How to make a better magnet? Insertion of additional bridging ligands into a magnetic coordination polymer

A three-dimensional cyanide-bridged coordination polymer based on FeII (S = 2) and NbIV (S = 1/2) {[FeII(H2O)2]2[NbIV(CN)8]·4H2O}n (Fe2Nb) was modified at the self-assembly stage by inserting an additional formate HCOO− bridge into its cyanide framework. The resulting mixed-bridged {(NH4)[(H2O)FeII-(μ-HCOO)-FeII(H2O)][NbIV(CN)8]·3H2O}n (Fe2NbHCOO) exhibited additional FeII-HCOO-FeII structural motifs connecting each of the two FeII centers. The insertion of HCOO− was possible due to the substitution of some of the aqua ligands and crystallization water molecules in the parent framework by formate anions and ammonium cations. The formate molecular bridge not only shortened the distance between FeII ions in Fe2NbHCOO from 6.609 Å to 6.141 Å, but also created additional magnetic interaction pathways between the magnetic centers, resulting in an increase in the long range magnetic ordering temperature from 43 K for Fe2Nb to 58 K. The mixed-bridged Fe2NbHCOO also showed a much broader magnetic hysteresis loop of 0.102 T, compared to 0.013 T for Fe2Nb

Approximate approach to magnetic and thermodynamic properties of mixed spin (1/2-S) chains with AB and AB2AB_2 topology

Motivated by the rapid development in the synthesis of novel molecule-based magnets, we have investigated magnetic and thermodynamic properties of mixed spin (s–S) exchange coupled chains displaying a simple linear AB or a knotted AB2 arrangement. Approximate approach for s = 1/2 and S ≥ 5/2, treating at an intermediate step spin S operator as a commuting variable and using the transfer matrix technique, is used. Susceptibility, magnetization and heat capacity of both spin systems are evaluated numerically from the corresponding free energy for S = 5/2. Uniform ferromagnetic and antiferromagnetic couplings are discussed. The procedure reproduces the right values of saturation magnetization and the entropy content of the systems, corroborating its correctness. χT curves are shown to depend crucially on the µBH/J ratio. For zero-field heat capacity a double-peak structure is revealed for the AB chain, whereas for the AB2 chain only one broad anomaly is observed

Bis(triphenylphosphine)iminium salts of dioxothiadiazole radical anions : preparation, crystal structures, and magnetic properties

Phenanthroline dioxothiadiazoles are redox active molecules that form stable radical anions suitable for the construction of supramolecular magnetic materials. Herein, the preparation, structures and magnetic properties of bis(triphenylphosphine)iminium (PPN) salts of [1,2,5]thiadiazole[3,4-f][1,10]phenanthroline 1,1-dioxide (L), [1,2,5]thiadiazole[3,4-f][4,7]phenanthroline 1,1-dioxide (4,7-L), 5-bromo-[1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline 2,2-dioxide (BrL), and 5,10-dibromo-[1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline 2,2-dioxide (diBrL) are reported. The preparation of new bromo derivatives of the L: 5-bromo-[1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline 2,2-dioxide (BrL) and 5,10-dibromo-[1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline 2,2-dioxide (diBrL)—suitable starting materials for further derivatization—are described starting from a commercially available and cheap 1,10-phenanthroline. All PPN salts show antiferromagnetic interactions between the pairs of radical anions, which in the case of PPN(diBrL) are very strong (−116 cm−1; using Ĥ = −2JSS type of exchange coupling Hamiltonian) due to a different crystal packing of the anion radicals as compared to PPN(L), PPN(4,7-L), and PPN(BrL)

Crystal engineering and photomagnetic studies of CN-bridged coordination polymers based on octacyanidometallates(IV) and [Ni(cyclam)]2+[Ni(cyclam)]^{2+}

[Image: see text] A series of new CN-bridged coordination networks of different dimensionality and topology was obtained through the modification of reaction conditions between [Ni(cyclam)](2+) (cyclam = 1,4,8,11-tetraazacyclotetradecane) and [W(CN)(8)](4–). The factors determining the reaction pathway are temperature and addition of the LiCl electrolyte. The products include three negatively charged frameworks incorporating Li(+) guests: the 1D Li(2)[Ni(cyclam)][W(CN)(8)]·6H(2)O (1) straight chain, the 1D Li(2)[Ni(cyclam)][W(CN)(8)]·2H(2)O (2) zigzag chain, and the 2D Li(2)[Ni(cyclam)](3)[W(CN)(8)](2)·24H(2)O (3) honeycomb-like network, as well as the 3D two-fold interpenetrating [Ni(cyclam)](5)[Ni(CN)(4)][W(CN)(8)](2)·11H(2)O (4) network and the 1D [Ni(cyclam)][Ni(CN)(4)]·2H(2)O (5) chain, which result from partial decomposition of the starting complexes. Together with the previously characterized 3D [Ni(cyclam)](2)[W(CN)(8)]·16H(2)O (6) network, they constitute the largest family of CN-bridged coordination polymers obtained from the same pair of building blocks. All compounds exhibit paramagnetic behavior because of the separation of paramagnetic nickel(II) centers through the diamagnetic polycyanidometallates. However, the presence of the photomagnetically active octacyanidotungstate(IV) ions allowed observation of the magnetic superexchange after the violet light excitation (405 nm) for compound 3, which constitutes the first example of the photomagnetic effect in a Ni(II)–[W(IV)(CN)(8)] system. The photomagnetic investigations for fully hydrated and dehydrated sample of 3, as well as for the isostructural octacyanidomolybdate(IV)-based network are discussed

Plasma treatment as an unconventional molecular magnet engineering method

Molecular magnetism aims to design materials with unique properties at the molecular level, focusing on the systematic synthesis of new chemical compounds. In this paper, we propose an alternative route to engineer molecular magnetic materials through plasma irradiation. Our research indicates that the long-range magnetic order temperature in the three-dimensional $\mathrm{\{[Mn^{II}(H_2O)_2]_2[Nb^{IV}(CN)_8]\cdot 4H_2O\}_n}$ molecular ferrimagnet increases by 20 K after plasma treatment. The core structure of the compound does not reveal significant changes after plasma processing, as confirmed by the X-ray powder diffraction analysis. The observed results are attributed to the release of crystallized water molecules. The described procedure can serve as a viable approach to altering the magnetic properties of the molecular systems.Comment: 6 pages, 4 figure