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Optically pure (RR)- and racemic (RR/SS)-trans-1,2-di(tetrazol-1-yl)cyclopentane were synthesized and used to prepare homo- and heterochiral Fe(II) coordination compounds. [Fe((RR/SS)-C7H10N8)2(CH3CN)2](BF4)2(1A), [Fe((RR/SS)-C7H10N8)2(C2H5CN)2](BF4)2(2A), [Fe((RR)-C7H10N8)2(CH3CN)2](BF4)2·2CH3CN (1B·solv), and [Fe((RR)-C7H10N8)2(C2H5CN)2](BF4)2(2B) form a family of one-dimensional coordination polymers. Fe(II) cations in these complexes are characterized by a heteroleptic coordination environment: the neighboring metal centers are bridged by two 1,2-di(tetrazol-1-yl)cyclopentane molecules, while the nitrile molecules (acetonitrile or propionitrile, respectively) occupy the axial positions. Independently of the kind of nitrile coligands, an ability to thermally induce spin crossover (SCO) is governed by chirality. 1B·solvand 2Bexhibit abrupt and complete SCO occurring at T1/2= 144 K and T1/2= 228 K, respectively. Desolvated form, 1B(of the same stoichiometry as 2B), also exhibits SCO (T1/2= 215 K). In contrast, an exchange within the polymeric chain of half of the RRmolecules with the SSenantiomeric form results in formation of 1Aand 2A, which remain in stable high-spin (HS) form down to 10 K. It has been shown that moving from a homochiral to a heterochiral system changes the structure of the polymeric unit (while maintaining the same polymer dimensionality and bridging fashion) that leads to the deep reorganization of the further coordination spheres, including the anion network.

A series of pentanuclear lanthanide complexes Ln5L6(μ-L)4(μ3-OH)4(μ4-OH) (LnIII= Nd, Dy, Ho, Er, Yb; L–= dimethyl N-benzoylamidophosphate ion, [C6H5C(O)–N–P(O)(OCH3)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 (χM) of the dysprosium, holmium, and erbium compounds were studied. It was found that χMvs 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 1:1 reaction of trans-[ReIIICl3(PPh3)2(MeCN)] with 2-(β-naphthalideneamino)-2-hydroxymethyl-1-propanol, H3L, in toluene gave the dinuclear complex [ReIII2Cl4(HL)(PPh3)]·2C7H8(1·2C7H8), while the 1:2 reaction led to the formation of complex [ReIVCl2(HL)(PPh3)] (2). In both species, the Schiff-base ligand exists in its doubly deprotonated form, HL2–, forming chelate rings around the metallic centers. In addition, 1·2C7H8displays 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 [ReIVCl2(HL)(PPh3)] (2) the two aromatic ligands, HL2–and PPh3, 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 1·2C7H8and 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 σ2π4δ1δ*1bond order of 3 for 1·2C7H8. In addition, the absorption spectrum of 1·2C7H8in CH2Cl2was simulated by means of DFT calculations and is in excellent agreement with both the crystallographic and theoretical studies. Complex 1·2C7H8is the first dinuclear rhenium complex with a triple metal–metal bond between trivalent rhenium centers.

The reaction between 1,1′-di(tetrazol-1-ylo)methane (1ditz) and iron(II) tetrafluoroborate carried out in the presence of adiponitrile (ADN) afforded the coordination compound [Fe2(μ-1ditz)4(μ-ADN)(ADN)2](BF4)4·2ADN. The 1ditz molecules bridge the Fe(II) ions in two directions, resulting in a polymeric layer, whereas adiponitrile molecules join 1ditz-based units, extending the structure into the three-dimensional network. One of the two axial coordination sites of Fe(II) is occupied by monodentately coordinating adiponitrile. Dinitrile can also act as guest molecules occupying the area between the 1ditz-based layers. Cooling from room temperature triggers the structural phase transitions HS(P1; a, b, c) → HS(P2; 2a, b, c) → LS(P3; a, b, c) (P, phase; HS, high spin; and LS, low spin) associated with the conformational changes of the adiponitrile molecules. In the cooling mode, T1/2↓= 160 K, while in the heating mode T1/2↑is equal to 185 K. Depending on the further path of change of the temperature, it is possible (i) to perform the same cooling/heating cycle (T1/2↓= 160 K; T1/2↑= 185 K) after the sample is reheated above 240 K or (ii) to execute the cooling with T1/2↓= 167 K after the heating is stopped at 190 K, where the phase with superlattice (P2) does not appear. Both ways are reversible, and they are managed by conformational changes of the adiponitrile molecules.