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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(BF 4 ) 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)](BF 4 ) 2 (1), [Fe(μ-hbtz) 2 (μ-ADN)](BF 4 ) 2 (2), [Fe(μ-1ditz) 2 (GLN) 2 ](BF 4 ) 2 ·GLN (3) and [Fe(μ-1ditz) 2 (μ-SUN)](BF 4 ) 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.

Cooling [Fe(bbtr) 3 ](BF 4 ) 2 (bbtr=1,4-di(1,2,3-triazol-1-yl)butane) triggers very slow spin crossover below 80 K (T 1/2 ↓ =76 K). The spin crossover (SCO) is accompanied by a hysteresis loop (T 1/2 ↑ =89 K). In contrast to isostructural perchlorate analogue [Fe(bbtr) 3 ](ClO 4 ) 2 in which spin crossover during cooling is preceded by phase transition at T PT =126 K in tetrafluoroborate phase transition does not occur to the beginning of spin crossover (80 K). Studies of mixed crystals [Fe(bbtr) 3 ](BF 4 ) 2(1-x) (ClO 4 ) 2x (0.5≤x≤0.9) showed that a phase transition precedes spin crossover, however, for x≅0.46 intersection of T 1/2 (x) and T PT (x) dependencies takes place. The application of pressure of 1 GPa shifts the spin crossover in [Fe(bbtr) 3 ](BF 4 ) 2 to a temperature above 270 K. High-pressure studies of neat tetrafluoroborate and perchlorate, as well as mixed crystals [Fe(bbtr) 3 ](BF 4 ) 2(1-x) (ClO 4 ) 2x (0.1≤x≤0.9), revealed that at 295 K P 1/2 value changes linearly with x indicating similar mechanism of spin crossover under elevated pressure in all systems under investigation. Variable pressure single crystal X-ray diffraction studies confirmed that in contrast to thermally induced spin crossover undergoing differently in tetrafluoroborate and perchlorate an application of high pressure removes this differentiation leading to a similar mechanism depending at first on start spin crossover and then P-3→P-1 phase transition occurs. In this report we have shown that 2D coordination polymer [Fe(bbtr) 3 ](BF 4 ) 2 (bbtr=1,4-di(1,2,3-triazol-1-yl)butane) treated to date as spin crossover silent shows thermally induced spin crossover phenomenon. Spin crossover in tetrafluoroborate is extremely slow. Determination of the spin crossover curve required carrying measurement in the settle mode-cooling from 85 to 70 K took about 600 h (average velocity of change of temperature ca. 0.0004 K/min)., (© 2023 Wiley-VCH GmbH.)

The resistance of Candida albicans and other pathogenic yeasts to azole antifungal drugs has increased rapidly in recent years and is a significant problem in clinical therapy. The current state of pharmacological knowledge precludes the withdrawal of azole drugs, as no other active substances have yet been developed that could effectively replace them. Therefore, one of the anti-yeast strategies may be therapies that can rely on the synergistic action of natural compounds and azoles, limiting the use of azole drugs against candidiasis. Synergy assays performed in vitro were used to assess drug interactions Fractional Inhibitory Concentration Index. The synergistic effect of fluconazole ( 1 ) and three synthetic lactones identical to those naturally occurring in celery plants-3- n -butylphthalide ( 2 ), 3- n -butylidenephthalide ( 3 ), 3- n -butyl-4,5,6,7-tetrahydrophthalide ( 4 )-against Candida albicans ATCC 10231, C. albicans ATCC 2091, and C. guilliermondii KKP 3390 was compared with the performance of the individual compounds separately. MIC 90 (the amount of fungistatic substance (in µg/mL) inhibiting yeast growth by 90%) was determined as 5.96-6.25 µg/mL for fluconazole ( 1 ) and 92-150 µg/mL for lactones 2-4. With the simultaneous administration of fluconazole ( 1 ) and one of the lactones 2-4 , it was found that they act synergistically, and to achieve the same effect it is sufficient to use 0.58-6.73 µg/mL fluconazole ( 1 ) and 1.26-20.18 µg/mL of lactones 2-4 . As fluconazole and phthalide lactones show synergy, 11 new fluconazole analogues with lower toxicity and lower inhibitory activity for CYP2C19, CYP1A2, and CYP2C9, were designed after in silico testing. The lipophilicity was also analyzed. A three-carbon alcohol with two rings was preserved. In all compounds 5-15, the 1,2,4-triazole rings were replaced with 1,2,3-triazole or tetrazole rings. The hydroxyl group was free or esterified with phenylacetic acid or thiophene-2-carboxylic acid chlorides or with adipic acid. In structures 11 and 12 the hydroxyl group was replaced with the fragment -CH 2 Cl or = CH 2 . Additionally, the difluorophenyl ring was replaced with unsubstituted phenyl. The structures of the obtained compounds were determined by 1 H NMR, and 13 C NMR spectroscopy. Molecular masses were established by GC-MS or elemental analysis. The MIC 50 and MIC 90 of all compounds 1-15 were determined against Candida albicans ATCC 10231, C. albicans ATCC 2091, AM 38/20, C. guilliermondii KKP 3390, and C. zeylanoides KKP 3528. The MIC 50 values for the newly prepared compounds ranged from 38.45 to 260.81 µg/mL. The 90% inhibitory dose was at least twice as high. Large differences in the effect of fluconazole analogues 5-15 on individual strains were observed. A synergistic effect on three strains- Candida albicans ATCC 10231, C. albicans ATCC 2091, C. guilliermondii KKP 339-was observed. Fractional inhibitory concentrations FIC 50 and FIC 90 were tested for the most active lactone, 3- n -butylphthalide, and seven fluconazole analogues. The strongest synergistic effect was observed for the strain C. albicans ATCC 10231, FIC 0.04-0.48. The growth inhibitory amount of azole is from 25 to 55 µg/mL and from 3.13 to 25.3 µg/mL for 3- n -butylphthalide. Based on biological research, the influence of the structure on the fungistatic activity and the synergistic effect were determined.

1,4-Di(1,2,3-triazol-1-yl)butane (bbtr) forms a two-dimensional (2D) coordination polymer (1) in a reaction with iron(II) triflate. In the crystal lattice there are two crystallographically unique iron(II) ions surrounded octahedrally by a 1,2,3-triazole ring coordinated through nitrogen atoms N3. Single crystal X-ray diffraction studies revealed that spin crossover for each crystallographically independent iron(II) ion proceeds at a different temperature ( T 1/2 (Fe1) = 201 K; T 1/2 (Fe2) = 216 K), while the magnetic measurements showed that there is one step, complete thermally induced spin crossover ( T 1/2 = 205 K). Complex 1 undergoes, with time, single crystal-to-single crystal transformation (SCSC) to the converted system (1c) from the R 3̄ to the P 6 3 space group, accompanied by significant changes in the lattice parameter c (a shortening of approximately one-third) and consequently unit cell volume. Structural transformation is associated with rebuilding of the polymeric layer as well as the anion network, which is reflected in the results of Mössbauer studies. In the polymorphic system (1c) there are three crystallographically independent iron(II) ions. The temperature dependence results for magnetic susceptibility indicated complete, one-step spin crossover very similar to that of 1; however, single-crystal X-ray diffraction studies of 1c revealed that spin crossover for each crystallographically independent iron(II) ion occurs in a different manner, revealing three elementary stages ( T 1/2 (Fe1) = 200 K; T 1/2 (Fe2) = 212 K, T 1/2 (Fe3) = 214 K).

Reaction of 1,2-di(tetrazol-2-yl)ethane (ebtz) with Fe(BF 4 ) 2 ⋅6 H 2 O in different nitriles yields one-dimensional coordination polymers [Fe(ebtz) 2 (RCN) 2 ](BF 4 ) 2 ⋅nRCN (n=2 for R=CH 3 (1) and n=0 for R=C 2 H 5 (2) C 3 H 7 (3), C 3 H 5 (4), CH 2 Cl (5)) exhibiting spin crossover (SCO). SCO in 1 and 3-5 is complete and occurs above 160 K. In 2, it is shifted to lower temperatures and is accompanied by wide hysteresis (T 1/2 ↓ =78 K, T 1/2 ↑ =123 K) and proceeds extremely slowly. Isothermal (80 K) time-resolved single-crystal X-ray diffraction studies revealed a complex nature for the HS→LS transition in 2. An initial, slow stage is associated with shrinkage of polymeric chains and with reduction of volume at 77 % (in relation to the difference between cell volumes V HS -V LS ) whereas only 16 % of iron(II) ions change spin state. In the second stage, an abrupt SCO occurs, associated with breathing of the crystal lattice along the direction of the Fe-nitrile bonds, while the nitriles reorient. HS→LS switching triggered by light (808 nm) reveals the coupling of spin state and nitrile orientation. The importance of this coupling was confirmed by studies of [Fe(ebtz) 2 (C 2 H 5 CN/C 3 H 7 CN) 2 ](BF 4 ) 2 mixed crystals (2 a, 2 b), showing a shift of T 1/2 to higher values and narrowing of the hysteresis loop concomitant with an increase of the fraction of butyronitrile. This increase reduces the capability of nitrile molecules to reorient. Density functional theory (DFT) studies of models of 1-5 suggest a particular possibility of 2 to adopt a low (140-145°) value of its Fe-N-C(propionitrile) angle., (© 2020 Wiley-VCH GmbH.)

An amino acid containing octanuclear heterometallic {[MnCa] 2 } cluster has been synthesized, alongside a structurally-related trigonal prismatic [MnCa] 2+ cage.

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.

Levan is a polysaccharide composed of fructose units with β-2,6-glycoside bonds. Microorganisms synthesize levan by levansucrase as a mixture of low- and high-molecular-weight fractions. Due to its properties, it has a wide range of applications in cosmetics, pharmaceuticals, food and medicine; it appears that the molecular weight of levan might impact its industrial use. To obtain one fraction of levan after biotransformation, ethanol precipitation with an increasing volume of alcohol was conducted. This precipitation process was also optimized. Several types of analyses were used. Low-molecular-weight levan was evaluated for toxicity in a normal human dermal fibroblast cell line and hemolytic potential on human erythrocytes. Levan was found to be non-cytotoxic and non-hemolytic in concentrations ranging from 0.01 to 1.00 mg/ml. Moreover, levan demonstrated antioxidant potential expressed as an ability to inhibit of oil/water emulsion oxidation and DPPH radical scavenging., (Copyright © 2019. Published by Elsevier Inc.)

A series of pentanuclear lanthanide complexes Ln 5 L 6 (μ-L) 4 (μ 3 -OH) 4 (μ 4 -OH) (Ln III = Nd, Dy, Ho, Er, Yb; L - = dimethyl N -benzoylamidophosphate ion, [C 6 H 5 C(O)-N-P(O)(OCH 3 ) 2 ] - ) was obtained by the reaction of sodium dimethyl N -benzoylamidophosphate with the corresponding lanthanide nitrates. The pentanuclear cores formed as a result of self-arrangement and their composition did not depend on the lanthanide ion. The complexes and sodium dimethyl N -benzoylamidophosphate have been characterized by single-crystal X-ray diffraction. The absorption spectra of the complexes were measured at 300 and 4 K. The dysprosium and ytterbium complexes exhibited weak emission in the visible and IR regions, respectively. Temperature dependences of magnetic susceptibility (χ M ) of the dysprosium, holmium, and erbium compounds were studied. It was found that χ M vs T dependences were governed by the crystal field splitting effects with the Δ parameter being in the range 5-17 cm -1 . Slow magnetic relaxation was found for the dysprosium complex by ac magnetic measurements, while no significant out-of-phase signals were detected for holmium and erbium complexes.

The electrostatic self-assembly reaction of the [Cu(HL)] 2+ cation, where HL = 2-(2-aminoethylamino) ethanol, and the N 3 - or [Fe(CN) 6 ] 4- anion leads to the formation of two coordination polymers with the general formula of [Cu 6 (μ 1,1 -N 3 ) 6 (μ 1,3 -N 3 ) 2 (μ 1,1,3 -N 3 ) 2 (μ 1,1,1,3 -N 3 ) 2 (HL) 2 ] n (1) and {[Cu(HL)] 2 [Fe(CN) 6 ]·H 2 O} 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, μ 1,1 , μ 1,1,3 , μ 1,1,1,3 , and μ 1,3 . The structure of compound 2 is a 2D heterometallic Cu II /Fe II layer in which the [Cu(HL)] 2 nodes and the octahedral [Fe(CN) 6 ] 4- linkers are joined by μ 2 - and unusual μ 3 -CN bridging modes. Detailed static and dynamic magnetic analyses of 1 reveal a dominant ferromagnetic intracluster interaction and a ferromagnetic 3D ordering transition below T c = 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.

The 1:1 reaction of trans-[Re III Cl 3 (PPh 3 ) 2 (MeCN)] with 2-(β-naphthalideneamino)-2-hydroxymethyl-1-propanol, H 3 L, in toluene gave the dinuclear complex [Re III 2 Cl 4 (HL)(PPh 3 )]·2C 7 H 8 (1·2C 7 H 8 ), while the 1:2 reaction led to the formation of complex [Re IV Cl 2 (HL)(PPh 3 )] (2). In both species, the Schiff-base ligand exists in its doubly deprotonated form, HL 2- , forming chelate rings around the metallic centers. In addition, 1·2C 7 H 8 displays a unique triple metal-to-metal bond between the two trivalent rhenium ions separated at a 2.229(1) Å bond distance, while in complex [Re IV Cl 2 (HL)(PPh 3 )] (2) the two aromatic ligands, HL 2- and PPh 3 , occupy axial positions, with the terminal Cl - ions in the trans position. Investigation of the magnetic properties revealed a Curie paramagnetic behavior ( S = 1/2) with a pronounced temperature independent paramagnetism (TIP) for 1·2C 7 H 8 and 2. Both the geometry and the electronic structure of both compounds have been studied by means of density functional theory (DFT) calculations, confirming the triplet and doublet spin ground state of the complexes and furthermore establishing an electron-rich σ 2 π 4 δ 1 δ *1 bond order of 3 for 1·2C 7 H 8 . In addition, the absorption spectrum of 1·2C 7 H 8 in CH 2 Cl 2 was simulated by means of DFT calculations and is in excellent agreement with both the crystallographic and theoretical studies. Complex 1·2C 7 H 8 is the first dinuclear rhenium complex with a triple metal-metal bond between trivalent rhenium centers.

In [Fe(ebbtr)2(CH3CN)2](CF3SO3)2·4CH3CN spin crossover is associated with the occurrence of "normal" and "reverse" hysteresis loops separated by a region of stable HS form. This results from trans-trans → gauche-trans conformational changes of ebbtr molecules and anion reorientation, which occur in different ways during cooling and during heating.

The abrupt high spin (HS)→low spin (LS) transition (T ↓ 1/2 =136 K) in [Fe(hbtz) 2 (CH 3 CN) 2 ](BF 4 ) 2 (hbtz=1,6-di(tetrazol-2-yl)hexane) is finished at 100 K and further thermal treatment influences the spin crossover. Subsequent heating involves a change of the spin state in the same way (T ↑ 1/2 =136 K) on cooling. In contrast, cooling below 100 K triggers different behavior and T ↑ 1/2 is shifted to 170 K. The extraordinary structural changes that occurred below 100 K are responsible for the observed diversity of properties. A unique feature of the low-temperature phase is the rebuilding of the anion network expressed by a shift of anions inside the polymeric layer at a distance of 1.2 Å as well as the relative shift of neighboring layers at over 4 Å. These structural alterations, connected with a phase transition, become the origin of the strain, which in most cases causes crystal cleaving. In a sample composed from crystals crushed as a result of the phase transition or as a result of mechanical crumbling, the hysteresis loop vanishes; however, annealing the sample allows to its partial restoration. A replacement of acetonitrile by other nitriles leads to preservation of the polymeric structure and spin crossover, but no phase transition follows., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In the two dimensional network [Fe(ebbtr)2(CH3CN)2](ClO4)2·4CH3CN a sequence of LS → HS → LS → HS transitions occurs as the exclusive result of the change in temperature. This property results from the extraordinary flexibility/elasticity manifested in the hierarchical arrangement of structural events involving the reorientation of coordinated/noncoordinated molecules as well as with the deformation and the mutual shift of the polymeric units.

A new family of [3 + 3] hexanuclear 3d-4f complexes [(μ 3 -CO 3 ){Co II Ln III L(μ 3 -OH)(OH 2 )} 3 ]-(ClO 4 )·mC 2 H 5 OH·nH 2 O (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) (H 3 L), Co(OAc) 2 ·4H 2 O 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 η 2 :η 2 :η 2 -μ 3 mode of bridging as revealed from X-ray crystallography. The metal centers in all these compounds, except the Gd III analogue (2), are coupled in antiferromagnetic manner while the nature of coupling in the CoGd complex is ferromagnetic. DFT calculations revealed that this ferromagnetic interaction occurs most likely by the Co II -Gd III superexchange, mediated via the bridging oxygen atoms. Only the Co II -Dy III 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/k B = 9.2 K and the relaxation time constant τ 0 = 1.0 × 10 -7 s.

(C3N2H5)2[CoCl4] (ICC) was characterized in a wide temperature range by the single-crystal X-ray diffraction method. Differential scanning calorimetry revealed two structural phase transitions: continuous at 245.5 K (from phase I to II) and a discontinuous one at 234/237 K (cooling/heating) (II → III). ICC adopts monoclinic space groups C2/c and P21/c in phase (I) and (III), respectively. The intermediate phase (II) appears to be incommensurately modulated. Dynamic properties of polycrystalline ICC were studied by means of dielectric spectroscopy and proton magnetic resonance ((1)H NMR). The presence of a low frequency dielectric relaxation process in phase III reflects libration motion of the imidazolium cations. The temperature dependence of the (1)H spin-lattice relaxation time indicated two motional processes with similar activation energies that are by about an order of magnitude smaller than the activation energy obtained from dielectric studies. There are no abrupt changes in the (1)H relaxation time at the phase transitions indicating that the dynamics of the imidazolium rings gradually varies with temperature; that is, it does not change suddenly at the phase transition. Negative values of the Weiss constant and the intermolecular exchange parameter were obtained, confirming the presence of a weak antiferromagnetic interaction between the nearest cobalt centers. Moreover, the magnitude of zero field splitting was determined. The AC susceptibility measurements show that a slow magnetic relaxation is induced by small external magnetic field.

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 (T(1)1/2(↓) = T(1)1/2(↑) = 198 K, T(2)1/2(↓) = 170 K, T(2)1/2(↑) = 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.

Novel tripodal ligand 1,1',1''-tris(tetrazol-1-ylmethyl)methane (111tz) and products of its reactions with perchlorate as well as with tetrafluoroborate salts of iron(II) are presented. The isostructural complexes, [Fe(111tz)₂](ClO₄)₂ and [Fe(111tz)₂](BF₄)₂, were isolated as two-dimensional (2D) coordination networks revealing a honeycomb-like pattern with cages occupied by disordered anions. 111tz 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(1/2)(↑) = T(1/2)(↓) = 176 K for perchlorate and T(1/2)(↑) = 193.8 and T(1/2)(↓) = 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(111tz)₂](ClO₄)₂ involves shortening of the Fe-N4 bond lengths from 2.171(2) Å (293 K) to 2.002(1) Å (100 K). In [Fe(111tz)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) Å, respectively. Perchlorate in [Fe(111tz)₂](ClO₄)₂ or tetrafluoroborate anions in [Fe(111tz)₂](BF₄)₂ are engaged in the formation of intermolecular contacts within as well as with the neighboring 2D layer.

In a 1D network of (1)(∞){[Fe(CH(3)CN)(4)(pyrazine)](ClO(4))(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.

A bitopic ligand 2-hydroxy-1-(tetrazol-1-yl)-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} infinity that exhibits a high-spin to low-spin transition (T1/2(downward arrow)=T1/2(upward arrow) congruent with 104 K). This is an unprecedented example of an iron(II) complex containing Fe(tetrazolyl) 4(MeCN)2 cores.