Copper(II) Carboxylate dimers prepared from ligands designed to form a robust π?π stacking synthon: Supramolecular structures and molecular properties

摘要

The reactions of bifunctional carboxylate ligands (1,8-naphthalimido) propanoate, (L _(C2) -), (1,8-naphthalimido)ethanoate, (L _(C1) -), and (1,8-naphthalimido)benzoate, (L _(C4) -) with Cu _2(O _2CCH _3) _4(H _2O) _2 in methanol or ethanol at room temperature lead to the formation of novel dimeric [Cu _2(L _(C2)) _4(MeOH) _2] (1), [Cu _2(L _(C1)) _4(MeOH) _2]·2(CH _2Cl _2) (2), [Cu _2(L _(C4)) _4(EtOH) _2]·2(CH _2Cl _2) (3) complexes. When the reaction of L _(C1) ~- with Cu _2(O _2CCH _3) _4(H _2O) _2 was carried out at -20 °C in the presence of pyridine, [Cu _2(L _(C1)) _4(py) _4]·2(CH _2Cl _2) (4) was produced. At the core of complexes 1-3 lies the square Cu _2(O _2CR) _4 "paddlewheel" secondary building unit, where the two copper centers have a nearly square pyramidal geometry with methanol or ethanol occupying the axial coordination sites. Complex 4 contains a different type of dimeric core generated by two κ ~1-bridging carboxylate ligands. Additionally, two terminal carboxylates and four trans situated pyridine molecules complete the coordination environment of the five-coordinate copper(II) centers. In all four compounds, robust π?π stacking interactions of the naphthalimide rings organize the dimeric units into two-dimensional sheets. These two-dimensional networks are organized into a three-dimensional architecture by two different noncovalent interactions: strong π?π stacking of the naphthalimide rings (also the pyridine rings for 4) in 1, 3, and 4, and intermolecular hydrogen bonding of the coordinated methanol or ethanol molecules in 1-3. Magnetic measurements show that the copper ions in the paddlewheel complexes 1-3 are strongly antiferromagnetically coupled with -J values ranging from 255 to 325 cm ~(-1), whereas the copper ions in 4 are only weakly antiferromagnetically coupled. Typical values of the zero-field splitting parameter D were found from EPR studies of 1-3and the related known complexes [Cu _2(L _(C2)) _4(py) _2]·2(CH _2Cl _2)· (CH _3OH), [Cu _2(L C3) _4(py) _2]·2(CH _2Cl _2) and [Cu _2(L C3) _4(bipy)] · (CH _3OH) _2· (CH _2Cl _2) _(3.37) (L_(C3) ~- = (1,8-naphthalimido)butanoate)), while its abnormal magnitude in [Cu _2(L _(C2)) _4(bipy)] was qualitatively rationalized by structural analysis and DFT calculations.