Two New Three-Dimensional Pillared-Layer Co(II) and Cu(II) Frameworks Involving a [M2(EO-N3)2] Motif from a Semi-Flexible N-Donor Ligand, 5,5′-Bipyrimidin: Syntheses, Structures and Magnetic Properties

Abstract

Abstract:Two new three-dimensional (3D) Co(II)-and Cu(II)-azido frameworks, [Co 2 (N 3 ) 4 (bpym) 2 ] n (1) and [Cu 2 (N 3 ) 4 (bpym)] n (2), were successfully synthesized by introducing a semi-flexible N-donor ligand, 5,5 -bipyrimidin (bpym), with different bridging modes and orientations. Compounds 1 and 2 were structurally characterized by X-ray crystallography, IR spectroscopy, thermogravimetry and elemental analysis. Compounds 1 and 2 are 3D pillared-layer frameworks with double end-on (EO) azido bridged dinuclear motifs, [M 2 (EO-N 3 ) 2 ]. In Compound 1, the bpym ligands show trans µ 2 -bridging mode and the role as pillars to connect the Co(II)-azido layers, composed of [Co 2 (EO-N 3 ) 2 ] motifs and single end-to-end (EE) azido bridges, to a 3D network with BN topology. In contrast, in 2, the bpym ligand adopts a twisted µ 4 -bridging mode, which not only connects the adjacent [Cu 2 (EO-N 3 ) 2 ] units to a layer, but also functions as a pillar for the layers of the 3D structure. The structural diversities between the two types of architectures can be attributed to the coordination geometry preference of the metal ions (octahedral for Co 2+ and square pyramidal for Cu 2+ ). Magnetic investigations revealed that Compound 1 exhibits ferromagnetic-like magnetic ordering due to spin canting with a critical temperature, T C = 33.0 K, and furthers the field-induced magnetic transitions of metamagnetism at temperatures below T C . Compound 2 shows an antiferromagnetic ordering with T N = 3.05 K and a field-induced magnetic transition of spin-flop at temperatures below the T N .

Temperature-Controlled Assembly/Reassembly of Two Dicarboxylate-Based Three-Dimensional Co(II) Coordination Polymers with an Antiferromagnetic Metallic Layer and a Ferromagnetic Metallic Chain

“…The equatorial positions on the octahedron are occupied by four oxygen atoms (O2, O3, and their symmetrical equivalents) derived from three Me 2 mal 2− ligands, while one nitrogen atom (N1) from one bpe ligand and one oxygen atom (O6) of a terminal water molecule occupied the axial positions. The Co–O bond lengths at the Co(II) vary from 2.0747(18)–2.124(19) Å and a Co–N bond length is 2.151(2) Å, which falls in the range of values for typical octahedral Co(II) complexes [52,53]. The two carboxylate groups of the Me 2 mal 2− ligand adopt a syn – anti µ 2 :η 1 ,η 1 -bridging mode (Scheme 2a), in which the Co(II) ion is chelated by each of one oxygen atoms (O2 and O3), and connects to two crystallographically equivalent Co(II) ions through each of the other two oxygen atoms (O1 and O4).…”

A Three-Dimensional Nickel(II) Framework from a Semi-Flexible Bipyrimidyl Ligand Showing Weak Ferromagnetic Behavior

“…Although five examples of CPs with bpym ligand have been reported [20,21,22,23], examples of multi-dimensional magnetic CPs based on the bpym ligand are still rare. Therefore, in a previous study, we selected bpym as a candidate for combining with azido anions to synthesise two new series of metal-azide-bpym magnetic CPs [24,25]. In this study, we report on the use of bpym to exclusively react with the NiBr 2 without any co-bridging groups, resulting in the formation of a new 3D Ni(II) coordination polymer, [Ni(Br) 2 (bpym) 2 ] n ( 1 ).…”