 3 ) bridging 5tpO − moieties. The triazolopyrimidine ligand binds the copper atoms through N3 and N4 in compounds 1 and 3 , whereas a novel binding mode through N3 and the exocyclic oxygen atom has been found in 2 . The study of the solution behaviour of 2 and 5 shows the important role of the solvent in the formation of the mono or binuclear complex. The reduction of the metal centres to Cu I has been observed by electrochemical methods, demonstrating that this ligand stabilizes this oxidation state. Magnetic susceptibility measurements and electronic paramagnetic resonance (EPR) spectra seem to indicate a dimeric nature also for compound 4 . The antiferromagnetic interaction between the copper atoms inside the dimer is very strong for 4 (2 J = −221.3 cm −1 ) and 1 (2 J = −104.9 cm −1 ), fairly strong for 3 (2 J = −21.6 cm −1 ), and very weak or non‐existent for 2 . The nature of the copper−copper interaction in compound 1 has been analyzed by using molecular orbital calculations.