Gadolinium sulfate modified by formate to obtain optimized magneto-caloric effect.

Three new Gd(III) based coordination polymers [Gd2(C2H6SO)(SO4)3(H2O)2]n (1), {[Gd4(HCOO)2(SO4)5(H2O)6]·H2O}n (2), and [Gd(HCOO)(SO4)(H2O)]n (3) were obtained by modifying gadolinium sulfate. With the gradual increase of the volume ratio of HCOOH and DMSO in synthesis, the formate anions begin to coordinate with metal centers; this results in the coordination numbers of sulfate anion increasing and the contents of water and DMSO molecules decreasing in target complexes. Accordingly, spin densities both per mass and per volume were enhanced step by step, which are beneficial for the magneto-caloric effect (MCE). Magnetic studies reveal that with the more formate anions present, the larger the negative value of magnetic entropy change (-ΔSm) is. Complex 3 exhibits the largest -ΔSm = 49.91 J kg(-1) K(-1) (189.51 mJ cm(-3) K(-1)) for T = 2 K and ΔH = 7 T among three new complexes.

Design and synthesis of stable cobalt-based weak ferromagnetic framework with large spin canting angle.

It still remains a great challenge to design and construct framework-structured weak ferromagnets with large canting angle which is an effective approach for high performance magnets. According to the strategy of antisymmetric interaction causing spin canting, we report the design of four cobalt compounds, which were tested by X-ray single crystal diffraction, TGA, PXRD, and magnetic measurement. Single-crystal structure analysis reveals that compound 1 has a 2D structure, complex 2 has a 3,4-connected 3D framework, and complex 3 exhibits a 3D net structure with rare 3,5-connected 2-nodal ß-SnF2 topology and the solvent MeOH trapped in the 3D channels as guests. The magnetic property of 3 is spin canting just as designed, with TN about 4.0 K and large canting angle of 14.8°. Highly stable compound 3 sustains its framework in air for more than 12 months, in which the guest MeOH molecules can be replaced by water to form complex 4.

New entangled coordination networks based on charge-tunable keggin-type polyoxometalates.

Investigation into a hydrothermal reaction system with transition-metal (TM) ions, 1,4-bis(1,2,4-triazol-1-lmethyl)benzene (BBTZ) and various charge-tunable Keggin-type polyoxometalates (POMs) led to the preparation of four new entangled coordination networks, [Co(II) (HBBTZ)(BBTZ)2.5 ][PMo12 O40 ] (1), [Cu(I) (BBTZ)]5 [BW12 O40 ]⋅H2 O (2), [Cu(II) (BBTZ)]3 [AsW(V) 3 W(VI) 9 O40 ]⋅10 H2 O (3), and [Cu(II) 5 (BBTZ)7 (H2 O)6 ][P2 W22 Cu2 O77 (OH)2 ]⋅6 H2 O (4). All compounds were characterized by using elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and single-crystal X-ray diffraction. The mixed valence of W centers in compound 3 was further confirmed by using XPS spectroscopy and bond-valence sum calculations. In the structural analysis, the entangled networks of 1-4 demonstrate zipper-closing packing, 3D polythreading, 3D polycatenation, and 3D self-penetration, respectively. Moreover, with the enhancement of POM negative charges and the use of different TM types, the number of nodes in the coordination networks of 1-4 increased and the basic metal-organic building motifs changed from a 1D zipper-type chain (in 1) to a 2D pseudorotaxane layer (in 2) to a 3D diamond-like framework (in 3) and finally to a 3D self-penetrating framework (in 4). The photocatalytic properties of compounds 1-4 for the degradation of methylene blue under UV light were also investigated; all compounds showed good catalytic activity and the photocatalytic activity order of Keggin-type species was initially found to be {XMo12 O40 }>{XW12 O40 }>{XW12-n TMn O40 }.