Synthesis, structure, and magnetism of heterobimetallic trinuclear complexes {[L2Co2Ln][X]} [Ln = Eu, X = Cl; Ln = Tb, Dy, Ho, X = NO3; LH3 = (S)P[N(Me)N=CH-C6H 3-2-OH-3-OMe]3]: A 3d-4f family of single-molecule magnets

Department of Chemistry, Indian Institute of Technology-Kanpur, Kanpur-208016, India.
Inorganic Chemistry (Impact Factor: 4.76). 02/2009; 48(3):1148-57. DOI: 10.1021/ic801905p
Source: PubMed


Sequential reaction of LH3 (LH3 = (S)P[N(Me)N=CH-C6H3-2-OH-3-OMe]3) with Co(OAc)2 x 4 H2O followed by reaction with lanthanide salts afforded trinuclear heterobimetalllic compounds {[L2Co2Ln][X]} [Ln = Eu (1), X = Cl; Ln = Tb (2), Dy (3), Ho (4), X = NO3] in excellent yields. These compounds retain their integrity in solution as determined by electrospray ionization mass spectrometry studies. The molecular structures of 1-4 were confirmed by a single-crystal X-ray structural study and reveal that these are isostructural. In all of the compounds, the three metal ions are arranged in a perfectly linear manner and are held together by two trianionic ligands, L3-. The two terminal Co(II) ions contain a facial coordination environment (3N, 3O) comprising three imino nitrogen atoms and three phenolate oxygen atoms. The coordination geometry about the cobalt atom is severely distorted. An all-oxygen coordination environment (12O) is present around the central lanthanide ion, which is present in a distorted icosahedral geometry. The coordination sphere around the lanthanide ion is achieved by utilizing three phenolate oxygen atoms and three methoxy oxygen atoms of each ligand. In all of these trinuclear complexes (1-4), the Co-Ln distances are around 3.3 A, while the Co-Co distances range from 6.54 to 6.60 A. The screw-type coordination mode imposed by the ligand induces chirality in the molecular structure, although all of the complexes crystallize as racemates. Magnetic properties of 1-4 have been studied in detail using dc and ac susceptibility measurements. Dynamic measurements reveal that 2-4 display a single-molecule magnet behavior, while the Co2Eu (1) analogue does not show any out-of-phase ac susceptibility.

3 Reads
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The coordination of methanol and ethanol molecules was observed in the construction of three 1D coordination polymers composed of anti-anti carboxylato-bridged Mn(III)(3)O(Brppz)(3) units [Brppz = 3-(5-bromine-2-phenolate)pyrazolate]. The difference in these 1D complexes' structures induced by methanol and ethanol solvents leads to the variation of the magnetic properties. The methanol solvent product 1 [Mn(III)(3)O(Brppz)(3)(MeOH)(3)(AcO)].0.5MeOH has a Mn(III)(3)O repeating unit with two octahedral configuration manganese(III) ions and one square-pyrimid configuration manganese(III) ion, showing a long-range magnetic ordering with a T(c) of 8.2 K, whereas the ethanol solvent products 2 [Mn(III)(3)O(Brppz)(3)(C(2)H(5)OH)(4)(AcO)] (alpha-phase) and 3 [Mn(III)(3)O(Brppz)(3)(C(2)H(5)OH)(4)(AcO)] (beta-phase) are polymorphs, both having a Mn(III)(3)O repeating unit with three octahedral configuration manganese(III) ions, displaying single-chain magnet behaviors. Products 2 and 3 represent the first examples of polymorphs of single-chain magnets. Furthermore, the bridging carboxylate ligand in these 1D complexes was generated by the decomposition of beta-diketones via the retro-Claisen condensation reactions in the presence of strong bases.
    Inorganic Chemistry 05/2009; 48(11):4980-7. DOI:10.1021/ic900345s · 4.76 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Modeled after boron-based scorpionate ligands, acyclic and cyclic phosphorus-containing compounds possessing reactive groups can serve as excellent precursors for the assembly of novel phosphorus-supported ligands that can coordinate multiple sites. In such ligands, the phosphorus atom does not have any role in coordination but is used as a structural support to assemble one or more coordination platforms. In this Account, we describe the utility of inorganic heterocyclic rings such as cyclophosphazenes and carbophosphazenes as well as acyclic phosphorus-containing compounds such as (S)PCl(3), RP(O)Cl(2), and R(2)P(O)Cl for building such multisite coordination platforms. We can modulate the number and orientation of such coordination platforms through the choice of the phosphorus-containing precursor. This methodology is quite general and modular and allows the creation of well-defined libraries of multisite coordination ligands. Phosphorus-supported pyrazolyl ligands are quite useful for building multimetallic architectures. Some of these ligands are prone to P-N bond hydrolysis upon metalation, but we have exploited the P-N bond sensitivity to generate hydrolyzed ligands in situ, which are useful to build multimetal assemblies. In addition, the intimate relationship between small molecule cyclophosphazenes and the corresponding pendant cyclophosphazene-containing polymer systems facilitated our design of polymer-supported catalysts for phosphate ester hydrolysis, plasmid DNA modification, and C-C bond formation reactions. Phosphorus hydrazides containing reactive amine groups are ideal precursors for integration into more complex ligand systems. The ligand (S)P[N(Me)N=CH-C(6)H(4)-2-OH](3) (LH(3)) contains six coordination sites, and its coordination response depends upon the oxidation state of the metal ion employed. LH(3) reacts with divalent transition metal ions to afford neutral trimetallic derivatives L(2)M(3), where the three metal ions are arranged in a perfectly linear manner in many cases. Incorporating an additional methoxy group into LH(3) affords the ligand (S)P[N(Me)N=CH-C(6)H(3)-2-OH-3-OMe](3) (L'H(3)), which contains nine coordination sites: three imino nitrogen atoms, three phenolate oxygen atoms, and three methoxy oxygen atoms. The reaction of L'H(3) with transition metal salts in 1:1 ratio leads to the in situ formation of a metalloligand (L'M), which on further treatment with lanthanide salts gives heterobimetallic trinuclear cationic complexes [L'(2)M(2)Ln](+) containing a M-Ln-M linear array (M = transition metal ion in a +2 oxidation state). Many of these 3d-4f compounds behave as single-molecule magnets at low temperatures. Although challenges remain in the development of synthetic methods and in the architectural control of the coordination platforms, we see opportunities for further research into coordination platforms supported by main group elements such as phosphorus. As we have shown in this Account, one potential disadvantage, sensitivity of P-N bonds to hydrolysis, can be used successfully to build larger assemblies.
    Accounts of Chemical Research 06/2009; 42(8):1047-62. DOI:10.1021/ar800221e · 22.32 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The reactions of Ln(NO3)3 with 1,4-phenylenediacetic acid (H2PDA) under hydrothermal conditions produced two isostructural lanthanide coordination polymers with the empirical formula [Ln2(PDA)3(H2O)]·2H2O [Ln = Nd (1), Sm (2)]. Single-crystal X-ray diffraction analyses revealed that both contain one-dimensionalmetal carboxylato chains, which are further connected by the–CH2C6H4CH2– spacers of PDA2– ligands to yield a three-dimensional metal-organic framework. Magnetic susceptibilities of 1 and 2 were measured. The experimental χmT value of both compounds decreases continuously with decreasing temperature over the whole temperature range. The best least-squares fit of the experimental data of 1 to a theoretical equation in the temperature range of 70–300 K gives the zero-field splitting parameter Δ = 2.21 cm–1 and the magnetic interaction between the NdIII ions 2zJ′ = –1.97 cm–1, which indicates the presence of antiferromagnetic interaction between the NdIII ions. The experimental χmT value of 2 at 2 K is much smaller than the expected value for two free SmIII ions (6H5/2, g = 2/7) in the ground state, indicating that an antiferromagnetic interaction possibly exists between SmIII ions at low temperature. Fitting the magnetic data of 2 above 110 K based on an equation deduced from the SmIII ion in a monomeric system with free-ion approximation gave a spin-orbit coupling parameter λ = 192(2) cm–1
    Zeitschrift für anorganische Chemie 06/2009; 636(7):1392-1396. DOI:10.1002/zaac.200900452 · 1.16 Impact Factor
Show more