Zhuo-Jia Lin

Pure Trinuclear 4 f Single-Molecule Magnets: Synthesis, Structures, Magnetism and Ab Initio Investigation

A family of linear Dy(3) and Tb(3) clusters have been facilely synthesized from the reactions of DyCl(3), the polydentate 3-methyloxysalicylaldoxime (MeOsaloxH(2) ) ligand with auxiliary monoanionic ligands, such as trichloroacetate, NO(3)(-), OH(-), and Cl(-). Complexes 1-5 contain a nearly linear Ln(3) core, with similar Ln···Ln distances (3.6901(4)-3.7304(3) Å for the Dy(3) species, and 3.7273(3)-3.7485(5) Å for the Tb(3) species) and Ln···Ln···Ln angles of 157.036(8)-159.026(15)° for the Dy(3) species and 157.156(8)-160.926(15)° for the Tb(3) species. All three Ln centers are bridged by the two doubly-deprotonated [MeOsalox](2-) ligands and two of the four [MeOsaloxH](-) ligands through the N,O-η(2)-oximato groups and the phenoxo oxygen atoms (Dy-O-Dy angles=102.28(16)-106.85(13)°; Tb-O-Tb angles=102.00(11)-106.62(11)°). The remaining two [MeOsaloxH](-) ligands each chelate an outer Ln(III) center through their phenoxo oxygen and oxime nitrogen atoms. Magnetic studies reveal that both Dy(3) and Tb(3) clusters exhibit significant ferromagnetic interactions and that the Dy(3) species behave as single-molecule magnets, expanding upon the recent reports of the pure 4f type SMMs.

Tuning the Spin States of Two Apical Iron(II) Ions in the Trigonal‐Bipyramidal [{FeII(μ‐bpt)3}2FeII3(μ3‐O)]2+ Cations Through the Choice of Anions

When located in octahedral environment, the iron(II) ion with a d electronic configuration may adopt two different stable electronic states, namely, a diamagnetic low-spin (LS) state and a paramagnetic high-spin (HS) state, which both give rise to different magnetic, optical and electronic properties. So tuning the spin state of the iron(II) ion is significant and contributes to the development of amazing materials that can be used as molecular switches, sensors and display devices. As is well established, the spin state depends on relative strength of spin paring energy (P) and splitting energy (D0). If the former is much stronger than the latter, the HS state will be stabilised, and if D0 is stronger then the LS state will be the ground state. If P and D0 are comparable a spin crossover (SCO) may occur between the HS and LS state by external perturbations such as temperature, pressure or light irradiation. So the main task is to make a judicious choice of ligand, which can impose a proper ligand-field strength. However, in reality, the spin state of the iron(II) ion is quite sensitive to even more subtle changes such as solvent molecules, polymorphism and counterions. As one of the best representatives of switchable molecules, SCO materials have attracted considerable interest in the chemistry and materials fields. Current work mainly focuses on the enhancement of cooperativity, which results in an abrupt transition and a wider thermal hysteresis. Another promising research area, but with few examples, is the combination of magnetic-exchange and spin-transition (ST) phenomena in the same molecule or polymeric network, which could eventually afford new switching materials with considerable amplification of the response signal. Much more work should be done to expand our knowledge of spin electronics. To induce a ST, the most common method is by varying the temperature. However, light-and pressure-induced SCOs play an increasingly important role owing to their potential applications as optical and pressure switches, for example. Moreover, the latter two methods are not restricted to thermal SCO compounds: LIESST (light-induced excited spinstate trapping) may also be observed in LS compounds, whereas HS compounds may experience STs with the application of external hydrostatic pressure. Although there are many examples that exhibit thermal STs, rare spin-crossover clusters of iron(II) have been found to exhibit a mixed-spin structure and synergy between ST and magnetic interaction. Fortunately, by introducing counterions, we have successfully tuned the spin states of two apical iron(II) ions in the pentanuclear [{Fe ACHTUNGTRENNUNG(m-bpt)3}2FeII3ACHTUNGTRENNUNG(m3-O)]2+ (Hbpt=3,5-bis(pyridin-2-yl)-1,2,4-triazole) cations through anions. Both apical ions are of LS states in [{Fe ACHTUNGTRENNUNG(mbpt)3}2Fe II 3ACHTUNGTRENNUNG(m3-O)] ACHTUNGTRENNUNG(NCS)2·10H2O (1), [{Fe ACHTUNGTRENNUNG(m-bpt)3}2FeII3ACHTUNGTRENNUNG(m3O)] ACHTUNGTRENNUNG(ClO4)2·3H2O (2) and [{FeIIACHTUNGTRENNUNG(m-bpt)3}2FeII3ACHTUNGTRENNUNG(m3-O)]I2· 4MeCN (3), and are of HS states in [{Fe ACHTUNGTRENNUNG(m-bpt)3}2FeII3ACHTUNGTRENNUNG(m3O)] ACHTUNGTRENNUNG[FeIII2ACHTUNGTRENNUNG(m-O)Cl6]·1/2H2O (4). In this new {Fe5} family, two new developments have been achieved: 1) The ligand 4amino-3,5-bis(pyridine-2-yl)-1,2,4-triazole (abpt) has been, for the first time, used to produce the oxo-centred polynuACHTUNGTRENNUNGcle ACHTUNGTRENNUNGar iron(II) complexes; 2) Two types of spin topology have been trapped in the [{Fe ACHTUNGTRENNUNG(m-bpt)3}2FeII3ACHTUNGTRENNUNG(m3-O)]2+ cluster that are controlled by counterions. Note that only one [a] X. Bao, J.-D. Leng, Z.-S. Meng, Dr. Z.-J. Lin, Prof. Dr. M.-L. Tong Key Laboratory of Bioinorganic and Synthetic Chemistry of Ministry of Education State Key Laboratory of Optoelectronic Materials and Technologies School of Chemistry & Chemical Engineering Sun Yat-Sen University, Guangzhou 510275 (P.R. China) Fax: (+86) 20-8411-2245 E-mail : tongml@mail.sysu.edu.cn [b] Dr. M. Nihei, Prof. Dr. H. Oshio Graduate School of Pure and Applied Sciences University of Tsukuba, Tennodai 1-1-1, Tsukuba 305-8571 (Japan) Fax: (+81) 29-853-4238 E-mail : oshio@chem.tsukuba.ac.jp Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201000526.

Chloride templated formation of {Dy12(OH)16}20+ cluster core incorporating 1,10-phenanthroline-2,9-dicarboxylate

Two unique dysprosium(III) coordination compounds with similar dodecanuclear clusters composed of four vertex-sharing cubane-like units, [2Cl− ⊂ {Dy12(OH)16(phenda)8(H2O)8}]2+, were reported. Magnetic studies reveal that both compounds exhibit slow magnetic relaxation.

Gadolinium oxalate derivatives with enhanced magnetocaloric effect via ionothermal synthesis.

Two new oxalate-bridged Gd(III) coordination polymers, namely, (choline)[Gd(C2O4)(H2O)3Cl]Cl·H2O (1) and [Gd(C2O4)(H2O)3Cl] (2), were first obtained ionothermally by using a deep eutectic solvent (DES). The magnetic studies and heat capacity measurements reveal that the two-dimensional Gd(III)-based coordination polymer of 2 has the higher magnetic density and exhibits a larger cryogenic magnetocaloric effect (MCE) (ΔS(m) = 48 J kg(-1) K(-1) for ΔH = 7 T at 2.2 K).

Synthesis, structure, photoluminescence and magnetic properties of new 3-D lanthanide-pyridine-2,4,6-tricarboxylate frameworks

Seven 3-D (3D) metal–organic framework solids [Nd2(pyta)2(H2O)6]n1 and {[Ln2(pyta)2(H2O)x]·yH2O}n (Ln = Sm 2, Eu 3, Gd 4 with x = 3, y = 2.5; Ln = Tb 5 with x = 2, y = 2.5, Ln = Dy 6, Ho 7 with x = 2, y = 2), H3pyta = 2,4,6-pyridinecarboxylic acid) have been prepared under hydrothermal conditions. X-Ray structural analysis shows that compound 1 crystallises in monoclinic space groupPc and all Ln(III) ions are nine-coordinated. The 3D framework of 1 is constructed from [Nd4(µ4-pyta)2]n chains with 1D small channels along the a axis. Isomorphous compounds 2–7 crystallise in C2/c space group and are composed of alternative [Ln4(µ5-pyta)2]n chains and [Ln6(µ4-pyta)2]n helical chains. The completely deprotonated pyta3− ligands adopt µ4-bridging coordination modes in 1, and µ4-, µ5-bridging modes in 2–7. The Sm(III) 2, Eu(III) 3, Tb(III) 5 and Dy(III) 6 compounds exhibit characteristic photoluminescence (PL) in the visible region and the Nd(III) 1 and Ho(III) 7 compounds show photoluminescence in the near-infrared (NIR) region. The magnetic properties of three heavy lanthanide ions Gd(III) 4, Dy(III) 6 and Ho(III) 7 compounds were investigated in the temperature range of 2–300 K.

Spin Crossover versus Low‐Spin Behaviour Exhibited in 2D and 3D Supramolecular Isomers of [FeII(2,4‐bpt)2]⋅Guest

The bistable properties (magnetic, structure and colour) of spin crossover (SCO) materials have resulted in a bright future for their applications as molecular memory, molecular switches, molecular sensors, data storage and display devices. Spin transitions (STs) between high(HS) and lowspin (LS) states can be achieved by external stimuli, such as temperature, pressure, light, magnetic or electrical switching. From practical aspects, the design and the synthesis of SCO compounds with high transition temperatures, wide thermal hysteresis and thermochroism are of crucial importance. Two strategies have been universally acknowledged to improve the cooperatives: 1) to construct covalently bridged coordination polymers; 2) to enrich intermolecular interactions, such as hydrogen bonding and p–p stacking. However, in reality, it is hard to predict theoretically the SCO property of a material until it has been characterised. The sensitivity of the SCO property to subtle changes does cause problems, but from another perspective, it may also be viewed as an opportunity to deepen our knowledge of the nature of SCO. To this end, the rich structural diversity of supramolecular isomers provided us a useful and unique perspective to understand structure–property relationships. As a branch of isomerism, polymorphism-dependent SCO compounds are not uncommon, however, most of which are mononuclear. To the best of our knowledge, only two examples focus on structural isomerism and another shows catenane isomerism-dependent SCO properties. Herein, we report the crystal structures and physical properties of four supramolecular isomers based on [FeACHTUNGTRENNUNG(2,4bpt)2]·guest (2,4-Hbpt= 3-(2-pyridyl)-5-(4-pyridyl)-1,2,4-triazole): a 2D SCO polymer [FeACHTUNGTRENNUNG(2,4-bpt)2] (1·Fe), two LS twofold interpenetrated 3D coordination polymers with NbO topology, [Fe ACHTUNGTRENNUNG(2,4-bpt)2]·2.17 H2O (2 a) and [Fe ACHTUNGTRENNUNG(2,4bpt)2]·2.5 H2O (2 b) and a LS non-interpenetrated 3D coordination polymer with NbO topology, [FeACHTUNGTRENNUNG(2,4bpt)2]·4 dioxane·4 H2O (3). It should be mentioned that these complexes include all kinds of isomers except for optical isomers, that is, structural, conformational and catenane supramolecular isomerism. Moreover, a cobalt analogue and a Fe Co solid solution species: [Co ACHTUNGTRENNUNG(2,4-bpt)2]·0.5 H2O (1·Co) and [FexCo1 x ACHTUNGTRENNUNG(2,4-bpt)2] (x=0.93) (1·Fe–Co) have also been synthesised and characterised. The latter compound allows us to investigate SCO properties in a doped system. Our work provides a good example to study magneto–structural relationships. We choose the 2,4-Hbpt ligand mainly for the following reasons: 1) as a variant of the well-studied ligand 2,2-Rbpt (2,2-Rbpt= 4-substituted 3,5-di(2-pyridyl)-1,2,4-triazole), it should also provide an appropriate ligand field favouring the occurrence of SCO; 2) it is a good candidate to construct a coordination polymer by using the 4-position N atom, thus enhancing cooperation between SCO sites; 3) the ligand can take on abundant conformations due to its rotatable feature, thus resulting in a variety of isomers and fits our need to study structure-dependent SCO properties. All products are synthesised in solvothermal conditions at 160 8C for 3 days. However, different solvent media have an important influence on the final products. By hydrothermal treatment, five products are captured, namely, two mononuclear polymorphs based on [FeACHTUNGTRENNUNG(2,4-bpt)2ACHTUNGTRENNUNG(H2O)2],[10] 1·Fe, 2 a and 2 b. However, there are problems with low yields for all products and also poor reproducibility. So it was laborious work to collect pure 1·Fe to study its magnetic behaviour. [a] X. Bao, J.-L. Liu, J.-D. Leng, Dr. Z. Lin, Prof. Dr. M.-L. Tong Key Laboratory of Bioinorganic and Synthetic Chemistry of Ministry of Education State Key Laboratory of Optoelectronic Materials and Technologies School of Chemistry & Chemical Engineering Sun Yat-Sen University Guangzhou 510275 (P.R.China) Fax: (+86) 20-8411-2245 E-mail : tongml@mail.sysu.edu.cn [b] Dr. M. Nihei, Prof. Dr. H. Oshio Graduate School of Pure and Applied Sciences University of Tsukuba, Tennodai 1-1-1, Tsukuba 305-8571 (Japan) [**] 2,4-Hbpt=3-(2-pyridyl)-5-(4-pyridyl)-1,2,4-triazole Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201001179.

Anion-dependent construction of copper(I/II)-1,2,4,5-tetra(4-pyridyl)benzene frameworks

The unique tetrapyridyl ligand 1,2,4,5-tetra(4-pyridyl)benzene (bztpy) isolated from previous hydrothermal in situ metal ligand reaction is found to exhibit remarkable anion-dependent assembly of a series of novel metal–organic frameworks (MOFs), [Cu2(CN)2(bztpy)] (1), [Cu(SO4)(bztpy)]·1.5H2O (2), [Cu2Br2(bztpy)]·MeCN (3) and [Cu10I10(bztpy)2]·2H2O (4), which were synthesized under hydro/solvothermal conditions. These MOFs were characterized by elemental analysis, IR and single-crystal X-ray diffraction. Compound 1 consists of [Cu(CN)]n chains that link the neighbouring ones via tetradentate bztpy bridges to form a corrugated 2D layer. When bztpy is treated with CuSO4, a 3D (3,5)-connected network 2 is obtained, in which novel [Cu(bztpy)]n ladders are interconnected by sulfate anions μ-bridges. However, Br− and I− anions assist the formation of {Cu2Br2} and {Cu10I10} SBU in the cluster-based metal–organic frameworks 3 and 4, respectively, and result in a completely different topology. Compound 3 shows a 3D PtS net, while compound 4 has a new 3D (4,8)-connected topology. A discussion of the crystal structures, as well as the coordination behaviour of the special tetrapyridyl ligand upon different geometries of the central connecter is provided. In addition, the photoluminescent properties of 1, 3 and 4 in the solid state at ambient temperature are also investigated.

Spontaneous resolution of four-coordinate Zn(II) complexes in the formation of three-dimensional metal–organic frameworks

The three-dimensional chiral helical framework of the four-coordinate zinc complexes, [Zn(bdt)]n (1a and 1b) (H2bdt = 1,4-benzeneditetrazol-5-yl), has been prepared via hydrothermal reaction. At the chiral centers, the tetrahedral zinc centers link with bdt ligands to form a chiral unc-type network, which exhibits an intense blue emission and spontaneous chiral resolution. The enantiomers of 1a and 1b have been confirmed by solid-state circular dichroism spectra.

Spontaneous resolution of chiral metal mandelates by stereochemical control

Spontaneous resolution of mandelic acid occurred upon coordination via stereochemical control on the metal centres. The ‘ideal’ octahedral coordination geometry with bis-chelation in cis-conformation is critical for chiral discrimination. The successful induction of homochiral packing of the mandelates by five different metals suggests general applicability of stereochemical control on the resolution of the chiral organic compounds.

Hydrothermal in situ ligand reaction: copper(II)-mediated stepwise oxidation of 2,3,5- and 2,4,6-trimethylpyridine to pyridinecarboxylates

Hydrothermal reactions of 2,3,5-trimethylpyridine (2,3,5-tmpy) yielded two pyridinecarboxylates, 3,5-dimethyl-2-pyridinecarboxylate (2-dmpya) and 3-methyl-2,5-pyridine dicarboxylate (2,5-mpyda) in the presence of copper nitrate. The in situ generated pyridinecarboxylates were derived from copper-mediated stepwise oxidation of 2- or/and 5-methyl groups on the pyridine by nitrate in acidic aqueous solution. The selectivity might be due to the different electronic distribution resulting from the asymmetric substitution on the aromatic ring and steric hindrance between two neighboring methyl groups. When 2,4,6-trimethylpyridine (2,4,6-tmpy) was used in the reactions, the three evenly-distributed methyl groups were oxidized simultaneously to form 2,4,6-pyridine tricarboxylate (2,4,6-pyta). Interestingly in nearly neutral solution a new ligand 3-hydroxy-2,4,6-pyridine tricarboxylate (2,4,6-Opyta) was yielded and trapped in the compound [Cu4(2,4,6-Opyta)2(H2O)6]·2H2O (4). The in situ copper-mediated oxidation of 2,4,6-tmpy to 2,4,6-Opyta4−via 2,4,6-pyta3− can be further supported by the formation of 4 from a hydrothermal reaction of 2,4,6-pyridine tricarboxylic acid with copper nitrate at 185 °C for 4 days. The new Opyta ligand was isolated as an ammonium (NH4)(2,4,6-OpytaH3)·H2O and characterized by NMR, MS and X-ray crystallography. The magnetic property of 4 was investigated.