M. A. Kiskin

Heterometallic Coordination Polymers Assembled from Trigonal Trinuclear Fe2Ni-Pivalate Blocks and Polypyridine Spacers: Topological Diversity, Sorption, and Catalytic Properties.

Linkage of the trigonal complex [Fe2NiO(Piv)6] (where Piv(-) = pivalate) by a series of polypyridine ligands, namely, tris(4-pyridyl)triazine (L(2)), 2,6-bis(3-pyridyl)-4-(4-pyridyl)pyridine (L(3)), N-(bis-2,2-(4-pyridyloxymethyl)-3-(4-pyridyloxy)propyl))pyridone-4 (L(4)), and 4-(N,N-diethylamino)phenyl-bis-2,6-(4-pyridyl)pyridine (L(5)) resulted in the formation of novel coordination polymers [Fe2NiO(Piv)6(L(2))]n (2), [Fe2NiO(Piv)6(L(3))]n (3), [Fe2NiO(Piv)6(L(4))]n·nHPiv (4), and [{Fe2NiO(Piv)6}4{L(5)}6]n·3nDEF (5, where DEF is N,N-diethylformamide), which were crystallographically characterized. The topological analysis of 3, 4, and 5 disclosed the 3,3,4,4-connected 2D (3, 4) or 3,4,4-connected 1D (5) underlying networks which, upon further simplification, gave rise to the uninodal 3-connected nets with the respective fes (3, 4) or SP 1-periodic net (4,4)(0,2) (5) topologies, driven by the cluster [Fe2Ni(μ3-O)(μ-Piv)6] nodes and the polypyridine μ3-L(3,4) or μ2-L(5) blocks. The obtained topologies were compared with those identified in other closely related derivatives [Fe2NiO(Piv)6(L(1))]n (1) and {Fe2NiO(Piv)6}8{L(6)}12 (6), where L(1) and L(6) are tris(4-pyridyl)pyridine and 4-(N,N-dimethylamino)phenyl-bis-2,6-(4-pyridyl)pyridine, respectively. It was shown that a key structure-driven role in defining the dimensionality and topology of the resulting coordination network is played by the type of polypyridine spacer. Compounds 2 and 3 possess a porous structure, as confirmed by the N2 and H2 sorption data at 78 K. Methanol and ethanol sorption by 2 was also studied indicating that the pores filled by these substrates did not induce any structural rearrangement of this sorbent. Additionally, porous coordination polymer 2 was also applied as a heterogeneous catalyst for the condensation of salicylaldehyde or 9-anthracenecarbaldehyde with malononitrile. The best activity of 2 was observed in the case of salicylaldehyde substrate, resulting in up to 88% conversion into 2-imino-2H-chromen-3-carbonitrile.

Manifestation of π–π Stacking Interactions in Luminescence Properties and Energy Transfer in Aromatically-Derived Tb, Eu and Gd Tris(pyrazolyl)borate Complexes

The three new complexes Tp(Py)Ln(CH3CO2)2(H2O) (Ln = Eu (1), Gd(2), or Tb (3)) were prepared and characterized crystallographically. In the crystal lattices of these complexes, separate molecules are connected in infinite chains by π-stacking interactions. Complexes 1 and 3 display intense photoluminescence and triboluminescence (red and green respectively), while compound 3 exhibits electroluminescence commencing at 9 V in an ITO/PVK/3/Al device (ITO = indium-tin oxide, PVK = poly(N-vinylcarbazole)). A series of Eu/Tb-doped Gd compounds was prepared by cocrystallization from mixtures of 1 and 2 or 2 and 3, respectively. It was shown that π-stacking interactions are involved in increasing the efficiency of energy transfer from the gadolinium complex to emitting [Tp(Py)Eu](2+) or [Tp(Py)Tb](2+) centers, and this energy transfer occurs through hundreds of molecules, resembling the process of energy harvesting in chloroplast stacks.

Redox-Active Porous Coordination Polymers Prepared by Trinuclear Heterometallic Pivalate Linking with the Redox-Active Nickel(II) Complex: Synthesis, Structure, Magnetic and Redox Properties, and Electrocatalytic Activity in Organic Compound Dehalogenation in Heterogeneous Medium

Linking of the trinuclear pivalate fragment Fe2CoO(Piv)6 by the redox-active bridge Ni(L)2 (compound 1; LH is Schiff base from hydrazide of 4-pyridinecarboxylic acid and 2-pyridinecarbaldehyde, Piv(-) = pivalate) led to formation of a new porous coordination polymer (PCP) {Fe2CoO(Piv)6}{Ni(L)2}1.5 (2). X-ray structures of 1 and 2 were determined. A crystal lattice of compound 2 is built from stacked 2D layers; the Ni(L)2 units can be considered as bridges, which bind two Fe2CoO(Piv)6 units. In desolvated form, 2 possesses a porous crystal lattice (SBET = 50 m(2) g(-1), VDR = 0.017 cm(3) g(-1) estimated from N2 sorption at 78 K). At 298 K, 2 absorbed a significant quantity of methanol (up to 0.3 cm(3) g(-1)) and chloroform. Temperature dependence of molar magnetic susceptibility of 2 could be fitted as superposition of χMT of Fe2CoO(Piv)6 and Ni(L)2 units, possible interactions between them were taken into account using molecular field model. In turn, magnetic properties of the Fe2CoO(Piv)6 unit were fitted using two models, one of which directly took into account a spin-orbit coupling of Co(II), and in the second model the spin-orbit coupling of Co(II) was approximated as zero-field splitting. Electrochemical and electrocatalytic properties of 2 were studied by cyclic voltammetry in suspension and compared with electrochemical and electrocatalytic properties of a soluble analogue 1. A catalytic effect was determined by analysis of the catalytic current dependency on concentrations of the substrate. Compound 1 possessed electrocatalytic activity in organic halide dehalogenation, and such activity was preserved for the Ni(L)2 units, incorporated into the framework of 2. In addition, a new property occurred in the case of 2: the catalytic activity of PCP depended on its sorption capacity with respect to the substrate. In contrast to homogeneous catalysts, usage of solid PCPs may allow selectivity due to porous structure and simplify separation of product.

Synthesis, structure, and luminescent properties of lanthanide coordination compounds with 3-methyl-4-formyl-1-phenylpyrazol-5-one

An exchange reaction of the sodium salt of 3-methyl-1-phenyl-4-formylpyrazol-5-one (HL) with chlorides or nitrates of lanthanides (Ln = La, Nd, Sm, Eu, Gd, Tb, Dy, and Yb) was used to synthesize coordination compounds of composition LnL3·nSolv (Solv = H2O or EtOH). According to powder X-ray diffraction data, these compounds constitute two series: one comprises lanthanum and neodymium complexes, and the other, samarium, europium, gadolinium, terbium, dysprosium, and ytterbium complexes. For the complexes of the first series, the structure was solved in a single-crystal diffraction experiment carried out on [La2(μ-L)3(L)3(H2O)3]·2MeOH. The lanthanum atoms in the complex are at a distance of 4.222(2) — from each other, and they are structurally nonequivalent and linked by three 5-hydroxy-4-formylpyrazole anions. Solid-phase samples of the coordination compounds under study feature weak luminescence in the spectral regions intrinsic to lanthanide cations.

The Influence of Diamagnetic Substrates Absorption on Magnetic Properties of Porous Coordination Polymers

Reported cases of the influence of guest molecules absorption/desorption on magnetic properties of porous co- ordination polymers (PCP) of transition metals are reviewed. Interaction of PCPs with guest molecules can modify mag- netic susceptibility in wide temperature range, as well as can lead to change of the magnetic ordering or spin-crossover temperature and other magnetic characteristics. The reasons of such influence can be divided into several groups - guest molecule coordination to metal ion or decoordination; formation or cleavage of bonds in the group, which transmits ex- change interactions between metal ions; or change of bond lengths or angles in coordination polymer because of crystal lattice adaptation to the guest molecule.

Synthesis, structure, and properties of trinuclear pivalate {Zn2Eu} complexes with N-donor ligands

New luminescent heterometallic complexes of Eu3+ and Zn2+ were synthesized: Zn2Eu(NO3)(Piv)6(L)2 (Piv is pivalate anion, L = MeCN (1), 2,3-lutidine (2), 2,2′-bpy (3)) and [Zn2(Piv)3(2,2′-bpy)2][ZnEu(NO3)3(Piv)3(2,2′-bpy)] (4). In the case of 2,2′-bpy, the order of mixing of the reagents ([Zn(Piv)2]n, Eu(NO3)3·6H2O, and 2,2′-bpy) affects the composition of the final reaction product: the reaction of [Zn(Piv)2]n and Eu(NO3)3·6H2O (in the ratio Zn : Eu = 3 : 1) in MeCN affords complex 1 and the subsequent addition of 2,2′-bpy (Zn : L = 1 : 1) affords complex 3. Complex 4 is formed in the reaction of [Zn(Piv)2]n and 2,2′-bpy (Zn : L = 1 : 1) in MeCN followed by the addition of Eu(NO3)3·6H2O (Zn : Eu = 3 : 1). The luminescence spectra of compounds 1–4 (Zn : Eu = 3 : 1) exhibit metal-centered luminescence of Eu3+. The most efficient ligand-antenna is 2,2′-bpy, which is due to the optimum position of the triplet level of this ligand.

Polymeric heterometallic CuII dimethylmalonate complexes with potassium and cadmium ions

A reaction of (HPiv)2Cu2(Piv)4 with dimethylmalonic acid dipotassium salt (K2Me2mal) leads to the formation of a cage coordination polymer {(μ-H2O)6K8[(μ-H2O)Cu-(μ3,κ2-Me2mal)(μ6,κ2-Me2mal)]2[Cu2(μ5,κ2-Me2mal)2(μ5,κ2-Me2mal)2]}n (1). It was found that when 1 reacted with CdSO4·8H2O in a mixture of EtOH-H2O (3: 1), the potassium ions in 1 were displaced with cadmium(ii) ions with the formation of a heterometallic 1D-polymer [(κ1-H2O)4CdCu(μ,κ2-Me2mal)2]n (2). Compounds 1 and 2 were characterized by X-ray crystallography and ESR spectroscopy.

Synthesis, structure, physicochemical properties, and solid-phase thermolysis of Co2Sm(Piv)7(2,4-Lut)2

Heterometallic pivalate Co2Sm(Piv)7(2,4-Lut)2 (1) was prepared for the first time and structurally characterized at 293 and 160 K. Antiferromagnetic exchange interactions are dominant in complex 1. This compound experiences a first-order phase transition within 210–260 K. A set of thermodynamic functions was obtained for this complex (Cp, HT0 - H1800, and ST0), and parameters were determined for solid-phase thermolysis where samarium cobaltate SmCoO3 is the only product.

Synthesis, structure, electrochemical and magnetic properties of 2,6-bis(5-trifluoromethylpyrazol-3-yl)pyridine and its NiII complexes

Abstract2,6-Bis(5-trifluoromethylpyrazol-3-yl)pyridine (H2L) and its mono-, tri-, and tetranuclear NiII complexes were synthesized for the first time. All the obtained compounds were characterized by single-crystal X-ray diffraction analysis. In the complexes, 2,6-bis(5-trifluoromethylpyrazol-3-yl)pyridine exists in the neutral and dianionic forms and exhibits different coordination modes (κ3-, μ2-κ3:κ1-, and μ3-κ3:κ1:κ1). The electrochemical and magnetic properties of all compounds were studied. The tetranuclear NiII complex with the L2− dianion is reduced in two sequential reversible one-electron steps.

Unusual structure of new dimethylmalonate coordination polymer with strontium atoms and VO2+ fragments

A reaction of vanadyl sulfate VOSO4·3H2O with dimethylmalonic acid strontium salt led to the coordination polymer {Sr(H2O)8[VO(Me2mal)2]}n (1, Me2mal is the dimethylmalonic acid dianion), in which the carboxylate dianions did not form chelate metallocycles with the vanadyl ions. The complex was studied by ESR spectroscopy. The compound 1 exhibited weak spin-spin exchange interactions of ferromagnetic type between the VIV atoms.