Solvent Control of Supramolecular Architectures Derived from 4,4′-Bipyridyl-Bridged Copper(II) Dipicolinate Complexes

Treatment of [Cu(dipic)(OH2)3] [dipic2 = pyridine-2,6-dicarboxylate (dipicolinate)] 1 with diverse bipyridyl bridging ligands of varying length [pyrazine (pyz), 4,4′-bipyridine (bipy), trans-4,4′-azobis(pyridine) (azpy), 1,2-bis(pyridin-4-yl)ethene (bpe), 3,6-bis(pyridin-4-yl)-1,2,4,5-tetrazene (pytz) and 1,4-bis{2-(pyridin-4-yl)ethenyl}benzene (bpeb)] under a variety of conditions yielded [Cu2(dipic)2(bipy)]·4H2O, 2, [Cu2(dipic)2(bpe)]·2H2O, 3, [{Cu(dipic)(OH2)}(μ-pyz)0.5]·H2O, 4, [{Cu(dipic)(OH2)}(μ-pyz)0.5], 5, [{Cu(dipic)(OH2)}(μ-bipy)0.5][{Cu(dipic)(OH2)0.75(OHMe)0.25}(μ-bipy){Cu(dipic)(OH2)}]·2.25H2O·0.5CH3OH, 6, {[{Cu(dipic)}2(μ-bipy)]·2H2O·CH2Cl2}∞, 7, [{Cu(dipic)(OH2)}(μ-bpe){Cu(dipic)}]·3H2O, 8, {[{Cu(dipic)}(μ-azpy)0.5]·CH2Cl2}∞, 9, {[{Cu(dipic)}(μ-azpy)0.5]·CH3OH}∞, 10, [{Cu(dipic)(OH2)}2(μ-pytz)]·2H2O, 11, [Cu2(dipic)2(bpeb)]·4H2O, 12 and [{Cu(dipic)(OHMe)}2(μ-bpeb)], 13. Complexes 4−11 and 13 were characterized by single crystal X-ray diffraction which confirmed the presence of binuclear building blocks in which two square-pyramidal Cu(II) centers are linked by bipyridyl bridges. The differences in the structures lie in the choice of ligand located at the apical site of the Cu(II) center, the basal sites being occupied by one N- and two O-donors of the mer-bound dipicolinate ligand and an N-donor from the bridging heterocyclic ligand. In the presence of excess coordinating solvent such as H2O or MeOH, recrystallization affords products with the apical sites occupied by solvent molecules to give extensive hydrogen-bonding networks within 3-D matrices in 4−6, 8, 11, 13. With reduced levels of coordinating solvent in the crystallizing medium, the apical sites are occupied by carboxylate oxygens of adjacent [Cu(dipic)] moieties giving 2-D coordination polymers of 63 topology as in 7, 9, 10.