Design and synthesis of copper(ii) malonates with N,N′-containing linkers

Abstract

Knowledge-based approach to the design of coordination polymers with a given architecture in general requires knowledge of regularities between the local coordination of metal atoms (or polynuclear metal-containing units), coordination modes of all ligands in a complex, and the entire framework topology. The effect of the local coordination on the dimensionality and topology of the underlying nets was demonstrated on the example of 4,4′-bipyridine (bipy), 1,2-bis(4-pyridyl)ethylene (bpe) and 1,2-bis(4-pyridyl)ethane (bpa) containing copper(II) malonates. The most abundant networks were evaluated for these compounds and compared with those for previously analyzed and synthesized zinc(II)-containing analogs. Eight novel complexes, namely [Cu(bpe)(mal)]·2CH₃CN, [Cu₄(bipy)₄(Me₂mal)₄(H₂O)₅]·3H₂O, [Cu(bpe)(HMe₂mal)₂]·H₂O, [Cu(bpe)(Me₂mal)]·H₂O, [Cu₄(bpe)₃(Et₂mal)₄]·5H₂O, [Cu₄(bpa)₃(Et₂mal)₄]·5.5H₂O, [Cu(bpe)(Amal)]·0.25H₂O, and [Cu(bpa)(Amal)]·0.25H₂O (H₂mal = malonic acid, H₂Me₂mal = dimethylmalonic acid, H₂Et₂mal = diethylmalonic acid, H₂Amal = allylmalonic acid), were synthesized and characterized. Four of them realized the square lattice topology (sql) of their underlying nets, which is highly abundant for copper(II) malonates with N,N′-containing linkers but rarely occurs in similar complexes based on other transition metals. The UV-sensitivity of the bpe-containing complexes as well as of the previously reported complex [Cu₄(bpe)₃(mal)₄]·6H₂O was studied; and [Cu₄(bpe)₃(mal)₄]·6H₂O was found to undergo a single-crystal-to-single-crystal photoinitiated [2 + 2] cycloaddition reaction to [Cu₄(bpe)(tpcb)(mal)₄]·6H₂O (tpcb = rctt-1,2,3,4-tetrakis(pyridin-4-yl)cyclobutane). The dc-magnetic measurements of the complexes [Cu(bpe)(Me₂mal)]·H₂O, [Cu(bpe)(Amal)]·0.25H₂O and [Cu(bpa)(Amal)]·0.25H₂O indicated the presence of very weak antiferromagnetic intermolecular interactions. Using EPR spectroscopy, it was shown that the distortion of the polyhedron of the copper(II) atom corresponded to a change in the anisotropy of the g-tensor.