Syntheses, Structures And Magnetic Properties Of Coordination Polymers With Azacyclic Ligands Or Azides

Coordination polymers, which exhibit admirable potential application in porous, catalysis, optic, electricity, and magnetism, have attracted considerable attention in recent years. To build novel coordination compounds, discover new magnetic phenomena, and investigate the correlationship between structure and magnetic properties, twenty-eight transition metal coordination compounds based on azacyclic ligands or azides have been prepared and structurally characterized, and the magnetic properties of some of them have been characterized.This dissertation covers the following four parts:1. Coordination polymers with tetrazolate-5-carboxylate (H2tzc)The tetrazolate-5-carboxylate (H2tzc), which is the simplest ligand that contains both tetrazolate and carboxylate, has not yet been explored in coordination chemistry. The ligand is expected to be a versatile bridge that can mediate strong magnetic coupling. Based on above consideration, we investigated the coordination chemistry and magnetism of H2tzc.(i) We have revealed nine binuclear compounds synthesized by the reaction of H2tzc, a system of chelating pyridine ligands, and transitional metal ions of Mn(II), Co(II), Ni(II) and Zn(II). In all the binuclear compounds, the tzc ligand exhibits double N-N bridging modes. Magnetic properties revealed that the double N-N bridges can transmit weak ferromagnetic couplings in some binuclear compounds, which is unusual in compounds which bear the similar N-N bridge.(ii) Syntheses, structures, and properties of a system of transition metal (Mn(II), Co(II) and Zn(II)) coordination polymers from one-dimensional (1D) to three-dimensional (3D) with different pyridine bridging ligands 4,4'-pyridine (4,4'-bpy),1,2-bis(4-pyridyl)ethane (bpea), 1,3-bis(4-pyridyl)propane (bpp) as coligands. As 4,4'-bpy as coligand, a two-dimensional (2D) layer structure has been obtained, while the bpp ligand lead to a cocrystal of Mn(II)-tzc chain. It is worth noting that isomorphous compounds [M2(tzc)2(bpea)](M=Mn(14), Co(15)), in which bpea as coligands, exhibit a unprecedented self-penetrated 3,4-connected topology (4·82·103)(4-82). Meanwhile, because of the different single-ion anisotropy, the two compounds show distinct bulk magnetic behaviors:the CoⅡcompound shows a combination of canted antiferromagnetism and metamagnetism, whereas the MnⅡcompound is a typical antiferromagnetic system.2. Coordination polymers with bis(5-tetrazolyl)methane (H2btm)The bis(5-tetrazolyl)methane (H2btm) may lead to various structures and magnetic properties for it bearing two tetrazol groups. The magnetic investigation of H2btm compounds had not been reported before our work. Two Manganese(II) coordination polymers with H2btm ligand and neutral pyridine auxiliary ligands (phen or 2,2'-bpy) have been synthesized, and structurally and magnetically characterized. In these two compounds, btm exhibits different coordination modes, and all the modes lead to weak antiferromagnetic couplings.3. Azido coordination compounds with methylpyridiniumcarboxylates (mpc-2-mpc-4) as co-ligandsCarboxylate and azide are both strong magnetic mediator. Thus, in order to obtain strong magnetic couplings, we try to obtain cobridges of both carboxylate and azide with simple N-methylpyridinium-n-carboxylate ligands (mpc-2, mpc-3 and mpc-4 for n=2,3 and 4, respectively).Seven Manganese(II), Cobalt(II) and Nickel(II) compounds with mixed azide and zwitterionic carboxylate ligands, have been synthesized, and structurally and magnetically characterized. [M(N3)2(mpc-2)] (mpc-2= N-methylpyridinium-2-carboxylate, and M=Co for 20 and Mn for 21), [M(N3)2(mpc-4)] (mpc-4= N-methylpyridinium-4-carboxylate, and M= Co for 22, Mn for 23, and Ni for 26), [Co(N3)2(mpc-3)(CH3OH)] (24) and [Mn3(N3)6(mpc-3)2] (25). Compounds 20,21,22 and 26 consist of 1D uniform chain compounds with (μ-EO-N3)2(μ-COO) triple bridges (EO= end-on); 24 is also a chain compound but with alternating triple [(μ-EO-N3)2(μ-COO)] and double EO-N3 bridges; compound 23 contains 2D layers with alternating triple [(μ-EO-N3)2(μ-COO)], double [(μ-EO-N3)(μ-COO)] and single (EE-N3) bridges (EE=end-to-end); 25 is a 2D compound in which the chains similar to those in 5 are cross-linked byμ3-1,1,3-N3 azide.(i) The above simultaneous azide and carboxylate triple bridges mediate antiferromagnetic coupling in Mn(II) chains (21) but ferromagnetic coupling in Co(II) and Ni(II) chains (20,22,24 and 26).(ii) Magnetic measurement shows that the two Co(II) compounds (20 and 22) with similar 1D chain structure all exhibit intrachain FM interactions but with different bulk properties:20 displays SCM-like (SCM=single-chain-magnet) relaxation dynamics,22 is an antiferromagnet with field-induced metamagnetism. The differences have been justified based on the interchain interactions related to the different interchainπ-πstacking and/or the intrachain FM coupling through the different intrachain bridges.(iii) [Co(N3)2(mpc-3)(CH3OH)] (24), in which both the triple bridges and double bridges mediate strong ferromagnetic couplings, behaves as a non-innocent SCM influenced by weak antiferromagnetic interchain interactions.(iv) The 2D Mn(II) layers, compounds 23 and 25 exhibit different weak ferromagnetism due to spin-canting.4. Azido coordination compounds with oxazoline ligands (Lo1 and Lo2) as co-ligandsFor the study of magneto-structural correlations, particular attention has been paid to binuclear Cu(II) systems. For this system, nature and magnitude of the magnetic exchange depend on the positions of the N briding atom and the Cu-N-Cu bridging angle. The EO azide bridge may adopt the "symmetric" equatorial-equatorial (eq-eq) fashion or the asymmetric equatorial-axial (eq-ax) fashion.As two oxazoline as coligands, two double EO azido copper (II) binuclear complexes have been synthesized and structurally and magnetically characterized. In compound 27, the eq-ax EO azide bridges transmit antiferromagnetic behavior. It is worth noting that in compound 27, the two Cu-N-Cu bridging angles are respectively smaller and larger than the critical 108°value which distinguishes the ferromagnetic and antiferromagnetic regimes in eq-eq systems. Magnetic measurements shows that the two different bridges compete to settle a net antiferromagnetic coupling between the Cu(II) ions. These features are intriguing from the viewpoints of magneto-structural studies.