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1.
Chemistry ; 20(25): 7593-7, 2014 Jun 16.
Artigo em Inglês | MEDLINE | ID: mdl-24807853

RESUMO

A family of magnetic metal-organic frameworks, (Ph3PMe)2[M2(TCNQ)3] {M=Fe(2+), Co(2+), Ni(2+) and Zn(2+)} have been prepared and structurally characterized. The honeycomb-like "layers" consist of M(II) ions doubly bridged with dinitrilomethane moieties of two 7,7,8,8-tetracyanoquinodimethane (TCNQ) dianions which are further connected through phenyl rings to form a 3D dianionic framework [M2TCNQ3](2-) with Ph3PMe(+) cations filling cavities that run along the c axis. Studies of the magnetic coupling through the TCNQ dianion in these structures revealed that it can promote long-range magnetic ordering despite the long coupling pathway.

2.
Dalton Trans ; 43(18): 6802-10, 2014 May 14.
Artigo em Inglês | MEDLINE | ID: mdl-24647575

RESUMO

Treatment of [Mn(dpop)(H2O)2]Cl2 (dpop = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo-[12.3.1]octadeca-1(18),2,12,14,16-pentaene) with K4[Mo(CN)7]·2H2O under varied synthetic conditions afforded four different compounds: {[Mn(dpop)]4[(dpop)Mn(H2O)]2[Mo(III)(CN)7]3·27H2O}n (1), {[(dpop)Mn(H2O)][Mo(III)(CN)7][Mn(dpop)]3[Mo(IV)(CN)8]·29H2O}n (2), {[(dpop)Mn(H2O)]2[Mo(IV)(CN)8]2[Mn(dpop)]4[Mo(III)(CN)7]·12H2O}n (3), and [(dpop)Mn(H2O)]2[Mo(IV)(CN)8]·9H2O (4). Compound 1 contains only [Mo(III)(CN)7](4-) anions and exhibits a corrugated two-dimensional layered architecture. The structure of 2 with a 1 : 1 ratio of Mo(III) : Mo(IV) is best described as a ladder-like chain composed of [Mo(III)(CN)7](4-)-based pentanuclear [Mo(III)Mn(II)4] fragments which are further linked by in situ produced [Mo(IV)(CN)8](4-) anions. In the case of 3, [Mn8Mo8] rings containing bent [Mo(III)Mn(II)2] fragments are extended into a two-dimensional layer with the ratio of [Mo(CN)7](4-) : [Mo(CN)8](4-) being 1 : 2. Compound 4 exhibits a bent trinuclear structure in which two CN(-) groups of [Mo(CN)8](4-) function as µ2-bridges to [Mn(dpop)(H2O)](2+) fragments. Magnetic studies suggest significant antiferromagnetic coupling interactions occur between Mo(III) and Mn(II) ions while, not surprisingly, interactions between the Mn(ii) ions through diamagnetic [Mo(IV)(CN)8](4-) anions are negligible. Compound 1 exhibits ferrimagnetic ordering below 3.0 K whereas 2 shows the signature of single molecule magnet behavior with slow relaxation of the magnetization and an effective energy barrier (U(eff)) of 8.1 K.

3.
Dalton Trans ; 42(41): 14693-701, 2013 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-23943045

RESUMO

A series of isostructural octanuclear lanthanide complexes of general formula [Ln8(sao)4(µ3-OH)4(NO3)12(DMF)12] (Ln = Nd (), Sm (), Eu (), Gd (), Tb (), Dy (), Ho (), Er (); DMF = dimethylformamide) have been prepared via reactions of salicylaldoxime (saoH2), tetramethylammonium hydroxide (Me4NOH) with the appropriate lanthanide nitrate salt (Ln(NO3)3·6H2O). The metallic skeletons of the complexes describe [Ln4] tetrahedra encapsulated inside a [Ln4] square with the inner core stabilised through µ3-OH(-) ions and the periphery by µ4-sao(2-) ligands. The magnetic properties of compounds were investigated by dc and ac magnetometry. Temperature dependent ac magnetic susceptibility data reveal that the dysprosium analogue () displays an out-of-phase signal in the absence of an applied magnetic field indicative of slow relaxation of the magnetization typical of a Single-Molecule Magnet (SMM). Micro-SQUID measurements reveal temperature and sweep rate dependent hysteresis below 1.0 K.

4.
J Am Chem Soc ; 135(10): 4040-50, 2013 Mar 13.
Artigo em Inglês | MEDLINE | ID: mdl-23414430

RESUMO

Hydrothermal reactions of copper(II) acetate, tetrazolate-5-carboxylate (tzc), and the neutral N-donor spacer ligand 1,3-di(4-pyridyl)propane (dpp) lead in a single reaction vial to the simultaneous formation of three different single-crystalline solvates [Cu(tzc)(dpp)]n·0.5C6H14·0.5H2O (1), [Cu(tzc)(dpp)]n·4.5H2O (2), and [Cu(tzc)(dpp)]n·1.25C6H14 (3). All three structures were characterized by single crystal X-ray diffraction. None of these solvates can be prepared as phase-pure bulk materials, but reaction conditions similar to those used for single crystal synthesis yield a phase-pure polycrystalline bulk material of an additional forth solvate phase [Cu(tzc)(dpp)]n·2H2O (4). Investigations of its thermal properties by in situ temperature-dependent synchrotron-based powder diffraction experiments have shown interesting phase transitions upon heating in a helium stream. Initially, the precursor dihydrate 4 transforms to an anhydrous phase [Cu(tzc)(dpp)]n (6I) via the intermediate monohydrate phase [Cu(tzc)(dpp)]n·H2O (5). Upon further heating, phase 6I transforms to a new anhydrous polymorph 6II, which transforms upon cooling to a further new phase 6III. Thermogravimetric measurements performed in tandem with differential scanning calorimetry as well as infrared spectroscopic investigations are in agreement with these findings. The de/resolvation behavior is accompanied by a dramatic change in their magnetic properties: The dihydrate phase shows antiferromagnetic exchange interactions, whereas ferromagnetic properties are observed for the trimorphic anhydrate system. This magnetic sponge-like behavior can be reversibly cycled upon de/resolvation of the material.


Assuntos
Compostos Ferrosos/química , Compostos Organometálicos/química , Temperatura , Cobre/química , Cristalografia por Raios X , Campos Magnéticos , Modelos Moleculares , Compostos Organometálicos/síntese química , Transição de Fase , Solventes/química
5.
Inorg Chem ; 52(4): 1670-2, 2013 Feb 18.
Artigo em Inglês | MEDLINE | ID: mdl-23350834

RESUMO

The reaction of 2-pyridylphosphonic acid (LH(2)) with iron(II) perchlorate and iron(III) nitrate afforded an interconnected, double-layered, cationic iron cage, [{Fe(36)L(44)(H(2)O)(48)}](20+) (1a), the largest interconnected, polynuclear ferric cage reported to date. Magnetic studies on 1a revealed antiferromagnetic coupling between the spins on adjacent Fe(III) ions.


Assuntos
Compostos Férricos/química , Nitratos/química , Organofosfonatos/química , Percloratos/química , Cristalografia por Raios X , Modelos Moleculares
7.
Dalton Trans ; 41(14): 3995-4006, 2012 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-22362359

RESUMO

The use of a moderately hydrophobic ionic liquid, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([BdMIM][BF(4)]), as a cosolvent with water, has been investigated in the synthesis of metal phosphonates. This hydro-ionothermal synthesis has been carried out through a systematic combinatorial investigation of several divalent metal chlorides and two related ligands, iminobis(methylphosphonic acid) and N-methyliminiobis(methylphosphonic acid). These reactions resulted in five new divalent metal phosphonates. We present here the synthetic techniques utilized as well as the X-ray structures and characteristic properties of each of these compounds. Co(HO(3)PCH(2)NH(2)CH(2)PO(3)H)(2), (1), consists of sheets that are hydrogen bonded together by pairs of P-O···H groups. Co(H(2)O)(2)(HO(3)PCH(2)NH(2)CH(2)PO(3)H)(2), (2), consists of chains that are connected through an extensive network of hydrogen bonds. Co(HO(3)PCH(2)NH(CH(3))CH(2)PO(3)H)(2), (3), is made up of sheets that are hydrogen bonded together by pairing P-O···H interactions. Zn(3)(O(3)PCH(2)NH(2)CH(2)PO(3))(2), (4), is isostructural to a previously reported cobalt compound which is a non-porous 3-dimensional network. CuClPO(3)CH(2)NH(2)CH(3), (5), formed as a result of an in situ N-C bond cleavage. Ladders built of Cu-O-P-O 8-membered rings are crosslinked by bridging chloride atoms to form sheets. 1, 3, 4 and 5 have been synthesized using the hydrophobic ionic liquid 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([BdMIM][BF(4)]) with water as a cosolvent, while 2 has been synthesized from identical conditions in the absence of the [BdMIM][BF(4)]. We also report the microwave assisted hydro-ionothermal synthesis of the known polymorph of 2, Co(H(2)O)(2)(HO(3)PCH(2)NH(2)CH(2)PO(3)H)(2), (6), synthesized in two hours providing high quality crystals in good yield. The compounds have been characterized by thermogravimetric analysis and IR spectroscopy, and their magnetic properties have been investigated.

8.
Inorg Chem ; 50(7): 2782-9, 2011 Apr 04.
Artigo em Inglês | MEDLINE | ID: mdl-21391549

RESUMO

Three members of the family of trigonal bipyramidal (TBP) complexes of general formula [M(tmphen)(2)](3)[M'(CN)(6)](2) (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline) or [M(3)M'(2)], which are known to exhibit thermally induced spin crossover and charge transfer, have been investigated for optical and photomagnetic properties. The light-induced excited spin-state trapping (LIESST) effect found in classical spin crossover compounds, such as [Fe(phen)(2)(NCS)(2)], was explored for the [Fe(3)Fe(2)] and [Fe(3)Co(2)] compounds. Similarly, inspired by the light-induced charge-transfer properties of K(0.2)Co(1.4)[Fe(CN)(6)]·6.9H(2)O and related Prussian blue materials, the possibility of photo-induced magnetic changes was investigated for the [Co(3)Fe(2)] TBP complex. Optical reflectivity and magnetic susceptibility measurements were used to evaluate the photoactivity of these compounds. A comparison of these data before and after light irradiation demonstrates that (i) the spin crossover of the Fe(II) centers in the [Fe(3)Fe(2)] and [Fe(3)Co(2)] analogues and the (ii) charge transfer events in the [Co(3)Fe(2)] complex occur with temperature and irradiation. In addition, photomagnetic behavior is exhibited by all three compounds. The photo-conversion efficiency has been estimated at 20% of photo-induced high spin Fe(II) centers in [Fe(3)Co(2)], 30% of paramagnetic Co(II)-Fe(III) pairs in [Co(3)Fe(2)], and less than 2% of photo-induced high spin Fe(II) centers in [Fe(3)Fe(2)].


Assuntos
Luz , Nitrilos/química , Compostos Organometálicos/química , Cristalografia por Raios X , Modelos Moleculares , Compostos Organometálicos/síntese química
9.
10.
Dalton Trans ; 39(18): 4341-52, 2010 May 14.
Artigo em Inglês | MEDLINE | ID: mdl-20422092

RESUMO

Reactions between trivalent rare earth ions (M(III) = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er and Yb) and the radical anion of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (TCNQF(4)) produce a family of mononuclear complexes {M[(TCNQF(4))](2)[H(2)O](x)}.(TCNQF(4))(3H(2)O), x = 6, 7. The cationic complex {M(III)([TCNQF(4)](-) )(2)[H(2)O](x)}(+) cocrystallizes with one [TCNQF(4)](-) radical anion and three water molecules. One of the coordinated [TCNQF(4)](-) radicals is involved in pi-pi stacking interactions with the uncoordinated [TCNQF(4)](-) radicals which leads to the antiferromagnetic coupling for these ((TCNQF(4))(2))(2-)pi-dimers. The second coordinated [TCNQF(4)](-) remains as a radical ligand and is not involved in pi-pi interactions. Magnetic studies indicate that the Sm compound magnetically orders at 4.4 K and that a fraction of the Gd and Dy samples undergo magnetic ordering at 3.7 K and 4.3 K respectively due to partial dehydration (loss of interstitial water molecules). Diamagnetic metal ions were used to generate magnetically dilute Gd, and Dy compounds that do not exhibit any signs of magnetic ordering.

11.
Dalton Trans ; 39(20): 4968-77, 2010 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-20422113

RESUMO

Derivatives of the single molecule magnet (SMM) {[Re(triphos)(CN)(3)](4)[MnCl](4)} (Re(4)Mn(4)) {[Re(triphos)(CN)(3)](4)[Mn(CH(3)CN)](4)}(ClO(4))(4) (2) and {[Re(triphos)(CN)(3)](4)[Mn(ClO(4))](3)[Mn(CH(3)OH)(CH(3)O)]} (3), were prepared by reacting [Et(4)N][Re(triphos)(CN)(3)] (1) with Mn(ClO(4))(2)·6H(2)O. Reaction of sodium dicyanamide, NaN(CN)(2), with compound 2 in CH(2)Cl(2) results in the product {[Re(triphos)(CN)(3)](4)[Mn(N(CN)(2))](4)} (4), in which each Mn(II) site is terminated by a dicyanamide ligand. A similar reaction of compound 3 in CH(2)Cl(2)-MeOH solution with LiTCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) leads to the formation of {[Re(triphos)(CN)(3)](4)[Mn(TCNQ-TCNQ)(3)(Mn(HTCNQ)(CH(3)O))]} (5) whose structure is best described as a chain of dimers of Re(4)Mn(4) cubes bridged by sigma-bonded (TCNQ(2))(2-) linkers with one capping HTCNQ ligand.

13.
Chemistry ; 15(42): 11390-400, 2009 Oct 26.
Artigo em Inglês | MEDLINE | ID: mdl-19760709

RESUMO

A series of isostructural compounds with formula [M(TCNQF(4))(2)(H(2)O)(6)]TCNQF(4)3 H(2)O (M=Tb (1), Y (2), Y:Tb (74:26) (3), and Y:Tb (97:3) (4); TCNQF(4)= tetrafluorotetracyanoquinodimethane) were prepared and their magnetic properties investigated. Compounds 1, 3, and 4 show the beginning of a frequency-dependent out-of-phase ac signal, and decreasing intensity of the signal with decreased concentration of Tb(III) ions in the diluted samples is observed. No out-of-phase signal was observed for 2, an indication that the behavior of 1, 3, and 4 is indicative of slow paramagnetic relaxation of Tb(III) ions in the samples. A more detailed micro-SQUID study at low temperature revealed an interplay between single-molecule magnetic (SMM) behavior and a phonon bottleneck (PB) effect, and that these properties depend on the concentration of diamagnetic yttrium ions. A combination of SMM and PB phenomena was found for 1, whereby the PB effect increases with increasing dilution until eventually a pure PB effect is observed for 2. The PB behavior is interpreted as being due to the presence of a "sea of organic S=1/2 radicals" from the TCNQF(4) radicals in these compounds. The present data underscore the fact that the presence of an out-of-phase ac signal may not, in fact, be caused by SMM behavior, particularly when magnetic metal ions are combined with organic radical ligands such as those found in the organocyanide family.

14.
Solid State Nucl Magn Reson ; 36(3): 129-36, 2009 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-19765956

RESUMO

Supermicroporous paramagnetic materials SiO(2)-Al(2)O(3)-MnO and SiO(2)-MnO with different manganese concentrations have been probed by solid-state (29)Si NMR and magnetic susceptibility measurements. The (29)Si T(1) and T(2) experiments, performed in static and spinning samples, have resulted in determination of electron relaxation times, providing, in turn, quantitative interpretations of (29)Si T(1) times in terms of distances Mn-Si. The NMR relaxation data have revealed (29)Si T(1) time distributions, which are close to Gaussian and observed as different T(1) values obtained in MAS NMR experiments for isotropic (29)Si resonances and their sidebands. Such (29)Si T(1) distributions, being a common phenomenon in paramagnetic silica-based materials, can be however masked by the bulk magnetic susceptibility (BMS) effects increasing with concentrations of paramagnetic centers. The presence of T(1) distributions, in itself, is not a criterion for incorporation of paramagnetic ions into the silica matrix or its surface. However, a quantitative analysis of the experimentally-observed short (29)Si T(1) components, based on the well-determined electron relaxation times, can provide such a criterion.


Assuntos
Espectroscopia de Ressonância Magnética/métodos , Compostos de Manganês/química , Óxidos/química , Dióxido de Silício/química , Óxido de Alumínio/química , Isótopos , Porosidade , Silício
15.
Angew Chem Int Ed Engl ; 48(12): 2140-3, 2009.
Artigo em Inglês | MEDLINE | ID: mdl-19199312

RESUMO

Fixing a hole: Hydrothermal chemistry has been exploited in the preparation of a 3D framework material exhibiting 48% accessible void volume and 1.5% hydrogen uptake by weight at 120 kPa (see picture). The title compound also exhibits single-chain magnetic behavior and reversible changes in magnetic properties upon solvation and desolvation.

16.
Inorg Chem ; 48(13): 5725-35, 2009 Jul 06.
Artigo em Inglês | MEDLINE | ID: mdl-20507100

RESUMO

Water-free rare earth(III) hexacyanoferrate(III) complexes, {Ln(DMF)(6)(mu-CN)(2)Fe(CN)(4)}(infinity) (DMF = N,N-dimethylformamide; Ln = Sm, 1; Eu, 2; Gd, 3; Tb, 4; Dy, 5; Ho, 6; Er, 7; Tm, 8; Yb, 9; Lu, 10; Y, 11; La, 12; Ce, 13; Pr, 14; Nd, 15), were synthesized in dry DMF through the metathesis reactions of [(18-crown-6)K](3)Fe(CN)(6) with LnX(3)(DMF)(n) (X = Cl or NO(3)). Anhydrous DMF solutions of LnX(3)(DMF)(n) were prepared at room temperature from LnCl(3) or LnX(3).nH(2)O under a dynamic vacuum. All compounds were characterized by IR, X-ray powder diffraction (except for 10), and single crystal X-ray diffraction (except for 2, 7, 10). Infrared spectra reveal that a monotonic, linear relationship exists between the ionic radius of the lanthanide and the nu(mu-CN) stretching frequency of 1-10, 12-15 while 11 deviates slightly from the ionic radius relationship. X-ray powder diffraction data are in agreement with powder patterns calculated from single crystal X-ray diffraction results, a useful alternative for bulk sample confirmation when elemental analysis data are difficult to obtain. Eight-coordinate Ln(III) metal centers are observed for all structures. trans-cyanide units of [Fe(CN)(6)](3-) formed isocyanide linkages to Ln(III) resulting in one-dimensional polymeric chains. Structures of compounds 1-9 and 11 are isomorphous, crystallizing in the space group C2/c. Structures of compounds 12-15 are also isomorphous, crystallizing in the space group P2/n. One unique polymeric chain exists in the structures of 1-9 and 11 while two unique polymeric chains exist in structures of 12-15. One of the polymeric chains of 12-15 is similar to that observed for 1-9, 11 while the other is more distorted and has a shorter Ln-Fe distance. Magnetic susceptibility measurements for compounds 3-6, 8, 11 were performed on polycrystalline samples of the compounds.

17.
J Am Chem Soc ; 130(44): 14729-38, 2008 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-18839950

RESUMO

In this article we report for the first time experimental details concerning the synthesis and full characterization (including the single-crystal X-ray structure) of the spin-canted zigzag-chain compound [Co(H2L)(H2O)]infinity [L = 4-Me-C6H4-CH2N(CPO3H2)2], which contains antiferromagnetically coupled, highly magnetically anisotropic Co(II) ions with unquenched orbital angular momenta, and we also propose a new model to explain the single-chain magnet behavior of this compound. The model takes into account (1) the tetragonal crystal field and the spin-orbit interaction acting on each Co(II) ion, (2) the antiferromagnetic Heisenberg exchange between neighboring Co(II) ions, and (3) the tilting of the tetragonal axes of the neighboring Co units in the zigzag structure. We show that the tilting of the anisotropy axes gives rise to spin canting and consequently to a nonvanishing magnetization for the compound. In the case of a strong tetragonal field that stabilizes the orbital doublet of Co(II), the effective pseudo-spin-1/2 Hamiltonian describing the interaction between the Co ions in their ground Kramers doublet states is shown to be of the Ising type. An analytical expression for the static magnetic susceptibility of the infinite spin-canted chain is obtained. The model provides an excellent fit to the experimental data on both the static and dynamic magnetic properties of the chain.

18.
Inorg Chem ; 47(6): 2074-82, 2008 Mar 17.
Artigo em Inglês | MEDLINE | ID: mdl-18275140

RESUMO

The syntheses, structures, and magnetic properties of a series of tetranuclear cyanide-bridged compounds are reported. This family of molecular squares, [{M(II)Cl2}2{Co(II)(triphos)(CN)2}2] (M = Mn ([CoMn]), Fe ([CoFe]), Co ([CoCo]), Ni ([CoNi]), and Zn ([CoZn]), triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane), has been synthesized by the reaction of Co(II)(triphos)(CN)2 and MCl2 (M = Mn, Co, Ni, Zn) or Fe4Cl8(THF)6 in a CH2Cl2/EtOH mixture. These complexes are isostructural and consist of two pentacoordinate Co(II) and two tetrahedral M(II) centers. The resulting molecular squares are characterized by antiferromagnetic coupling between metal centers that generally follows the spin-coupling model S total = SM(II)1 - SCo1 + SM(II)2 - SCo2. Magnetic parameters for all the complexes were measured using SQUID magnetometry. Additionally, [CoZn] and [CoMn] were studied by both conventional and high-frequency and high-field electron paramagnetic resonance.


Assuntos
Cloretos/química , Cianetos/química , Compostos Ferrosos/química , Compostos de Manganês/química , Níquel/química , Compostos de Zinco/química , Magnetismo , Modelos Químicos , Modelos Moleculares
19.
Inorg Chem ; 47(5): 1453-9, 2008 Mar 03.
Artigo em Inglês | MEDLINE | ID: mdl-18225859

RESUMO

A new cobalt(II) carboxylate-phosphonate, namely, Co[HO2C(CH2)3NH(CH2PO3H)2]2, with a layered architecture has been synthesized by hydrothermal reactions. The Co(II) ion in the title compound is octahedrally coordinated by six phosphonate oxygen atoms from four carboxylate phosphonate ligands. Neighboring CoO6 octahedra are interconnected by phosphonate groups into a 2D layer with a 4,4-net topology. Adjacent layers are further cross-linked via hydrogen bonds between the noncoordinate carboxylate groups and noncoordinate phosphonate oxygens. The ac and dc magnetic susceptibility and magnetization measurements indicate that Co[HO2C(CH2) 3NH(CH2PO3H)2]2 is a canted antiferromagnet with T(c) = 8.75 K.

20.
Chem Commun (Camb) ; (44): 4611-3, 2007 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-17989808

RESUMO

Removal of methanol molecules from the interstices of a metal-organic framework based on a 2-D hexagonal Mn(II)-TCNQF(4) net results in stronger magnetic interactions and leads to a glassy magnetically ordered state; the magnetic behavior can be reversibly cycled upon solvation-desolvation of the material.


Assuntos
Manganês/química , Nitrilos/química , Compostos Organometálicos/química , Cristalografia por Raios X , Magnetismo , Modelos Moleculares , Estrutura Molecular , Porosidade , Solubilidade , Temperatura
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