RESUMO
The dynamic susceptibility study of photoinduced magnetism in a molecule-based magnet, K1-2xCo1+x[Fe(CN)(6)];yH(2)O (0.2=x=0.4,y approximately 5), is reported. Upon excitation with visible light the material has substantial changes in linear and nonlinear ac susceptibility and dc magnetization. The results demonstrate cooperative freezing of magnetic moments and absence of true long-range magnetic order. The ground and photoexcited states are described within a cluster glass model, with photoinduced increase in spin concentration leading to a shift of the dynamics to longer length and time scales and higher temperatures.
RESUMO
Synthons Tl1[TCNE]*- (1) and Tl12[TCNE]2- (2), for [TCNE]*- and [TCNE]2-, respectively, in metathesis reactions have been quantitatively prepared and characterized. The structure of 1 was solved and refined in a monoclinic unit cell at 27 degrees C [C2/c, a = 12.6966 (12) angstroms, b=7.7599 (7) angstroms, c=15.5041 (15) angstroms, beta = 96.610 (5) degrees , V= 1517.4 (2) angstroms3, Dcalcd = 2.911 gcm-3, Z=8, R1 = 0.0575, omegaR2=0.0701] and exhibits nuCN absorptions at 2,191 (s) and 2,162 (s) cm-1 consistent with metal-bound [TCNE]*-. The structure of 1 consists of a distorted square antiprismatic octacoordinate Tl1 bound to six monodentate [TCNE]*-s with TlN separations ranging from 2.901 to 3.171 angstroms averaging 3.020 angstroms, and one bidentate [TCNE]*- with TlN separations averaging 3.279 angstroms. The TlN bonding is attributed to electrostatic bonding. The [TCNE]*-s form dimerized zigzag chains with intra- and interdimer separations of 2.87 and 3.29 angstroms, respectively. The tight pi-[TCNE](2)2- dimer is diamagnetic and has the shortest intradimer [TCNE]*- distance reported. These synthons for [TCNE]*- and [TCNE]2- in metathesis reactions lead to the precipitation of, for example, TlIX (X = Cl, Br, OAc). Reaction of 1 with MnIII(porphyrin)X (X = Cl, OAc) forms the molecule-based magnets of [MnIII(porphyrin)][TCNE] composition, while the reaction of [CrI(C6H6)2]Br and (Me2N)2CC(NMe2)2Cl2, [TDAE]Cl2, with 1 forms [CrI(C6H6)2] [TCNE] and [TDAE][TCNE]2, respectively. The structure of [TDAE][TCNE]2.MeCN was solved and refined in an orthorhombic unit cell at 21 degrees C [I222, a = 10.2332(15), b = 13.341(6), c = 19.907(8) angstroms, V= 2717.7 angstroms3, Z = 4; Dcalcd = 1.216 gcm-3, R=0.083, Romega = 0.104] and exhibits upsilonCN absorptions at 2,193 (m), 2,174 (s), and 2,163 (s) cm-1 consistent with isolated [TCNE](2)2- , in contrast to the aforementioned TlI bound [TCNE](2)2-. The reaction of 2 with [TDAE]Cl2 forms [TDAE]2+[TCNE]2-.
RESUMO
The reaction of hexacyanobutadiene (HCBD) and meso-tetrakis(4-chlorophenyl)porphinatomanganese(II) pyridine [MnIITClPPpy] (1Cl) leads to two phases of [MnIIITClPPpy][HCBD].PhMe (alpha-2Clpy, beta-2Clpy). Similarly, the reaction of HCBD and tetrakis(4-bromophenyl)porphinatomanganese(II) pyridine [MnIITBrPPpy] (1Br) leads to two products [MnIIITBrPPpy] [HCBD] * PhMe (2 Brpy) and [MnIIITBrPP][HCBD]*2 PhMe (3Br). The structure of dark-green alpha-2Clpy consists of one porphyrin unit with MnIII in a square pyramidal coordination environment axially bound to one pyridine. The cation forms [MnIIITCIPPpy](2)2+ as cofacial dimerized porphyrins. Each [HCBD]*- is nonplanar with a torsion angle of 170.8(4) degrees about the center C-C bound, and forms [HCBD](2)2- dimers in the solid state with sub-van der Waals contacts of 3.325 and 3.340 angstroms. The magnetic data above 10 K obey the Curie-Weiss expression with a theta of -2.5 K, and mueff (300 K) = 4.91 muB as expected for S=2MnIII and S = 0 [HCBD](2)2-. The magnetic data for alpha-2Clpy can be fit with an zero-field-splitting D of -1.45 K. beta-2 Clpy consists of one porphyrin unit with MnIII in a distorted octahedral coordination environment axially bound to py and to a monodentate [HCBD]*- bound via an exo-nitrile. [HCBD]*- is nonplanar with a torsion angle of 169.7(5) degrees about the center C-C bound. The ueff (350 K) is 5.09 muB; however, the magnetic data do not obey the Curie-Weiss expression above 70 K. The low temperature data may be fit with a theta of -5.4 K. The data was modeled to an isolated S = 2 and S = 1/2 dinuclear spin system with J/kappaB = - 90 K. Decomposition of [HCBD]*- to [C4(CN)5O]- was evidenced by the determination of the structure of [MnIIITCIPP][C4(CN)5O] 2PhMe (3ClO). Crystals of 3 Cl-O were prepared by reaction of HCBD and 1Cl in the presence of a drop of water. The molecular structure consists of [HCBD]*-trans-mu-N-2,3-bound to [MnIIITBrPP]+ forming a 1-D coordination polymer of alternating [MnIIITBrPP]+ and [HCBD]*-. The intrachain Mn***Mn distance was 10.675(3) angstroms, with important interchain Mn***Mn distances of 10.832, 11.016, and 14.696 A. The magnetic data were fit to a Curie-Weiss law (10 < T< 290 K) with a theta of -3.5 K, and D = 0.3 K with mueff = 4.97 muB at 300 K.