Circular and Chainlike Copper(II)-Lanthanide(III) Complexes Generated by Assembly Reactions of Racemic and Chiral Copper(II) Cross-Linking Ligand Complexes with LnIII(NO3)3·6H2O (LnIII = GdIII, TbIII, DyIII).

The 1:1 assembly reaction of the racemic form of the cross-linking ligand complex Na[CuIILdpen(1R2R/1S2S)] with LnIII(NO3)3·6H2O gave the centrosymmetric circular (CuIILnIII)2 complex [CuIILdpen(1R2R/1S2S)LnIII(NO3)2]2 (1Ln: Ln = Gd, Tb, Dy), while the reaction of the enantiopure form Na[CuIILdpen(1R2R)] with LnIII(NO3)3·6H2O gave the chiral chainlike (CuIILnIII)1∞ complex [CuIILdpen(1R2R)LnIII(NO3)2(CH3CN)]1∞·CH3CN (2Ln: Ln = Gd, Tb, Dy), where {CuIILdpen(1R2R)}- is (N-((1R,2R)-2-(((E)-3-ethoxy-2-oxybenzylidene)amino)-1,2-diphenylethyl)-2-oxybenzamide)copper(II) and {CuIILdpen(1R2R/1S2S)}- is the racemic mixture of {CuIILdpen(1R2R)}- and {CuIILdpen(1S2S)}-. The copper(II) component functions as a cross-linking ligand complex and bridges two LnIII ions at two phenoxo oxygen atoms and one ethoxy oxygen atom, as well as at an amido oxygen atom. For 1Ln, two binuclear species of [CuIILdpen(1R2R)LnIII(NO3)2] and [CuIILdpen(1S2S)LnIII(NO3)2] with opposite chiralities are linked by two amido oxygen atoms O3 and O3* to form a centrosymmetric circular structure with Gd-Cu = 3.370(1) Å and Gd-Cu* = 5.627(1) Å. For 2Ln, binuclear species with the same chirality are bridged by Gd-O3* = 2.228(5) Å to form a chiral chainlike structure with Gd-Cu = 3.3348(9) Å and Gd-Cu* = 6.2326(9) Å. The bridged angles through the amido group of Gd-O3*═C7* are 133.9(5) and 177.6(4)° for 1Gd and 2Gd, respectively. The magnetic susceptibilities of 1Gd and 2Gd were analyzed by the spin-only Hamiltonian on the basis of the circular tetranuclear (-CuIIGdIII-)2 and linear chainlike (-CuIIGdIII-)1∞ structures, respectively. The CuII-GdIII magnetic interactions through two phenoxo bridges and a three-atom N-C═O bridge, J1 and J2, are both ferromagnetic to be J1 = +4.6 cm-1 and J2 = +1.8 cm-1 for 1Gd and J1 = +4.2 cm-1 and J2 = +0.037 cm-1 for 2Gd. The J2 value of 2Gd is much smaller than that of 1Gd. When the temperature was lowered, 1Ln and 2Ln (Ln = Tb, Dy) showed a decrease in the χMT vs T plot due to crystal field effects on the LnIII ion (Stark splitting) and an increase due to the ferromagnetic CuII-LnIII interaction. The magnetization values of 1Ln and 2Ln (Ln = Tb, Dy) without liquid paraffin are considerably larger than the corresponding values with liquid paraffin, indicating the presence of strong magnetic anisotropy. 1Tb and 1Dy showed frequency dependence of ac magnetic susceptibility under zero external dc magnetic field, showing the behavior of single-molecule magnets (SMMs). 2Tb and 2Dy showed no frequency dependence under a zero external magnetic field but showed a meaningful frequency dependence under an external magnetic field. Their energy barriers, Δ/kB, estimated by the Arrhenius plots are 29.4(6) and 20.6(3) K for 1Tb and 2Tb under dc bias fields of 0 and 1000 Oe, respectively, and those of 1Dy and 2Dy are 13.1(9) K and 16.4(2) K under dc bias fields of 0 and 1000 Oe, respectively.

Scan Rate Dependent Spin Crossover Iron(II) Complex with Two Different Relaxations and Thermal Hysteresis fac-[Fe(II)(HL(n-Pr))3]Cl·PF6 (HL(n-Pr) = 2-Methylimidazol-4-yl-methylideneamino-n-propyl).

Solvent-free spin crossover Fe(II) complex fac-[Fe(II)(HL(n-Pr))3]Cl·PF6 was prepared, where HL(n-Pr) denotes 2-methylimidazol-4-yl-methylideneamino-n-propyl. The magnetic susceptibility measurements at scan rate of 0.5 K min(-1) showed two successive spin transition processes consisting of the first spin transition T1 centered at 122 K (T1↑ = 127.1 K, T1↓ = 115.8 K) and the second spin transition T2 centered at ca. 105 K (T2↑ = 115.8 K, T2↓ = 97.2 K). The magnetic susceptibility measurements at the scan rate of 2.0, 1.0, 0.5, 0.25, and 0.1 K min(-1) showed two scan speed dependent spin transitions, while the Mössbauer spectra detected only the first spin transition T1. The crystal structures were determined at 160, 143, 120, 110, 95 K in the cooling mode, and 110, 120, and 130 K in the warming mode so as to follow the spin transition process of high-spin HS → HS(T1) → HS(T2) → low-spin LS → LS(T2) → LS(T1) → HS. The crystal structures at all temperatures have a triclinic space group P1̅ with Z = 2. The complex-cation has an octahedral N6 coordination geometry with three bidentate ligands and assume a facial-isomer with Δ- and Λ-enantimorphs. Three imidazole groups of fac-[Fe(II)(HL(n-Pr))3](2+) are hydrogen-bonded to three Cl(-) ions. The 3:3 NH(imidazole)···Cl(-) hydrogen-bonds form a stepwise ladder assembly structure, which is maintained during the spin transition process. The spin transition process is related to the structural changes of the FeN6 coordination environment, the order-disorder of PF6(-) anion, and the conformation change of n-propyl groups. The Fe-N bond distance in the HS state is longer by 0.2 Å than that in the LS state. Disorder of PF6(-) anion is not observed in the LS state but in the HS state. The conformational changes of n-propyl groups are found in the spin transition processes except for HS → HS(T1) → HS(T2).

Crystal field splitting of the ground state of terbium(III) and dysprosium(III) complexes with a triimidazolyl tripod ligand and an acetate determined by magnetic analysis and luminescence.

Terbium(III) and dysprosium(III) complexes with a tripodal N7 ligand containing three imidazoles (H3L) and a bidentate acetate ion (OAc(-)), [Ln(III)(H3L)(OAc)](ClO4)2·MeOH·H2O (Ln = Tb, 1; Ln = Dy, 2), were synthesized and studied, where H3L = tris[2-(((imidazol-4-yl)methylidene)amino)ethyl]amine. The Tb(III) and Dy(III) complexes have an isomorphous structure, and each Tb(III) or Dy(III) ion is coordinated by the tripodal N7 and the bidentate acetate ligands, resulting in a nonacoordinated capped-square-antiprismatic geometry. The magnetic data, including temperature dependence of the magnetic susceptibilities and field dependence of the magnetization, were analyzed by a spin Hamiltonian, including the crystal field effect on the Tb(III) ion (4f(8), J = 6, S = 3, L = 3, g(J) = 3/2, (7)F6) and the Dy(III) ion (4f(9), J = 15/2, S = 5/2, L = 5, g(J) = 4/3, (6)H(15/2)). The Stark splittings of the ground states (7)F6 of the Tb(III) ion and (6)H(15/2) of the Dy(III) ion were evaluated from the magnetic analyses, and the energy diagram patterns indicated an easy axis (Ising type) anisotropy for both complexes, which is more pronounced for 2. The solid-state emission spectra of both complexes displayed sharp bands corresponding to the f-f transitions, and the fine structures assignable to the (5)D4 → (7)F6 transition for 1 and the (6)F(9/2) → (6)H(15/2) transition for 2 were related to the energy diagram patterns from the magnetic analyses. 1 and 2 showed an out-of-phase signal with frequency dependence in alternating current (ac) susceptibility under a dc bias field of 1000 Oe, indicative of a field-induced SIM.

Synthesis, structure, luminescence, and magnetic properties of a single-ion magnet "mer"-[tris(N-[(imidazol-4-yl)-methylidene]-DL-phenylalaninato)terbium(III) and related "fac"-DL-alaninato derivative.

Two Tb(III) complexes with the same N6O3 donor atoms but different coordination geometries, "fac"-[Tb(III)(HL(DL-ala))3]·7H2O (1) and "mer"-[Tb(III)(HL(DL-phe))3]·7H2O (2), were synthesized, where H2L(DL-ala) and H2L(DL-phe) are N-[(imidazol-4-yl)methylidene]-DL-alanine and -DL-phenylalanine, respectively. Each Tb(III) ion is coordinated by three electronically mononegative NNO tridentate ligands to form a coordination geometry of a tricapped trigonal prism. Compound 1 consists of enantiomers "fac"-[Tb(III)(HL(D-ala))3] and "fac"-[Tb(III)(HL(L-ala))3], while 2 consists of "mer"-[Tb(III)(HL(D-phe))2(HL(L-phe))] and "mer"-[Tb(III)(HL(D-phe))(HL(L-phe))2]. Magnetic data were analyzed by a spin Hamiltonian including the crystal field effect on the Tb(III) ion (4f(8), J = 6, S = 3, L = 3, gJ = 3/2, (7)F6). The Stark splitting of the ground state (7)F6 was evaluated from magnetic analysis, and the energy diagram pattern indicated easy-plane and easy-axis (Ising type) magnetic anisotropies for 1 and 2, respectively. Highly efficient luminescences with Φ = 0.50 and 0.61 for 1 and 2, respectively, were observed, and the luminescence fine structure due to the (5)D4 → (7)F6 transition is in good accordance with the energy diagram determined from magnetic analysis. The energy diagram of 1 shows an approximate single-well potential curve, whereas that of 2 shows a double- or quadruple-well potential within the (7)F6 multiplets. Complex 2 displayed an onset of the out-of-phase signal in alternating current (ac) susceptibility at a direct current bias field of 1000 Oe on cooling down to 1.9 K. A slight frequency dependence was recorded around 2 K. On the other hand, 1 did not show any meaningful out-of-phase ac susceptibility. Pulsed-field magnetizations of 1 and 2 were measured below 1.6 K, and only 2 exhibited magnetic hysteresis. This finding agrees well with the energy diagram pattern from crystal field calculation on 1 and 2. DFT calculation allowed us to estimate the negative charge distribution around the Tb(III) ion, giving a rationale to the different magnetic anisotropies of 1 and 2.

Abrupt spin transition with thermal hysteresis of iron(III) complex [Fe(III)(Him)2(hapen)]AsF6 (Him = imidazole, H2hapen = N,N'-bis(2-hydroxyacetophenylidene)ethylenediamine).

The solvent-free spin crossover iron(III) complex [Fe(III)(Him)2(hapen)]AsF6 (Him = imidazole, H2hapen = N,N'-bis(2-hydroxyacetophenylidene)ethylenediamine), exhibiting thermal hysteresis, was synthesized and characterized. The Fe(III) ion has an octahedral coordination geometry, with N2O2 donor atoms of the planar tetradentate ligand (hapen) and two nitrogen atoms of two imidazoles at the axial positions. One of two imidazoles is hydrogen-bonded to the phenoxo oxygen atom of hapen of the adjacent unit to give a hydrogen-bonded one-dimensional chain, while the other imidazole group is free from hydrogen bonding. The temperature dependencies of the magnetic susceptibilities and Mössbauer spectra revealed an abrupt spin transition between the high-spin (S = 5/2) and low-spin (S = 1/2) states, with thermal hysteresis.

Synthesis, structure, luminescent, and magnetic properties of carbonato-bridged Zn(II)2Ln(III)2 complexes [(µ4-CO3)2{Zn(II)L(n)Ln(III)(NO3)}2] (Ln(III) = Gd(III), Tb(III), Dy(III); L(1) = N,N'-bis(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato, L(2) = N,N'-bis(3-ethoxy-2-oxybenzylidene)-1,3-propanediaminato).

Carbonato-bridged Zn(II)2Ln(III)2 complexes [(µ4-CO3)2{Zn(II)L(n)Ln(III)(NO3)}2]·solvent were synthesized through atmospheric CO2 fixation reaction of [Zn(II)L(n)(H2O)2]·xH2O, Ln(III)(NO3)3·6H2O, and triethylamine, where Ln(III) = Gd(III), Tb(III), Dy(III); L(1) = N,N'-bis(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato, L(2) = N,N'-bis(3-ethoxy-2-oxybenzylidene)-1,3-propanediaminato. Each Zn(II)2Ln(III)2 structure possessing an inversion center can be described as two di-µ-phenoxo-bridged {Zn(II)L(n)Ln(III)(NO3)} binuclear units bridged by two carbonato CO3(2-) ions. The Zn(II) ion has square pyramidal coordination geometry with N2O2 donor atoms of L(n) and one oxygen atom of a bridging carbonato ion at the axial site. Ln(III) ion is coordinated by nine oxygen atoms consisting of four from the deprotonated Schiff-base L(n), two from a chelating nitrate, and three from two carbonate groups. The temperature-dependent magnetic susceptibilities in the range 1.9-300 K, field-dependent magnetization from 0 to 5 T at 1.9 K, and alternating current magnetic susceptibilities under the direct current bias fields of 0 and 1000 Oe were measured. The magnetic properties of the Zn(II)2Ln(III)2 complexes are analyzed on the basis of the dicarbonato-bridged binuclear Ln(III)-Ln(III) structure, as the Zn(II) ion with d(10) electronic configuration is diamagnetic. ZnGd1 (L(1)) and ZnGd2 (L(2)) show a ferromagnetic Gd(III)-Gd(III) interaction with J(Gd-Gd) = +0.042 and +0.028 cm(-1), respectively, on the basis of the Hamiltonian H = -2J(Gd-Gd)SGd1·SGd2. The magnetic data of the Zn(II)2Ln(III)2 complexes (Ln(III) = Tb(III), Dy(III)) were analyzed by a spin Hamiltonian including the crystal field effect on the Ln(III) ions and the Ln(III)-Ln(III) magnetic interaction. The Stark splitting of the ground state was so evaluated, and the energy pattern indicates a strong easy axis (Ising type) anisotropy. Luminescence spectra of Zn(II)2Tb(III)2 complexes were observed, while those of Zn(II)2Dy(III)2 were not detected. The fine structure assignable to the (5)D4 → (7)F6 transition of ZnTb1 and ZnTb2 is in good accord with the energy pattern from the magnetic analysis. The Zn(II)2Ln(III)2 complexes (Ln(III) = Tb(III), Dy(III)) showed an out-of-phase signal with frequency-dependence in alternating current susceptibility, indicative of single molecule magnet. Under a dc bias field of 1000 Oe, the signals become significantly more intense and the energy barrier, Δ/kB, for the magnetic relaxation was estimated from the Arrhenius plot to be 39(1) and 42(8) K for ZnTb1 and ZnTb2, and 52(2) and 67(2) K for ZnDy1 and ZnDy2, respectively.

Syntheses, structures, and magnetic properties of acetato- and diphenolato-bridged 3d-4f binuclear complexes [M(3-MeOsaltn)(MeOH)x(ac)Ln(hfac)2] (M = Zn(II), Cu(II), Ni(II), Co(II); Ln = La(III), Gd(III), Tb(III), Dy(III); 3-MeOsaltn = N,N'-bis(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato; ac = acetato; hfac = hexafluoroacetylacetonato; x = 0 or 1).

A series of 3d-4f binuclear complexes, [M(3-MeOsaltn)(MeOH)x(ac)Ln(hfac)2] (x = 0 for M = Cu(II), Zn(II); x = 1 for M = Co(II), Ni(II); Ln = Gd(III), Tb(III), Dy(III), La(III)), have been synthesized and characterized, where 3-MeOsaltn, ac, and hfac denote N,N'-bis(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato, acetato, and hexafluoroacetylacetonato, respectively. The X-ray analyses demonstrated that all the complexes have an acetato- and diphenolato-bridged M(II)-Ln(III) binuclear structure. The Cu(II)-Ln(III) and Zn(II)-Ln(III) complexes are crystallized in an isomorphous triclinic space group P1, where the Cu(II) or Zn(II) ion has square pyramidal coordination geometry with N2O2 donor atoms of 3-MeOsaltn at the equatorial coordination sites and one oxygen atom of the bridging acetato ion at the axial site. The Co(II)-Ln(III) and Ni(II)-Ln(III) complexes are crystallized in an isomorphous monoclinic space group P2(1)/c, where the Co(II) or Ni(II) ion at the high-spin state has an octahedral coordination environment with N2O2 donor atoms of 3-MeOsaltn at the equatorial sites, and one oxygen atom of the bridged acetato and a methanol oxygen atom at the two axial sites. Each Ln(III) ion for all the complexes is coordinated by four oxygen atoms of two phenolato and two methoxy oxygen atoms of "ligand-complex" M(3-MeOsaltn), four oxygen atoms of two hfac(-), and one oxygen atom of the bridging acetato ion; thus, the coordination number is nine. The temperature dependent magnetic susceptibilities from 1.9 to 300 K and the field-dependent magnetization up to 5 T at 1.9 K were measured. Due to the important orbital contributions of the Ln(III) (Tb(III), Dy(III)) and to a lesser extent the M(II) (Ni(II), Co(II)) components, the magnetic interaction between M(II) and Ln(III) ions were investigated by an empirical approach based on a comparison of the magnetic properties of the M(II)-Ln(III), Zn(II)-Ln(III), and M(II)-La(III) complexes. The differences of χ(M)T and M(H) values for the M(II)-Ln(III), Zn(II)-Ln(III) and those for the M(II)-La(III) complexes, that is, Δ(T) = (χ(M)T)(MLn) - (χ(M)T)(ZnLn) - (χ(M)T)(MLa) = J(MLn)(T) and Δ(H) = M(MLn)(H) - M(ZnLn)(H) - M(MLa)(H) = J(MLn)(H), give the information of 3d-4f magnetic interaction. The magnetic interactions are ferromagnetic if M(II) = (Cu(II), Ni(II), and Co(II)) and Ln = (Gd(III), Tb(III), and Dy(III)). The magnitudes of the ferromagnetic interaction, J(MLn)(T) and J(MLn)(H), are in the order Cu(II)-Gd(III) > Cu(II)-Dy(III) > Cu(II)-Tb(III), while those are in the order of M(II)-Gd(III) ≈ M(II)-Tb(III) > M(II)-Dy(III) for M(II) = Ni(II) and Co(II). Alternating current (ac) susceptibility measurements demonstrated that the Ni(II)-Tb(III) and Co(II)-Tb(III) complexes showed out-of-phase signal with frequency-dependence and the Ni(II)-Dy(III) and Co(II)-Dy(III) complexes showed small frequency-dependence. The energy barrier for the spin flipping was estimated from the Arrhenius plot to be 14.9(6) and 17.0(4) K for the Ni(II)-Tb(III) and Co(II)-Tb(III) complexes, respectively, under a dc bias field of 1000 Oe.

Carbonato-bridged Ni(II)2Ln(III)2 (Ln(III) = Gd(III), Tb(III), Dy(III)) complexes generated by atmospheric CO2 fixation and their single-molecule-magnet behavior: [(µ4-CO3)2{Ni(II)(3-MeOsaltn)(MeOH or H2O)Ln(III)(NO3)}2]·solvent [3-MeOsaltn = N,N'-bis(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato].

Atmospheric CO2 fixation of [Ni(II)(3-MeOsaltn)(H2O)2]·2.5H2O [3-MeOsaltn = N,N'-bis(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato], Ln(III)(NO3)3·6H2O, and triethylamine occurred in methanol/acetone, giving a first series of carbonato-bridged Ni(II)2Ln(III)2 complexes [(µ4-CO3)2{Ni(II)(3-MeOsaltn)(MeOH)Ln(III)(NO3)}2] (1Gd, 1Tb, and 1Dy). When the reaction was carried out in acetonitrile/water, it gave a second series of complexes [(µ4-CO3)2{Ni(II)(3-MeOsaltn)(H2O)Ln(III)(NO3)}2]·2CH3CN·2H2O (2Gd, 2Tb, and 2Dy). For both series, each Ni(II)2Ln(III)2 structure can be described as two di-µ-phenoxo-bridged Ni(II)Ln(III) binuclear units bridged by two carbonato CO3(2-) units to form a carbonato-bridged (µ4-CO3)2{Ni(II)2Ln(III)2} structure. The high-spin Ni(II) ion has octahedral coordination geometry, and the Ln(III) ion is coordinated by O9 donor atoms from Ni(II)(3-MeOsaltn), bidentate NO3(-), and one and two oxygen atoms of two CO3(2-) ions. The NO3(-) ion for the first series roughly lie on Ln-O(methoxy) bonds and are tilted toward the outside, while for the second series, the two oxygen atoms roughly lie on one of the Ln-O(phenoxy) bonds due to the intramolecular hydrogen bond. The temperature-dependent magnetic susceptibilities indicated a ferromagnetic interaction between the Ni(II) and Ln(III) ions (Ln(III) = Gd(III), Tb(III), Dy(III)) for all of the complexes, with a distinctly different magnetic behavior between the two series in the lowest-temperature region due to the Ln(III)-Ln(III) magnetic interaction and/or different magnetic anisotropies of the Tb(III) or Dy(III) ion. Alternating-current susceptibility measurements under the 0 and 1000 Oe direct-current (dc) bias fields showed no magnetic relaxation for the Ni(II)2Gd(III)2 complexes but exhibited an out-of-phase signal for Ni(II)2Tb(III)2 and Ni(II)2Dy(III)2, indicative of slow relaxation of magnetization. The energy barriers, Δ/kB, for the spin flipping were estimated from the Arrhenius plot to be 12.2(7) and 6.1(3) K for 1Tb and 2Tb, respectively, and 18.1(6) and 14.5(4) K for 1Dy and 2Dy, respectively, under a dc bias field of 1000 Oe. Compound 1Dy showed relatively slow relaxation of magnetization reorientation even at zero dc applied field with Δ/kB = 6.6(4) K.

A hydrogen bond motif giving a variety of supramolecular assembly structures and spin-crossover behaviors.

A series of spin-crossover (SCO) iron(II) compounds, fac-[Fe(II)(HL(R))(3)]Cl·PF(6) [R = methyl (Me, 1), ethyl (Et, 2), n-propyl (n-Pr, 3), n-butyl (n-Bu, 4), and n-pentyl (n-Pen, 5)], were synthesized, where HL(R) denotes a series of [(2-methylimidazol-4-yl)methylidene]monoalkylamines. The cations fac-[Fe(II)(HL(R))(3)](2+) and chloride anions associate through 3:3 imidazole···chloride hydrogen bonding. This hydrogen-bonding motif gives rise to a variety of assembly structures consisting of a one-dimensional ladder for 3 and 4, two kinds of two-dimensional networks for 1 and 2, and a cubane-like structure for 5. The compounds exhibit various types of SCO transitions between high-spin (S = 2) and low-spin (S = 0) states as a result of their intermolecular interactions.

1D and 2D assembly structures by imidazole···chloride hydrogen bonds of iron(II) complexes [Fe(II)(HL(n-Pr))3]Cl·Y (HL(n-Pr) = 2-methylimidazol-4-yl-methylideneamino-n-propyl; Y = AsF6, BF4) and their spin states.

Two Fe(II) complexes fac-[Fe(II)(HL(n-Pr))(3)]Cl·Y (Y = AsF(6) (1) and BF(4) (2)) were synthesized, where HL(n-Pr) is 2-methylimidazole-4-yl-methylideneamino-n-propyl. Each complex-cation has the same octahedral N(6) geometry coordinated by three bidentate ligands and assumes facial-isomerism, fac-[Fe(II)(HL(n-Pr))(3)](2+) with Δ- and Λ-enantiomorphs. Three imidazole groups per Δ- or Λ-fac-[Fe(II)(HL(n-Pr))(3)](2+) are hydrogen-bonded to three Cl(-) ions or, from the viewpoint of the Cl(-) ion, one Cl(-) ion is hydrogen-bonded to three neighbouring fac-[Fe(II)(HL(n-Pr))(3)](2+) cations. The 3 : 3 NH···Cl(-) hydrogen bonds between Δ- or Λ-fac-[Fe(II)(HL(n-Pr))(3)](2+) and Cl(-) generate two kinds of assembly structures. The directions of the 3 : 3 NH···Cl(-) hydrogen bonds and hence the resulting assembly structures are determined by the size of the anion Y, though Y is not involved into the network structure and just accommodated in the cavity. Compound 1 has a 1D ladder structure giving a larger cavity, in which the Δ- and Λ-fac-[Fe(II)(HL(n-Pr))(3)](2+) enantiomorphs are bridged by two NH···Cl(-) hydrogen bonds. Compound 2 has a 2D network structure with a net unit of a cyclic trimer of {fac-[Fe(II)(HL(n-Pr))(3)](2+)···Cl(-)}(3) giving a smaller cavity, in which Δ- or Λ-fac-[Fe(II)(HL(n-Pr))(3)](2+) species with the same chirality are linked by NH···Cl(-) hydrogen bonds to give a homochiral 2D network structure. Magnetic susceptibility and Mössbauer spectral measurements demonstrated that compound 1 showed an abrupt one-step spin crossover with 4.0 K thermal hysteresis of T(c↓) = 125.5 K and T(c↑) = 129.5 K and compound 2 showed no spin transition and stayed in the high-spin state over the 5-300 K temperature range.

Nanoscale self-hosting of molecular spin-states in the intermediate phase of a spin-crossover material.

A new spin-crossover (SC) complex [Fe(II)H(2)L(2-Me)][AsF(6)](2) has been synthesized, in which H(2)L(2-Me) denotes the chirogenic hexadentate N(6) Schiff-base ligand bis{[(2-methylimidazol-4-yl)methylidene]-3-aminopropyl}ethylenediamine. This complex has revealed a rich variety of phases during its two-step thermal crossover, as well as photoinduced spin-state switching. A high-symmetry high-spin (HS, S=2) phase, a low-symmetry low-spin (LS, S=0) phase, an intermediate phase characterized by an unprecedented lozenge pattern of 12 predominantly HS molecular crystallographic sites confining 18 predominantly LS molecular crystallographic sites, and a photoinduced low-symmetry HS phase have been accurately evidenced by temperature-dependent magnetic susceptibility, Mössbauer spectroscopy, and crystallographic studies. This variety of phases illustrates the multi-stability of this system, which results from coupling between the electronic states and structural instabilities.

One-dimensional spin-crossover Iron(II) complexes bridged by intermolecular imidazole-pyridine NH...N hydrogen bonds, [Fe(HL(Me))(3)]X(2) (HL(Me) = (2-methylimidazol-4-yl-methylideneamino-2-ethylpyridine; X = PF(6), ClO(4), BF(4)).

2-Methylimidazol-4-yl-methylideneamino-2-ethylpyridine (abbreviated as HL(Me)) is the 1:1 condensation product of 2-methyl-4-formylimidazole and 2-aminoethylpyridine and functions as a bidentate ligand to the iron(II) ion to produce the 3:1 complexes together with anions, [Fe(HL(Me))(3)]X(2) (X = PF(6) (1), ClO(4) (2), BF(4) (3)). The magnetic susceptibilities, differential scanning calorimetric measurements, and Mossbauer spectral measurements demonstrated that complexes 1, 2, and 3 showed a steep one-step spin crossover (SCO) between the high-spin (HS, S = 2) and low-spin (LS, S = 0) states with small thermal hysteresis. Three complexes have an isomorphous structure and are crystallized in the same monoclinic space group, C2/c, both in the HS and LS states. The iron(II) ion has the octahedral coordination geometry of a facial isomer with N(6) donor atoms of three bidentate ligands, in which an imidazole and an imine nitrogen atom per ligand participate in the formation of the coordination bond, but the pyridine nitrogen is free from coordination. The complex cation fac-[Fe(HL(Me))(3)](2+) is a chiral species with a Delta or Lambda isomer, and the adjacent Delta and Lambda isomers are linked alternately by an intermolecular imidazole-pyridine NH...N hydrogen bond to produce an achiral 1D chain. The two remaining imidazole moieties per complex are hydrogen-bonded to the anions that occupy the space among the chains. The SCO profile becomes steeper with the decrease of the anion size (73.0 A(3) for PF(6)(-), 54.4 A(3) for ClO(4)(-), and 53.4 A(3) for BF(4)(-)). The SCO transition temperature T(1/2) of the PF(6) (1), ClO(4) (2), and BF(4) (3) salts estimated from the magnetic susceptibility measurements are (T( downward arrow) = 151.8 K, T( upward arrow) = 155.3 K), (T( downward arrow) = 184.5 K, T( upward arrow) = 186.0 K), and (T( downward arrow) = 146.4 K, T( upward arrow) = 148.2 K), respectively, indicating that the T(1/2) value is not in accord with the anion size.

One-step and two-step spin-crossover iron(II) complexes of ((2-methylimidazol-4-yl)methylidene)histamine.

A tridentate ligand ((2-methylimidazol-4-yl)methylidene)histamine (abbreviated as H(2)L(2-Me)), that is, the 1:1 condensation product of 2-methyl-4-formylimidazole and histamine, was used for the syntheses of a new family of iron(II) spin-crossover (SCO) complexes with the general chemical formulas [Fe(H(2)L(2-Me))(2)]X(2) x solvent (X = Cl, ClO(4), and BPh(4); solvent = 2-PrOH and CH(3)CN) and [Fe(H(2)L(2-Me))(2)]X x Y x solvent (X = Cl and Br; Y = ClO(4), BF(4), PF(6), and AsF(6); solvent = EtOH and 2-PrOH). The complex cation [Fe(H(2)L(2-Me))(2)](2+) is a chiral species due to an octahedral coordination of two unsymmetrical tridentate ligands, has a ligand field strength around the spin-crossover point, and is hydrogen-bonded to anions to form a variety of network structures. The dichloride complexes [Fe(H(2)L(2-Me))(2)]Cl(2) x 2-PrOH x 0.5 H(2)O (1) and [Fe(H(2)L(2-Me))(2)]Cl(2) x 2-PrOH x H(2)O (1') have a one-dimensional (1D) structure, in which adjacent two chiral complex-cations are doubly bridged by two Cl(-) ions through NH(histamine)...Cl(-)...HN(2-methyl-4-formylimidazole) hydrogen bonds to give a chiral 1D rod. The chiral rods with the same chirality are stacked in the crystal lattices to give a conglomerate, 1, and those with the opposite chiralities are stacked to give a racemic compound, 1'. The enantiomeric circular dichromism spectra of 1 gave definitive evidence of the conglomerate. Compound 1 showed a two-step SCO, while the desolvated sample showed a steep one-step SCO at T(1/2) = 180 K. A series of complexes, [Fe(H(2)L(2-Me))(2)]Cl x X x EtOH (X = ClO(4) (2a), BF(4) (2b), PF(6) (2c), and AsF(6) (2d)), [Fe(H(2)L(2-Me))(2)]Cl x ClO(4) x 0.5(1-PrOH) x 1.5 H(2)O (2a'), and [Fe(H(2)L(2-Me))(2)]Br x ClO(4) x 0.5 EtOH (2a''), display an isomorphous two-dimensional (2D) network at room temperature (296 K), in which the structure is constructed by the NH...Cl(-) (or Br(-)) hydrogen bonds between the imidazole NH groups of [Fe(H(2)L(2-Me))(2)](2+) and the Cl(-) (or Br(-)) ion as a connector. The complexes showed a variety of SCO properties depending on the anion, solvent molecule, and the kind of bridging halogen ion. The complexes of ClO(4)(-) (2a, 2a', 2a'') and BF(4)(-) (2b) with smaller anions showed a two-step SCO with a wide temperature region of the intermediate state of (high-spin (HS) + low-spin (LS))/2 state, their values of (T(1/2,1), T(1/2,2)) being (75, 255 K), (100, 220 K), (110, 220 K), and (100, 260 K), respectively, where the crystal changes from monoclinic P2(1)/n in the HS state to triclinic P1 in the intermediate state. The complexes of PF(6)(-) (2c) and AsF(6)(-) (2d) with larger anions showed a one-step SCO at T(1/2) = 198 and 173 K, respectively, in which the crystal system and space group showed no change during the spin transition. The crystal solvent and halide ion also affected the completeness of the SCO in the lower-temperature region and the steepness of the SCO profile. The experimental results were correlated to the theoretical results based on an Ising-like model. [Fe(H(2)L(2-Me))(2)](BPh(4))(2) x CH(3)CN (3) has no network structure. [Fe(H(2)L(2-Me))(2)](ClO(4))(2) (4) assumes a chiral 3D network structure constructed by the hydrogen bonds between the imidazole groups of one enantiomorph [Fe(H(2)L(2-Me))(2)](2+) and the bridging ClO(4)(-) ion. Compounds 3 and 4 in the solid states are in the HS state, demonstrating that the formation of imidazole-Cl(-) or Br-hydrogen bonds can give SCO properties, but the hydrogen bond of imidazole-ClO(4)(-) cannot give SCO.

Structures and spin states of bis(tridentate)-type mononuclear and triple helicate dinuclear iron(II) complexes of imidazole-4-carbaldehyde azine.

Mononuclear [Fe(H(2)L(R))(2)](2+) and dinuclear [Fe(2)(H(2)L(R))(3)](4+) (R = H, 2-Me, 5-Me) complexes containing the new imidazole-4-carbaldehyde azine ligand (H(2)L(H)) and its derivatives (H(2)L(2-Me) and H(2)L(5-Me)) prepared from the condensation reaction of 4-formylimidazole or 2-methyl- or 5-methyl-4-formylimidazole with hydrazine (2:1) were prepared, and their magnetostructural relationships were studied. In the mononuclear complexes, H(2)L(R) acts as an unsymmetrical tridentate ligand with two imidazole nitrogen atoms and one azine nitrogen atom, while in the dinuclear complexes, H(2)L(R) acts as a dinucleating ligand employing four nitrogen atoms to form a triple helicate. At room temperature, [Fe(2)(H(2)L(H))(3)](ClO(4))(4) and [Fe(2)(H(2)L(2-Me))(3)](ClO(4))(4) were in the high-spin (HS) and low-spin (LS) states, respectively. The results are in accordance with the ligand field strength of H(2)L(2-Me) with electron-donating methyl groups being stronger than H(2)L(H), with the order of the ligand field strengths being H(2)L(2-Me) > H(2)L(H). However, in the mononuclear [Fe(H(2)L(H))(2)](ClO(4))(2) and [Fe(H(2)L(2-Me))(2)](ClO(4))(2) complexes, a different order of ligand field strengths, H(2)L(H) > H(2)L(2-Me), was observed because [Fe(H(2)L(H))(2)](ClO(4))(2) was in the LS state while [Fe(H(2)L(2-Me))(2)](ClO(4))(2) was in the HS state at room temperature. X-ray structural studies revealed that the interligand steric repulsion between a methyl group of an H(2)L(2-Me) ligand and the other ligand in [Fe(H(2)L(2-Me))(2)](ClO(4))(2) is responsible for the observed change in the spin state. Two kinds of crystals, needles and blocks, were isolated for [Fe(2)(H(2)L(H))(3)](BF(4))(4), and both exhibited a sharp spin transition, [LS-HS] <--> [HS-HS]. The spin transition of the block crystals is more abrupt with a hysteresis, T(c) upward arrow = 190 K and T(c) downward arrow = 183 K with DeltaT = 7 K.

Synthesis, structures, and magnetic properties of face-sharing heterodinuclear Ni(II)-Ln(III) (Ln = Eu, Gd, Tb, Dy) complexes.

Heterodinuclear [(Ni (II)L)Ln (III)(hfac) 2(EtOH)] (H 3L = 1,1,1-tris[(salicylideneamino)methyl]ethane; Ln = Eu, Gd, Tb, and Dy; hfac = hexafluoroacetylacetonate) complexes ( 1.Ln) were prepared by treating [Ni(H 1.5L)]Cl 0.5 ( 1) with [Ln(hfac) 3(H 2O) 2] and triethylamine in ethanol (1:1:1). All 1.Ln complexes ( 1.Eu, 1.Gd, 1.Tb, and 1.Dy) crystallized in the triclinic space group P1 (No. 2) with Z = 2 with very similar structures. Each complex is a face-sharing dinuclear molecule. The Ni (II) ion is coordinated by the L (3-) ligand in a N 3O 3 coordination sphere, and the three phenolate oxygen atoms coordinate to an Ln (III) ion as bridging atoms. The Ln (III) ion is eight-coordinate, with four oxygen atoms of two hfac (-)'s, three phenolate oxygen atoms of L (3-), and one ethanol oxygen atom coordinated. Temperature-dependent magnetic susceptibility and field-dependent magnetization measurements showed a ferromagnetic interaction between Ni (II) and Gd (III) in 1.Gd. The Ni (II)-Ln (III) magnetic interactions in 1.Eu, 1.Tb, and 1.Dy were evaluated by comparing their magnetic susceptibilities with those of the isostructural Zn (II)-Ln (III) complexes, [(ZnL)Ln(hfac) 2(EtOH)] ( 2.Ln) containing a diamagnetic Zn (II) ion. A ferromagnetic interaction was indicated in 1.Tb and 1.Dy, while the interaction between Ni (II) and Eu (III) was negligible in 1.Eu. The magnetic behaviors of 1.Dy and 2.Dy were analyzed theoretically to give insight into the sublevel structures of the Dy (III) ion and its coupling with Ni (II). Frequency dependence in the ac susceptibility signals was observed in 1.Dy.

Chiral recognition and conglomerate crystallization induced by self-organization of cobalt(III) complexes of a tripodal ligand containing three imidazole groups.

The effect of a counteranion on chiral recognition inducing conglomerate crystallization of a cobalt(III) complex is reported. An achiral tripodal ligand involving three imidazole groups, tris{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H3L), was prepared by condensation of tris(2-aminoethyl)amine and 4-formylimidazole in a 1:3 mole ratio. The reaction of H3L and trans-[CoIIICl2(py)4]+ afforded the chiral (Delta or Lambda) [CoIII(H3L)]3+ complex. The formally hemideprotonated complexes [CoIII(H(1.5)L)]X(1.5).nH2O (where X = Cl, Br, I, BF4, ClO4, or PF6) were synthesized by controlled deprotonation of the uncoordinated imidazole NH groups of [Co(H3L)]3+. In crystals of the hemideprotonated complex, two components, [Co(H3L)]3+ and [Co(L)], with the same absolute configuration are linked by imidazole-imidazolate hydrogen bonds to form an extended homochiral 2D sheet structure, which is composed of a hexanuclear unit with a trigonal void. There are two ways of stacking the sheets: One is via homochiral stacking, and the other is via heterochiral stacking. When the size of the counterion is small (i.e., X = Cl, Br, I, or BF4), adjacent homochiral sheets with the same chirality are stacked to form a homochiral crystal (conglomerate). With large anions (i.e., ClO4- and PF6-), a homochiral sheet consisting of Delta enantiomers and a sheet consisting of Lambda enantiomers are stacked alternately to give a heterochiral crystal (a racemic crystal). Optically active Lambda-[Co(H(1.5)L)](ClO4)(1.5).H2O was synthesized from Lambda-[Co(H3L)]3+, and the crystal structure was compared to that of the racemic complex. There are two conflicting factors governing the crystal structure: the skeletal density; the size of the channels. The 2D sheets are more closely packed in the homochiral crystal than in the heterochiral crystal. However, the channels, where the counterions are accommodated, are smaller in the homochiral crystal, and the steric congestion between the anions increases with increasing anion size. The heterochiral crystal has a flexible, zigzag channel structure, and the size of the channels can increase to accommodate larger anions. Thus, complexes with large anions (i.e., ClO4- and PF6-) preferentially form heterochiral crystals rather than homochiral crystals.

Magnetic interactions in CuII-LnIII cyclic tetranuclear complexes: is it possible to explain the occurrence of SMM behavior in CuII-TbIII and CuII-DyIII complexes?

An extensive series of tetranuclear CuII2LnIII2 complexes [CuIILLnIII(hfac)2]2 (with LnIII being all lanthanide(III) ions except for the radioactive PmIII) has been prepared in order to investigate the nature of the CuII-LnIII magnetic interactions and to try to answer the following question: What makes the CuII2TbIII2 and CuII2DyIII2 complexes single molecule magnets while the other complexes are not? All the complexes within this series possess a similar cyclic tetranuclear structure, in which the CuII and LnIII ions are arrayed alternately via bridges of ligand complex (CuIIL). Regular SQUID magnetometry measurements have been performed on the series. The temperature-dependent magnetic susceptibilities from 2 to 300 K and the field-dependent magnetizations from 0 to 5 T at 2 K have been measured for the CuII2LnIII2 and NiII2LnIII2 complexes, with the NiII2LnIII2 complex containing diamagnetic NiII ions being used as a reference for the evaluation of the CuII-LnIII magnetic interactions. These measurements have revealed that the interactions between CuII and LnIII ions are very weakly antiferromagnetic if Ln=Ce, Nd, Sm, Yb, ferromagnetic if Ln=Gd, Tb, Dy, Ho, Er, Tm, and negligible if Ln=La, Eu, Pr, Lu. With the same goal of better understanding the evolution of the intramolecular magnetic interactions, X-ray magnetic circular dichroism (XMCD) has also been measured on CuII2TbIII2, CuII2DyIII2, and NiII2TbIII2 complexes, either at the L- and M-edges of the metal ions or at the K-edge of the N and O atoms. Last, the CuII2TbIII2 complex exhibiting SMM behavior has received a closer examination of its low temperature magnetic properties down to 0.1 K. These particular measurements have revealed the unusual very slow setting-up of a 3D order below 0.6 K.

Two-dimensional iron(II) spin crossover complex constructed of bifurcated NH...O- hydrogen bonds and pi-pi interactions: [FeII(HLH,Me)2](ClO4)2.1.5MeCN (HLH,Me = imidazol-4-yl-methylidene-8-amino-2-methylquinoline).

A 2D iron(II) spin crossover complex, [FeII(HLH,Me)2](ClO4)2.1.5MeCN (1), was synthesized, where HLH,Me = imidazol-4-yl-methylidene-8-amino-2-methylquinoline. 1 showed a gradual spin transition between the HS (S = 2) and LS (S = 0) states from 180 to 325 K within the first warming run from 5 to 350 K, in which 1.5MeCN is removed, and there was an abrupt spin transition at T1/2 downward arrow = 174 K in the first cooling run from 350 to 5 K. Following the first cycle, the compound showed an abrupt spin transition at T1/2 upward arrow = 185 K and T1/2 downward arrow = 174 K with 11 K wide hysteresis in the second cycle. The crystal structures of 1 were determined at 296 (an intermediate between the HS and LS states) and 150 K (LS state). The structure consists of a 2D extended structure constructed of both the bifurcated NH...O- hydrogen bonds between two ClO4- ions and two neighboring imidazole NH groups of the [FeII(HLH,Me)2]2+ cations and the pi-pi interactions between the two quinolyl rings of the two adjacent cations. Thermogravimetric analysis showed that solvent molecules are gradually eliminated even at room temperature and completely removed at 369 K. Desolvated complex 1' showed an abrupt spin transition at T1/2 upward arrow = 180 K and T1/2 downward arrow = 174 K with 6 K wide hysteresis.

Structural-electronic correlation in the first-order phase transition of [FeH2L2-Me](ClO4)2 (H2L2-Me = bis[((2-methylimidazol-4-yl)methylidene)-3- aminopropyl]ethylenediamine).

The synthesis and detailed study of the new mononuclear spin crossover complex [Fe(II)H2L(2-Me)](ClO4)2 (where H2L(2-Me) = bis[((2-methylimidazol-4-yl)methylidene)-3-aminopropyl]ethylenediamine) are reported. Variable-temperature magnetic susceptibility measurements show the occurrence of a steep spin crossover centered at 171.5 K with a hysteresis loop of ca. 5 K width (T(/2)(increasing) = 174 K and T(1/2)(decreasing) = 169 K, for increasing and decreasing temperatures, respectively). The crystal structure has been resolved for the high-spin (HS) and low-spin (LS) states at 200 and 123 K, respectively, revealing a crystallographic phase transition that occurs concomitantly to the spin crossover: at 200 K, the complex crystallizes in the monoclinic system, space group P2(1)/n, while the space group is P2(1) at 123 K. The mean Fe-N distances are shortened by 0.2 A, but the thermal spin crossover is accompanied by significant structural changes: the rearrangement of the central atom C12 of a six-membered chelate ring of [Fe(II)H2L(2-Me)]2+ to two positions (C12A and C12B) and, consequently, the lack of an inversion center at 123 K (P2(1) space group). Both HS and LS supramolecular structures involve all possible hydrogen bonds between imidazole and amine NH functions, and perchlorate anions; however, the HS supramolecular structure is a one-dimensional (1D) network, and the LS phase may better be described as a two-dimensional (2D) extended structure of A and B molecules. The structural phase transition of [FeH2L(2-Me)](ClO4)2 seems to trigger the steep and hysteretic spin crossover. Discontinuities in the temperature dependence of the Mössbauer parameters (isomer shift and quadrupole splitting) at the spin crossover temperature confirmed the occurrence of a structural phase transition. The experimental enthalpy and entropy variations were determined by differential scanning calorimetry (DSC) as 7.5 +/- 0.4 kJ/mol and 45 +/- 3 J K(-1) mol(-1), respectively. The regular solution theory was applied to the experimental data, yielding an interaction parameter of Gamma = 3.36 kJ/mol, which is larger than 2RT(1/2), which fulfills the condition for observing hysteresis.