Konstantin S. Gavrilenko

Delicate Crystal Structure Changes Govern the Magnetic Properties of 1D Coordination Polymers Based on 3d Metal Carboxylates

Homo- and heterometallic 1D coordination polymers of transition metals (Co II, Mn II, Zn II) have been synthesized by an in-situ ligand generation route. Carboxylato-based complexes [Co(PhCOO)2]n (1 a, 1 b), [Co(p-MePhCOO)2]n (2), [ZnMn(PhCOO)4]n (3), and [CoZn(PhCOO)4]n (4) (PhCOOH=benzoic acid, p-MePhCOOH=p-methylbenzoic acid) have been characterized by chemical analysis, single-crystal X-ray diffraction, and magnetization measurements. The new complexes 2 and 3 crystallize in orthorhombic space groups Pnab and Pcab respectively. Their crystal structures consist of zigzag chains, with alternating M(II) centers in octahedral and tetrahedral positions, which are similar to those of 1 a and 1 b. Compound 4 crystallizes in monoclinic space group P2 1/c and comprises zigzag chains of M II ions in a tetrahedral coordination environment. Magnetic investigations reveal the existence of antiferromagnetic interactions between magnetic centers in the heterometallic complexes 3 and 4, while ferromagnetic interactions operate in homometallic compounds (1 a, 1 b, and 2). Compound 1 b orders ferromagnetically at TC=3.7 K whereas 1 a does not show any magnetic ordering down to 330 mK and displays typical single-chain magnet (SCM) behavior with slowing down of magnetization relaxation below 0.6 K. Single-crystal measurements reveal that the system is easily magnetized in the chain direction for 1 a whereas the chain direction coincides with the hard magnetic axis in 1 b. Despite important similarities, small differences in the molecular and crystal structures of these two compounds lead to this dramatic change in properties.

A new approach towards ferromagnetic conducting materials based on TTF-containing polynuclear complexes

Five complexes containing binuclear cation [Cu2(LH)2]2+ (LH2 = 1 : 2 Schiff base of 1,3-diaminobenzene and butanedione monoxime) were prepared and characterized. Metathesis of one perchlorate anion in [Cu2(LH)2(H2O)2](ClO4)2 (1) by anionic TTF-carboxylate (TTF–CO2−) leads to the complex [Cu2(LH)2(CH3OH)2](TTF–CO2)(ClO4)·H2O (2). Reactions of 1 with substituted pyridines bipy, dpe and TTF–CH = CH–py result in formation of the complexes {[Cu2(LH)2(bipy)](ClO4)2}n·2nH2O (3), [Cu2(LH)2(dpe)2](ClO4)2·2CH3OH (4) and [Cu2(LH)2(TTF–CH = CH–py)(H2O)](ClO4)2·1.5H2O (5), where bipy = 4,4′-bipyridine, dpe = trans-(4-pyridyl)-1,2-ethylene and TTF–CH = CH–py = 1-(2-tetrathiafulvalenyl)-2-(4-pyridyl)ethylene. Whereas complex 2 is built from discrete ionic particles (with rather long Cu–S contacts), compounds 1 and 3 contain 1D polymeric chains, in which structural units are bonded through Cu–O bonds or through bridging bipy molecule, respectively. Dinuclear complexes 4 and 5 are linked though π-stacking of dpe or TTF–CH = CH–py, respectively. All complexes are characterized by dominating ferromagnetic behavior with J values in the range from +9.92(8) cm−1 to +13.4(2) cm−1 for Hamiltonian H = –JS1S2. Magnetic properties of the compounds, containing stacks of aromatic molecules in crystal structures (4 and 5), correspond to ferromagnetic intradimer and antiferromagnetic intermolecular interactions (zJ′ = −0.158(3) and −0.290(2) cm−1, respectively). It was found that TTF–CH = CH–py ligand in [Cu2(LH)2(TTF–CH = CH–py)(H2O)]2+ could be electrochemically oxidized to cation-radical form in the solution.

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.

Synthesis, magnetochemistry, and spectroscopy of heterometallic trinuclear basic trifluoroacetates [Fe2M(μ3-O)(CF3COO)6 (H2O)3]·H2O (M = Mn, Co, Ni)

Three new µ3-oxo(trifluoroacetato) complexes [FeIII2MII(μ3-O)(CF3COO)6(H2O)3]·H2O [M = Mn (1), Co (2), Ni (3)] have been prepared. Compounds 1 and 2 crystallize in the monoclinic space groups C2/c [a = 22.002(5), b = 13.647(3), c = 24.767(4) A, β = 98.23(3)°] and C2/m [a = 21.426(4), b = 15.100(2), c = 14.815(3) A, β = 117.99(2)°], respectively. The coordination spheres of the metal ions are essentially octahedral, with the Fe−O distances [1.870(5) A] falling in the usual range for these systems. Magnetochemical studies reveal the presence of antiferromagnetic exchange in the isosceles triangular skeletons of the polynuclear species. Application of the isotropic spin Hamiltonian H = −2JFeM[SFe1SM + SMSFe2] − 2JFeFe[SFe1SFe2] gives the fitting parameters: gFe = gMn = 2.00, JFe-Fe = −56.50(7) and JFe-Mn = −16.23(4) cm−1 (1), gmol = 2.09(1), JFe-Fe = −42.8(3.5) cm−1, JFe-Co = −17.8(1.4) cm−1 (2) and gFe = 2.00, gNi = 2.215(2), JFe-Fe = −45.60(1) and JFe-Ni = −16.96(2) cm−1 (3). A Mossbauer investigation confirms that no electron transfer from MnII or CoII to FeIII occurs during the syntheses of these complexes. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)