A rare isostructural series of 3d-4f cyanido-bridged heterometallic squares obtained by assembling [FeIII{HB(pz)3}(CN)3]- and LnIII ions: synthesis, X-ray structure and cryomagnetic study

A new series of cyanido-bridged {Fe^IIILn^III}₂ neutral molecular squares of general formula [Fe{HB(pz)₃}(CN)(μ-CN)₂Ln(NO₃)₂(pyim)(Ph₃PO)]₂·2CH₃CN [Ln = Ce (1), Pr (2), Nd (3), Gd (4), Tb (5), Dy (6) and Er (7); {HB(pz)₃}^- = hydrotris(pyrazolyl)borate, pyim = 2-(1H-imidazol-2-yl)pyridine and Ph₃PO = triphenylphosphine oxide] were obtained by reacting the low-spin [Fe{HB(pz)₃}(CN)₃]^- species with the preformed [Ln^III(pyim)(NO₃)₂(pyim)(Ph₃PO)]⁺ complex anions (generated in situ by mixing the nitrate salt of each Ln(III) ion with pyim and Ph₃PO molecules). Single-crystal X-ray diffraction studies show that 1-7 are isostructural compounds that crystallize in the triclinic P1̄ space group. Their crystal structures consist of centrosymmetric cyanido-bridged {Fe^IIILn^III}₂ molecular squares where two [Fe{HB(pz)₃}(CN)₃]^- units adopt bis-monodentate coordination modes towards two [Ln^III(pyim)(NO₃)₂(pyim)(Ph₃PO)]⁺ moieties. The cis-oriented convergent sites from both low-spin Fe^III and Ln^III fragments form a quasi square-shaped molecule in which the 3d and 4f ions alternatively occupy the corners of the square. Both Fe^III ions show a distorted octahedral surrounding (C_3v symmetry), whereas the Ln^III ions exhibit a distorted muffin-like geometry (C_s symmetry) in 1-7. The intramolecular Fe^III⋯Ln^III distances across the two cyanido-bridges range from ca. 5.48/5.46 up to ca. 5.58/5.61 Å. The molecular squares in 1-7 are interlinked through hydrogen bonds, weak π⋯π stacking and very weak C-H⋯π type interactions into three-dimensional supramolecular networks. The analysis of the solid-state direct-current (dc) magnetic susceptibility data of 1-7 in the temperature range 1.9-300 K reveals the occurrence of weak intra- and intermolecular antiferromagnetic interactions. The small intramolecular antiferromagnetic couplings in 4 compare well with those previously reported for parent systems. Although the coexistence of the spin-orbit coupling (SOC) of the low-spin iron(III) and lanthanide(III) ions in the remaining compounds together with the ligand field effects mask the visualization and make difficult the evaluation of the possible magnetic interactions in them, we were able to do it through a SOC model applied on exact or effective Hamiltonians. Frequency-dependent alternating current magnetic susceptibility signals in the temperature range 2.0-9.0 K under zero and non-zero static fields were observed for 5-7 which indicate slow magnetic relaxation (SMM) behavior. The usual absence of χ''_M maxima moved us to estimate their energy barriers through ln(χ''_M/ χ'_M) vs. 1/T plots, obtaining values from 25 to 40 cm^-1.

Slow Magnetic Relaxation, Antiferromagnetic Ordering, and Metamagnetism in MnII (H2 dapsc)-FeIII (CN)6 Chain Complex with Highly Anisotropic Fe-CN-Mn Spin Coupling

Reactions of [Mn(H₂ dapsc)Cl₂ ]⋅H₂ O (dapsc=2,6- diacetylpyridine bis(semicarbazone)) with K₃ [Fe(CN)₆ ] and (PPh₄ )₃ [Fe(CN)₆ ] lead to the formation of the chain polymeric complex {[Mn(H₂ dapsc)][Fe(CN)₆ ][K(H₂ O)_3.5 ]}_n ⋅1.5n H₂ O (1) and the discrete pentanuclear complex {[Mn(H₂ dapsc)]₃ [Fe(CN)₆ ]₂ (H₂ O)₂ }⋅4 CH₃ OH⋅3.4 H₂ O (2), respectively. In the crystal structure of 1 the high-spin [Mn^II (H₂ dapsc)]²⁺ cations and low-spin hexacyanoferrate(III) anions are assembled into alternating heterometallic cyano-bridged chains. The K⁺ ions are located between the chains and are coordinated by oxygen atoms of the H₂ dapsc ligand and water molecules. The magnetic structure of 1 is built from ferrimagnetic chains, which are antiferromagnetically coupled. The complex exhibits metamagnetism and frequency-dependent ac magnetic susceptibility, indicating single-chain magnetic behavior with a Mydosh-parameter φ=0.12 and an effective energy barrier (U_eff /k_B ) of 36.0 K with τ₀ =2.34×10^-11  s for the spin relaxation. Detailed theoretical analysis showed highly anisotropic intra-chain spin coupling between [Fe^III (CN)₆ ]^3- and [Mn^II (H₂ dapsc)]²⁺ units resulting from orbital degeneracy and unquenched orbital momentum of [Fe^III (CN)₆ ]^3- complexes. The origin of the metamagnetic transition is discussed in terms of strong magnetic anisotropy and weak AF interchain spin coupling.

A novel octacyanido dicobalt(iii) building block for the construction of heterometallic compounds

The first bimetallic 3d cyanido-bearing complex with 2,5-dpp as a bridge, (Ph₄P)₂[Co₂^III(μ-2,5-dpp)(CN)₈]·2H₂O, is obtained and used as a metalloligand with the [Mn(MAC)(H₂O)₂]²⁺ cation to build a {Co^IIIMn^II} heterobimetallic chain.

Syntheses, structures and magnetic properties of cyano-bridged one-dimensional Ln3+–Fe3+ (Ln = La, Dy, Ho and Yb) coordination polymers

Four new heterometallic one-dimensional coordination polymers with formulae trans-[La(o-phen)₃(H₂O)(μ-CN)₂Fe(CN)₄]·7H₂O (1) and trans-[Ln(H₂O)₂(phen)₂(μ-CN)₂Fe(CN)₄]·nH₂O [Ln/n = Dy/8 (2), Ho/7 (3) and Yb/7 (4), (o-phen = 1,10-phenanthroline)] have been synthesized.

Structural and magnetic properties of heptacoordinated MnII complexes containing a 15-membered pyridine-based macrocycle and halido/pseudohalido axial coligands

Heptacoordinated Mn^II compounds with a pentadentate 15-membered pyridine-based macrocycle and two axially coordinated halido/pseudohalido coligands, having a monomeric or polymeric composition, were investigated.

Synthesis, crystal structure and magnetic characterization of a cyanide-bridged Mo–Ni nanosized molecular wheel

By using K4[Mo(CN)8] and [Ni(L)(H2O)2][ClO4]2 as reagents (L = 2,12-dimethyl-3,7,11,17-tetraazabicyclo [11.3.1]heptadeca-1(17),13,15-triene), a new cyanide-bridged Mo–Ni complex containing the building blocks [Ni(H2O)(L)]2+ and [Ni(L)]2+ bridged by [Mo(CN)8]4− units has been obtained. The complex with the formula {[Ni(H2O)(L)][Ni(L)][Mo(CN)8]}6 · 36H2O · 2CH3OH (1) was characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction. The structure determination reveals an octadecanuclear cluster in the form of a 36-membered macrocycle, in which the largest intramolecular W···W and Ni···Ni distances are 16.5 and 14.4 Å, respectively, indicating that complex 1 is a nanosized molecular wheel. Investigation of its magnetic properties has shown weak antiferromagnetic coupling between the adjacent Ni(II) ions bridged by the diamagnetic [Mo(CN)8]4− ions.

Magneto-structural variety of new 3d–4f–4(5)d heterotrimetallic complexes

Three families of heterotrimetallic chains with different topologies, have been obtained by reacting Schiff-base bicompartmental [Cu^II(L¹)] complexes and lanthanide(iii) salts, with (NHBu₃)₃[M(CN)₈] (M = Mo^V, W^V).

{CoIIIMnIII}ncorrugated chains based on heteroleptic cyanido metalloligands

The use of cyanide-bearing complexes affords one-dimensional coordination polymers with the formulas {[Mn^III(salen)(μ-NC)₂Co^III(4,4-dmbipy)(CN)₂]·H₂O}_n(1) and {[Mn^III(salen)(μ-NC)₂Co^III(dmphen)(CN)₂]}_n(2) .

Syntheses, structures, and magnetic properties of three new cyano-bridged complexes based on the [Mn(CN)6]3−building block

By tuning the reaction conditions and using macrocyclic ligands, three [Mn(CN)₆]³⁻-based magnetic complexes were prepared and characterized.

Synthesis of a novel heptacoordinated Fe(III) dinuclear complex: experimental and theoretical study of the magnetic properties

A new functionalized bis-pyrazol-pyridine ligand has been prepared by reaction with hydrazine of the corresponding bis-β-diketone precursor, also unprecedented. The aerobic reaction of this ligand with ferrous thiocyanate in the presence of ascorbic or oxalic acid affords the dinuclear complex of seven-coordinate Fe(III), [Fe₂(H₄L2)₂(ox)(NCS)₄] (1), as revealed by single crystal X-ray diffraction. This may represent an entry into a new family of [Fe₂] compounds with heptacoordinate metal centres. The capacity of this unusual chromophore to undergo magnetic super-exchange was investigated by means of bulk magnetization and DFT calculations. Both approaches confirmed the presence of antiferromagnetic interactions within the molecule. The theoretical investigation has served to describe the magnetic orbitals of Fe(III) in this unusual coordination geometry, as well as the exchange mechanism. A brief review of the scarce number of iron heptacoordinate complexes reported in the literature is also included and discussed.

New cyanide-bridged Mn(III)-M(III) heterometallic dinuclear complexes constructed from [M(III)(AA)(CN)4]- building blocks (M = Cr and Fe): synthesis, crystal structures and magnetic properties

Three Mn(III)-M(III) (M = Cr and Fe) dinuclear complexes have been obtained by assembling [Mn(III)(SB)(H(2)O)](+) and [M(III)(AA)(CN)(4)](-) ions, where SB is the dianion of the Schiff-base resulting from the condensation of 3-methoxysalicylaldehyde with ethylenediamine (3-MeOsalen(2-)) or 1,2-cyclohexanediamine (3-MeOsalcyen(2-)): [Mn(3-MeOsalen)(H(2)O)(µ-NC)Cr(bipy)(CN)(3)]·2H(2)O (1), [Mn(3-MeOsalen)(H(2)O)(µ-NC)Cr(ampy)(CN)(3)][Mn(3-MeOsalen)(H(2)O)(2)]ClO(4)·2H(2)O (2) and [Mn(3-MeOsalcyen)(H(2)O)(µ-NC)Fe(bpym)(CN)(3)]·3H(2)O (3) (bipy = 2,2'-bipyridine, ampy = 2-aminomethylpyridine and bpym = 2,2'-bipyrimidine). The [M(AA)(CN)(4)](-) unit in 1-3 acts as a monodentate ligand towards the manganese(III) ion through one of its four cyanide groups. The manganese(III) ion in 1-3 exhibits an elongated octahedral stereochemistry with the tetradentate SB building the equatorial plane and a water molecule and a cyanide-nitrogen atom filling the axial positions. Remarkably, the neutral mononuclear complex [Mn(3-MeOsalen)(H(2)O)(2)]ClO(4) co-crystallizes with the heterobimetallic unit in 2. The values of the Mn(III)-M(III) distance across the bridging cyanide are 5.228 (1), 5.505 (2) and 5.265 Å (3). The packing of the neutral heterobimetallic units in the crystal is governed by the self-complementarity of the [Mn(SB)(H(2)O)](+) moieties, which interact each other through hydrogen bonds established between the aqua ligand from one fragment with the set of phenolate- and methoxy-oxygens from the adjacent one. The magnetic properties of the three complexes have been investigated in the temperature range 1.9-300 K. Weak antiferromagnetic interactions between the Mn(III) and M(III) ions across the cyanido bridge were found: J(MnM) = -5.6 (1), -0.63 (2) and -2.4 cm(-1) (3) the Hamiltonian being defined as H = -JS(Mn)·S(M). Theoretical calculations based on density functional theory (DFT) have been used to substantiate both the nature and magnitude of the exchange interactions observed and also to analyze the dependence of the magnetic coupling on the structural parameters within the Mn(III)-N-C-M(III) motif in 1-3.

Self-assembly of the unique heterotrimetallic Cu/Co/M complexes possessing triangular antiferromagnetic {Cu2CoPb}2and linear ferromagnetic {Cu2CoCd2} cores

Two novel heterotrimetallic octa-[Cu2CoPbCl4(L)4]2 (1) and pentanuclear [Cu2CoCd2Cl6(L)4(HOMe)2] (2) complexes have been prepared in one-pot reactions of zerovalent copper with metal chlorides in a methanol (for 1) or acetonitrile (for 2) solution of 2-(dimethylamino)ethanol (HL) in open air. The crystal structures of both compounds consist of discrete centrosymmetric heterotrimetallic molecules revealing triangular (1) and unique consecutive (2) arrangements of magnetic CuII(2)CoII cores. The complex 1 can be viewed as a dimer made up of tetranuclear Cu2CoPbCl4(L)4 units linked through the two micro(2)-Cl atoms. The molecular structure of 2 is a pentanuclear assembly containing the previously unknown Cu(micro-O)(2)Co(micro-O)(2)Cu core. The magnetic studies of 1 revealed an antiferromagnetic coupling (J(CoCu) = 37 cm(-1) and J(CuCu) = 87 cm(-1)) while 2 exhibits a weak ferromagnetic behavior (J(CoCu) = -3.2 cm(-1) and J(CuCu) = -14.2 cm(-1)). The correlations between magnetic behaviour and structures as well as synthetic features are also discussed.