ABSTRACT
The CoRu2(dpa)4Cl2 (1) (dpa: 2,2'-dipyridylamide) is synthesized by the reaction of Ru2(OAc)4Cl and Co3(dpa)4Cl2. By mixing 1 with NH3, Co2+ can be removed and result in the formation of unique binuclear complex 4,0-Ru2(dpa)4Cl (2) featuring one coordination pocket supported by free pyridine groups. Hence, this complex can act as an outstanding precursor for the formation of heterotrimetallic chains with MRu2 cores. A series of M-Ru25+ complexes (M = Co2+ (3), Ag+ (4), Mn2+ (5), Fe2+ (6), Zn2+ (7), Cd2+ (8), Pd2+ (9), Rh2+ (10), and Ir2+ (11)) were prepared and isolated, representing the most complete series of heterotrimetallic chains to date. All these metal string complexes are in a linear trimetallic framework helically wrapped by four dpa- ligands, characterized by X-ray diffraction measurements. The bending of the trinuclear metal cores in RhRu2 (10) and IrRu2 (11) (â Ru-Ru-Rh: 167.58° and â Ru-Ru-Ir: 167.61°) indicates that a heterometallic metal-metal bonds (Ru-Rh; Ru-Ir) are generated. The studies from DFT calculation of 10 and 11 coincide with the experimental results. Furthermore, the MRu25+ distances are regulated by the factors including the bonding force of M-pyridyl and the static repulsion between M and Ru25+ unit. Interestingly, the trend for these distances is in line with that observed in trans-M(py)4Cl2 complexes.
ABSTRACT
Using the planar 1,8-naphthyridin-2(1H)-one (Hnpo) ligand, novel nonhelical HMSCs [Mo2M(npo)4(NCS)2] (M = Fe, Co, Ni) were synthesised and they exhibited high single-molecule conductance.
ABSTRACT
Striding to extend the length of metal-atom strings, oligo-α-pyridylamino ligands are modulated with naphthyridyl moieties leading to the undeca-nickel mixed-valence complexes [Ni11(bnatpya)4Cl2]4+ (1) and [Ni11(bnatpya)4Cl2]2+ (2). The first single-molecule conductance measurements of a linear undeca-nickel chain were performed.
ABSTRACT
A dimeric molybdenum precursor and nickel ions are used to synthesize a symmetric heteropentanuclear complex, [Mo2NiMo2(tpda)4(NCS)2]. This complex possesses unique structural features, as the four ligands are coordinated to the metal framework in a meso configuration. Furthermore, the central Ni2+ ion is in a high spin state.
ABSTRACT
The new ligand, 2-(α-(5-phenyl)pyridylamino)-1,8-naphthyridine (Hphpyany), was synthesised by a palladium(0)-catalysed reaction of 2-chloro-1,8-naphthyridine with 2-amino-5-phenylpyridine in the presence of potassium tert-butoxide. Linear tetranickel metal complexes, [Ni4(phpyany)4Cl2](CF3SO3) 1, [Ni4(phpyany)4Cl2](BF4)22, [Ni4(phpyany)4(NCS)2](ClO4) 3 and [Ni4(phpyany)4(NCS)2](CF3SO3)24 were prepared and crystallographically characterised. Complexes 1-4 demonstrate that, for the first time, four asymmetric ligands align unidirectionally and thus configure (4,0)-form tetranickel strings, specifically, with the phenyl groups of the four phpyany- pointing to one side of the Ni4 chain and naphthyridyl to the other. The remarkably short Ni-Ni distances (ca. 2.33 Å) for 1 and 3 indicate partial metal-metal bonding, which can be viewed as both complexes containing one mixed-valence Ni23+ unit. The measurements of the magnetic susceptibility reveal that Ni47+ complexes 1 and 3 exhibit antiferromagnetic interactions (J = -42 cm-1 for 1 and -46 cm-1 for 3) between the terminal Ni2+ ion and the Ni23+ unit, while Ni48+ complexes 2 and 4 exhibit antiferromagnetic interactions (J = -33 cm-1 for 2 and -35 cm-1 for 4) between the two terminal Ni2+ ions. The results of the cyclic voltammetry indicate the presence of two reversible redox couples at E1/2(1) = 0.12 V, E1/2(2) = -0.65 V for 1, and at E1/2(1) = 0.12 V, E1/2(2) = -0.72 V for 3. The products of the first oxidation for 1 and 3 are the oxidised species 2 and 4, respectively. The values of single-molecule resistance (15.4 (±3.46) MΩ for 3 and 16.2 (±5.04) MΩ for 4) were determined by STM-based break-junction methods. The results represent the first conductance measurements of linear tetranickel chains.
ABSTRACT
The mononuclear complex (Bu4N)2[ReIVCl4(CN)2]·2DMA (DMA = N,N-dimethylacetamide) displays intricate magnetization dynamics, implying Orbach, direct, and Raman-type relaxation processes. The Orbach relaxation process is characterized by an energy barrier of 39 K (27 cm-1) that is discussed based on high-field electron paramagnetic resonance (EPR), inelastic neutron scattering and frequency-domain THz EPR investigations.
ABSTRACT
Determination of the electronic energy spectrum of a trigonal-symmetry mononuclear Yb(3+) single-molecule magnet (SMM) by high-resolution absorption and luminescence spectroscopies reveals that the first excited electronic doublet is placed nearly 500 cm(-1) above the ground one. Fitting of the paramagnetic relaxation times of this SMM to a thermally activated (Orbach) model {τ = τ0 × exp[ΔOrbach/(kBT)]} affords an activation barrier, ΔOrbach, of only 38 cm(-1). This result is incompatible with the spectroscopic observations. Thus, we unambiguously demonstrate, solely on the basis of experimental data, that Orbach relaxation cannot a priori be considered as the main mechanism determining the spin dynamics of SMMs. This study highlights the fact that the general synthetic approach of optimizing SMM behavior by maximization of the anisotropy barrier, intimately linked to the ligand field, as the sole parameter to be tuned, is insufficient because of the complete neglect of the interaction of the magnetic moment of the molecule with its environment. The Orbach mechanism is expected dominant only in the cases in which the energy of the excited ligand field state is below the Debye temperature, which is typically low for molecular crystals and, thus, prevents the use of the anisotropy barrier as a design criterion for the realization of high-temperature SMMs. Therefore, consideration of additional design criteria that address the presence of alternative relaxation processes beyond the traditional double-well picture is required.
ABSTRACT
The nature of the magnetic interaction through fluoride in a simple, dinuclear manganese(III) complex (1), bridged by a single fluoride ion in a perfectly linear fashion, is established by experiment and density functional theory. The magnitude of the antiferromagnetic exchange interaction and the manganese(III) zero-field-splitting parameters are unambiguously determined by inelastic neutron scattering to yield J = 33.0(2) cm(-1) (H = JS1·S2 Hamiltonian definition) and single-ion D = -4.0(1) cm(-1). Additionally, high-field, high-frequency electron paramagnetic resonance and magnetic measurements support the parameter values and resolve |E| ≈ 0.04 cm(-1). The exchange coupling constant (J) is 1 order of magnitude smaller than that found in comparable systems with linear oxide bridging but comparable to typical magnitudes through cyanide, thus underlining the potential of fluoride complexes as promising building blocks for novel magnetic systems.
ABSTRACT
A facile synthesis of the [ReF6 ](2-) ion and its use as a building block to synthesize magnetic systems are reported. Using dc and ac magnetic susceptibility measurements, INS and EPR spectroscopies, the magnetic properties of the isolated [ReF6 ](2-) unit in (PPh4 )2 [ReF6 ]â 2 H2 O (1) have been fully studied including the slow relaxation of the magnetization observed below ca. 4â K. This slow dynamic is preserved for the one-dimensional coordination polymer [Zn(viz)4 (ReF6 )]∞ (2, viz=1-vinylimidazole), demonstrating the irrelevance of low symmetry for such magnetization dynamics in systems with easy-plane-type anisotropy. The ability of fluoride to mediate significant exchange interactions is exemplified by the isostructural [Ni(viz)4 (ReF6 )]∞ (3) analogue in which the ferromagnetic Ni(II) -Re(IV) interaction (+10.8â cm(-1) ) dwarfs the coupling present in related cyanide-bridged systems. These results reveal [ReF6 ](2-) to be an unique new module for the design of molecule-based magnetic materials.
ABSTRACT
The observed angular variation of the magnetic exchange coupling parameter in a series of fluoride-bridged chromium(III)-gadolinium(III) complexes is explained by DFT calculations.
Subject(s)
Chromium/chemistry , Fluorides/chemistry , Gadolinium/chemistry , Organometallic Compounds/chemistry , Models, Molecular , Quantum TheoryABSTRACT
We have investigated the single-molecule magnets [Mn(III)2 (5-Brsalen)2 (MeOH)2 M(III) (CN)6 ]NEt4 (M=Os (1) and Ru (2); 5-Brsalen=N,N'-ethylenebis(5-bromosalicylidene)iminate) by frequency-domain Fourier-transform terahertz electron paramagnetic resonance (THz-EPR), inelastic neutron scattering, and superconducting quantum interference device (SQUID) magnetometry. The combination of all three techniques allows for the unambiguous experimental determination of the three-axis anisotropic magnetic exchange coupling between Mn(III) and Ru(III) or Os(III) ions, respectively. Analysis by means of a spin-Hamiltonian parameterization yields excellent agreement with all experimental data. Furthermore, analytical calculations show that the observed exchange anisotropy is due to the bent geometry encountered in both 1 and 2, whereas a linear geometry would lead to an Ising-type exchange coupling.
