MII Ions Research Articles

Magnetocaloric Effect of Two Isostructural Heterometallic Organic Frameworks Based on {MII GdIII 2 } Clusters (MII =Mn, Ni).

Two isostructural heterometallic coordination polymers (HCPs) based on {MII GdIII 2 } clusters (MII =Mn and Ni) have been obtained from the conventional one-pot self-assembly of GdIII ions and H4 abtc ligands (H4 abtc=3,3',5,5'-azobenzenetetracarboxylic acid) with corresponding transition-metal ions in mixed N,N-dimethylformamide (DMF)/H2 O solvents. The formulas are expressed as {[NH2 (CH3 )2 ]2 [MII GdIII 2 (HCOO)2 (abtc)2 ]}n (MII =Mn for 1 and Ni for 2). The common features of both HCPs are that two GdIII ions and one MII ion interconnected through abtc4- ligands present "hourglass"-type {MII GdIII 2 } clusters, which are further linked by HCOO- and abtc4- ligands to produce 3D (4,4,10)-connected topological frameworks. Magnetic results reveal that both 1 and 2 possess remarkable magnetocaloric effects (MCE) with maximum -ΔSm values of 31.9 and 29.5 J kg-1 K-1 at 3.0 K for an applied field of 70 kOe, respectively. Furthermore, the skeletons of two HCPs were stable up to at least 310 °C as supported by thermogravimetric (TG) analyses and in situ variable-temperature powder X-ray diffraction (PXRD) patterns.

Tetranuclear Complexes with {M4O4} (M = CoII, NiII) Cubane‐Like Core: Synthesis, Crystal Structure, and Magnetic Properties

AbstractTwo tetranuclear clusters of formula [M4L4(HOMe)4] {H2L = (E)‐1‐[(2‐(hydroxymethyl)phenylimino)methyl]naphthalen‐2‐ol} [M = Co (1), Ni (2)] were hydrothermally synthesized by reaction of M(OAc)2·4H2O with H2L and NaOH in MeOH. X‐ray crystal structure analysis revealed that complexes 1 and 2 are isostructural. In the core of the structures, four MII ions and four oxygen atoms occupied alternate vertices of [M4O4] cubane. The magnetic property measurements of 1 and 2 revealed that overall ferromagnetic MII···MII exchange interactions exist in both complexes.

Theoretical insights into the origin of magnetic exchange and magnetic anisotropy in {Re(IV)-M(II)} (M = Mn, Fe, Co, Ni and Cu) single chain magnets.

Density functional calculations have been performed on a series of {Re(IV)-M(II)} (M = Mn(), Fe(), Co(), Ni(), Cu()) complexes to compute the magnetic exchange interaction between the Re(IV) and M(II) ions, and understand the mechanism of magnetic coupling in this series. DFT calculations yield J values of -5.54 cm(-1), +0.44 cm(-1), +10.5 cm(-1), +4.54 cm(-1) and +19 cm(-1) for complexes respectively, and these estimates are in general agreement with the experimental reports. Using molecular orbital (MO) and overlap integral analysis, we have established a mechanism of coupling for a {3d-5d} pair and the proposed mechanism rationalises both the sign and the magnitude of J values observed in this series. Our proposed mechanism of coupling has five contributing factors: (i) (Re)dyz-dyz(3d) overlap, (ii) (Re)dxz-dxz(3d) overlap, (iii) (Re)dxy-dxy(3d) overlap, (iv) (Re)eg-t2g(3d) overlaps and (v) (Re)eg-eg(3d) overlaps. Here, the first two terms are found to contribute to the antiferromagnetic part of the exchange, while the other three contribute to the ferromagnetic part. The last two terms correspond to the cross-interactions and also contribute to the ferromagnetic part of the exchange. A record high ferromagnetic J value observed for the {Re(IV)-Cu(II)} pair in complex is found to be due to a significant cross interaction between the dz(2) orbital of the Re(IV) ion and the dx(2)-y(2) orbital of the Cu(ii) ion. Magneto-structural correlations are developed for Re-C and M-N bond lengths and Re-C-N and M-N-C bond angles. Among the developed correlations, the M-N-C bond angle is found to be the most sensitive parameter which influences the sign and strength of J values in this series. The J values are found to be more positive (or less negative) as the angle increases, indicating stronger ferromagnetic coupling at linear M-N-C angles. Apart from the magnetic exchange interaction, we have also estimated the magnetic anisotropy of [ReCl4(CN)2](2-) and [(DMF)4(CN)M(II)(CN)] (M(II)-Fe(II), Co(II) and Ni(II)) units using the state-of-the-art ab initio CASSCF/PT2/RASSI-SO/SINGLE_ANISO approach. The calculated D and E values for these building units are found to be in agreement with the available experimental results. Particularly a large positive D computed for the [ReCl4(CN)2](2-) unit was found to arise from dxz/dyz → dxy excitations corresponding to the low-lying doublet states. Similarly, a very large positive D value computed for Fe(II) and Co(II) units are also rationalised based on the corresponding ground state electronic configurations computed. The non-collinearity of the Re(IV) ion and the M(II) ion axial anisotropy (DZZ) axis are found to diminish the anisotropy of the building unit, leading to the observation of moderate relaxation barriers for these molecules.

Syntheses, crystal structures and magnetic properties of two heterometallic cyanide-bridged [MII2MnII2] (M = Fe and Os) square complexes

Two tetra-nuclear cyanide-bridged square complexes [cis-Fe(bpy)2(CN)2Mn(L)]2[PF6]4 (1) and [cis-Os(bpy)2(CN)2Mn(L)]2[PF6]2[ClO4]2 (2) (bpy=2,2′-bipyridine, L=1,6-diphenyl-2,5-bis(2-methylpyridyl)-2,5-diazahexane) were synthesized and fully characterized. The tetra-nuclear [cis-M(bpy)2(CN)2Mn(L)]24+ (M=Fe (1), Os (2)) cation is composed of two [M(bpy)2(CN)2] and two [Mn(L)]2+ centers. Each MII ion adopts a distorted [MN4C2] octahedral coordination, surrounded by four nitrogen atoms from two bpy ligands and two carbon atoms from the cyanide groups in a cis position. Each Mn2+ ion adopts a distorted [MnN6] octahedral coordination, occupied by four nitrogen atoms from L and two nitrogen atoms from the cyanide groups in a cis position. The magnetic susceptibilities measurements indicate 1 is weak ferromagnetic, and 2 is weak antiferromagnetic.

Synthesis of homo- and heterobimetallic NiII–MII (M = Fe, Co, Ni, Zn) complexes based on an unsymmetric ligand framework: Structures, spectroscopic features, and redox properties

Several homo- and heterobimetallic NiII–MII complexes (MII=Fe, Co, Ni, Zn) supported by an unsymmetric polydentate ligand (L13−) are reported (L13− is the trianion of 2-[bis(2-hydroxy-3,5-tert-butylphenyl)aminomethyl]-4-methyl-6-[(2-pyridylmethyl)iminomethyl]phenol). The L13− chelate provides two distinct coordination environments: a planar tridentate {N2O} site (A) and a tetradentate {NO3} site (B). Reaction of L13− with equimolar amounts of NiII and MII salts provides bimetallic complexes in which the NiII ion exclusively occupies the tetragonal A-site and the MII ion is found in the tripodal B-site. X-ray crystal structures revealed that the two metal centers are bridged by the central phenolate donor of L13− and an anionic X-ligand, where X=μ-1,1-acetate, hydroxide, or methoxide. The metal ions are separated by 3.0–3.1Å in the MAMBX structures, where MA and MB indicate the ion located in the A and B sites, respectively, and X represents the second bridging ligand. Analysis of magnetic data and UV–Vis–NIR spectra indicate that, in all cases, the two metal ions adopt high-spin states in solution. The NiAII centers undergo one-electron reduction at −1.17 V vs. SCE, while the NiII and CoII ions in the phenolate-rich B-site are reduced at lower potentials. Significantly, the NiAII center possesses three open or labile coordination sites in a meridional geometry, which are generally occupied by solvent-derived ligands in the crystal structures. The NiMBX complexes serve as structural mimics of heterometallic Ni-containing sites in biology, such as the C-cluster of carbon monoxide dehydrogenase (CODH).

Structural Rearrangement Through Lanthanide Contraction in Dinuclear Complexes

A new series of lanthanide complexes was synthesized, and the geometry and preliminary magnetic measurements of the complexes were explored. The specific ligand used (N'-(2-hydroxy-3-methoxybenzylidene)benzhydrazide) (H2hmb) was synthesized using a Schiff-base approach and was employed due to the presence of a coordination pocket that is able to accommodate magnetically selective lanthanide ions. The series can be divided into two groups that are categorized by a drastic structural rearrangement. The first group, Type I, contains six analogous complexes with the formula [M(III)2(Hhmb)3(NCS)3]·2MeOH·py (M = Y 1, Eu 2, Gd 3, Tb 4, Dy 5, Ho 6), while the second group, Type II, contains two dinuclear complexes with formula [M(III)2(Hhmb)2(NCS)4(MeOH)2] (M = Er 7, and Yb 8). Single-crystal X-ray analysis revealed that all M(III) ions in Type I exhibit monocapped distorted square antiprismatic geometries, while those of Type II exhibit distorted dodecahedron geometry. The direct current and alternating current magnetic measurements were carried out on all complexes, with 5, 7, and 8 exhibiting slow relaxation of the magnetization under an applied optimum dc field. Furthermore, complex 8 is the first example of a dinuclear Yb-based single-molecule magnet showing field-dependent multiple relaxation processes.

Heterodinuclear M(II)-Ln(III) single molecule magnets constructed from exchange-coupled single ion magnets.

The synthesis and characterization of four dinuclear 3d-4f complexes [M(II)Ln(III)(L)(DBM)3] (ZnDy = 1, CoY = 2, CoDy = 3·3.5CH3CN, CoGd = 4·3.5CH3CN) are reported (H2L = N,N'-dimethyl-N,N'-(2-hydroxy-3-methoxy-5-methyl-benzyl)ethylenediamine, DBM(-) = anion of 1,3-diphenyl-propane-1,3-dione). In each of the four complexes, the M(II) ion occupies the internal N2O2 site whereas the Ln(III) ion occupies the external O4 site. There are diphenoxo bridges between the M(II) and Ln(III) ions in these complexes. The remaining coordination sites are occupied by three DBM(-) anions. Direct current (dc) magnetic susceptibility measurements indicate the presence of intramolecular ferromagnetic interactions in complexes 3 and 4. The magnetic coupling constant, JCoGd, of complex 4 is estimated to be 0.26 cm(-1) (H = -2JCoGdSCoSGd). Alternating current (ac) magnetic susceptibility studies reveal that complexes 1 and 2 show field-induced single molecule magnet behavior, with ΔE values of 36.5 K and 8.56 K, respectively. Complex 3 shows frequency dependent out-of-phase signals, indicating the presence of a slow relaxation of the magnetization, whereas complex 4 does not display slow magnetization relaxation.

Four new metal–organic coordination polymers with non-coordinating biphenyl groups: Synthesis, characterization, magnetic and luminescent properties

Four new coordination polymers, namely [Mn(L)2(H2O)2]∞ (1), [Co(L)2(H2O)2]∞ (2), [Zn(L)2(H2O)2]∞ (3) and [Cd(L)2(H2O)2]∞ (4) (L=biphenyl-4-carboxylate), were synthesized and structurally characterized by elemental analyses, IR spectra, X-ray powder diffraction and single crystal X-ray diffraction analysis. Structural analyses show that 1–4 all assume isostructural two-dimensional (2D) 44 networks. The results indicate that non-coordinating biphenyl groups of ligands play an important role in governing the formation of the final frameworks. There exist antiferromagnetic coupling interactions between the MII ions in 1 as well as in 2. Moreover, intense luminescent emissions of 3 and 4 were attributed to the ligand-to-ligand charge transfer (LLCT).

LiFe1−xMIIxPO4/C (MII = Co, Ni, Mg) as cathode materials for lithium-ion batteries

LiFe1−xMIIxPO4/C (MII=Co, Ni, Mg) composites had been obtained by sol–gel method. Structure and morphology of the obtained materials have been studied with the use of the XRD-analysis, SEM and Mössbauer spectroscopy. Their electrochemical behavior has been investigated with the use of charge/discharge tests. The materials doped by cobalt and nickel were shown to be characterized by an increased lithium intercalation and deintercalation rates, and retain a high capacity during charge and discharge the battery at high currents densities (LiFe0.9Ni0.1PO4 capacity amounts to 145 and 62mAh/g at a discharge current 50 and 3000mA/g). Mg2+ incorporation into LiFePO4/C cathode material results in the slight increase of charge/discharge rate and significant capacity decrease. Mössbauer spectroscopy has shown that MII ions in the LiFe1−xMIIxPO4/C (MII=Co, Ni) materials are orderly distributed both in charged and discharged states, each iron ion has no more than one MII ion in the nearest environment. In the case of Ni-doped samples the ordering is less pronounced. The reasons of the changes observed in the electrochemical performances and charge/discharge rate have been discussed on the base of Mössbauer spectroscopy and XRD data.

Two isostructural 3D metal–organic frameworks constructed from 1D [H2Mo4O14]n2n− chains and the flexible bis-pyridyl-bis-amide ligand

Abstract Two new isostructural metal–organic frameworks based on 1D [H2Mo4O14]n2n − chains and the flexible N,N′-bis(3-pyridinecarboxamide)-1,2-ethane (L), [M(L)(H2Mo4O14)(H2O)2] (M = CoII for 1, NiII for 2), have been hydrothermally synthesized and characterized by single crystal X-ray diffraction. In the title complexes, the unusual 1D [H2Mo4O14]n2n − chains are linked by the MII ions to form a 2D inorganic bimetallic layer. The adjacent 2D layers are further connected by the L ligands to construct a 3D framework with CdSO4 topology. The electrochemical behaviors and the photocatalytic activities of the title complexes have been investigated.

Structural and magnetic properties of four layered dicyanamide-based coordination polymers: M{N(CN)2}2(DMSO)2, [M = Mn, Fe, Co, Ni

The crystal structures and magnetic properties of four μ-(1,5) singly bridging dicyanamide complexes, specifically Mn{N(CN)2}2(DMSO)2 (1), Fe{N(CN)2}2(DMSO)2 (2), Co{N(CN)2}2(DMSO)2 (3), and Ni{N(CN)2}2(DMSO)2 (4), (DMSO=dimethyl sulfoxide) are presented. The compounds are isostructural, in which the MII ions adopt a distorted octahedral geometry, coordinating to four nitrile N atoms of the dicyanamide ligand and to the two DMSO molecules, giving rise to (4,4) pseudo-2D square grid sheets. Magnetic interactions in these materials are via the five atom dicyanamide bridge [NCNCN], which is known to propagate weak magnetic exchange, and the complexes do not undergo long-range ordering down to 2K. Single crystal X-ray diffraction, FTIR spectroscopy, CHN analyses, and SQUID magnetometry were used to characterize these materials.

Examples of Heterometallic 3d–3d Azido Complexes by One‐Pot Synthesis

AbstractThe assembly of CuII, MII (CoII or NiII), azido, and isonicotinate acid N‐oxide under hydrothermal conditions straightforwardly gives two isomorphic heterometallic 3d–3d azido complexes formulated [Cu2M(N3)4(INO)2(H2O)4]∞ (INO = isonicotinate N‐oxide; M = Co for 1 and Ni for 2). In the structure of the complexes, CuII ions have a trigonal‐bipyramidal‐coordinated configuration, whereas the MII ions have octahedral geometry with two water molecules in the apical positions. The structure of the complexes is based on azido‐carboxylate mixed‐coordination Cu–M–Cu trimers, which are further linked by double end‐on (EO) azido anions through the CuII ions to form a chain structure, and the 1D structure can be described as EO azido/syn–syn carboxylates and double EO azido mixed‐bridge spin‐sequence chains with –1/2–J1–3/2–J1–1/2–J2–1/2– for 1 and –1/2–J1–1–J1–1/2–J2–1/2– for 2. Magnetic studies indicated that 1 and 2 are both metamagnets for the weak antiferromagnetic interactions between the ferromagnetic chains.

Comparative study on MnII, NiII and CuII supramolecular complexes obtained from a proton transfer methodology: solid- and solution-state studies

In this study, the solution chemistry and solid-state structures of a novel proton transfer compound, (pipzH2)(pyc)2·H2O 1, and three metal–organic complexes of [Mn(pyc)2(H2O)2]2·2H2O 2, [Ni(pyc)2(H2O)2]·H2O 3 and [Cu(pyc)2H2O] n 4, (pyc = pyridine-2-carboxylate, pipz = piperazine) were investigated. On the basis of crystallographic data, each MII ion is coordinated to pyridine-2-carboxylate as bidentate ligand. Furthermore, these complexes form a three-dimensional structure by a variety of noncovalent interactions such as extensive O–H···O, O–H···N, N–H···O, N–H···N, C–H···O hydrogen bonds, C–H···π and C–O···π interactions. The equilibrium constants for the binary pyc-pipz proton transfer system, the stoichiometry and stability of complexation of this system with Mn2+, Ni2+ and Cu2+ ions in aqueous solution were investigated by potentiometric pH titration method. In each case, the stoichiometry of the dominant metal complex species in solution was compared with that obtained from the crystal structure.

Coordination Assemblies of CoII, NiII, ZnII, and CuII with 3,3′,4,4′-Biphenyltetracarboxylic Acid and Three Positional Isomeric Ligands

Eight different complexes with three positional isomeric dipyridyl ligands (3,3′-Hbpt, 3,4′-Hbpt, and 4,4′-Hbpt) (here, 3,3′-Hbpt = 1H-3,5-bis(3-pyridyl)-1,2,4-triazole, 3,4′-Hbpt = 1H-3-(3-pyridyl)-5-(4-pyridyl)-1,2,4-triazole, and 4,4′-Hbpt = 1H-3,5-bis(4-pyridyl)-1,2,4-triazole), as well as 3,3′,4,4′-biphenyltetracarboxylic acid (H4bptc), namely, {[M(bptc)0.5(3,3′-Hbpt)(H2O)2]·H2O}n (M = Co (1), M = Ni (2)), {[Zn2(bptc)(3,3′-Hbpt)2]·3H2O}n (3), [Co(bptc)0.5(3,4′-Hbpt)(H2O)]n (4), [Ni(bptc)0.5(3,4′-Hbpt)2(H2O)2]n (5), {[Cu(bptc)0.5(3,4′-Hbpt)(H2O)]·H2O}n (6), and {[M(bptc)0.5(4,4′-Hbpt)2(H2O)]·4H2O}n (M = Co (7), and Ni (8)) were synthesised and characterised by single-crystal X-ray diffraction. The crystallographic analysis demonstrates that bptc influences the MII (M = Co, Ni, Cu, and Zn) ions to form 2D layers, which are further connected via the isomeric bpt connectors, leading to many types of coordination polymers, such as 2D layers(for 1–3, 5), 3D four-connected nets with a short Schläfli symbol of (64.82) (for 4, 6), and 3D four-connected nets with a short Schläfli symbol of (64.82)(5.63.72)0.5 (for 7–8). This work demonstrates that the isomeric effects of the bpt ligands influence the construction of these frameworks. The thermal stability of complexes 1–6 was investigated.

Wheel-Shaped Icosanuclear Homo- and Heterometallic Complexes of NiII, CoII, and CuII Ions Supported by Unsymmetrical Aminoalcohol Ligands

Reactions of M(OAc)2·4H2O (M = Ni, Co) with 3-[benzyl(2-hydroxyethyl)amino]-1-propanol (H2L) in the presence of pyridine or triethylamine afforded novel homometallic icosanuclear wheel-shaped complexes [M20L4(HL)4(OAc)28] (M = Ni (1), Co (2)), which consist of a central M(II)12 single-stranded, nearly planar loop with four peripheral [M2(HL)(OAc)2] fragments attached in an S4 symmetrical fashion. The complexes can alternatively be recognized as saddle-shaped wheel structures, in which four tetranuclear units of [M4L(HL)(OAc)7](2-) are connected by four M(2+) ions (M5). The tetranuclear unit itself can be derived from an ideal C2 symmetrical [M4(HL)2(μ-η(2)-OAc)4(μ-η(1),η(1)-OAc)2(η(1),η(1)-OAc)](-) structure through deprotonation of the HL(-) ligand, and is composed of two plane-shared M3O4 incomplete cubanes in which the M2 and M3 atoms are involved in the central fused plane and the M1 and M4 atoms are disposed at the apex sites. Mixed-metal icosanuclear complexes [NixM20-xL4(HL)4(OAc)28] (3, M = Co, x = 9.5) and [Ni12M8L4(HL)4(OAc)28] (4, M = Cu) were also synthesized by using equimolar amounts of Ni(II) and M(II) ions, and were shown to have similar structures to 1 and 2. X-ray crystallographic and fluorescent analyses revealed that complex 3 contains nonstoichiometric amounts of Ni(2+) and Co(2+) ions in the ratio of 9.5:10.5 and that these are disordered at every metal site. In striking contrast, complex 4 has a stoichiometric formula of Ni12Cu8, which was confirmed by the Jahn-Teller elongation of Cu(2+) ions, and consequently, the M2 and M5 positions are occupied exclusively by the Cu(2+) ions. The temperature-dependent direct current (dc) magnetic susceptibility data showed the presence of ferromagnetic exchange interactions in the Ni homometallic (1) and NiCu bimetallic (4) complexes, while the Co homometallic (2) and NiCo bimetallic (3) complexes exhibited antiferromagnetic interactions due to spin-orbit coupling effects of the octahedral Co(II) ions. The present results demonstrate that the unsymmetrical aminoalcohol ligand H2L is quite effective in organizing the homo- and heterometallic icosanuclear wheel-shaped metal arrangements.

New insights in the bonding regime and ligand field in Wernerian complexes. A density functional study

We advance challenging new observations about the bonding regime and ligand field (LF) effects in the Wernerian complexes, with the help of several computer experiments realized exploiting the specific leverages of the ADF (Amsterdam density functional) code. Assembling the molecular systems from preliminarily prepared metal ion and individual ligand fragments and analyzing the components of the total bonding energy (Pauli repulsion, electrostatic interactions and orbital part), we noticed interesting correlations between the orbital part and the simple formulas of the qualitatively defined ligand field stabilization energy (LFSE). The facts are beyond the obvious or predictable comprehension, since the orbital components incorporate the subtle balance of intra- and inter-fragment density rearrangements, charge transfer and orbital mixing. The energy decomposition analysis was performed considering metal ions and ligand sets in their nominal oxidation states, or with fractional charges, resulted after a preliminary step of electronegativity equalization driven charge transfer. We worked on series of prototypic simple octahedral units: [MqF6]q−6 , [Mq(CN)6]q−6 and [Mq(H2O)6]q complexes with MII and MIII ions selected from the M=Cr to Cu 3d series. Besides, as illustration of observed regularities in the case of more complex ligands and intermediate symmetries, we considered [Mq(bpca)2]q−2 complexes (Hbpca=bis(2-pyridilcarbonyl)amine) with D2d symmetry. Using the ADF facilities of orbital population control and fractional occupation schemes, we devised two simple ways to estimate 10Dq parameters by numerical experiments that simulate the effects of Ligand Field stabilization and electron promotion. To the best of our knowledge, though simple, such considerations on bonding regime or methodological procedures designed to meet the phenomenological demands of LF models have not been discussed before. Interesting new aspects can yet be discovered exploring the subtle details of coordination bonding as intermediate between ionic and covalent bonding regime.

Geometric parameters of molecular structures of macrotricyclic chelates in MII ion—hydrazinomethane thioamide—butane-2,3-dione ternary systems (M = Co, Ni, Cu) according to the DFT B3LYP quantum chemical calculation

The geometric parameters of the macrotricyclic CoII, NiII, CuII, and ZnII chelates with (NSSN) coordination of the donor centers of the ligand, which are formed by complex formation between the metal ions, hydrazinomethane thioamide H2N-HN-C(=S)-NH2, and butane-2,3-dione Me-C(=O)-C(=O)-Me in aqueous solutions and gelatin-immobilized matrix implants, were calculated using the DFT B3LYP hybrid method in the 6-31G(d) standard basis set and the Gaussian03 program. The bond lengths, bond and torsion angles in the coordination compounds are presented. All the complexes are nearly planar.

End-to-end thiocyanato-bridged zig-zag polymers of CuII, CoII and NiII with a hydrazone ligand: EPR, magnetic susceptibility and biological study

The reactions of a tridentate hydrazone ligand, N′-[1-(pyridin-2-yl)ethylidene]acetohydrazide (LH), derived from condensation of 2-acetylpyridine with acetic hydrazide, with M(NO3)2·nH2O [M=Cu, Co and Ni] in the presence of thiocyanate afford three end-to-end zig-zag coordination polymers, [CuLH(NO3)(μ1,3-NCS)]n·nH2O (1), [CoLH(NCS)(μ1,3-NCS)]n (2) and [NiLH(NCS)(μ1,3-NCS)]n (3) (where LH=CH3C(O)–N–NCCH3C5H4N). Single-crystal X-ray structural determination studies reveal that in all the complexes, the hydrazone ligand in the neutral keto form (LH) coordinates a MII ion that is bridged to two neighboring metal centers by SCN− anions, generating a 1-D helical coordination chain. In 1, the CuII atom adopts a distorted tetragonal bipyramid geometry whereas in 2 and 3, the central CoII or NiII atom possesses into a distorted octahedral environment. All the aforementioned compounds have been fully characterized by elemental analysis, IR, UV–Vis and EPR spectra. Variable temperature magnetic susceptibility measurement of 1 accounts the weak antiferromagnetic interactions whereas 2 shows single-ion anisotropy. Compound 3 is well described as a 3-D ferromagnetic. The inhibitory effects of all the complexes on the cell population growth of human lung carcinoma cells (A549 cells), human colorectal carcinoma cells (COLO 205 cells and HT-29 cells), and human hepatocellular carcinoma cells (PLC5 cells) were determined by MTT assays.

One pot synthesis of heterometallic 3d–3d azido architectures: assembling strategy and magnetic properties

The Cu(II) ions usually have different coordinated geometry to other 3d ions, especially Ni(II) and Co(II) ions, in azido-carboxylate mixed ligand systems. That provides a potential way to synthesize rare heterometallic 3d-3d azido complexes with peculiar magnetic properties. Assembling Cu(II), M(II) (M = Ni and Co), azido and nicotinic acid in hydrothermal condition, two novel isomorphic 3D heterometallic 3d-3d azido complexes, [CuM(N(3))(2)(nicotinate)(2)](∞) (M = Ni(II) for 1 and Co(II) for 2) were obtained. The structure of the complexes can be described as EO azido and syn,syn carboxylate mixed bridged spin sequence chains (-1/2-J(1)-1-J(2)-1/2- for 1 and -1/2-J(1)-3/2-J(2)-1/2- for 2) linked by the pyridyl groups. Dominant ferromagnetic interactions were observed between the Cu(II) and M(II) ions in the chains despite the largest M-N-M angle of about 129° in the 3d metal azido-carboxylate mixed coordinated systems and weak antiferromagnetic interactions between the chains. At low temperature, a spin-flop phase transition was present in the Co(II) involved complex 2.

Self-assembly, metal binding ability, and magnetic properties of dinickel(ii) and dicobalt(ii) triple mesocates

Two metallacyclic complexes of general formula Na8[MII2L3]·xH2O [M = Ni (4) and Co (5) with x = 15 (4) and 17 (5)] have been self-assembled in aqueous solution from N,N′-1,3-phenylenebis(oxamic acid) (H4L) and M2+ ions in a ligand/metal molar ratio of 3 : 2 in the presence of NaOH acting as base. X-Ray structural analyses of 4 and 5 show triple-stranded, dinuclear anions of the meso-helicate-type (so-called mesocates) with C3h molecular symmetry. The two octahedral metal–tris(oxamate) moieties of opposite chiralities (Δ,Λ form) are connected by three m-phenylene spacers at intermetallic distances of 6.822(2) (4) and 6.868(2) A (5) to give a metallacryptand core. In the crystal lattice, the binding of these heterochiral dinickel(II) and dicobalt(II) triple mesocates to sodium(I) ions leads to oxamato-bridged heterobimetallic three-dimensional open-frameworks with a hexagonal diamond architecture having small pores of 17.566(4) (4) and 17.640(2) A (5) in diameter where the crystallization water molecules and the sodium(I) countercations are hosted. Variable temperature (2.0–300 K) magnetic susceptibility measurements reveal relatively anisotropic S = 2 NiII2 (4) and S = 3 CoII2 (5) ground states resulting from the moderate to weak intramolecular ferromagnetic coupling between the two high-spin NiII (SNi = 1) or CoII (SCo = 3/2) ions across the m-phenylenediamidate bridges [J = +3.6 (4) and +1.1 cm−1 (5); H = −JS1·S2]. A simple molecular orbital analysis of the electron exchange interaction identifies the π-type pathways of the meta-substituted phenylene spacers involving the dz2 and dx2−y2 pairs of magnetic orbitals of the two trigonally distorted octahedral high-spin MII ions (M = Ni and Co) as responsible for the overall ferromagnetic coupling observed in 4 and 5 in agreement with a spin polarization mechanism. The decrease of the overall ferromagnetic coupling from 4 to 5 is in turn explained by the additional antiferromagnetic exchange contribution involving the dxy pair of magnetic orbitals of the two trigonally distorted octahedral high-spin CoII ions across the σ-type pathway of the meta-substituted phenylene spacers.