Separating the ferromagnetic and glassy behavior within the metal-organic magnetNi(TCNQ)2 (original) (raw)
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Journal of Physics: Condensed Matter, 2020
The search for ferromagnetic organic-based compounds has been a particular challenge to both chemists and physicists over the past few decades. The synthesis of the Ni2A, where A is an organic acceptor; tetracyanoethene (TCNE), 3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or 7,7,8,8-tetracyanoquinodimethane (TCNQ) (Jain et al 2007 Nature 445 291), was reported to be a great advancement with claims that the ferromagnetism persisted to well above room temperature. There were, however some substantial flaws in the methodology associated with the synthesis and physical characterisation. Our work solely studies the Ni2TCNQ compound where we find no evidence for the existence of inherent ferromagnetism within the material that was reported in the original paper. Instead, we find that the magnetism is due to superparamagnetic nickel nanoparticles embedded in an amorphous matrix. It is hoped that our work will also show that one must be careful when using Ni(COD)2 as a precursor in the syn...
Chemistry of Materials, 2003
The homologous series M(TCNQ) 2 (M) Mn(II), Fe(II), Co(II), and Ni(II); TCNQ) 7,7,8,8tetracyanoquinodimethane) prepared from reactions of [M(CH 3 CN) 6 ][BF 4 ] 2 and [n-Bu 4 N]-[BF 4 ] in CH 3 CN has been carefully analyzed from the perspective of synthetic issues and physical characterization, including complete magnetic analyses by the tools of dc and ac magnetometry. The preparative method was optimized to definitively establish the reproducibility of the chemistry as judged by infrared spectroscopy, thermal gravimetric analysis, powder X-ray crystallography, and elemental analysis. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) studies results are also in accord with the conclusion that these materials are pure, isostructural phases. The dc magnetic measurements reveal a spontaneous magnetization for the four materials at low temperatures with a weak field coercivity of 20, 750, 190, and 270 G at 2 K for Mn(TCNQ) 2 , Fe(TCNQ) 2 , Co-(TCNQ) 2 , and Ni(TCNQ) 2 , respectively. At low temperatures, ac susceptibility measurements confirm the presence of a magnetic phase at 44, 28, 7, and 24 K for Mn(TCNQ) 2 , Fe(TCNQ) 2 , Co(TCNQ) 2 , and Ni(TCNQ) 2 , respectively, but do not support the description of this system as a typical magnet. In the absence of the ac magnetic data, the behavior is indicative of ferri-or ferromagnetic ordering (depending on the metal), but in fact a complete investigation of their physical properties revealed their true nature to be a glassy magnet. The glassiness, which is a high magnetic viscosity known to originate from randomness and frustration, is revealed by a frequency dependence of the ac susceptibility data and is further supported by a lack of a lambda peak in the heat capacity data. These results clearly demonstrate that molecule-based materials with a presumed magnetic ordering may not always be exhibiting truly cooperative behavior.
Chemistry of Materials, 2003
The homologous series M(TCNQ) 2 (M ) Mn(II), Fe(II), Co(II), and Ni(II); TCNQ ) 7,7,8,8tetracyanoquinodimethane) prepared from reactions of [M(CH 3 CN) 6 ][BF 4 ] 2 and [n-Bu 4 N]- [BF 4 ] in CH 3 CN has been carefully analyzed from the perspective of synthetic issues and physical characterization, including complete magnetic analyses by the tools of dc and ac magnetometry. The preparative method was optimized to definitively establish the reproducibility of the chemistry as judged by infrared spectroscopy, thermal gravimetric analysis, powder X-ray crystallography, and elemental analysis. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) studies results are also in accord with the conclusion that these materials are pure, isostructural phases. The dc magnetic measurements reveal a spontaneous magnetization for the four materials at low temperatures with a weak field coercivity of 20, 750, 190, and 270 G at 2 K for Mn(TCNQ) 2 , Fe(TCNQ) 2 , Co-(TCNQ) 2 , and Ni(TCNQ) 2 , respectively. At low temperatures, ac susceptibility measurements confirm the presence of a magnetic phase at 44, 28, 7, and 24 K for Mn(TCNQ) 2 , Fe(TCNQ) 2 , Co(TCNQ) 2 , and Ni(TCNQ) 2 , respectively, but do not support the description of this system as a typical magnet. In the absence of the ac magnetic data, the behavior is indicative of ferri-or ferromagnetic ordering (depending on the metal), but in fact a complete investigation of their physical properties revealed their true nature to be a glassy magnet. The glassiness, which is a high magnetic viscosity known to originate from randomness and frustration, is revealed by a frequency dependence of the ac susceptibility data and is further supported by a lack of a lambda peak in the heat capacity data. These results clearly demonstrate that molecule-based materials with a presumed magnetic ordering may not always be exhibiting truly cooperative behavior. (2) (a) Ferraris, J.; Cowan, D. O.; Valatka, V. V.; Perlstein, J. H. J. Am. Chem. Soc., 1973, 95, 948. (b) Coleman, L. B.; Cohen, M. J.; Sandman, D. J.; Yamagishi, F. G.; Garito A. F.; Heeger, A. Calabrese, J. C.; Harlow, R. L.; Dixon, D. A.; Zhang, J. H.; Reiff, W. M.; Chittipeddi, S.; Selover, M. A.; Epstein, A. J. J. Am. Chem. Soc. 1990, 112, 5496. (f) Miller, J. S.; Glatzhofer, D. T.; O'Hare, D. M.; Reiff, W. M.; Chakraborty, A.; Epstein, A. J. Inorg. Chem. 1989, 28, 2930. (g) Pukacki, W.; Pawlak, M.; Graja, A.; Lequan, M.; Lequan, R.
Noncollinear antiferromagnetic structure of the molecule-based magnetMn[N(CN)2]2
Physical Review B, 2000
The crystallographic and magnetic properties of the Mn[N(CN)2] 2 compound have been investigated by dc magnetization, ac susceptibility, specific heat, and zero-field neutron diffraction on polycrystalline samples. The magnetic structure consists of two sublattices which are antiferromagnetically coupled and spontaneously canted. The spin orientation is mainly along the a axis with a small uncompensated moment along the b axis. The ground state is a crystal-field sextet with large magnetic anisotropy. The crystal structure consists of discrete octahedra which are axially elongated and successively tilted in the ab plane. Comparisons of the magnetic structures for the isostructural M[N(CN)2] 2 (M = Mn, Fe, Co, NO series suggest that the spin direction is stabilized by crystal fields and the spin canting is induced by the successive tilting of the octahedra. We propose that the superexchange interaction is the mechanism responsible for the magnetic ordering in these compounds and we find that a crossover from noncollinear antiferromagnetism to collinear ferromagnetism occurs for a superexchange angle of a c= 142.0(5)°. 0.0441 mol) was dissolved in 1 mL water. Na[N(CN)2]2 (9.846 g, 0.111 mol) was dissolved in 50 mL water. The room-temperature mixture of the two solutions was allowed to evaporate over several days, and crystals of M n[N (CN)2] 2-3H 2O began to form. The crystals were placed in a suction filter and washed with a very small amount of cold water. Then the crystals were placed in a vial with a septum which was evacuated with a vacuum pump. After several days of pumping, the crystals were transformed into a white powder and microanalyzed. The microanalysis results are: Mn, found 29.01% , calc. 29.31% ; C, found 25.42% , calc. 25.69% ; and N, found 44.59% , calc. 44.93%. Perchlorate salts must be handled with extreme caution due to their explosive nature. The crystal structure at 222 K (monoclinic, space group P 2 1 / n , Z = 4) (Ref. 1 4 and mag netic properties paramagnetic down to 5 K of M n[N (CN)2] 2-3H 2O agree very well with the previously reported crystal structure at 123 K and magnetic properties.8,9 All data presented in this paper and the isofield magnetization between 2 and 300 K reported in Ref. 6 were performed on polycrystalline samples of Mn[N(CN)2]2 from this batch. Other methods of synthesis for Mn[N(CN)2]2 are given in Refs. 8 and 9 which use the same starting materials as described above but with variations in preparation for example, the application of heat , and Ref. 6 which uses
Advanced Materials, 1994
The preparation and characterization of molecule-based materials exhibiting cooperative magnetic interactions (i.e., ferro-and ferrimagnetic behavior) is a growing area of contemporary interdisciplinary research."-31 The electrontransfer salt [FeCp;]'@[TCNE]'O (where Cp* is pentamethylcyclopentadienide and TCNE is tetracyanoethylene) with a critical or ordering temperature T, of 4.8 K was the first bulk molecular ferromagnet reported.[41 Subsequently, [MnCp*,]"[TCNE]" was reported to have T, = 8.8 K.Ls1 The latter reaction was later extended to the V(C,H,); donor, which is isoelectronic to MnCp;', and led to the isolation of a highly disordered V(TCNE); y(solvent) magnet with a exceeding room temperature, T,-400 K.['] Subsequently, a new structure type exemplified by the metallomacrocyclic [MnTPP]"@[TCNE]" (TPP is meso-tetraphenylporphinato) was reported to exhibit bulk magnetic proper tie^.[^] [MnTPP]"@[TCNE]" is a covalently bonded extended linear chain (one-dimensional, 1D) complex that was characterized to be a ferrimagnet with a r, of 18 K, and its magnetic susceptibility x can be fit to the Curie-Weiss expression, X K I/(T-0) between 11 5 and 250 K (0 = + 61 K).17] With the goals of elucidating the importance of I D interactions with respect to 3D interactions, establishing the structure-function relationship for this new class of materials, and characterizing new molecule-based magnets with enhanced c' s and O's, we are studying this class of compounds. Herein, we report the results of our studies on the reaction of TCNE and manganese phthalocyanine, MnPc.['' The a-polymorph is obtained upon grinding MnPc and TCNE followed by dissolution of the soluble product into MeCN.['"] In contrast, the direct reaction of MnPc and TC-NE in refluxing MeCN leads to the P-polym~rph.[~~I For both preparative routes insoluble fractions possessing identical infrared spectra, elemental analyses, and magnetic properties were also isolated.
Inorganic Chemistry, 2001
Tetraphenylporphinatomanganate(III) tetracyanoethenide, [MnTPP][TCNE], is the prototype of a growing family of linear chain (1-D) coordination polymers that magnetically order as ferrimagnets. [MnTPP][TCNE]‚xS [S) PhMe (x) 2), 1,2-C 6 H 4 Me 2 (x) 1), 1,2-C 6 H 4 Cl 2 (x) 3), 1,2,4-C 6 H 3 Cl 3 (x) 2), and 1,3-C 6 H 4 Cl 2 (x) 2)] have been prepared and structurally and magnetically characterized. All form 1-D chain structures with intrachain Mn‚‚‚Mn separations ranging from 9.202 to 10.218 Å. The 173 K crystal structure of [MnTPP][TCNE]‚2PhMe has been rerefined, revealing that the [TCNE] •is 2-fold-disordered and coordinated to Mn III by a pair of trans cyano nitrogen atoms to form parallel one-dimensional chains. The two orientations of [TCNE] •are related by a 180°rotation about the diagonal axis joining the trans nitrogen atoms bound to Mn III. The major form has an occupancy of 83.3(4)% with a Mn-N TCNE distance of 2.328(3) Å and a MnNC angle of 146.8(8)°. The minor form, with 16.7(4)% occupancy, has a Mn-N TCNE distance of 2.176(15) Å and a MnNC angle of 152.3(39)°. Lattice packing and molecular bonding imply static as opposed to dynamic disorder. The magnetic properties depend on the type and quantity of the solvent present in the structure. Desolvation via heating in n-octane (127°C), n-dodecane (216°C), and/or vacuum thermolysis (175°C) leads to numerous different desolvated materials with differing magnetic properties. At higher temperatures the magnetic susceptibility can be fit by the Curie
Journal of Physics: Condensed Matter, 2013
The structural, spectroscopic and magnetic properties of the two-dimensional (2D) molecule-based magnets of [Mn II (TCNE)(NCMe) 2 ]X (X = PF 6 , AsF 6 , SbF 6 ; TCNE = tetracyanoethylene, NCMe = acetonitrile) composition are reported. It is shown that the alteration of the interlayer distance by increasing the anion size has little effect on the critical magnetic ordering temperature, T c , suggesting that it depends predominantly on the intra-plane magnetic exchange. The observed field-induced irreversibility in static magnetization, a slow decay of isothermal remanence below T c , and the dynamic susceptibility data are in accord with a re-entrant spin-glass nature of the ground state of all materials. In contrast to the isostructural Fe-based magnets, in which strong magnetocrystalline anisotropy facilitates the finite temperature magnetic ordering with the magnetization easy axis perpendicular to the µ 4-TCNE •− plane, in the studied Mn-based magnets the easy axis is canted away from the normal direction, due to a small magnetocrystalline anisotropy. The two magnetic transitions observed on cooling are assigned to the ferrimagnetic long-range ordering of the normal magnetization component followed by the re-entrant spin-glass type transition resulting from a random freezing of the in-plane magnetization component.
Structure–property trends in cyanido-bridged tetranuclear FeIII/NiII single-molecule magnets
Polyhedron, 2013
Treatment of [NEt 4 ][(Tp ⁄Me)Fe III (CN) 3 ]ÁH 2 O with nickel(II) trifluoromethanesulfonate affords {[(Tp ⁄Me)-Fe III (CN) 3 ] 2 [Ni II (DMF) 4 ] 2 [OTf] 2 }Á2DMF (1) while {[(Tp ⁄Me)Fe III (CN) 3 ] 2 [Ni II (bpy) 2 ] 2 [ClO 4 ] 2 }Á3MeCNÁ2H 2-OÁMeOH (2) is obtained from Ni(ClO 4) 2 Á6H 2 O and 2,2 0-bipyridine mixtures. In the frame of an isotropic Heisenberg model, the experimental vT versus T data were modeled well with the following best set of parameters: J/k B = +9.0(4) and +8.5(4) K and g av = 2.4(1) and 2.5(1) for 1 and 2, respectively; the first excited state (S = 2) for 1 and 2 are ca. 18 and 16.8 K above the S T = 3 ground state. Analysis of the ac susceptibility suggests that 1 exhibits fast quantum tunneling of the magnetization above ca. 1.8 K while 2 displays slow relaxation in the range seen for many SMMs; at H dc = 2.2 kOe an SMM energy barrier of D eff = 15.7 K is estimated for 2. Upon prolonged standing in air, 1 is readily transformed into a new system that exhibits a respectable energy barrier (D eff = 20.4 K) suggesting that the desolvation is able to dramatically alter the dynamics and the quantum properties of the square-shaped {Fe III 2 (l-CN) 4 Ni II 2 }SMM.