Elastic Modeling of Two-Step Transitions in Sterically Frustrated 1D Binuclear Spin-Crossover Chains

Among the large family of spin-crossover materials, binuclear systems play an important role due to their specific molecular configurations, allowing the presence of multi-step transitions and elastic frustration. Although this issue benefited from a significant number of spin-based theories, there is almost no elastic description of the spin transition phenomenon in binuclear systems. To overcome this deficiency, in this work we develop the first elastic modeling of thermal properties of binuclear spin-crossover solids. At this end, we investigated a finite spin-crossover open chain constituted of elastically coupled binuclear (A = B) blocks, ⋯A=B−A=B−A=B⋯, in which the considered equivalent A and B sites may occupy two configurations, namely low-spin (LS) and high-spin (HS) states. The sites of the binuclear unit interact via an intramolecular spring and couple to the neighboring binuclear units via other springs. The model also includes the change of length inside and between the binuclear units subsequent to the spin state changes. When injecting an elastic frustration inside the binuclear unit in the LS state, competing interactions between the intra- and the inter-binuclear couplings emerge. The latter shows that according to the intra- and inter-binuclear elastic constants and the strength of the frustration, multi-step transitions are derived, for which a specific self-organization of type (HS = HS)-(LS-LS)-(HS = HS)⋯ is revealed and discussed. Finally, we have also studied the relaxation of the metastable photoinduced HS states at low temperature, in which two relaxation regimes with transient self-organized states were identified when monitoring the elastic frustration rate or the ratio of intra- and intermolecular elastic interactions. These behaviors are reminiscent of the thermal dependence of the order parameters of the system. The present model opens several possibilities of extensions of elastic frustrations acting in polynuclear spin-crossover systems, which may lead to other types of spin-state self-organizations and relaxation dynamics.

Crystal structures of [(μ2-L1)dibromidodicopper(II)] dibromide and poly[[(μ2-L1)diiodidodicopper(I)]-di-μ-iodido-dicopper(I)], where L1 is 2,5,8,11,14,17-hexathia-[9.9](2,6,3,5)-pyrazinophane

The reaction of the hexathiapyrazinophane ligand, 2,5,8,11,14,17-hexathia-[9.9](2,6,3,5)-pyrazinophane (L1), with copper(II) dibromide led to the formation of a binuclear complex, [μ2-2,5,8,11,14,17-hexathia-[9.9](2,6,3,5)-pyrazinophane]bis[bromidocopper(II)] dibromide, [Cu2Br2(C16H24N2S6)]Br2, (I). The complex possesses inversion symmetry with the pyrazine ring being situated about a center of symmetry. The ligand coordinates to the copper(II) atom in a bis-tetradentate manner and the copper atom has a fivefold NS3Br coordination environment with a distorted shape. The reaction of ligand L1 with copper(I) iodide also gave a binuclear complex, which is bridged by a Cu2I2 unit to form a two-dimensional coordination polymer, poly[[μ2-2,5,8,11,14,17-hexathia-[9.9](2,6,3,5)-pyrazinophane]tetra-μ-iodido-tetracopper(I)], [Cu4I4(C16H24N2S6)] n , (II). The binuclear unit possesses inversion symmetry with the pyrazine ring being located about a center of symmetry. The Cu2I2 unit is also located about an inversion center. The two independent copper(I) atoms are both fourfold coordinate. That coordinating to the ligand L1 in a bis-tridentate manner has an NS2I coordination environment and an irregular shape, while the second copper(I) atom, where L1 coordinates in a bis-monodentate manner, has an SI3 coordination environment with an almost perfect tetrahedral geometry. In the crystal of I, the cations and Br− anions are linked by a number of C—H...S and C—H...Br hydrogen bonds, forming a supramolecular network. In the crystal of II, the two-dimensional coordination polymers lie parallel to the ab plane and there are no significant inter-layer contacts present.

Synthesis and Crystal Structure of Binuclear and Pentanuclear Nickel(II) Complexes Containing 4-(salicylaldiminato)antipyrine Schiff base

<div class="WordSection1"><p>The new title binuclear Ni (II) compound <strong> </strong>(<strong>1</strong>) and the novel pentanuclear Ni (II) cluster {[ } <strong>(2) </strong>are formed from the reaction of an asymmetric Schiff base ligand <strong>L </strong>(L = 4-(salicylaldiminato)antipyrine) with Ni .4 in the former or Ni(ClO₄)₂.6H₂O in presence of malonate in the later. Complex (<strong>1</strong>) consists of ( ]⁺cation) and one uncoordinated tetraphenylborate anion. The cation adopts a distorted octahedral arrangement around each metal center. In the binuclear unit both Ni(II) ions are linked through two phenolate (µ₂-O) oxygen atoms of L, and two oxygen atoms of a bridging carboxylate group. Each Ni (II) coordinates to four oxygen atoms at the basal plane, two oxygen atoms from two bridging phenolate groups, one from pyrazolone ring and the last of an aqua molecule, and at the axial positions to a bridging carboxylate-O atom and an azomethine nitrogen atom. In the pentanuclear cluster (<strong>2</strong>) consisting of [ ]⁺²cation and two tetraphenylborate anions, the core of the cation is assembled by four [Ni( )] units, linked to the central Ni-ion by two bridging water molecules. The resulting coordination sphere for the external symmetry related nickel ions is a pseudo octahedron. The central Ni-atom unusually adopts dodecahedron geometry through its coordination to eight bridging water molecules. In complex (<strong>1</strong>) each Ni-atom is coordinated to one tridentate <strong>L</strong> ligand and in complex (<strong>2</strong>) each [Ni ( )] unit is coordinated to two bidentate <strong>L</strong> ligands. Inter-and intramolecular hydrogen bonds are present in both crystal structures.</p></div>

Crystal structure ofcatena-poly[[diaquacobalt(II)]-bis[μ-5-(4-carboxyylatophenyl)picolinato]-κ3N,O2:O5;κ3O5:N,O2-[diaquacobalt(II)]-μ-1-[4-(1H-imidazol-1-yl)phenyl]-1H-imidazole-κ2N3:N3′]

The asymmetric unit of the title polymeric CoIIcomplex, [Co2(C13H7NO4)2(C12H10N4)(H2O)4]n, contains a CoIIcation, a 5-(4-carboxylatophenyl)picolinate dianion, two coordination water molecules and half of 1-[4-(1H-imidazol-1-yl)phenyl]-1H-imidazole ligand. The CoIIcation is coordinated by two picolinate dianions, two water molecules and one 1-[4-(1H-imidazol-1-yl)phenyl]-1H-imidazole molecule in a distorted N2O4octahedral coordination geometry. The two picolinate dianions are related by an inversion centre and link two CoIIcations, forming a binuclear unit, which is further bridged by the imidazole molecules, located about an inversion centre, into the polymeric chain propagating along the [-1-11] direction. In the crystal, the three-dimensional supramolecular architecture is constructed by O—H...O hydrogen bonds between the coordinating water molecules and the non-coordinating carboxylate O atoms of adjacent polymeric chains.

Facile Uptake of Manganese(III) by Apo- Transferrin: Possible Origin of Manganism

We have investigated the mechanism of manganese ion uptake by apo-transferrin using a capillary electrophoresis method, and obtained clear evidence that oxidation state +3 and the binuclear unit of a manganese chelate are essential factors for the facile uptake by apotransferrin, similar to that observed for Fe(III) chelates. These results may give valuable information to understand the pathogenesis of manganism and to develop new countermeasures for the neurotoxicity by manganese ions.

catena-Poly[[tetra-μ-anilinoacetamidato-bis(1,10-phenanthroline)dicerium(III)]-di-μ-anilinoacetamidato]

The title compound, [Ce2(C8H8N2O)6(C12H8N2)2] n , is a polymeric complex based on a binuclear unit with an inversion centre midway between the two CeIII ions, which are bridged by two tridentate, two bidentate and four monodentate (within the binuclear unit) acetamide groups. Each Ce atom is nine-coordinated by two 1,10-phenanthroline N atoms, four O and three N atoms of anilinoacetamide ligands. In the crystal structure, C—H...O, C—H...N, N—H...N and N—H...O hydrogen bonds result in the formation of a supramolecular network structure; an N—H...O hydrogen bond is also present within one ligand.

catena-Poly[hexakis(μ2-anilinoacetamide)bis(1,10-phenanthroline)dipraseodymium(III)]

The title compound, [Pr2(C8H9N2O)6C12H8N2)2] n , is a polymeric complex based on a binuclear unit with an inversion centre mid-way between the two PrIII ions, which are bridged by two tridentate, two bidentate and four monodentate (within the binuclear unit) acetamide groups. Each Pr atom is nine-coordinated by two 1,10-phenanthroline N atoms and four O and three N atoms of anilinoacetamide ligands. In the crystal structure, C—H...O, C—H...N, N—H...N and N—H...O hydrogen bonds result in the formation of a supramolecular network structure; an N—H...O hydrogen bond is also present within one ligand.

Crystal Structure and Magnetic Exchange Interaction in a Binuclear Copper(II) Schiff Base Complex with a Bridging m-Phenylenediamine Ligand

Condensation of 2-hydroxy-3-methoxybenzaldehyde with m-phenylenediamine (1,3-diaminobenzene) (m-pda) gives the ligand [N,N′-bis(2-hydroxy-3-methoxybenzylidene)-1,3-diaminobenzene] which reacts with cupric acetate to give the complex [Cu2(L-m-pda)2]·2H2O, [L = 2-hydroxy-3- methoxybenzaldehyde)]. The molecular structure of the complex [Cu2(L-m-pda)2]·2H2O has been determined by single-crystal X-ray analysis. (C44H40Cu2N4O8)·2H2O, triclinic, space group P1̄. Two [Cu(L-m-pda)] fragments, related by an inversion center, are connected by m-phenylene groups to form a binuclear unit. The coordination geometry around each copper(II) can be described as a distorted tetrahedron formed by the N2O2 donor set of the Schiff base ligands. The intramolecular Cu···Cu separation is 7.401(6) Å. The magnetic susceptibility of the complex in the 5 - 301 K temperature range can be rationalized by the parameters J = −0.4 cm−1 and g = 2.17. This indicates a weak intramolecular antiferromagnetic interaction. Extended Hückel molecular orbital (EHMO) calculations have been performed in order to gain insight into the molecular orbitals that participate in the super-exchange pathway.

Crystal Structure and Magnetic Properties of a Dinuclear Iron(III) Doubly Oxygen Bridged Schiff Base Complex

[Fe(L)Cl]2 (L = N-(4-methylphenyl)-3-methoxy-salicylaldimimine) was synthesized and its crystal structure determined. [C30H26Cl2Fe2N2O6], triclinic, space group P 1̄ , a = 9.278(2), b = 9.4050(10), c = 10.489(2) Å , α = 64.43(2), β = 74.540(10), γ = 62.40(2)° , V = 729.1(2) Å 3, Z = 1. Two identical [Fe(L)Cl] fragments, related by an inversion center, are connected by two bridging O atoms to form a binuclear unit. The iron(III) centers are separated by 3.196(2) Å and weakly antiferromagnetically coupled (J = -10.1(1) cm-1), as derived from temperature-dependent magnetic susceptibility measurements in the range 5.1-283.5 K.