Syntheses, Crystal Structures, Magnetic Behaviours, and Thermal Properties of Three Hydrogen-Bonding Networks Containing Dicyanamide and 4-Hydroxypyridine

Lingling Zheng

doi:10.1155/2013/291703

Abstract

Three new dicyanamide-bridged polymeric complexes of{[Mn(dca)2(L)2]·2H2O}n(1),{[Cd(dca)2(L)2]·2H2O}n(2), and{[Co(dca)2(L)2]2(L)}n(3) (dca = dicyanamide, L = pyridinium-4-olate) have been synthesized and structurally characterized. In the three compounds, the protons of hydroxyl groups of 4-hydroxypyridine transfer to pyridyl nitrogen atoms. Compounds1and2are isomorphous forming one-dimensional[M(dca)2(L)2]nchains where metals are connected by double dca anions. These one-dimensional chains are extended into two-dimensional layers through weak C–H⋯N hydrogen bonds. Further, these layers are assembled into a three-dimensional supramolecular network through N–H⋯O, O–H⋯O hydrogen bonds. Complex3is a coordination layer of (4, 4) topology with octahedral metal centers linked by four singleμ1,5-bridges. These layers are interlocked by N–H⋯O, O–H⋯O hydrogen bonds from coordinated water molecules and free L molecules, which leads to a three-dimensional supramolecular architecture. The variable temperature magnetic susceptibilities measurement of compounds1and3shows the existence of weak antiferromagnetic interactions between the metal centers. The thermogravimetric analyses of the compounds1–3are also discussed.

Highlights

The coordination polymers [1] based on dicyanamide [dca, N(CN)2−] have drawn great interest in the last two decades, due to their attractive structures and magnetic properties: three-dimensional rutile-like structure of [M(dca)2] shows long-range magnetic ordering [2,3,4] and low-dimensional system when auxiliary ligand is introduced to form [M(dca)2(L)x] [5,6,7,8,9,10,11]
We chose 4-(4H-imidazol-4-yl) benzenamine and isonicotinamide as the coligands, and five supramolecular architectures were obtained [20,21,22], in which the metal centers coordinates to the imidazole nitrogens or pyridyl nitrogen atoms, and the –NH2, –CONH2 groups act as hydrogen bond donor to form strong intermolecular hydrogen bonds
To further explore the work of metal dca and discuss the influence of hydrogen bonding interactions on the ultimate architecture, we focus on the context with other terminal ligands, in which 4-hydroxypyridine is employed as the auxiliary ligand, and three coordination polymers {[Mn(dca)2(L)2] ⋅ 2H2O}n (1), {[Cd(dca)2(L)2] ⋅ 2H2O}n (2), and {[Co(dca)2(L)2]2(L)}n (3) (L = pyridinium-4-olate) via dca connectors are prepared and structurally determined by X-ray single crystal diffraction

Summary

Introduction

The coordination polymers [1] based on dicyanamide [dca, N(CN)2−] have drawn great interest in the last two decades, due to their attractive structures and magnetic properties: three-dimensional rutile-like structure of [M(dca)2] shows long-range magnetic ordering [2,3,4] and low-dimensional system (one-dimension or two-dimension) when auxiliary ligand is introduced to form [M(dca)2(L)x] [5,6,7,8,9,10,11]. In addition to coordination interaction, some weak interactions, such as intra- and/or intermolecular hydrogen-bonding interactions, and π-π stacking supramolecular interactions greatly affect the ultimate structures, especially in the field of extending lowdimensional entities to higher-dimensional supramolecular frameworks [15, 16]. When terminal ligands are 4-picoline [17] and cyanopyridine [18], only one-dimensional chains are obtained, the intermolecular ππ stacking interactions extend these one-dimensional coordination chains into two-dimensional or three-dimensional networks, which indicates that intermolecular interactions play an important role in constructing supramolecular architectures. The research focus on crystal engineering of dca through intramolecular interactions remains limited [19], especially using hydrogen-bonding interaction to construct higher-dimensional architectures.

Methods

Discussion

Conclusion