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The complexes [M(3ditz)3]X2 [X = ClO4-, M = FeII (1), ZnII (2); X = BF4-, M = FeII (3), ZnII (4); 3ditz = 1,3-di(tetrazol-1-yl)propane] were prepared. Disordering of the propylene chain in 3ditz is not affected by thermally induced spin crossover in 1 (T1/2↓ = 149 K, T1/2↑ = 150 K) and 3 (T1/2↓ = 158, T1/2↑ = 161 K). Low-spin to high-spin (LS→HS) switching triggered by laser-light irradiation (520 nm) also does not influence the disordering of the ligand, leading to restoration of the initial HS phase. Pressurization of crystals results in a reduction of the Fe-N distances by about 0.19 Å, which indicates practically complete spin crossover (SCO). Also, in this case, the disordering of the ligand remains unchanged, although thermally and pressure-induced SCO is accompanied by different changes of 3ditz molecules. Upon thermally induced SCO, perturbation resulting from the reduction of the Fe-N distances is accompanied by a slight elongation of the bridging ligand. In contrast, in the range 0.25-0.55 GPa, the pressure-induced SCO is associated with shrinkage of the 3ditz molecule. Further elevation of pressure results in the inversion of structural changes and - similar to temperature-induced spin crossover - a slight elongation of the ligand molecule takes place. [ABSTRACT FROM AUTHOR]

The complexes [M(3ditz)3]X2 [X = ClO4-, M = FeII (1), ZnII (2); X = BF4-, M = FeII (3), ZnII (4); 3ditz = 1,3-di(tetrazol-1-yl)propane] were prepared. Disordering of the propylene chain in 3ditz is not affected by thermally induced spin crossover in 1 (T1/2↓ = 149 K, T1/2↑ = 150 K) and 3 (T1/2↓ = 158, T1/2↑ = 161 K). Low-spin to high-spin (LS→HS) switching triggered by laser-light irradiation (520 nm) also does not influence the disordering of the ligand, leading to restoration of the initial HS phase. Pressurization of crystals results in a reduction of the Fe-N distances by about 0.19 Å, which indicates practically complete spin crossover (SCO). Also, in this case, the disordering of the ligand remains unchanged, although thermally and pressure-induced SCO is accompanied by different changes of 3ditz molecules. Upon thermally induced SCO, perturbation resulting from the reduction of the Fe-N distances is accompanied by a slight elongation of the bridging ligand. In contrast, in the range 0.25-0.55 GPa, the pressure-induced SCO is associated with shrinkage of the 3ditz molecule. Further elevation of pressure results in the inversion of structural changes and - similar to temperature-induced spin crossover - a slight elongation of the ligand molecule takes place. [ABSTRACT FROM AUTHOR]

The role of the covalent connections of iron(II) spin-crossover centres in the transmission of perturbation produced by the HS ↔ LS transition has been investigated for the new 3D coordination polymer {[Fe(qbtr)3](ClO4)2}∞ [qbtr = 1,5-di(1,2,3-triazol-1-yl)pentane]. In this complex, a sequence of structural phase transitions occurs. A Ph1 (HS,HS) → Ph2 (HS,HS,HS) transition precedes spin crossover and is associated with an increased number of crystallographically unique iron(II) ions, whereas the change of spin state Ph2 (HS,HS,HS) → Ph3 (HS,LS) triggers another structural phase transition accompanied by a reduction in the number of the unique iron(II) sites. Iron(II) ions occupying two crystallographically unique Fe1 and Fe2 sites form the nodes of a coordination network in the Ph1 phase. The characteristic feature of the polymeric skeleton is the presence of three kinds of ligand bridges tethering the Fe1 ···Fe1, Fe1 ···Fe2 and Fe2 ···Fe2 sites. The ligand linkages differ from each other in rigidity, and the diversification of their properties arises from the susceptibility of the ligand molecules to undergo conformational changes. The high rigidity of the bridge established in the Ph2 phase between iron(II) ions occupying Fe2 sites allows for the propagation of the perturbation produced by the HS (Fe2) → LS (Fe2) transition through the crystal lattice. A strong compression along the Fe2 ···Fe2 bridging direction occurs. In contrast, the ligand molecules that form the two remaining types of bridge are disordered in the Ph2 phase and the change of spin state for the iron(II) ions occupying Fe2 sites induces their ordering, which leads to an increase in the separation between donor atoms. In effect, perturbation cannot be effectively transmitted along the Fe1 ···Fe1 and Fe1 ···Fe2 linkage directions because the 'elongation' of conformationally labile ligand molecules compensates for the shortening of the Fe2-N bond lengths. [ABSTRACT FROM AUTHOR]

New ligand (Z)-2-(1-methyl-2-(pyridine-2-ylmethylene)hydrazinyl)benzoxazole ( L ) reacts with Fe(II) ions what results in formation of mononuclear complexes of 2:1 stoichiometry (complexes 1 and 2 ), which crystallize in the rare space group Ia–3d (No. 230) with solvent–acetonitrile–molecules in the crystal structure. Obtained complexes were studied in terms of their properties in the solid state concerning thermal stability and magnetism. N 3 -donor Schiff base type L is a strong crystal field ligand, therefore both obtained Fe(II) complexes are diamagnetic at room temperature what has been confirmed by magnetic susceptibility measurements and Mössbauer spectroscopy. However, the reversible LS ( 1 A 1 ) ↔ HS ( 5 T 2 ) spin-transitions may be observed starting above room temperature, remaining incomplete even up to 400 K. The thermal stability and electronic reflectance spectra of complexes were determined as well. [ABSTRACT FROM AUTHOR]

A bitopic ligand 2-hydroxy-1-(tetrazol-1-yI)-3-(tetrazol-2-yl)propane (12pbtzOH) was synthesized and reacted with Fe(ClO4)2 · 6H2O, giving a 1D coordination polymer {(Fe(12pbtzOH)2(CH3CN)2](ClO4)2 · 2CH3CN}∞ that exhibits a high-spin to low-spin transition (T1/2↓ = T1/2↑ ≅ 104 K). This is an unprecedented example of an iron(II) complex containing Fe(tetrazolyl)4(MeCN)2 cores. [ABSTRACT FROM AUTHOR]

Novel tripodal ligand 1,1',l"-tris(tetrazol- I-ylnsethyl)methane (IIItz) and products of its reactions with perchlorate as well as with tetrafluoroborate salts of iron(II) are presented The isostructural complexes, [Fe(IIItz)2](C104)2 and [Fe(IIItv)2](BF4)2, were isolated as two-dimen- I sional (2D) coordination networks revealing a honeycomb-like pattern with cages occupied by disordered anions. IIItz molecules act as a tridentate ligand bridging three adjacent Fe(II) ions, and the nitrogen N4 atom of six tetrazole rings (tz) is placed in octahedron vertices of FeN6 chromophores. The complexes, crystallizing in the P3 space group, were characterized by variable-temperature single-crystal X-ray diffraction and variable-temperature magnetic susceptibility measurements. Variable-temperature magnetic susceptibility measurements show that both systems undergo abrupt and complete spin transition with T↑½ =T↓½ = 176 K for perchlorate and T↑½ = 193.8 and T↓½ = 192.8 K for the tetrafluoroborate analogue. Change of spin state in both complexes is accompanied by a thermochromic effect. The HS→LS transition in [Fe(IIItz)2](C104)2 involves shortening of the Fe-N4 bond lengths from 2.171(2) A (293 K) to 2.002(1) A (100 K). In [Fe(IIItz)2](BF4)2, lowering of temperature from 293 to 100 K is accompanied by shortening of the Fe-N4 distances from 2.179(2) to 1.987(2) A, respectively. Perchlorate in [Fe(IIItz2](C104)2 or tetrafluoroborate anions in [Fe(IIItz)2](BF4)2 are engaged in the formation of intermolecular contacts within as well as with the neighboring 2D layer. [ABSTRACT FROM AUTHOR]

In a 1D network of ¹8{[Fe(CH3CN)4(pyrazine)](ClO4)2}, the presence of four neutral nitrile molecules besides the pyrazine donors in the first coordination sphere of iron(II) allows one to achieve a ligand field strength appropriate for the "spin-crossover" occurrence. [ABSTRACT FROM AUTHOR]