Lanthanoid coordination prompts unusually distorted pseudo-octahedral NiII coordination in heterodinuclear Ni-Ln complexes: synthesis, structure and understanding of magnetic behaviour through experiment and computation.

In this work, a new family of binuclear NiII-LnIII complexes with the formula [NiLn(L)2(NO3)3]·0.5H2O (Ln = Gd, 1; Tb, 2; Dy, 3; Ho, 4; Er, 5; Yb, 6; Y, 7) was synthesized using a thioether group-bearing Schiff base. Due to the strict hard/soft dichotomy between the 4f and 3d metal ions, selective coordination of NiII and 4f metal ions was achieved with the adjacent soft ONS and hard OO binding pockets of the ligand. All the complexes 1-7 exhibit a NiII centre in a distorted pseudo-octahedral geometry with the LnIII centres in distorted bicapped square-antiprism geometry. The huge distortion around the NiII centres is triggered for the accommodation of larger lanthanoids to the adjacent OO coordination site, and this forces the NiII centres to have a tridentate coordination from the ONS, as intermediate between meridional and facial binding. Field-induced single-molecule magnetic behaviour was observed for heterodinuclear complexes involving Kramers lanthanide ions (LnIII = Dy, Er and Yb), with magnetic relaxation occurring through an Orbach process only for 5. DFT calculations using various functionals (BP86, B3LYP, PBE0, TPSSh, PWPB95, R2SCAN) were applied to calculate the isotropic exchange, showing good agreement with the experiment (JGd-Ni = +1.78 cm-1). CASSCF calculations for NiII and LnIII ions were also performed to reveal detailed information about their electronic structure and magnetic anisotropy, supporting the experimental observations. This study accentuates the mutual distortion of coordination geometry induced by flexibility of the ligand backbone with the simultaneous binding of two different metal ions.

Synthesis and characterization of two self-assembled [Cu6Gd3] and [Cu5Dy2] complexes exhibiting the magnetocaloric effect, slow relaxation of magnetization, and anticancer activity.

Two new paths for coordination driven self-assembly reactions under the binding support of 2-((1-hydroxy-2-methylpropan-2-ylimino)methyl)-6-methoxyphenol (H2L) have been discovered from the reactions of Cu(ClO4)2·6H2O, NEt3 and GdCl3/DyCl3·6H2O in MeOH/CHCl3 (2 : 1) medium. A similar synthetic protocol is useful to provide two different types of self-aggregated molecular clusters [Cu6Gd3(L)3(HL)3(µ3-Cl)3(µ3-OH)6(OH)2]ClO4·4H2O (1) and [Cu5Dy2(L)2(HL)2(µ-Cl)2(µ3-OH)4(ClO4)2(H2O)6](ClO4)2·2NHEt3Cl·21H2O (2). The adopted reaction procedure established the importance of the HO- and Cl- ions in the mineral-like growth of the complexes, derived from solvents and metal ion salts. In the case of complex 1, one GdIII center has been trapped at the central position of the core upheld by six µ3-OH and three µ3-Cl groups, whereas for complex 2 one CuII center was trapped using four µ3-hydroxo and two µ-chlorido groups. The magnetothermal behavior of 1 has been examined for a magnetocaloric effect of -ΔSm = 11.3 J kg-1 K-1 at 2 K for ΔH = 7 T, whereas the magnetic susceptibility measurements of 2 showed slow magnetic relaxation with Ueff = 15.8 K and τ0 = 9.8 × 10-7 s in zero external dc field. Cancer cell growth inhibition studies proved the potential of both the complexes with interestingly high activity for the Cu6Gd3 complex against human lung cancer cells. Both complexes 1 and 2 also exhibited DNA and human serum albumin (HSA) binding abilities in relation to the involved binding sites and thermodynamics.

From tetranuclear to pentanuclear [Co-Ln] (Ln = Gd, Tb, Dy, Ho) complexes across the lanthanide series: effect of varying sequence of ligand addition.

Two new families of cobalt(ii/iii)-lanthanide(iii) coordination aggregates have been reported: tetranuclear [LnCoL2(N-BuDEA)2(O2CCMe3)4(H2O)2]·(MeOH)n·(H2O)m (Ln = Gd, 1; Tb, 2; Dy, 3; n = 2, m = 10 for 1 and 2; n = 6, m = 2 for 3) and pentanuclear LnCoIICoL2(N-BuDEA)2(O2CCMe3)6(MeOH)2 (Ln = Dy, 4; Ho, 5) formed from the reaction of two aggregation assisting ligands H2L (o-vanillin oxime) and N-BuDEAH2 (N-butyldiethanolamine). A change in preference from a lower to higher nuclearity structure was observed on going across the lanthanide series brought about by the variation in the size of the LnIII ions. An interesting observation was made for the varying sequence of addition of the ligands into the reaction medium paving the way to access both structural types for Ln = Dy. HRMS (+ve) of solutions gave further insight into the formation of the aggregates via different pathways. The tetranuclear complexes adopt a modified butterfly structure with a more complex bridging network while trapping of an extra CoII ion in the pentanuclear complexes destroys this arrangement putting the Co-Co-Co axis above the Ln-Ln axis. Direct current (dc) magnetic susceptibility measurements reveal weak antiferromagnetic coupling in 1. Complexes 2 and 5 display no slow magnetic relaxation, whereas complexes 3 and 4 display out-of-phase signals at low temperature in ac susceptibility measurements. All compounds were analyzed with DFT and CASSCF calculations and informations about the single-ion anisotropies and mutual 4f-4f/4f-3d magnetic interactions were derived.

Synthesis, characterization, magnetism and theoretical analysis of hetero-metallic [Ni2Ln2] partial di-cubane assemblies.

A family of four isostructural [Ln2Ni2(L)2(µ3-OCH3)2(µ1,3-PhCO2)2(PhCO2)2(CH3OH)4]·2CH3OH [where Ln = Gd (1), Tb (2), Dy (3) and Ho (4)] complexes has been synthesized using Schiff base ligand 2-[{(2-hydroxybenzyl)imino}methyl]-6-methoxyphenol (H2L). All the complexes possess a partial di-cubane core structure where the growth of the core is contingent upon the ligand anions and solvent generated µ3-OCH3 groups. DC magnetic analysis revealed dominating ferromagnetic interactions between the metal ions, however, we find no slow relaxation characteristics in the AC susceptibility. Further insight into the magnetic behavior of the reported complexes was achieved using DFT and CASSCF theoretical calculations, leading to the comprehension of the fast relaxation characteristics observed by magnetometry.

Carboxylate-Decorated Aggregation of Octanuclear Co4Ln4 (Ln = Dy, Ho, Yb) Complexes from Ligand-Controlled Hydrolysis: Synthesis, Structures, and Magnetic Properties.

One-pot reactions of an asymmetric carboxy-ether-phenol based Schiff base H2L (2-((2-hydroxy-3-methoxybenzylidene)amino)benzoic acid) with selected Ln(NO3)3·nH2O and [Co2(µ-OH2)(O2CCMe3)4(HO2CCMe3)4] (Co2-Piv) in basic MeOH medium resulted in a family of three octanuclear complexes, [CoII4LnIII4L4(µ1,3-Piv)4(µ1,1,3-Piv)2(η1-Piv)2(µ3-OH)4(MeOH)2]·mMeOH·nH2O (Ln = Dy; m = 3, n = 1 (1), Ho; m = 4, n = 0 (2), Yb; m = 3, n = 1 (3)). The coordination aggregates thus obtained were nicely sustained by four ligand anions and eight externally added carboxylate anions showing three different modes of intermetallic connectivity. The options for incorporating different 4f ions in an investigative synthesis, without altering the resulting intermetallic core structure, were successful for the three representative examples. Single-crystal X-ray diffraction studies revealed that the compounds are isostructural and built from two initially formed partial dicubane-type Co2Ln2L2 units. In each of the tetranuclear parts, the metal ion centers are held together by two L2-, two µ3-HO-, three Piv- bridges, one terminal Piv-, and one terminal MeOH. Four carboxylate ends of four L2- units are responsible for connecting two Co2Ln2 units into octanuclear structures. The unique distortion around the CoII centers is achieved from the facile coordination of bigger 4f ions to the adjacent hard OO sites. The distortion is further maintained by the presence of terminal COO- groups from L2-. The dc magnetic susceptibility data revealed ferromagnetic coupling between the CoII and LnIII centers within the series, whereas the ac magnetic susceptibility measurements identified only 1, having a highly anisotropic DyIII ion, as a single-molecule magnet in the absence of any external magnetic field, with an energy barrier Ueff of 12.5 K.

Solvent-induced structural transformation from heptanuclear to decanuclear [Co-Ln] coordination clusters: trapping of unique counteranion and understanding of aggregation pathways.

Five new cobalt(ii/iii)-lanthanide(iii)-based coordination aggregates, [LnIII3CoII2CoIII2(L1)2(O2CCMe3)8(OH)4(OMe)2(H2O)4]·Ln(η1-O2CCMe3)2(η2-O2CCMe3)2(MeOH)2·2MeOH·2H2O (where Ln = Tb (1), Ho (3), and H2L1 = N-(2-hydroxyethyl)-salicylaldimine), TbIII3CoII3CoIII4(L1)4(O2CCMe3)9(OH)10(H2O) (4) and LnIII3CoII2CoIII5(L1)4(O2CCMe3)10(OH)10 (Ln = Dy (5), Ho (6)) have been synthesized and characterized, including structural analysis via single-crystal X-ray diffraction. The dysprosium analogue (2) of 1 and 3 was previously reported by us. The heptanuclear monocationic clusters in 1 and 3 were formed by placement of seven metal ions (4 Co and 3 Ln) in a vertex shared dicubane structure from the control of two Schiff base anions and crystallized in the presence of in situ generated and literature unknown counter anions Tb(η1-O2CCMe3)2(η2-O2CCMe3)2(MeOH)2- and Ho(η1-O2CCMe3)2(η2-O2CCMe3)2(MeOH)2-. Interesting solvent-induced cluster structure transformation was observed on dissolving the heptanuclear aggregates in MeCN for the formation of decanuclear clusters 4-6. These high nuclearity clusters consist of a vertex shared heptanuclear dicubane part and a curved trinuclear chain linking the two cubic halves. The dicubane unit differs from that of the heptanuclear precursors in the presence of CoII/III at the shared vertex as opposed to LnIII and the absence of OMe- bridges. HRMS (+ve) analysis shed light on the pathway of formation of these heptanuclear molecules, while at the same time revealing a different aggregation process for the decanuclear clusters.

Sterically hindering the trajectory of nucleophilic attack towards p-benzynes by a properly oriented hydrogen atom: an approach to achieve regioselectivity.

Nucleophilic addition to p-benzynes derived via Bergman cyclization has become a topic of keen interest. Studying the regioselectivity in such addition can reveal important information regarding the parameters controlling such addition. Recently, high regioselectivity has been achieved in nucleophilic addition to a p-benzyne derived from an ortho substituted benzo fused cyclic azaenediyne. Rather than having a freely rotating substitution, a rigid hydrogen atom coming from a suitable naptho fused enediyne and residing in the plane of the p-benzyne ring can offer hindrance to the trajectory of the nucleophile. This can lead to regioselectivity provided the other side remains relatively free of such hindrance. Based on that approach, halide addition to p-benzynes derived from naphtho fused cyclic azaenediynes was studied and a high level of regioselectivity was observed. Steric hindrance to the trajectory of nucleophile by the bay hydrogen was found to be the main cause of such regioselectivity; however, differential electrostatic potential as well as distortions at reactive centres have a minor role in controlling the regioselectivity. The products of such high yielding addition are the halo naphtho tetrahydroisoquinolines.

Hydroxido supported and differently networked octanuclear Ni6Ln2 [Ln = GdIII and DyIII] complexes: structural variation, magnetic properties and theoretical insights.

The design and synthesis of a Schiff base H2L, (2-{[(2-hydroxy-3-methoxybenzyl)imino]methyl}phenol), bearing an ONOO donor set has been explored for its reactivity pattern with LnCl3·6H2O (Ln = GdIII and DyIII) and Ni(CH3CO2)2·4H2O in the presence of NEt3 for molecular aggregation. Coordination driven spontaneous self-assembly reactions provide [Gd2Ni6L4(µ3-OH)6(µ-OH)2(CH3CO2)2(µ-H2O)2(H2O)3(MeOH)]·8H2O (1) having a 'butterfly-shaped' core and [Dy2Ni6L4(µ3-OH)4(µ-Cl)2Cl4(H2O)2(MeOH)2]·2MeOH·4H2O (2) with a 'candy-shaped' core. Fusion of six partial cubane units led to a mineral-like core in 1, developed around the central Ni2(OH)2 moiety, whereas in the case of 2, four such partial cubanes collapsed on Dy2(OH)2. Direct-current (dc) magnetic susceptibility measurements revealed that predominant ferromagnetic interactions lead to a high-spin S = 13 ground state for 1. Complex 2 exhibits slow relaxation of magnetization under an applied small dc field with an energy barrier to reorientation of the magnetization, Ueff = 19.3 K. The static and dynamic magnetic data are analysed and corroborated by density functional theory (DFT) and detailed CASSCF based calculations.

Selective Coordination of Self-Assembled Hexanuclear [Ni4Ln2] and [Ni2Mn2Ln2] (Ln = DyIII, TbIII, and HoIII) Complexes: Stepwise Synthesis, Structures, and Magnetic Properties.

The versatility for a unique aggregation of heterometallic 3d-4f and 3d-3d'-4f ions by the new Schiff base ligand 2-{[(2-hydroxy-3-methoxybenzyl)imino]methyl}phenol (H2L) providing O3N donors has been examined. A series of complexes having the general formula [Ln2Ni4(L)4(µ1,3-CH3CO2)2(µ3-OH)4(MeOH)2]·xCH3OH·yH2O [where Ln = DyIII, x = 4, y = 0 (1), Ln = TbIII, x = 0, y = 4 (2), and Ln = HoIII, x = 4, y = 0 (3)] were obtained from the sequential use of lanthanide(III) nitrate salts and Ni(CH3CO2)2·4H2O. The incorporation of two different 3d ions and one 4f ion in the same coordination aggregate was achieved through the isomorphic replacement of two NiII centers by MnIII ions as second group of cationic complexes, [Ln2Ni2Mn2(L)4(µ1,3-CH3CO2)2(µ3-OH)4(MeOH)2](NO3)2·2CH3OH [where Ln = DyIII (4), TbIII (5), and HoIII (6)]. Direct-current (dc) magnetic susceptibility studies hint to the possibility of ferromagnetic interactions occurring in the aggregates, whereas alternating-current susceptibility measurements find both the DyIII analogues, 1 and 4, to show out-of-phase components at zero applied dc field, characteristic of single-molecule-magnet (SMM) behavior. Micro-SQUID studies reveal open hysteresis loops for 1, corroborating its SMM character. Further detailed complete-active-space self-consistent-field and density functional theory calculations were also performed, supporting the experimental findings in complexes 1 and 4.

Octanuclear Ni4 Ln4 Coordination Aggregates from Schiff Base Anion Supports and Connecting of Two Ni2 Ln2 Cubes: Syntheses, Structures, and Magnetic Properties.

A family of 3d-4f aggregates have been reported through guiding the dual coordination modes of ligand anion (HL- ) and in situ generated ancillary bridge driven self-assembly coordination responses toward two different types of metal ions. Reactions of lanthanide(III) nitrate (Ln=Gd, Tb, Dy, Ho and Yb), nickel(II) acetate and phenol-based ditopic ligand anion of 2-[{(2-hydroxypropyl)imino}methyl]-6-methoxyphenol (H2 L) in MeCN-MeOH (3 : 1) mixture and LiOH provided five new octanuclear Ni-4f coordination aggregates from two Ni2 Ln2 cubanes. Single-crystal X-ray diffraction analysis reveals that all the members of the family are isostructural, with the central core formed from the coupling of two distorted [Ni2 Ln2 O4 ] heterometallic cubanes [Ni2 Ln2 (HL)2 (µ3 -OH)2 (OH)(OAc)4 ]+ (Ln=Gd (1), Tb (2), Dy (3), Ho (4) and Yb (5)). Higher coordination demand of 4f ions induced the coupling of the two cubes by (OH)(OAc)2 bridges. Variable temperature magnetic study reveals weak coupling between the Ni2+ and Ln3+ ions. For the Tb (2) and Dy (3) analogs, the compounds are SMMs without an applied dc field, whereas the Gd (1) analogue is not an SMM. The observation revealed thus that the anisotropy of the Ln3+ ions is central to display the SMM behavior within this structurally intriguing family of compounds.

Self-assembled octanuclear [Ni5Ln3] (Ln = Dy, Tb and Ho) complexes: synthesis, coordination induced ligand hydrolysis, structure and magnetism.

The variable coordination behavior of 2-{[(2-hydroxy-3-methoxybenzyl)imino]methyl}-6-methoxyphenol (H2L) and its hydrolyzed congener towards NiCl2·6H2O and LnIII nitrate salts provides a family of coordination aggregates containing an [Ni5Ln3] octanuclear core structure. Room temperature reactions in MeOH-CHCl3 medium and in the presence of NEt3 yielded isostructural [Ni5Ln3(L)4(µ-OH)2(µ3-OH)6(o-val)2(H2O)6]NO3·7H2O (Ln = Dy3+ (1), Tb3+ (2), and Ho3+ (3); o-val = o-vanillin) heterometallic complexes. All the three complexes hold an octanuclear fused partial hexacubane topology from the utilization of phenolate-based ligand anions, clipping five 3d and three 4f ions. Direct current magnetic susceptibility measurements showed an upsurge at low temperature for complexes 1 and 2, indicative of ferromagnetic interactions, while antiferromagnetic exchange interaction predominates for complex 3. AC magnetic susceptibility measurements were not able to show any slow relaxation property to the magnetization. CASSCF calculations for complex 1 indicate that all three Dy3+ centres have anisotropic axes but the relative orientation of the magnetic axes reduces the probability of this molecule to behave like an SMM which is further established by the POLY_ANISO calculations.

Synthetic diversity and change in nuclearity in [Co-Dy] coordination aggregates: bridge removal, solvent induced structural reorganization and AC susceptibility measurements.

Three new cobalt(ii/iii)-dysprosium(iii) complexes, [DyIII3CoII2CoIII2(L1)2(O2CCMe3)8(OH)4(OMe)2(H2O)4]·Dy(η1-O2CCMe3)2(η2-O2CCMe3)2(MeOH)2·4H2O (1), [DyIII3CoII2CoIII2(L2)2(O2CCMe3)8(OH)4(OMe)2(MeOH)2(H2O)2]·Dy(η1-O2CCMe3)2(η2-O2CCMe3)2(MeOH)2·4MeOH (2) and DyIII2CoII2CoIII2(L2)2(O2CCMe3)10(OH)2 (3) have been reported. In the heptanuclear 3d-4f monocationic aggregates in 1 and 2 the three dysprosium and four cobalt sites are arranged into a vertex shared dicubane structure, induced by two structure-directing ligands. Interestingly, a unique and previously unknown dysprosium(iii)-pivalate based counter anion, Dy(η1-O2CCMe3)2(η2-O2CCMe3)2(MeOH)2-, was trapped by the monocationic cores during crystallization. MeCN induced structural rearrangement of 2 through loss of OMe- bridges and dysprosium(iii) ions at the shared vertex resulted in the hexanuclear 3d-4f neutral aggregate 3, in which two dysprosium and four cobalt sites exhibit a near planar disposition. HRMS(+ve) of solutions of 1 and 2 revealed the pathway for aggregation processes and solvent induced structural transformation along with the importance of bridging OMe- in directing the formation of these compounds. Magnetic studies show a non-zero out-of-phase component in the AC susceptibility measurements of 1 but not in 2 and 3, although 1 and 2 have a very similar {CoIII2CoII2DyIII3} core and another DyIII center. Ab initio single-ion calculations point to the different single-ion anisotropic behavior for DyIII centers (energy in cm-1 and g-tensors) as well as negative and positive D values for CoII sites in 1 and 2 respectively reaffirming the experimental result. However, calculations envision that, zero-field out-of-phase signal and no out-of-phase signal in 1 and 2 respectively do not solely generate from the single-ion Dy/Co anisotropies and the overall relaxation mechanism can be understood by considering the exchange interactions between DyIII-DyIII and DyIII-CoII centres.

Unusually Distorted Pseudo-Octahedral Coordination Environment Around CoII from Thioether Schiff Base Ligands in Dinuclear [CoLn] (Ln = La, Gd, Tb, Dy, Ho) Complexes: Synthesis, Structure, and Understanding of Magnetic Behavior.

The synthesis, structural characterization, and magnetic behavior of a new family of binuclear CoII-LnIII complexes of formula [LnIIICoIIL2(NO3)3]·H2O (Ln = La, 1; Gd, 2; Tb, 3; Dy, 4; Ho, 5; HL = 3-methoxy-N-(2-(methylsulfanyl)phenyl)salicylaldimine) have been reported. The chosen ligand system HL has adjacent soft ONS and hard OO binding pockets ideal for selective coordination of CoII and 4f metal ions. All the complexes 1-5 exhibit a CoII center in a highly distorted octahedral geometry with the LnIII centers in bicapped square-antiprism geometry. The unique distortion about the CoII center is introduced by the coordination of 4f metal ions in the hard OO coordination site. The distortion is further supported by the presence of -SMe groups giving an S donor atom which owing to its larger size can support large bond distances and angles. The geometry around the CoII centers is intermediate between meridional and facial geometric isomers. The magnetic properties of these complexes have been investigated by a "full model" approach using CONDON with the experimental magnetochemical analysis revealing ferromagnetic Co-Ln coupling in compounds 2-5. Ab initio calculations on the X-ray crystal structures of 1-5 paint a semiquatitative picture about the contribution of the individual anisotropic centers toward the overall magnetic properties of the compounds. Theoretical analysis predicts 1 and 2 as weak single-ion magnet (SIM) and single-molecule magnet (SMM) respectively with CoII being solely responsible for the complex anisotropy. In 2, JCoGd plays a crucial role in preserving the anisotropy contribution of Co by channelizing relaxation via a higher excited exchange doublet. Because of the inefficiency of JCoTb, JCoDy, and JCoHo in quenching single-ion Ln fragment transverse anisotropy and preserving CoII high axial anisotropy (favoring rhombicity), 3-5 lack SMM behavior.

Entrapment of a Pseudo-Tetrahedral CoII Center by Thioether Sulfur Bound {Co2 (µ-L)} Fragments: Synthesis, Field-Induced Single-Ion Magnetism and Catechol Oxidase Mimicking Activity.

Simultaneous incorporation of both CoII and CoIII ions within a new thioether S-bearing phenol-based ligand system, H3 L (2,6-bis-[{2-(2-hydroxyethylthio)ethylimino}methyl]-4-methylphenol) formed [Co5 ] aggregates [CoII CoIII 4 L2 (µ-OH)2 (µ1,3 -O2 CCH3 )2 ](ClO4 )4 ⋅H2 O (1) and [CoII CoIII 4 L2 (µ-OH)2 (µ1,3 -O2 CC2 H5 )2 ](ClO4 )4 ⋅H2 O (2). The magnetic studies revealed axial zero-field splitting (ZFS) parameter, D/hc=-23.6 and -24.3 cm-1 , and E/D=0.03 and 0.00, respectively for 1 and 2. Dynamic magnetic data confirmed the complexes as SIMs with Ueff /kB =30 K (1) and 33 K (2), and τ0 =9.1×10-8  s (1), and 4.3×10-8  s (2). The larger atomic radius of S compared to N gave rise to less variation in the distortion of tetrahedral geometry around central CoII centers, thus affecting the D and Ueff /kB values. Theoretical studies also support the experimental findings and reveal the origin of the anisotropy parameters. In solutions, both 1 and 2 which produce {CoIII 2 (µ-L)} units, display solvent-dependent catechol oxidation behavior toward 3,5-di-tert-butylcatechol in air. The presence of an adjacent CoIII ion tends to assist the electron transfer from the substrate to the metal ion center, enhancing the catalytic oxidation rate.

Two Types of Hexanuclear Partial Tetracubane [Ni4Ln2] (Ln = Dy, Tb, Ho) Complexes of Thioether-Based Schiff Base Ligands: Synthesis, Structure, and Comparison of Magnetic Properties.

New Schiff base ligand H2L containing N2O4S donor atoms has been explored for its ability to provide complexes of selected 3d and 4f metal ions. Room temperature reaction of H2L with NiCl2·6H2O and Ln(NO3)3·5H2O in the presence of Et3N in MeCN-MeOH (2:1) medium resulted in [Ni4Ln2(L)2(µ-Cl)2(µ3-OH)4(H2O)6]Cl4·2H2O (where Ln = Dy3+ (1), Tb3+ (2), and Ho3+ (3) and H2L = 2-((2-(2-(2-hydroxy-3-methoxybenzylideneamino)ethylthio)ethylimino)methyl)-6-methoxyphenol). Use of Ni(SCN)2·4H2O during synthesis provided SCN- ions for bridging and terminal coordination in [Ni4Ln2(L)2(µ-NCS)2(µ3-OH)4(NCS)4(H2O)2]·xMeOH·yH2O (where Ln = Dy3+ (4), x = 2, y = 4; Tb3+ (5) and Ho3+ (6), x = 0, y = 14.1). All six complexes possess a hexanuclear defective tetracubane topology having exchangeable bridging groups. The study of direct current magnetic susceptibility measurements revealed that the Ni(II) ions are engaged in ferromagnetic interaction with the DyIII, TbIII, and HoIII ions and have significant magnetic anisotropy in all six complexes. Alternating current susceptibility measurements confirmed that both of the two types of compounds qualify as zero-field single-molecule magnets (SMMs), and the effective barrier for the reversal of the magnetic moment was found to be in the range Ueff = 23-31 K for 1-2 and 4-5, respectively. Detailed insight into the electronic structure and magnetic properties was calculated using DFT- and CASSCF-based analyses. The found isotropic exchange parameter (J) values are JNi-Ni = -4.7 cm-1 for 1 and JNi-Ni = +29.2 cm-1 for 4 and clearly indicate that the µ-NCS-bridge is a better candidate than µ-Cl for ferromagnetic exchange interactions. Out of the six complexes, only complex 5 displays TbIII centered emission peaks at 451 and 480 nm.

Rapid Fluorescent-Based Detection of New Delhi Metallo-ß-Lactamases by Photo-Cross-Linking Using Conjugates of Azidonaphthalimide and Zinc(II)-Chelating Motifs.

A method for rapid detection of metallo-ß-lactamases NDM-5 and NDM-7 using conjugates of azidonaphthalimide and Zn(II) chelating motifs (like sulfonamides, hydroxamate, and terpyridine) is described. Incubation and irradiation, followed by gel electrophoresis, clearly show the presence of NDMs. The o-sulfonamide-based probe has the highest efficiency of detection for both the NDMs. The proteins are detectable at nM concentrations, and the method is also selective, works both in vitro and in vivo, as revealed by cellular imaging and also with clinical isolates.

Thioether sulfur-bound [Cu2] complexes showing catechol oxidase activity and DNA cleaving behaviour.

Rational ligand design approaches allowed {Cu2(µ-OH/OMe)} cores to be accommodated within µ-phenoxido bis(tetradentate) and µ-phenoxido bis(tridentate) ligands having thioether donors. The complexes [Cu2(µ-H2L1)(µ-OH)](ClO4)2·2H2O (1), [Cu2(µ-L2)(µ-OH)(OH2)](ClO4)2 (2a) and [Cu2(µ-L2)(µ-OCH3)(OH2)](ClO4)2 (2b) were obtained from an N2O3S2 donor set bearing the H3L1 ligand (2,6-bis-[{2-(2-hydroxyethylthio)ethylimino}methyl]-4-methylphenol) and N2OS2 donor set containing the HL2 ligand (4-methyl-2,6-bis-[{2-(methylthio)phenylimino}methyl]phenol) without showing double phenoxido bridging or any type of preformed inter-fragment aggregation. Previously, we showed that H3L (2,6-bis[((2-(2-hydroxyethoxy)ethyl)imino)methyl]-4-methylphenol), the ether analogue of H3L1, in the presence of carboxylate anions, was responsible for the self-aggregation of preformed {Cu2} fragments and gave two types of [Cu4] complexes comprising [Cu4O] and [Cu4(OH)2] cores (T. S. Mahapatra, A. Bauzá, D. Dutta, S. Mishra, A. Frontera and D. Ray, ChemistrySelect, 2016, 1, 64-74). The molecular structures of 1, 2a and 2b were determined via single crystal X-ray diffraction and solution studies, which indicated the presence of [Cu2] species. This was further confirmed via UV-vis spectroscopy and HRMS analysis. The synthesized complexes were screened for their potential as catalysts for the catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBCH2). A change in the mechanism of catalytic oxidation was observed with a change in the ligand backbone. All three complexes also showed DNA binding properties, which were further substantiated via molecular docking studies. Their DNA binding affinities were quantitatively ascertained using their intrinsic binding constant, Kb, values which were found to be 4.2 × 104, 5.6 × 104 and 4.8 × 104 M-1, respectively. Furthermore, the complexes displayed efficient DNA cleavage behaviour with pBR322 and the oxidative path was established in presence of ROS, singlet oxygen, 1O2, and the superoxide anion, O2·-.

Strategic synthesis of [Cu2], [Cu4] and [Cu5] complexes: inhibition and triggering of ligand arm hydrolysis and self-aggregation by chosen ancillary bridges.

The Schiff base ligand HL1 ({2,6-bis(allylimino)methyl}-4-methylphenol) having no coordinating donor arm has been examined for its reaction medium and ancillary bridge dependent reactivity for a hierarchical family of CuII complexes. The ligand showed a unique reactivity pattern toward CuII in solution. The bridging nature of in situ generated HO- ions in the absence and presence of externally added carboxylates (RCOO-; R = CF3, C6H5 and CH3) has been utilized to produce complexes {[Cu2(µ-L2)2(H2O)]2[Cu2(µ-L2)2(H2O)2](ClO4)6} (1) (HL2 = 3-{(allylimino)methyl}-2-hydroxy-5-methylbenzaldehyde), [Cu4(µ4-O)(µ-L1)2(µ1,3-O2CCF3)4] (2), [Cu4(µ4-O)(µ-L1)2(µ1,3-O2CC6H5)4]·H2O (3), and [Cu5(µ3-OH)2(µ-L1)2(µ1,3-OAc)2(OAc)2(H2O)4][Cu5(µ3-OH)2(µ-L1)2(µ1,3-OAc)2(OAc)3(H2O)](ClO4)3·2C2H5OH (4). The absence of carboxylate anions did not yield HO- ions in situ and triggered single ligand arm hydrolysis. The formation of tetra- and pentanuclear aggregates as well as ligand hydrolyzed dinuclear products has been rationalized to identify the possible roles of carboxylate anions in solution. Detailed characterization of the complexes in the solid state and in solution has been carried out using spectroscopic measurements, X-ray crystallography, variable temperature magnetic measurements and functional behavior. In MeOH solutions at 298 K, the complexes 1-4 showed catalytic oxidation of 3,5-di-tert-butyl catechol (3,5-DTBCH2) saturated with O2 from the air.

Trapping of a Pseudotetrahedral CoIIO4 Core in Mixed-Valence Mixed-Geometry [Co5] Coordination Aggregates: Synthetic Marvel, Structures, and Magnetism.

A systematic one-step one-pot multicomponent reaction of Co(ClO4)2·6H2O, H3L (2,6-bis((2-(2-hydroxyethylamino)ethylimino)methyl)-4-methylphenol), and readily available carboxylate salts (RCO2Na; R = CH3, C2H5) resulted in the two structurally novel coordination aggregates [CoIICoIII4L2(µ1,3-O2CCH3)2(µ-OH)2](ClO4)4·4H2O (1) and [CoIICoIII4L2(µ1,3-O2CC2H5)2(µ-OH)(µ-OMe)](ClO4)4·5H2O (2). At room temperature, reactions of H3L in MeOH with cobalt(II) perchlorate salts led to coassembly of initially formed ligand-bound {CoII2} fragments following aerial oxidation of metal centers and bridging by in situ generated hydroxido/alkoxido groups and added carboxylate anions. Available alkoxido arms of the initially formed {L(µ1,3-O2CCH3)(µ-OH/OMe)Co2}+ fragments were utilized to trap a central CoII ion during the formation of [Co5] aggregates. In the solid state, both complexes have been characterized by X-ray crystallography, variable-temperature magnetic measurements, and theoretical studies. Both 1 and 2 show field-induced slow magnetic relaxation that arises from the single pseudo- T d CoII ion present. The structural distortion leads to an easy-axis magnetic anisotropy ( D = -31.31 cm-1 for 1 and -21.88 cm-1 for 2) and a small but non-negligible transverse component ( E/ D = 0.11 for 1 and 0.08 for 2). The theoretical studies also reveal how the O-Co-O bond angles and the interplanar angles control D and E values in 1 and 2. The presence of two diamagnetic {Co2(µ-L)} hosts controls the distortion of the central {CoO4} unit, highlighting a strategy to control single-ion magnetic anisotropy by trapping single ions within a diamagnetic coordination environment.