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Reactions between 1,2-di(tetrazol-2-yl)ethane (ebtz), 1,6-di(tetrazol-2-yl)hexane (hbtz) or 1,1′-di(tetrazol-1-yl)methane (1ditz) and Fe(BF4)2 in the presence of adiponitrile (ADN), glutaronitrile (GLN) or suberonitrile (SUN) resulted in the formation of coordination polymers [Fe(μ-ebtz)2(μ-ADN)](BF4)2 (1), [Fe(μ-hbtz)2(μ-ADN)](BF4)2 (2), [Fe(μ-1ditz)2(GLN)2](BF4)2·GLN (3) and [Fe(μ-1ditz)2(μ-SUN)](BF4)2·SUN (4). It was established that the application of dinitriles allows an increase in the dimensionality of the ebtz and hbtz based systems while maintaining the structure of the polymeric units characteristic of previously studied mononitrile based analogues. In 3 and 4, regardless of the type of dinitrile coligand, the motif of 2D polymeric layers constituted by 1ditz molecules remains preserved. However, the dimensionality of 1ditz based networks is governed by the coordination modes of dinitriles. 3, based on a shorter molecule of glutaronitrile, crystallizes as a two-dimensional (2D) coordination polymer. In this compound, dinitriles coordinate monodentately or play the role of guest molecules. The substitution of glutaronitrile with suberonitrile enables the bridging of neighboring polymeric layers, resulting in a 3D network. The intentional selection of bis(tetrazoles) and dinitriles as building blocks has led, as expected, to obtaining systems with the structure of the first coordination sphere consisting of four tetrazole rings and two axially coordinated nitrile molecules. It created the conditions required for the occurrence of thermally induced spin crossover. Magnetic measurements and single crystal X-ray diffraction studies were used for the characterization of the spin crossover properties of 1–4. [ABSTRACT FROM AUTHOR]

An amino acid containing octanuclear heterometallic {[Mn III3 Ca]2} cluster has been synthesized, alongside a structurally-related trigonal prismatic [Mn III6 Ca]2+ cage. [ABSTRACT FROM AUTHOR]

1,4-Di(1-ethyl-1,2,3-triazol-5-yl)butane (bbtre) was prepared by lithiation of 1-ethyl-1,2,3-triazole, followed by alkylation with 1,4-dibromobutane. The ligand bbtre forms a three-dimensional network with Fe(II), [Fe(bbtre)3](ClO4)2·2CH3CN, that exhibits thermally induced spin crossover (SCO). A change of temperature or change of spin state results in various types of structural transformation, leading to different structures that are stable in strictly defined temperature ranges. As a result, there are three spin crossover transitions arranged via two different paths. Thus, cooling below 280 K involves a HT(HS) → LT(HS) (HT, high temperature structure; LT, low temperature structure; HS, high spin) phase transition (PT), which is associated with conformational changes of the bbtre molecules and with deformation of the polymeric skeleton. In the LT phase incomplete and reversible LT(HS) LT(HS/LS) spin crossover occurs (LS, low spin). In contrast, rapid cooling (of a sample not previously thermally treated) allows the HT(HS) → LT(HS) phase transition to be avoided, and so complete HT(HS) → HT1(LS) SCO occurs. This means that the PT plays the role of a switch, which allows a choice of one of two ways in which the SCO will proceed. After rapid cooling, further heating to 150 K and subsequent cooling results in a reversible HT1(HS) HT1(LS) spin crossover (T ↓1/2 = 130 K, T ↑1/2 = 131 K). However, raising the temperature to 170–200 K leads to formation of a modulated structure HT2(HS) exhibiting the next reversible HT2(HS) HT2(LS) SCO (T ↓1/2 = 121 K, T ↑1/2 = 123 K). Finally, heating above 200 K involves the HT2(HS) → LT(HS) PT and results in a LT(HS) structure exhibiting incomplete LT(HS) LT(HS/LS) spin crossover. [ABSTRACT FROM AUTHOR]

The electrostatic self-assembly reaction of the [Cu(HL)]2+ cation, where HL = 2-(2-aminoethylamino) ethanol, and the N3− or [Fe(CN)6]4− anion leads to the formation of two coordination polymers with the general formula of [Cu6(μ1,1-N3)6(μ1,3-N3)2(μ1,1,3-N3)2(μ1,1,1,3-N3)2(HL)2]n (1) and {[Cu(HL)]2[Fe(CN)6]·H2O}n (2), respectively. The resulting compounds have been structurally characterized by a single-crystal X-ray diffraction technique. Compound 1 possesses a rare 3D structure. It contains centrosymmetric hexanuclear repeating units, which act as six-connected nodes in the final network and copper(ii) ions are joined together by azide anions with four different types of bridging modes, μ1,1, μ1,1,3, μ1,1,1,3, and μ1,3. The structure of compound 2 is a 2D heterometallic CuII/FeII layer in which the [Cu(HL)]2 nodes and the octahedral [Fe(CN)6]4− linkers are joined by μ2- and unusual μ3-CN bridging modes. Detailed static and dynamic magnetic analyses of 1 reveal a dominant ferromagnetic intracluster interaction and a ferromagnetic 3D ordering transition below Tc = 5 K. The variable temperature magnetic susceptibility measurements of compound 2 show a very weak ferromagnetic coupling between the nearest Cu(ii) ions. Also, EPR spectroscopy of these compounds has been investigated in the solid state. Nanocrystals of compound 2 have also been synthesized by a sonochemical process under different reaction conditions. The results show that the crystallinity degree and uniform distribution of nanosheets are inversely dependent on the irradiation time. [ABSTRACT FROM AUTHOR]

A new family of [3 + 3] hexanuclear 3d–4f complexes [(μ3-CO3){CoIILnIIIL(μ3-OH)(OH2)}3]-(ClO4)·mC2H5OH·nH2O (1–5) [Ln = La (1), Gd (2), Tb (3), Dy (4), and Ho (5)] have been prepared in moderate to high yields (62–78%) following a self-assembly reaction between the ligand 6,6′,6′′-(nitrilotris(methylene))tris-(2-methoxy-4-methylphenol) (H3L), Co(OAc)2·4H2O and the lanthanide ion precursors in the mandatory presence of tetrabutylammonium hydroxide. During the reaction, atmospheric carbon dioxide is fixed in the product molecule as a bridging carbonato ligand which connects all the three lanthanide centers of this molecular assembly through a rare η2:η2:η2–μ3 mode of bridging as revealed from X-ray crystallography. The metal centers in all these compounds, except the GdIII analogue (2), are coupled in antiferromagnetic manner while the nature of coupling in the CoII3GdIII3 complex is ferromagnetic. DFT calculations revealed that this ferromagnetic interaction occurs most likely by the CoII–GdIII superexchange, mediated via the bridging oxygen atoms. Only the CoII–DyIII compound (4) displayed a slow relaxation of the magnetization at a very low temperature as established by AC susceptibility measurements. The data provides an estimation of the activation energy U/kB = 9.2 K and the relaxation time constant τ0 = 1.0 × 10−7 s. [ABSTRACT FROM AUTHOR]

2D structurally related iron(ii) coordination networks {[Fe(hbtz)2(RCN)2](ClO4)2}∞ featuring, besides tetrazol-2-yl rings in the first coordination sphere, also axially coordinated propionitrile or allyl cyanide molecules (R = C3H5–, 1; R = C2H5–, 2) were synthesized. Thermally induced spin crossover (SCO) in 1 takes place in two poorly resolved stages (T11/2↓ = T11/2↑ = 198 K, T21/2↓ = 170 K, T21/2↑ = 171 K) whereas in 2 complete and relatively gradual one step SCO (T1/2↓ = T1/2↑ = 160 K) occurs. Diversification of the SCO properties of the complexes originates from the ability of coordinated allyl cyanide in 1 to undergo conformational alterations, which is not observed for propionitrile molecules in 2. SCO in 1 is accompanied by a non-monotonic change of the contribution of allyl cyanide conformers which is related to reconstruction of the network of intermolecular contacts established between polymeric layers. The coordination network 1 exhibits extraordinary elasticity and in the second stage SCO, accompanied by conformational changes of allyl cyanide, triggers a crystallographic phase transition which leads to the formation of a superstructure. What is important, the formation of the superstructure is not caused by long range ordering of HS and LS iron(ii) ions. The structural alteration is associated with corrugation of the polymeric skeleton and disappearance of nitrile disorder. Irradiation of a single crystal of 1 at 15 K with laser light (520 nm) allowed producing a novel low temperature HS phase of 1 in which, contrary to the high temperature HS phase, disordering of anion and allyl cyanide molecules is not observed and the corrugated nature of the polymeric layer, characteristic of the LS phase, is preserved. [ABSTRACT FROM AUTHOR]

2D structurally related iron(ii) coordination networks {[Fe(hbtz)2(RCN)2](ClO4)2}∞ featuring, besides tetrazol-2-yl rings in the first coordination sphere, also axially coordinated propionitrile or allyl cyanide molecules (R = C3H5–, 1; R = C2H5–, 2) were synthesized. Thermally induced spin crossover (SCO) in 1 takes place in two poorly resolved stages (T11/2↓ = T11/2↑ = 198 K, T21/2↓ = 170 K, T21/2↑ = 171 K) whereas in 2 complete and relatively gradual one step SCO (T1/2↓ = T1/2↑ = 160 K) occurs. Diversification of the SCO properties of the complexes originates from the ability of coordinated allyl cyanide in 1 to undergo conformational alterations, which is not observed for propionitrile molecules in 2. SCO in 1 is accompanied by a non-monotonic change of the contribution of allyl cyanide conformers which is related to reconstruction of the network of intermolecular contacts established between polymeric layers. The coordination network 1 exhibits extraordinary elasticity and in the second stage SCO, accompanied by conformational changes of allyl cyanide, triggers a crystallographic phase transition which leads to the formation of a superstructure. What is important, the formation of the superstructure is not caused by long range ordering of HS and LS iron(ii) ions. The structural alteration is associated with corrugation of the polymeric skeleton and disappearance of nitrile disorder. Irradiation of a single crystal of 1 at 15 K with laser light (520 nm) allowed producing a novel low temperature HS phase of 1 in which, contrary to the high temperature HS phase, disordering of anion and allyl cyanide molecules is not observed and the corrugated nature of the polymeric layer, characteristic of the LS phase, is preserved. [ABSTRACT FROM AUTHOR]