Biomedical subjects

Cai-Feng Wang

Publications and source records attributed to Cai-Feng Wang.

6 recordsLinked to original sources

PubMed2006

Structural and magnetic studies on cyano-bridged rectangular Fe2M2 (M = Cu, Ni) clusters.

Using the tricyano precursor, (Bu4N)[(Tp)Fe(CN)3] (Tp = Tris(pyrazolyl) hydroborate) (1), four new tetranuclear clusters, [(Tp)Fe(CN)3Cu(Tp)]2.2H2O (2), [(Tp)Fe(CN)3Cu(bpca)]2.4H2O (3) (bpca = bis(2-pyridylcarbonyl)amidate anion), [(Tp)Fe(CN)3Ni(tren)]2(ClO4)2.2H2O (4) (tren = tris(2-amino)ethylamine), and [(Tp)Fe(CN)3Ni(bipy)2]2[(Tp)Fe(CN)3]2.6H2O (5) (bipy = 2,2'-bipyridine), have been synthesized and structurally characterized. The four clusters possess similar square structures, where FeIII and MII (M = CuII or NiII) ions alternate at the rectangle corners. There exist intermolecular - stacking interactions through pyrazolyl groups of Tp- ligands in complexes 2 and 4, which lead to 1D chain structures. Complex 5 shows a 3D network structure through the coexistence of - stacking effects and hydrogen-bonding interactions. Magnetic studies show intramolecular ferromagnetic interactions in all four clusters. The exchange parameters are +11.91 and +1.38 cm(-1) for clusters 2 and 3, respectively, while uniaxial molecular anisotropy can be detected in complex 3 due to the distorted core in its molecular structure. Complex 4 has a ground state of S = 3 and shows SMM behavior with an effective energy barrier of U = 18.9 cm(-1). Unusual spin-glass-like dynamic relaxations are observed for complex 5.

Journal Article↗

PubMed2006

Synthesis, crystal structures, and magnetic properties of cyano-bridged heterobimetallic chains based on [(Tp)Fe(CN)3]-.

With the use of the tailored cyanometalate precursor, (Bu4N)[(Tp)Fe(CN)3] (Tp = Tris(pyrazolyl)hydroborate) as the building block to react with fully solvated Cu(II), Co(II), and Ni(II) cations, four one-dimensional (1D) heterobimetallic cyano-bridged chain complexes of squares, [(Tp)2Fe(III)2(CN)6Cu(CH3OH).2CH3OH]n (1), [(Tp)2Fe(III)2(CN)6Cu(DMF).DMF]n (2), [(Tp)2Fe(III)2(CN)6M(CH3OH)2.2CH3OH]n (M = Co (3) and Ni (4)), have been prepared. In complexes 1 and 2, the Cu(II) ions are pentacoordinated in the form of a slightly distorted square-based pyramid, and they are linked by distorted octahedrons of [(Tp)Fe(CN)3]- to form 1D chains of squares. In complexes 3 and 4, both the central Co(II) and Ni(II) ions have a slightly distorted octahedral coordination geometry, and they are bridged by [(Tp)Fe(CN)3]- to form similar 1D chains of squares. There are weak interchain pi-pi stacking interactions through the pyrazolyl groups of the Tp ligands for complexes 3 and 4. The crystal structures and magnetic studies demonstrate that complexes 1 and 2 exhibit intrachain ferromagnetic coupling and single-chain magnets behavior, and the blocking temperature is ca. 6 K for complex 1 and ca. 3 K for complex 2. Complexes 3 and 4 show significant metamagnetic behavior, where the cyanides mediate the intrachain ferromagnetic coupling between Fe(III) and Co(II) or Ni(II) ions and the interchain pi-pi stacking interactions lead to antiferromagnetic couplings. The field dependence of the magnetization measurements shows that the critical field is around 1 kOe for complex 3 and 0.8 kOe for complex 4 at 1.8 K.

Journal Article↗

PubMed2006

Chiral molecule-based ferrimagnets with helical structures.

Two enantiopure one-dimensional complexes with helical structures, [Mn(3)((R,R)-Salcy)(3)(H2O)(2)Fe(CN)(6).2H2O]n (1) and [Mn(3)((S,S)-Salcy)(3)(H2O)(2)Fe(CN)(6).2H2O]n (2) [Salcy = N,N'-(1,2-cyclohexanediylethylene)bis(salicylideneiminato) dianion], have been synthesized and characterized. Magnetic studies show that both complexes are ferrimagnets with the magnetic transition temperature at 3 K.

Crystallography, X-Ray↗

PubMed2006

Symmetry-based magnetic anisotropy in the trigonal bipyramidal cluster [Tp2(Me3tacn)3Cu3Fe2(CN)6]4+.

Reaction of [(Me3tacn)Cu(H2O)2]2+ (Me3tacn = N,N',N' '-trimethyl-1,4,7-triazacyclononane) with [TpFe(CN)3]- (Tp- = hydrotris(pyrazolyl)borate) in a mixture of ethanol and acetonitrile affords the pentanuclear cluster [Tp2(Me3tacn)3Cu3Fe2(CN)6]4+. Single-crystal X-ray analysis reveals a trigonal bipyramidal structure featuring a D3h-symmetry core in which two opposing FeIII (S = 1/2) centers are linked through cyanide bridges to an equatorial triangle of three CuII (S = 1/2) centers. Fits to variable-temperature dc magnetic susceptibility data are consistent with ferromagnetic coupling to give an S = 5/2 ground state, while fits to low-temperature magnetization data indicate the presence of a large axial zero-field splitting (D = -5.7 cm-1). Frequency dependence observed in the ac magnetic susceptibility data confirms single-molecule magnet behavior, with an effective spin reversal barrier of Ueff = 16 cm-1. When compared with the much lower anisotropy barrier previously observed for the face-centered cubic cluster [Tp8(H2O)6Cu6Fe8(CN)6]4+, the results demonstrate the enormous influence of the geometry in which a given set of metal ions are arranged.

Journal Article↗

PubMed2006

Syntheses, structures, and magnetic properties of cyano-bridged heterobimetallic complexes based on [Fe(bpca)(CN)3]-.

Two new cyano-bridged one-dimensional heterobimetallic coordination polymers, [(bpca)(2)Fe(III)(2)(CN)(6)Cu(H(2)O)(2).1.5H(2)O](n)() (2) and [(bpca)Fe(III)(CN)(3)Cu(bpca)(H(2)O).H(2)O](n)() (3), and a trinuclear complex, [(bpca)(2)Fe(III)(2)(CN)(6)Mn(CH(3)OH)(2)(H(2)O)(2)].2H(2)O (4), have been synthesized using the tailored tricyanometalate precursor (Bu(4)N)[Fe(bpca)(CN)(3)].H(2)O (1) (Bu(4)N(+) = tetrabutylammonium cation; bpca = bis(2-pyridylcarbonyl)amidate anion) as a building block and structurally characterized. In complex 2, the Cu(II) ions are six-coordinated in an elongated distorted octahedral environment, and they are linked by distorted octahedrons of [Fe(bpca)(CN)(3)](-) to form 1D chain of squares. Complex 3 is an unexpected chiral heterobimetallic helical chain complex, in which the helical chain consists of the asymmetric unit of [(bpca)Fe(CN)(3)Cu(bpca)(H(2)O)]. In complex 4, there are two independent trinuclear clusters in one asymmetric unit, and the coordination modes of the two methanol and two water molecules coordinating to the central Mn(II) ion are different (cis and trans). Complex 2 shows metamagnetic behavior with a Neel temperature of T(N) = 2.2 K and a critical field of 250 Oe at 1.8 K, where the cyanides mediate the intrachain ferromagnetic coupling between the Cu(II) and Fe(III) ions. Complex 3 shows ferromagnetic coupling between Cu(II) and Fe(III) ions, the best-fit for chi(M)T versus T using a 1D alternating chain model leads to the parameters J(1) = 7.9(3) cm(-)(1), J(2) = 1.03(2) cm(-)(1), and g = 2.196(3). Complex 4 exhibits ferrimagnetic behavior caused by the noncompensation of the local interacting spins (S(Mn) = 5/2 and S(Fe) = 1/2) which interact antiferromagnetically through bridging cyano groups.

Journal Article↗

PubMed2005

One-dimensional azido-bridged chiral metal complexes with ferromagnetic or antiferromagnetic interactions: syntheses, structures, and magnetic studies.

One-dimensional chiral copper(II) and manganese(II) coordination polymers with single asymmetric end-to-end (EE) azide bridges, [Cu(R-L)2(N3)]n(ClO4)n (1), [Cu(S-L)2 (N3)]n(ClO4)n (2), [Mn(R-L)2(N3)]n(ClO4)n (3), and [Mn(S-L)2(N3)]n(ClO4)n (4) (R-L or S-L = R- or S-pyridine-2-carbaldehyde-imine), have been synthesized, using azide ions as bridging groups and chiral Schiff bases as auxiliary ligands, and characterized. The crystal structure determination of complexes 1 and 2 reveals the formation of one-dimensional chiral chains, in which the central Cu(II) ion is six-coordinate in the form of an elongated octahedron. Complex 3 consists of chiral helical polymeric chains, in which the central Mn(II) has a slightly distorted octahedral geometry. They all crystallize in the chiral space group P2(1). Complexes 1 and 2 are rare examples that exhibit ferromagnetic interaction between copper(II) ions through the single end-to-end azido bridge. Fitting the susceptibility data for 1 using a 1D uniform chain model led to the parameters J = 0.70(3) cm(-1), g = 2.06(2), and zj' = 0.07(2) cm(-1). The magnetic studies on 3 and 4 show that there is weak antiferromagnetic coupling between the manganese(II) ions.

Journal Article↗