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A new rare‐earth reduction system is described in which trivalent yttrium and dysprosium react as though present in their unstable divalent oxidation state. This masked divalent reactivity is achieved using the isocarbonyl‐bridged dimers [( Cp2ttt ${{{\rm { Cp}}}_{{\rm { 2}}}^{{\rm { ttt}}}}$ M)(μ‐Fp)]2 (M=Y, 1Y; M=Dy, 1Dy; Cpttt=1,2,4‐C5tBu3H2; Fp=CpFe(CO)2), where the reducing electrons originate from the bridging [Fp]− ligands. The reactivity of 1Y and 1Dy is showcased by reducing the N‐heterocycles 2,2′‐bipyridyl (bipy), phenazine (phnz) and hexaazatrinaphthylene (HAN) to give corresponding mono‐, di‐ and tri‐metallic rare‐earth complexes, respectively, with the heterocyclic ligands present in their singly, doubly and triply reduced forms, respectively. The dynamic magnetic properties of the dysprosium compounds are described. Compound 1Dy is a single‐molecule magnet (SMM) with an appreciable energy barrier of 449(17) cm−1, whereas [( Cp2ttt ${{{\rm { Cp}}}_{{\rm { 2}}}^{{\rm { ttt}}}}$ Dy)2(μ‐phnz)] (3Dy) is not an SMM because of a strong, competing equatorial crystal field. Surprisingly, [( Cp2ttt ${{{\rm { Cp}}}_{{\rm { 2}}}^{{\rm { ttt}}}}$ Dy)3(HAN)] (4Dy) is also not an SMM, the origins of which are traced to the impact of the tert‐butyl substituents on the dysprosium centre and its interaction with the radical [HAN]3− ligand. [ABSTRACT FROM AUTHOR]

Two novel isostructural cyanide‐bridged hexadecanuclear complexes with the general formula {[Fe(CN)6]6[M{en(Bn)py}]10}2+ [M=Fe (12+), Ni (22+)] have been synthesized. The structural analyses disclose the presence of multivalent Fe centres with different spin states in complex 12+ whereas all the Fe centres share a conserved oxidation state in complex 22+. The DC magnetic study revealed antiferromagnetic interactions between the adjacent metal centres and ferrimagnetic behaviour in 12+. On the other hand, ferromagnetic interactions were observed in complex 22+ due to nearly orthogonal orientation of the interacting orbitals and poor spatial overlap as observed in BS‐DFT calculations. [ABSTRACT FROM AUTHOR]

The potassium silole K2[SiC4‐2,5‐(SiMe3)2‐3,4‐Ph2] reacts with [M(η8‐COT)(THF)4][BPh4] (M=Er, Y; COT=cyclo‐octatetraenyl) in THF to give products that feature unprecedented insertion of the nucleophilic silicon centre into a carbon‐oxygen bond of THF. The structure of the major product, [(μ‐η8 : η8‐COT)M(μ‐L1)K]∞ (1M), consists of polymeric chains of sandwich complexes, where the spiro‐bicyclic silapyran ligand [C4H8OSiC4(SiMe3)2Ph2]2− (L1) coordinates to potassium via the oxygen. The minor product [(μ‐η8 : η8‐COT)M(μ‐L1)K(THF)]2 (2M) features coordination of the silapyran to the rare‐earth metal. In forming 1M and 2M, silole insertion into THF only occurs in the presence of potassium and the rare‐earth metal, highlighting the importance of bimetallic synergy. The lower nucleophilicity of germanium(II) leads to contrasting reactivity of the potassium germole K2[GeC4‐2,5‐(SiMe3)2‐3,4‐Me2] towards [M(η8‐COT)(THF)4][BPh4], with intact transfer of the germole occurring to give the coordination polymers [{η5‐GeC4(SiMe3)2Me2}M(η8‐COT)K]∞ (3M). Despite the differences in reactivity induced by the group 14 heteroatom, the single‐molecule magnet properties of 1Er, 2Er and 3Er are similar, with thermally activated relaxation occurring via the first‐excited Kramers doublet, subject to effective energy barriers of 122, 80 and 91 cm−1, respectively. Compound 1Er is also analysed by high‐frequency dynamic magnetic susceptibility measurements up to 106 Hz. [ABSTRACT FROM AUTHOR]

The first germole‐ligated single‐molecule magnets are reported, with contrasting properties found for the near‐linear sandwich complexes [(η8‐COT)Ln(η5‐CpGe]−, where Ln=Dy (1Dy) or Er (1Er), COT is cyclo‐octatetraenyl and CpGe is [GeC4‐2,5‐(SiMe3)2‐3,4‐Me2]2−. Whereas 1Er has an energy barrier of 120(1) cm−1 in zero applied field and open hysteresis loops up to 10 K, the relaxation in 1Dy is characterized by quantum tunneling within the ground state. [ABSTRACT FROM AUTHOR]

Tuning the bridging fashion of anilato ligand in dinuclear DyIII complexes, reveals a sizable effect on the slow relaxation of magnetization. Combined experimental and theoretical studies divulge that the geometry with high order axial symmetry (pseudo square antiprism) reduces the transverse crystal fields corresponding to QTM (quantum tunneling of magnetization) resulting in a significant increase in energy barrier (Ueff=518 cm-1) through the Orbach relaxation process whereas the geometry with lower symmetry (triangular dodecahedron, pseudo D2d) enhances the transverse crystal fields that accelerate the ground state QTM process. Notably, the value 518 cm-1 represents the highest energy barrier among anilato ligand based SMMs. [ABSTRACT FROM AUTHOR]

A pair of tridentate ligands incorporating heterocyclic hydrazones of 9,10‐phenanthrenequinone viz,. pyridyl‐hydrazino‐phenathrenequinone HLPy1a and benzothiazolyl‐hydrazino‐phenathrenequinone HLBenz1b have been synthesized and both behave as monoanionic towards nickel(II), forming meridional octahedral complexes of type [Ni(LPy)2] 2a and [Ni(LBenz)2] 2b as evident from single crystal X‐ray diffraction studies. The complexes are electro‐active in solution and nature of redox orbitals has been analysed by theoretical means. They display two oxidative and two reductive responses that have been ascribed to the redox processes of coordinated ligands. The electronic absorption spectral patterns of two complexes are analogous barring the fact that lower energy transition for 2b is marginally bathochromically shifted relative to that of 2a and it has been clarified by TD‐DFT studies. Anti‐bacterial efficacy of the ligands HLPy1a, HLBenz1b and complexes [Ni(LPy)2] 2a, [Ni(LBenz)2] 2b against four Gram‐positive and four Gram‐negative strains has been explored. [Ni(LPy)2] 2a exhibits more pronounced efficacy than [Ni(LBenz)2] 2b and these are greater than those of the corresponding ligands. The mode of action of 2a is essential via DNA damage while protein leakage and membrane lipid damage were observed upon treatment with 2b. [ABSTRACT FROM AUTHOR]

Herein, we report the synthesis, structure, and magnetic properties of three new halo‐substituted benzotriazinyl radicals (Rad3a‐3c where a=Cl, b=Br, c=I) and two metal complexes [M(hfac)2(Rad3c)⋅CHCl3](M=Cu(II) (1), Zn(II) (2) and hfac: hexafluoroacetylacetonate) as representative examples. Structural analyses disclose that all the radicals are isostructural. Compared to the reported benzotriazinyl radicals, the N4 atom of pyridine flips opposite to the spin bearing (N1) centre, and it is stabilized by secondary C−H⋅⋅⋅N interaction. The π⋅⋅⋅π stacking interaction between the spin bearing centre and pyridyl ring decreases as the size of the halogen increases from ‐Cl to ‐I. The stacking distance is substantially longer than the other coordinating benzotriazinyl radicals reported so far. The dc magnetic studies reveal the presence of strong intermolecular antiferromagnetic exchange interaction between the radical dimers, which decreases in the order of Rad3a→Rad3b→Rad3c. Complex 1 shows a strong intramolecular through‐bond metal‐radical ferromagnetic interaction, whereas a weak intermolecular through‐space radical⋅⋅⋅radical antiferromagnetic exchange interaction is observed in complex 2. Furthermore, the broken symmetry (BS)‐DFT calculations were performed to get more insight into the exchange interaction for all the radicals and metal complexes. [ABSTRACT FROM AUTHOR]

The importance of equatorial crystal fields on magnetic anisotropy of ytterbium single molecule magnets (SMMs) is observed for the first time. Herein, we report three similar dinuclear ytterbium complexes with the formula [Yb2(3‐OMe‐L)2(DMF)2(NO3)2]⋅DMF (1), [Yb2(3‐H‐L)2(DMF)2(NO3)2]⋅DMF⋅H2O (2), and [Yb2(3‐NO3‐L)2(DMF)2(NO3)2] (3), [where 3‐X‐H2L=N′‐(2‐hydroxy‐3‐X‐benzylidene)picolinohydrazide, X=OMe (1), H (2) NO2 (3)]. Detailed magnetic measurements reveal the presence of weak antiferromagnetic interactions between the Yb centers and a field‐induced slow relaxation of magnetization in all complexes. A higher energy barrier for spin reversal was observed for complex 1 (Ueff=50 K) and it decreases in the order of 2 (47 K) to 3 (40 K). Notably, complex 1 shows a remarkable energy barrier within the frequency range of 1–850 Hz reported for Yb‐based SMMs. Further, ab initio calculations show a higher axial anisotropy and lower quantum tunneling of magnetization (QTM) in the ground state for 1 compared to 2 and 3. It was also observed that the presence of a strong crystal field in the equatorial plane (when the ∡ O1−Yb−O3 bond angle is close to 90°) enhances the axial anisotropy and improves the SMM behavior in the studied complexes. Both the experimental and theoretical analysis of relaxation dynamics discloses that Raman and QTM play major role on slow relaxation process for all complexes. To provide more insight into the exchange interactions, broken‐symmetry DFT calculations were performed. [ABSTRACT FROM AUTHOR]

Herein, we report a CN‐bridged alternating FeII−NiII 1D chain to ensure the alignment of axial anisotropy and improve the single molecule magnet (SMM) behavior in seven coordinated FeII compound. The chain was constructed from hepta coordinated Fe(II) complex as an anisotropic building unit and diamagnetic nickel tetra cyanate as a bridging ligand. The magnetic measurements show the easy‐axis anisotropy of the seven coordinated Fe(II) complex and field induced SMM behavior with spin reversal energy barrier Ueff=61(2) K (42 cm−1) and pre‐exponential relaxation time τ0=1.9×10−8 s. The detailed analysis of the relaxation dynamics discloses that the Orbach process plays an important role in slow relaxation of magnetization for this compound. Notably, this example represents a remarkable energy barrier observed in hepta coordinated Fe(II) SMMs. The ab initio calculations estimate the magnitude of axial anisotropy and show the parallel orientation of the anisotropic axis throughout the 1D polymeric chain. In addition, it is also reported that the presence of weak π accepter ligands in the distorted axial position enhance the easy‐axis anisotropy. [ABSTRACT FROM AUTHOR]

Herein, two coordination polymers (CPs) [{Dy(Cl2An)1.5(CH3OH)}⋅4.5 H2O]n (1) and [Dy(Cl2An)1.5(DMF)2]n (2), in which Cl2An is chloranilate (2,5‐dihydroxy‐1,4‐benzoquinone dianion), exhibiting field‐induced single‐molecule magnet behavior with moderate barrier of magnetization reversal are reported. Detailed structural and topological analysis disclosed that 1 has a 3D network, whereas 2 has a 2D layered‐type structure. In both CPs, magnetic measurements showed weak antiferromagnetic exchange interaction between the dysprosium centers and field‐induced slow magnetic relaxation with barriers of 175(9)K and 145(7)K for 1 and 2, respectively. Notably, the energy barriers of magnetization reversal of 1 and 2 are remarkable for metal–chloranilate‐based 3D (1) and 2D (2) CPs. The temperature and field dependence of relaxation time indicate the presence of multiple relaxation pathways, such as direct, quantum tunneling of magnetization, Raman, and Orbach processes, in both CPs. Ab initio theoretical calculations reinforced the experimentally observed higher energy barrier in 1 as compared with 2 due to the presence of large transverse anisotropy in the ground state in the latter. The average transition magnetic moment between the computed low‐lying spin–orbit states also rationalized the relaxation as Orbach and Raman processes through the first excited state. BS‐DFT calculations were carried out for both CPs to provide more insight into the exchange interaction. [ABSTRACT FROM AUTHOR]

The reaction of Fe(NCS)3 prepared in situ in MeOH with 5‐X‐SalEen ligands (5‐X‐SalEen=condensation product of 5‐substituted salicylaldehyde and N‐ethylethylenediamine) provided three Fe(III) complexes, [Fe(5‐X‐SalEen)2]NCS; X=Me (1), X=Br (2), X=OMe (3). All the complexes reveal similar structural features but a very different magnetic profile. Complex 1 shows a gradual spin crossover while complexes 2 and 3 show a sharp spin transition. The T1/2 for complex 2 is 237 K while for complex 3 it is much higher with a value of 361 K. The spin transition temperature is shifted towards higher temperature with increasing electron‐donation ability of the ligand substituents. This experimental observation has been rationalized with DFT calculations. UV‐Vis and cyclic voltammetry studies support the fact that the electron density on the ligand increases from Me to Br to OMe substituents. To understand the change in spin states, temperature‐dependent EPR spectra have been recorded. The spin state equilibrium in the liquid state has been probed with Evans NMR spectroscopic method, and thermodynamic parameters have been evaluated for all complexes. [ABSTRACT FROM AUTHOR]

Three lanthanide‐based two‐dimensional (2D) coordination polymers (CPs), [Ln(L)(H2O)2]n, {H3L=(HO)2P(O)CH2CO2H; Ln=Dy3+ (CP 1), Er3+ (CP 2)} and [{Gd2(L)2(H2O)3}.H2O]n, (CP 3) were hydrothermally synthesized using phosphonoacetic acid as a linker. Structural features revealed that the dinuclear Ln3+ nodes were present in the 2D sheet of CP 1 and CP 2 while in the case of CP 3, nodes were further connected to each other forming a chain‐type arrangement throughout the network. The magnetic studies show field‐induced slow magnetic relaxation property in CP 1 and CP 2 with Ueff values of 72 K (relaxation time, τ0=3.05×10−7 s) and 38.42 K (relaxation time, τ0=4.60×10−8 s) respectively. Ab‐initio calculations suggest that the g tensor of Kramers doublet of the lanthanide ion (Dy3+ and Er3+) is strongly axial in nature which reflects in the slow magnetic relaxation behavior of both CPs. CP 3 exhibits a significant magnetocaloric effect with −ΔSm=49.29 J kg−1 K−1, one of the highest value among the reported 2D CPs. Moreover, impedance analysis of all the CPs show high proton conductivity with values of 1.13×10−6 S cm−1, 2.73×10−3 S cm−1 and 2, 6.27×10−6 S cm−1 for CPs 1–3, respectively, at high temperature (>75 °C) and maximum 95 % relative humidity (RH). [ABSTRACT FROM AUTHOR]