Homochiral coordination polymers constructed from V-shaped oxybisbenzoyl-based amino acid derivatives: structures, magnetic and photoluminescence properties

Abstract

Five novel homochiral coordination polymers (HCPs) [Cu₂(ODBALa)₂(bpa)₂H₂O]·7H₂O (1), [M(ODBALa)H₂O]·H₂O (M = Mn for 2; Co for 3), [Cu(ODBPRo)(bpe)]·7H₂O (4) and [Cd_2.5(ODBPRo)(HODBPRo)₃(bpe)_2.5]·13H₂O (5) have been successfully synthesized by using designed chiral 4,4′-oxybisbenzoyl alanine/proline derivatives in the absence/presence of N-donor ancillary ligands, where H₂ODBALa = 4,4′-oxybisbenzoyl-bis(L-alanine), H₂ODBPRo = 4,4′-oxybisbenzoyl-bis(L-proline), bpa = 1,2-bis(4-pyridyl)ethane, and bpe = 1,2-bis(4-pyridyl)ethene. Interestingly, the combination of the chiral derivatives and metal ions gives various chiral metal–organic fragments, which are connected by N-donor ancillary ligands to construct the intriguing homochiral structures. In 1, 40-membered [Cu₂(ODBALa)₂] metallacycles as beads are strung by bpa ligands, yielding a one-dimension (1D) tortuous chain. Compounds 2 and 3 are isomorphous and possess a 3D metal–organic framework, embedding the unique (μ₂-COO)(μ₂-O_carboxylate)(μ₂-H₂O) triple-bridges and twisted (–Mn₄(ODBALa)₄–)_n left-handed helical chains. In 4, the [Cu(ODBPRo)]_n left-handed helical chains are linked by bpe ligands to constitute a high undulated 2D layer. In 5, the crab-like [(Cd1)₂(Cd2)(Cd3)₂(HODBPRo)₆(ODBPRo)₂] fragments are joined together to form a 1D left-handed helical chain, which is further connected by bpe ligands to build a remarkable layered network. Magnetic susceptibility measurements of 2 and 3 indicate typical antiferromagnetic behaviour between the triple-bridging Mn(II) ions in 2, whereas ferromagnetic coupling between the triple-bridging Co(II) ions exists in 3. Moreover, the photoluminescent spectrum of 5 exhibits a strong solid-state emission at 414 nm.