Syntheses, characterization, and luminescent properties of four alkaline earth metal-organic frameworks based on two similar N-containing carboxylates

Four coordination polymers ([Ca(3-pa)(2)(H(2)O)(2)]center dot 3H(2)O) (1), ([Sr(3-pa)(2)(H(2)O)(2)]center dot 3H(2)O} (2), {[Ca(4-pa)(2)(H(2)O)(4)]} (3) and ([Sr(4-pa)(H(2)O)(6)]center dot[4-pa]} (4), (3-pa = pyridine-3-carboxylate, 4-pa = pyridine-4-carboxylate) have been synthesized and structurally characterized. Lots of noncovalent interactions were found in the four compounds, aiding the formation of high-dimensional architectures from the low-dimensional structures. Complex I and 2 feature similar I-D chain structures, which adopt face-to-face orientation to form an interesting 2-D network with pipe-like motif. Chain-like water clusters consisting of infinite tetragonal unit are trapped and stabled in the vacuums of the pipelines. The 2-D sheets are further connected into 3-D architecture by noncovalent interactions. Complex 3 has a discrete mononuclear structure, which is further connected into a 3-D framework by hydrogen bonds and pi center dot center dot center dot pi interactions. In complex 4, the zigzag-like chain structure units are parallel to each other and pack in ABAB mode to give rise to a 2-D network, which is stabled by pi center dot center dot center dot pi stacking and hydrogen bonds. The counteranions in 4 are hosted between the nets and act as "glue" linking the 2-D networks into a 3-D architecture. In addition, the photoluminescence properties of the compounds have been investigated. (C) 2009 Elsevier Ltd. All rights reserved.