Thermal-, pressure-, and light-induced spin transition in novel cyanide-bridged FeII-AgI bimetallic compounds with three-dimensional interpenetrating double structures (FeIILx[Ag(CN)2]2).G

Low-spin, high-spin and spin-transition behaviours have been observed for the doubly interpenetrating three-dimensional bimetallic compounds (FeII(pz)[Ag(CN)2]2).pz (pz = pyrazine), (FeII(4,4'-bipy)2[Ag(CN)2]2) (4,4'-bipy = 4,4'-bipyridine), and (FeII(bpe)2[Ag(CN)2]2) (bpe = bispyridylethylene), respectively. The single crystals of the bpe derivative undergo a spin transition with a large hysteresis loop at about 95 K. After several warming and cooling cycles, the single crystals become a microcrystalline powder with 50% spin transition. Influence of pressure--as well as light-induced excited spin-state trapping (LIESST) on the thermal 50% spin transition of the microcrystalline sample has also been investigated. Thermal spin-transition behaviour has also been induced at pressures higher than 1 bar for the 4,4'-bipy derivative. Both the 4,4'-bipy and bpe derivatives show strong pressure dependence of the spin state at 300 K.     

Synthesis, structural diversity and fluorescent characterisation of a series of d10 metal-organic frameworks (MOFs): reaction conditions, secondary ligand and metal effects

Along with our recent investigation on the flexible ligand of H(2)ADA (1,3-adamantanediacetic acid), a series of Zn(II) and Cd(II) metal-organic frameworks, namely, [Zn(3)(ADA)(3)(H(2)O)(2)](n)·5nH(2)O (1), [Zn(ADA)(4,4'-bipy)(0.5)](n) (2), [Zn(2)(ADA)(2)(bpa)](n) (3), [Zn(2)(ADA)(2)(bpa)](n) (4), [Zn(2)(ADA)(2)(bpp)](n) (5), [Cd(HADA)(2)((4,4'-bipy)](n) (6), [Cd(3)(ADA)(3)(bpa)(2)(CH(3)OH)(H(2)O)](n) (7), and [Cd(2)(ADA)(2)(bpp)(2)](n)·7nH(2)O (8) have been synthesized and structurally characterized (where 4,4'-bipy = 4,4'-dipyridine, bpa = 1,2-bis(4-pyridyl)ethane and bpp = 1,3-bis(4-pyridyl)propane). Due to various coordination modes and conformations of the flexible dicarboxylate ligand and the different pyridyl-containing coligands, these complexes exhibit structural and dimensional diversity. Complex 1 exhibits a three-dimensional (3D) framework containing one-dimensional (1D) Zn(II)-O-C-O-Zn(II) clusters. Complex 2 exhibits a 2D structure constructed by 1D double chains based on [Zn(2)ADA(2)] units and a 4,4'-bipy pillar. Complexes 3 and 4 possess isomorphic 2D layer structures, resulting from the different coordination modes of carboxylate group of ADA ligands. Complex 5 features a 2D 4(4) layer in which ADA ligands and Zn(II) atoms construct a 1D looped chain and the chains are further connected by bpp ligands. Complex 6 is composed of 1D zig-zag chains that are entangled through hydrogen-bonding interactions to generate a 2D network. Complex 7 is a rare (3,5)-connected network. Complex 8 possesses a 3D microporous framework with lots of water molecules encapsulated in the channels. The structural diversity of the complexes perhaps mainly results from using diverse secondary ligands and different metal centre ions, and means the assistant ligand and metal centre play important roles in the design and synthesis of target metal-organic frameworks. This finding revealed that ADA could be used as an effective bridging ligand to construct MOFs and change coordination modes and conformational geometries in these complexes. The thermogravimetric analyses, X-ray powder diffraction and solid-state luminescent properties of the complexes have also been investigated.     

Unusual spin transition behavior in 2,6-bis((pyrazol-3-yl)-pyridine) iron(II)-bis-oxalato-platinate(II)

[Fe(bpp)2][Pt(ox)2].H2O (with bpp=2,6-bis(pyrazol-3-yl)-pyridine and ox=oxalate) was prepared, and its spin crossover behavior was characterized. The two-step spin transition behavior changes over several cycles. The original behavior is restored when the sample is allowed to relax for a week. Furthermore, the ST exhibits a strong dependence on the heating and cooling rate. Heating the compound at 1 K/min leads to a spin transition with a third step and a second plateau at gammaHS approximately 0.8. Quenching the sample to 77 K also affects the spin transition behavior. The kinetic relaxation is followed after quenching and after light-induced excited spin state trapping experiments.     

Pressure-induced structural, magnetic, and transport transitions in the two-legged ladder Sr3Fe2O5

The layered compound SrFeO(2) with an FeO(4) square-planar motif exhibits an unprecedented pressure-induced spin state transition (S = 2 to 1), together with an insulator-to-metal (I-M) and an antiferromagnetic-to-ferromagnetic (AFM-FM) transition. In this work, we have studied the pressure effect on the structural, magnetic, and transport properties of the structurally related two-legged spin ladder Sr(3)Fe(2)O(5). When pressure was applied, this material first exhibited a structural transition from Immm to Ammm at P(s) = 30 ± 2 GPa. This transition involves a phase shift of the ladder blocks from (1/2,1/2,1/2) to (0,1/2,1/2), by which a rock-salt type SrO block with a 7-fold coordination around Sr changes into a CsCl-type block with 8-fold coordination, allowing a significant reduction of volume. However, the S = 2 antiferromagnetic state stays the same. Next, a spin state transition from S = 2 to S = 1, along with an AFM-FM transition, was observed at P(c) = 34 ± 2 GPa, similar to that of SrFeO(2). A sign of an I-M transition was also observed at pressure around P(c). These results suggest a generality of the spin state transition in square planar coordinated S = 2 irons of n-legged ladder series Sr(n+1)Fe(n)O(2n+1) (n = 1, 2, 3, ...). It appears that the structural transition independently occurs without respect to other transitions. The necessary conditions for a structural transition of this type and possible candidate materials are discussed.     

Hydrothermal syntheses, crystal structures, and magnetic properties of inorganic-organic hybrid vanadium selenites with zero- to three-dimensional structures: (1,10-phenanthroline)(2)V(2)SeO(7), (2,2'-bipyridine)VSeO(4), (4,4'-bipyridine)V(2)Se(2)O(8), and (4,4'-bipyridine)(2)V(4)Se(3)O(15).H(2)O

A family of inorganic-organic hybrid vanadium selenites with zero-, one-, two-, and three-dimensional structures, (1,10-phen)(2)V(2)SeO(7), (2,2'-bipy)VSeO(4), (4,4'-bipy)V(2)Se(2)O(8), and (4,4'-bipy)(2)V(4)Se(3)O(15).H(2)O (where phen = phenanthroline and bipy = bipyridine), were hydrothermally synthesized and characterized by single-crystal X-ray diffraction. Different bidentate organodiamine ligands and reactant concentrations were used in the four reaction systems, which are responsible for the variety of structural dimensions of the compounds. (1,10-phen)(2)V(2)SeO(7) crystallizes in a monoclinic system with space group P2(1)/n and cell parameters a = 8.6509(3) A,( )b = 7.8379(2) A, c = 34.0998(13) A, beta = 91.503(2) degrees, and Z = 4. (2,2'-bipy)VSeO(4) crystallizes in a monoclinic system with space group C2/c and cell parameters a = 17.0895(12) A, b = 14.7707(10) A, c = 11.7657(8) A, beta = 131.354(3) degrees, and Z = 8. (4,4'-bipy)V(2)Se(2)O(8) crystallizes in a triclinic system with space group Ponemacr; and cell parameters a = 7.1810(10) A, b = 10.8937(13) A, c = 11.1811(15) A, alpha = 115.455(3) degrees, beta = 107.582(3) degrees, gamma = 91.957(4) degrees, and Z = 2. (4,4'-bipy)(2)V(4)Se(3)O(15).H(2)O crystallizes in a monoclinic system with space group Pc and cell parameters a = 7.9889(9) A, b = 7.8448 A, c = 23.048(3) A, beta = 99.389(4) degrees, and Z = 2. (1,10-phen)(2)V(2)SeO(7) has an isolated structure, (2,2'-bipy)VSeO(4) has a chain structure, (4,4'-bipy)V(2)Se(2)O(8) has a layered structure, and (4,4'-bipy)(2)V(4)Se(3)O(15).H(2)O has a framework structure. The chains are constructed from VO(4)N(2) octahedra and SeO(3) pyramids, laced by organic ligands (2,2'-bipy). The layers consist of vanadium selenite chains [(VO)(2)(SeO(3))(2)]( infinity ), linked by 4,4'-bipy molecules. The framework is composed of vanadium selenite sheets [V(4)Se(3)O(16)]( infinity ), pillared by 4,4'-bipy molecules. All of the compounds are thermally stable to 300 degrees C, and the magnetic susceptibilities confirm the existence of tetravalent V atoms in the antiferromagnetic (4,4'-bipy)V(2)Se(2)O(8) complex and mixed tetravalent and pentavalent V atoms in the paramagnetic complex (4,4'-bipy)(2)V(4)Se(3)O(15).H(2)O.     

Novel hydrogen-bonded three-dimensional networks encapsulating one-dimensional covalent chains: [M(4,4'-bipy)(H2O)(4)](4-abs)(2).nH2O (4,4'-bipy = 4,4'-bipyridine; 4-abs = 4-aminobenzenesulfonate) (M = Co,n = 1; M = Mn,n = 2)

Two novel compounds, [Co(4,4'-bipy)(H(2)O)(4)](4-abs)(2).H(2)O (1) and [Mn(4,4'-bipy)(H(2)O)(4)](4-abs)(2).2H(2)O (2) (4,4'-bipy = 4,4'-bipyridine; 4-abs = 4-aminobenzenesulfonate), have been synthesized in aqueous solution and characterized by single-crystal X-ray diffraction, elemental analyses, UV-vis and IR spectra, and TG analysis. X-ray structural analysis revealed that 1 and 2 both possess unusual hydrogen-bonded three-dimensional (3-D) networks encapsulating one-dimensional (1-D) covalently bonded infinite [M(4,4'-bipy)(H(2)O)(4)](2+) (M = Co, Mn) chains. The 4-abs anions in 1 form 1-D zigzag chains through hydrogen bonds. These chains are further extended through crystallization water molecules into 3-D hydrogen-bonded networks with 1-D channels, in which the [Co(4,4'-bipy)(H(2)O)(4)](2+) linear covalently bonded chains are located. Crystal data for 1: C(22)H(30)CoN(4)O(11)S(2), monoclinic P2(1), a = 11.380(2) A, b = 8.0274(16) A, c = 15.670(3) A, alpha = gamma = 90 degrees, beta = 92.82(3) degrees, Z = 2. Compound 2 contains interesting two-dimensional (2-D) honeycomb-like networks formed by 4-abs anions and lattice water molecules via hydrogen bonding, which are extended through other crystallization water molecules into three dimensions with 1-D hexagonal channels. The [Mn(4,4'-bipy)(H(2)O)(4)](2+) linear covalent chains exist in these channels. Crystal data for 2: C(22)H(32)MnN(4)O(12)S(2), monoclinic P2(1)/c, a = 15.0833(14) A, b = 8.2887(4) A, c = 23.2228(15) A, alpha = gamma = 90 degrees, beta = 95.186(3) degrees, Z = 4.     

Hydrothermal syntheses and crystal structures of complex-linked three-Dimensional coordination vanadium selenites: M(4,4'-bipy)(H(2)O)V(2)Se(2)O(10) (M = Co,Ni)

Two inorganic-organic hybrid compounds with the formula M(4,4'-bipy)(H(2)O)V(2)Se(2)O(10) (M = Co, Ni) were hydrothermally synthesized and characterized by single-crystal X-ray diffraction. Compounds Co(4,4'-bipy)(H(2)O)V(2)Se(2)O(10) (1) and Ni(4,4'-bipy)(H(2)O)V(2)Se(2)O(10) (2), which are structural analogues, crystallize in the triclinic space group Ponemacr; with crystal data a = 7.9665(3) A, b = 8.1974(3) A, c = 13.8096(4) A, alpha = 85.704(2) degrees, beta = 73.5180(10) degrees, gamma = 75.645(2) degrees, V = 837.76(5) A(3), and Z = 2 and a = 7.9489(19) A, b = 8.128(2) A, c = 13.709 A, alpha = 85.838(6) degrees, beta = 73.736(8) degrees, gamma = 75.594(9) degrees, V = 823.5(4) A(3), and Z = 2, respectively. [M(4,4'-bipy)(H(2)O)V(2)Se(2)O(10)] (M = Co, Ni) have a three-dimensional structure and consist of two subunits, [(VO(2))(SeO(3))](-) infinite chains and [M(4,4'-bipy)(H(2)O)](2+) fragments. The [(VO(2))(SeO(3))](-) chains are composed of [V(2)Se(4)O(14)](4)(-) clusters linked by VO(4)N triangular bipyramids. The 4,4'-bipy molecule as a bifunctional organic ligand is directly linked to Co or Ni and V atoms, affording the three-dimensionality. The compounds were characterized by infrared spectroscopy and differential thermal and thermogravimetric analyses.     

Construction of polyoxometalates-based coordination polymers through direct incorporation between polyoxometalates and the voids in a 2D network

A series of polyoxometalates (POMs)-based coordination polymers, namely, {[Cu(2,3-Me2pz)(2,5-Me2pz)0.5]4(SiW12O40)(2,5-Me2pz)}n (2,3-Me2pz = 2,3-dimethylpyrazine; 2,5-Me2pz = 2,5-dimethylpyrazine; 1), {[Cu2(4,4'-bipy)4(H2O)4](SiW12O40)(H2O)18}n (4,4'-bipy = 4,4'-bipyridine; 2), {[Cu(2-Mepz)1.5]3(PMo12O40)(H2O)3.5}n (2-Mepz = 2-methylpyrazine; 3), {[Ag(2,3-Me2pz)1.5]4(SiW12O40}n (4), {[Cu(pz)1.5]4(SiW12O40)(H2O)3}n (pz = pyrazine; 5), {[Cu(2,3-Me2pz)1.5]4(SiW12O40)}n (6), {[Cu(4,4'-bipy)1.75]4(SiW12O40)(H2O)2}n (7), and {[Cu2(4,4'-bipy)4(H2O)4](SiW12O40)(4,4'-bipy)2(H2O)4}n (8), were synthesized through direct incorporation between POMs and the voids of the 2D network. Crystal structural analysis reveals that the relationship between the size of the void of the 2D network and that of POMs is of key importance for successful synthesis of POMs-based open metal-organic frameworks. Guest replacement shows that the pore size of the framework constructed through direct incorporation between POMs and the voids of the 2D network is very sensitive to guest molecules.     

Synthesis, Crystal Structure and Water-induced Reversible Crystal-to-amorphous Transformation Property of [{Ni(IBG)(4,4'-bipy)(a2O)2}·3a2O]n

A novel NiⅡ complex[{Ni(IBG)(4,4'-bipy)(H2O)2}·3H2O]n1(H2IBG=isophthaloylbisglycine and 4,4'-bipy=4,4'-bipyridine)has been synthesized and characterized by singlecrystal X-ray diffraction,elemental analysis,IR spectra and thermogravimetric analysis.It crystallizes in monoclinic,space group P2/c with a=15.5420(7),b=22.4344(1),c=8.3455(5)(A),β=101.538(3)°,V=2670.1(7)(A)3,Z=4,C22H32N4NiO13,Mr=619.23,Dc=1.443 g/cm3,F(000)=1296.0,μ(MoKa)=0.750 mm-1,the final R=0.0570 and wR=0.1445 for 2296 observed reflections with I>2σ(I).In the structure,the NiⅡ metal center is coordinated in an octahedral environment arranged by two water molecules,two carboxylate oxygen atoms and two nitrogen atoms from two4,4'-bipy ligands.Thermal decomposition and powder X-ray diffraction results indicate that the transformation from the crystal form,[{Ni(IBG)(4,4'-bipy)(H2O)2}·3H2O]n,to the amorphous powder,Ni(IBG)(4,4'-bipy)(H2O)2,is reversible,so the latter form may be utilized as an absorbing agent for water and water vapor.     

Syntheses, structures, and properties of five coordination polymers containing fluorescent whitener

Fluorescent whitener (4,4'-bis(2-sulfonatostiryl)biphenyl) was incorporated with M/4,4'-bipy (M=Cd, Co; 4,4'-bipy=4,4'-bipyridine) 2D frameworks, Mn/4,4'-bipyH fragment, and the [Zn2(Im)2(ImH)4]2+ (ImH=imidazole) chain under hydrothermal conditions to obtain seven new coordination polymers: [Cd(4,4'-bipy)(L)(H2O)2] (1), [Co(4,4'-bipy)2(L)].2H2O (2), [Co(4,4'-bipy)2(H2O)2](4,4'-bipy)(L).2H2O (3), [Mn(4,4'-bipyH)2(L)2(H2O)2].4H2O (4), and [Zn2(Im)2(ImH)4](L) (5). Their structures were determined by single-crystal X-ray diffraction. In 1, binuclear [Cd2] units are bridged by 4,4'-bipys into a 2D cationic framework, which is further penetrated by L anions. 2 has an organic-inorganic hybrid layer consisting of [Co(4,4'-bipy)2] squarelike motifs and L anions. 3 features a pcu-like 3D cationic framework with the inclusion of L anions. In 4, the [Mn(4,4'-bipyH)2(H2O)2]4+ cationic fragment is sandwiched by L anions into a sandwichlike hybrid layer. 5 exhibits a 3D honeycomb-like structure with each nanotube encapsulating two parallel L anionic chains. TGA and PXRD indicate solids 1, 4, and 5 are thermally stable up to 280, 200, and 250 degrees C under an air atmosphere, respectively. 1 has bright blue-green luminescence with a peak maximum band at about 470 nm. 4 exhibits tunable emission between dark-red and weak-green under the excitation of 500 and 280 nm, respectively. 5 displays a bright blue-green emission with a peak band at 454 nm and a shoulder peak at 473 nm. It is attractive that the luminescent properties of solids 1, 4, and 5 are almost retained after heat treatment at 200, 200, and 250 degrees C for 2 h under an air atmosphere, respectively.     

Synthesis,Crystal Structure and Water-induced Reversible Crystal-to-amorphous Transformation Property of [{Ni(IBG)(4,4'-bipy)(H_2O)_2}·3H_2O]_n

A novel NiII complex [{Ni(IBG)(4,4'-bipy)(H2O)2}·3H2O]n 1 (H2IBG = isophthaloylbisglycine and 4,4'-bipy = 4,4'-bipyridine) has been synthesized and characterized by singlecrystal X-ray diffraction, elemental analysis, IR spectra and thermogravimetric analysis. It crystallizes in monoclinic, space group P2/c with a = 15.5420(7), b = 22.4344(1), c = 8.3455(5), β = 101.538(3)o, V = 2670.1(7)3, Z = 4, C22H32N4NiO13, Mr = 619.23, Dc = 1.443 g/cm3, F(000) = 1296.0, μ(MoKα) = 0.750 mm-1, the final R = 0.0570 and wR = 0.1445 for 2296 observed reflections with I 2σ(I). In the structure, the NiII metal center is coordinated in an octahedral environment arranged by two water molecules, two carboxylate oxygen atoms and two nitrogen atoms from two 4,4'-bipy ligands. Thermal decomposition and powder X-ray diffraction results indicate that the transformation from the crystal form, [{Ni(IBG)(4,4'-bipy)(H2O)2}·3H2O]n, to the amorphous powder, Ni(IBG)(4,4'-bipy)(H2O)2, is reversible, so the latter form may be utilized as an absorbing agent for water and water vapor.     

Thermal, pressure and light induced spin transition in the two-dimensional coordination polymer [Fe(pmd)2[Cu(CN)2]2

A complete structural, calorimetric, and magnetic characterisation of the 2D coordination spin crossover polymer [Fe(pmd)(2)[Cu(CN)(2)](2)] is reported. The crystal structure has been investigated below room temperature at 180 K and 90 K, and at 30 K after irradiating the sample at low temperature with green light (lambda = 532 nm). The volume cell contraction through the thermal spin transition is only 18 A(3) which is lower than the usually observed value of around 25-30 A(3) while the average Fe-N bond distances decrease by the typical value of about 0.19 A. The structural data of the irradiated state indicate that the high spin state is well induced since the cell parameters are consistent with the data at 180 K. Calorimetric and photo-calorimetric experiments have also been performed. The entropy content for the thermal spin transition, DeltaS = 35-37 J mol(-1) K(-1) lies in the lowest range of the typical values and correlates with the low volume cell contraction. The combination of the crystallographic and calorimetric data predicts, in accordance with a mean-field approach, a linear pressure dependence of the critical temperature with a slope of 302 K GPa(-1). Magnetic measurements under pressure reveal an anomalous behaviour since the critical temperature and hysteresis do not change up to 0.22 GPa but an apparent linear dependence is obtained for higher pressures (up to 0.8 GPa) with a slope two times higher than the mean-field estimation.     

A new enantiopure unsaturated dicarboxylate as a 4-connected unit in a flexible homochiral PtS-type framework

Metal cation mediated chiral ligand transformation of (S)-camphanic acid leads to a new enantiopure unsaturated dicarboxylate that links tetrahedral Zn(2+) sites into 3-D homochiral 4-connected PtS-type framework structures, Zn(tced) (1, H(2)tced=1,2,2-trimethyl-3-cyclopentene-1,3-dicarboxylic acid) and Zn(4)(tced)(4)(4,4'-bipy) (2, 4,4'-bipy=4,4'-bipyridine).     

Cooperative spin transition in the two-dimensional coordination polymer [Fe(4,4'-bipyridine)2(NCX)2]·4CHCl3 (X = S, Se)

Two new isostructural two-dimensional (2D) coordination polymers exhibiting spin crossover (SCO) behavior of formulation [Fe(4,4'-bipy)(2)(NCX)(2)]·4CHCl(3) (4,4'-bipy = 4,4'-bipyridine; X = S [1·4CHCl(3)], Se [2·4CHCl(3)]) have been synthesized and characterized, and both undergo cooperative spin transitions (ST). For 1·4CHCl(3) the ST takes place in two steps with critical temperatures of T(c1)(down) = 143.1 K, T(c2)(down) = 91.2 K, T(c1)(up) = 150.7 K, and T(c2)(up) = 112.2 K. 2·4CHCl(3) displays half ST characterized by T(c)(down) = 161.7 K and T(c)(up) = 168.3 K. The average enthalpy and entropy variations and cooperativity parameters associated with the ST have been estimated to be ΔH(1)(av) = 5.18 kJ mol(-1), ΔS(1)(av) = 35 J K(-1) mol(-1), and Γ(1) = 2.8 kJ mol(-1) and ΔH(2)(av) = 3.55 kJ mol(-1), ΔS(2)(av) = 35 J K(-1) mol(-1), and Γ(2) = 2.6 kJ mol(-1) for 1·4CHCl(3), and ΔH(av) = 6.25 kJ mol(-1), ΔS(av) = 38.1 J K(-1) mol(-1), and Γ = 3.2 kJ mol(-1) for 2·4CHCl(3). At T > [T(c1) (1·4CHCl(3)); T(c) (2·4CHCl(3))], both compounds are in the space group P2/c while at T < [T(c1) (1·4CHCl(3)); T(c) (2·4CHCl(3))] they change to the C2/c space group and display an ordered checkerboard-like arrangement of iron(II) sites where the high- and low-spin states coexist at 50%.     

On the viability of cyclometalated Ru(II) complexes as dyes in DSSC regulated by COOH group, a DFT study

The Ru(II) complexes [Ru(bpp)(dcbpy)Cl](+) (1), [Ru(tcbpp)(bpy)Cl](+) (2), and [Ru(tc'bpp)(bpy)Cl](+) (3) (bpp = 2,6-bis(N-pyrazolyl)pyridine, dcbpy = 4,4'-dicarboxyl-bipyridine, bpy = bipyridine, tcbpp = 4-carboxyl-2,6-bis(2-carboxyl-N-pyrazolyl)pyridine, tc'bpp = 4-carboxyl-2,6-bis(4-carboxyl-N-pyrazolyl)pyridine) are studied theoretically using density functional theory (DFT) techniques to explore their properties as dye in a solar cell. The calculated geometry structure and absorption spectrum of 1 are consistent with its experimental results. The calculation results indicate which sites the COOH groups attach to can significantly influence the electronic structure of the complex. By migrating the COOH groups from the bpy ligand in 1 to bpp ligand in 2 and 3, the nature of LUMO changes from bpy-localized to bpp dominated. The calculated low-lying absorptions at λ > 370 nm of the three complexes are categorized as metal-to-ligand charge-transfer (MLCT) transitions and the transition terminates at the orbital populated by the COOH appended ligand. The atomic spin density analysis also indicates that the ligand which is modified by the COOH groups is the ideal spot for the captured electron to situate. It can be predicted that the performance of 2 and 3 in the dye-sensitized solar cell can be enhanced as compared with 1.     

Mass effect on the equienergetic high-spin/low-spin states of spin-crossover in 4,4'-bipyridine-bridged iron(II) polymeric compounds: synthesis,structure, and magnetic,Mössbauer,and theoretical studies

The suitability of the system [Fe(4,4'-bipy)(H(2)O)(2)(NCX)(2)].(4,4'-bipy), where 4,4'-bipy stands for 4,4'-bipyridine and X = S (1) and Se (2), as a precursor for the synthesis of new polymeric spin-crossover compounds has been studied. The reaction of 1 or 2 with bt (2,2'-bithiazoline) afforded the polymeric compounds of formula [Fe(4,4'-bipy)(bt)(NCX)(2)] (X = S (3), Se (4)). Compounds 3 and 4 are isostructural, but only the crystal structure of 3 has been fully determined. It crystallizes in the orthorhombic system, Fdd2 space group, Z = 24, with a = 38.962(8) A, b = 11.545(2) A, c = 30.889(6) A, V = 13895(5) A(3). The structure consists of linear chains constituted by trans-4,4'-bipy linked iron(II) ions; two cis equatorial positions are occupied by two pseudohalide ligands, and the remaining positions are filled by the bidentate bt ligand. Investigation of their magnetic properties and M?ssbauer spectra has revealed the occurrence of a low-spin (LS) <--> high-spin (HS) conversion involving 12% (3, S) and 20% (4, Se) of the Fe(II) ions. The thermal variation of the HS fraction is gradual with onset temperatures as low as 60 K. A theoretical approach based on the Ising-like model, completed with molecular vibrations, through harmonic oscillators, fits the data successfully, leading to an energy gap of 65 cm(-1) (3) and 86 cm(-1) (4) between the lowest LS and HS levels, and an average vibration frequency ohgrmacr;(LS) of 382 cm(-1) (3) and 365 cm(-1) (4) in the LS state. The ca. 1.05 omega(LS(3))/omega(LS(4)) ratio is close to the ca. 1.09 Se/S molar mass ratio. The simple electrovibrational Ising-like model permits us to explain, for the first time, a mass effect through the molecular vibrations in a spin-crossover complex that is in the unusual situation of equienergy among the HS and LS states.     

A Ferroelectric Iron(II) Spin Crossover Material

A dual‐function material in which ferroelectricity and spin crossover coexist in the same temperature range has been obtained. Our synthetic strategy allows the construction of acentric crystal structures in a predictable way and is based on the high directionality of hydrogen bonds. The well‐known iron(II) spin crossover complex [Fe(bpp)₂]²⁺ (bpp=2,6‐bis(pyrazol‐3‐yl)pyridine), a four‐fold noncentrosymmetric H‐bond donor, was combined with a disymmetric H‐bond acceptor such as the isonicotinate (isonic) anion to afford [Fe(bpp)₂](isonic)₂⋅2 H₂O. This low‐spin iron(II) compound crystallizes in the acentric nonpolar I space group and shows piezoelectricity and SHG properties. Upon dehydration, it undergoes a single‐crystal to single‐crystal structural rearrangement to a monoclinic polar Pc phase that is ferroelectric and exhibits spin crossover.     

Syntheses, structures, and optical properties of novel zinc(ii) complexes with multicarboxylate and N-donor ligands

Five novel coordination polymers [Zn(2)(OA)(4,4'-bipy)(H(2)O)].0.5(4,4'-bipy), [Zn(2)(OA)(dib)(H(2)O)].H(2)O, [Zn(2)(OA)(bbi)(2)].3H(2)O, [Zn(2)(OA)(phen)(2)(H(2)O)] and [Zn(4)(OA)(2)(2,2'-bipy)(2)(H(2)O)].2H(2)O were obtained by hydrothermal reactions of Zn(NO(3))(2).6H(2)O with a V-shaped multicarboxylate ligand 3,3',4,4'-oxydiphthalic acid (H(4)OA) and a series of N-donor ligands, namely 4,4'-bipyridine (4,4'-bipy), 1,4-di(1-imidazolyl)benzene (dib), 1,1'-(1,4-butanediyl)bis(imidazole) (bbi), 1,10-phenanthroline (phen), 2,2'-bipyridine (2,2'-bipy). The structures of the complexes were established by single-crystal X-ray diffraction analysis. Complex exhibits a robust 3D porous structure with uncoordinated 4,4'-bipy molecules filling the cavities. Complexes and show a complicated 3D framework, while complexes and have a 2D network and a 1D helical chain structure, respectively. The results indicate that the multicarboxylate OA(4-) ligand can adopt varied coordination modes in the formation of the complexes and the influence of the N-donor ligand on the structure of the complexes is discussed. The photoluminescence properties of H(4)OA and were studied in the solid state at room temperature. Moreover, nonlinear optical measurements showed that displayed a second-harmonic-generation (SHG) response of 0.5 times of that for urea. The results suggested that the configuration and flexibility of the ligands play a key role in directing the related properties of the complexes.     

Formation of a three-dimensional bispyridyl based metal-organic architecture containing unique Ag...Ag （d^10-d^10） interactions

A novel co-ordination polymer based on IB metal thiocyanates, [Ag2（NCS）2（4,4＇-bipy）]. （1）（4,4＇-bipy = 4,4＇-bispyridine）, has been synthesized by the pre-assembly method and characterized by X-ray crystallography. The complex exists as a three- dimensional network consisting of （AgSCN）. undulating layers linked by 4,4＇-bipy bridges.     

N-heterocyclic amine-directed structures and properties of two Cu(II) diphosphonates

By introducing the second organic N-heterocyclic ligands 4'-(4-pyridyl)-4,2':6',4'-terpyridine (pyterpy) and 4,4'-bipyridyl (4,4'-bipy), two examples of Cu(II)-diphosphonates, [Cu(3)(HL)(2)(Hpyterpy)(2)]·2H(2)O 1 and [Cu(4)(HL)(2)(4,4'-bipy)(H(2)O)(5)] 2 based on 1-hydroxyethylidenediphosphonic acid (H(5)L = CH(3)C(OH)(PO(3)H(2))(2)), have been hydrothermally obtained and characterized by powder X-ray diffraction, elemental analysis, IR, TG-DSC. The single-crystal X-ray diffractions reveal that compound 1 has a one-dimensional fishbone-like chain constructed by anions [Cu(3)(HL)(2)(2-)](n) while simultaneously organic cations [Hpyterpy(+)](n) suspending both sides, and compound 2 exhibits two-dimensional inorganic-organic alternate arrangement layer built from 1-D ladder-like inorganic chain with tetranuclear cluster [Cu(4)O(10)] via 4,4'-bipy linkage. The results of electrochemical measurements indicate half-wave potential of 1 (E(1/2)(1) = 1.01 V) is less than that of 2 (E(1/2)(2) = 1.20 V), indicating a good D-A system in ICT for 1. Moreover fluorescent measurements reveal that emission intensity of 1 centered at 422 nm is larger than that of 2 emitted at 420 nm, caused by intraligand π*-π emission state of organic N-heterocyclic amine (λ(ex) = 233 nm). Magnetism data indicate that compound 1 exhibits ferrimagnetic interactions between metal centers, while compound 2 has antiferromagnetic property.