| Octacyanometallates[M(CN)8]n-(M=Nb,Mo and W)are of great importance for constructing molecular magnets.The stereochemical flexibility of these building blocks facilitates the construction of various topologies and magnetic properties.They can combine Fe? ion and some pyridine-like ligands to form 3D SCO coordination polymers.The use of[M(CN)8]n-can increase not only the dimensionality for 3D magnets but also the cooperativeness of the complexes.Furthermore,it is expected that the spin-crossover magnets may show the larger thermal hysteresis loop because the complexes with ferromagnetic coupling will enhance their magnetization comparing with the pure paramagnetic complexes.In addition,they can link the metal ion with the larger magnetic anisotropy(such as Co?,et.al.)to form low dimensional magnets such as SMMs and SCMs with the help of the larger organic blocking ions.So in this paper,we synthesized a series of octacyanometallates(?)-based iron(?)complexes,clusters and one-dimension ladder-like complexes.The preparation,crystal structures and magnetic properties for all complexes were investigated in details.The content includes three parts as follow:Part ?.Using[W(CN)8]n-and[Mo(CN)8]n-unit as precursors and choosing appropriate accessorial ligands(meta-substituent and para-pyridine),reacting with Fe?,we obtained complexes 1-14.The IR spectroscopy,elemental analyses,single crystal structure and the magnetic properties of the complexes have been studied.Single crystal X-ray diffraction analysis reveals that the Fe? ions lie in the center of compressed[FeN6]octahedron in all complexes.Fe? and W? ions are alternatively bridged by cyano groups forming a three-dimensional(3D)bimetallic framework.Magnetic analysis shows complexes 1,7 and 14 display a gradual spin-crossover(SCO)phenomenon,other complexes are in the high-spin state and do not exhibit spin-crossover properties in the range of 1.8-300 K.Comparing the octahedral geometry of[FeN6]for complexes 1-6 at room temperature,the distortion of complex 1 is largest as a result of the intermolecular hydrogen bonds,which shortens the Fe-N bond distances and strengthens the ligand field around Fe? site.Meanwhile,the magnetic measurements of dehydrated samples show that the fractional conversion from high-spin to low-spin state is reduced as the increasing of vacuum drying temperature.Crystal structures and magnetic properties of 7-11 are similar to 1-5,respectively,and the powder of 7 has been reported,so they are not described in details in this work any longer.For 12-14,bpa and bpe were acted as bismonodenatate ligands.Complex 14 displays an extremely gradual and unobvious transition and only 23%of the Fe? centers switch to low spin.Part ?:Using[WV(CN)8]3-unit,Co? ions and selecting appropriate accessorial ligand 3-Mepyridine and 4-Mepyridine,with the help of bulky counter Ph4P+,we obtained two cyano-bridged CoW complexes:a linear septanuclear Co3W4 cluster(15)and trinuclear CoW2 cluster.The magnetic analysis shows that complexe 15 exhibits ferromagnetic interaction,16 represents the mixed AF-F interaction.It's a great pity to find that there is no detectable signal in the out-of-phase magnetic susceptibility above 1.8 K precluding the SMM behavior.Using[WV(CN)8]3-unit,Fe? and appropriate accessorial ligands(2-pyridyl)methanol,we obtained two iron cluster complexes 17-18.Unfortunately,[WV(CN)8]3-unit has transformed into[WIV(CN)8]4during the synthesis.Complexes 17 and 18 are composed of[Fe6O10]4+cations and the counter anions:[WIV(CN)8]4-for 17 and[Fe2?W2IV]4-for 18.The cores of the Fe6 cations all comprise two triangular[Fe?3(?3-O)(2-pyCH20H)4Cl]2+ units connected at two of their apices by two sets of bridging liangds,which are tipycal hexanuclear spin frustration system.However,they are sensitive to water so that the magnetic determination is difficult.Now we are trying our best to find an effective method.Part ?:Using[Wv(CN)s]3-unit,the Co? ions,Cu? ions and selecting appropriate accessorial ligand 3-Mepyridine,with the help of two bulky counter cations Ph4P+and Ph4As+,we obtained three unique cryano-bridged 3,3-ladder complexes 19-21 and a zigzag chain complexe 22.For 19-20,because of the intrachain ferromagnetic interaction,strong magnetic anisotropy,as well as the well isolation of individual chains,these 1D complexes,19 and 20,behave as single-chain magnets with record high spin reversal barriers(252(9)and 224(7)K)for the cyano-bridged SCMs.Furthermore,hysteresis loops can be observed for both compounds below 5 K with large coercivities of 26.2 and 22.6 kOe at 1.8 K.The structure of complex 21 is similar to 19 and 20.Magnetic investigation shows that 21 exhibits ferromagnetic behaviour with an ordering temperature Tc of ca.2.0 K.Complex 22 exhibits ferromagnetic behaviour,and signal in the out-of-phase magnetic susceptibility above 1.8 K was not detected. |
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