Sasankasekhar Mohanta

Heterobridged dinuclear, tetranuclear, dinuclear-based 1-d, and heptanuclear-based 1-D complexes of copper(II) derived from a dinucleating ligand: syntheses, structures, magnetochemistry, spectroscopy, and catecholase activity.

The work in this paper presents syntheses, characterization, crystal structures, variable-temperature/field magnetic properties, catecholase activity, and electrospray ionization mass spectroscopic (ESI-MS positive) study of five copper(II) complexes of composition [Cu(II)(2)L(μ(1,1)-NO(3))(H(2)O)(NO(3))](NO(3)) (1), [{Cu(II)(2)L(μ-OH)(H(2)O)}(μ-ClO(4))](n)(ClO(4))(n) (2), [{Cu(II)(2)L(NCS)(2)}(μ(1,3)-NCS)](n) (3), [{Cu(II)(2)L(μ(1,1)-N(3))(ClO(4))}(2)(μ(1,3)-N(3))(2)] (4), and [{Cu(II)(2)L(μ-OH)}{Cu(II)(2)L(μ(1,1)-N(3))}{Cu(II)(μ(1,1)-N(3))(4)(dmf)}{Cu(II)(2)(μ(1,1)-N(3))(2)(N(3))(4)}](n)·ndmf (5), derived from a new compartmental ligand 2,6-bis[N-(2-pyridylethyl)formidoyl]-4-ethylphenol, which is the 1:2 condensation product of 4-ethyl-2,6-diformylphenol and 2-(2-aminoethyl)pyridine. The title compounds are either of the following nuclearities/topologies: dinuclear (1), dinuclear-based one-dimensional (2 and 3), tetranuclear (4), and heptanuclear-based one-dimensional (5). The bridging moieties in 1-5 are as follows: μ-phenoxo-μ(1,1)-nitrate (1), μ-phenoxo-μ-hydroxo and μ-perchlorate (2), μ-phenoxo and μ(1,3)-thiocyanate (3), μ-phenoxo-μ(1,1)-azide and μ(1,3)-azide (4), μ-phenoxo-μ-hydroxo, μ-phenoxo-μ(1,1)-azide, and μ(1,1)-azide (5). All the five compounds exhibit overall antiferromagnetic interaction. The J values in 1-4 have been determined (-135 cm(-1) for 1, -298 cm(-1) for 2, -105 cm(-1) for 3, -119.5 cm(-1) for 4). The pairwise interactions in 5 have been evaluated qualitatively to result in S(T) = 3/2 spin ground state, which has been verified by magnetization experiment. Utilizing 3,5-di-tert-butyl catechol (3,5-DTBCH(2)) as the substrate, catecholase activity of all the five complexes have been checked. While 1 and 3 are inactive, complexes 2, 4, and 5 show catecholase activity with turn over numbers 39 h(-1) (for 2), 40 h(-1) (for 4), and 48 h(-1) (for 5) in dmf and 167 h(-1) (for 2) and 215 h(-1) (for 4) in acetonitrile. Conductance of the dmf solution of the complexes has been measured, revealing that bridging moieties and nuclearity have been almost retained in solution. Electrospray ionization mass (ESI-MS positive) spectra of complexes 1, 2, and 4 have been recorded in acetonitrile solutions and the positive ions have been well characterized. ESI-MS positive spectrum of complex 2 in presence of 3,5-DTBCH(2) have also been recorded and, interestingly, a positive ion [Cu(II)(2)L(μ-3,5-DTBC(2-))(3,5-DTBCH(-))Na(I)](+) has been identified.

Magnetic Exchange Interactions and Magneto-Structural Correlations in Heterobridged μ-Phenoxo-μ1,1-Azide Dinickel(II) Compounds: A Combined Experimental and Theoretical Exploration

This investigation presents the syntheses, crystal structures, magnetic properties, and density functional theoretical modeling of magnetic behavior of two heterobridged μ-phenoxo-μ(1,1)-azido dinickel(II) compounds [Ni(II)(2)(L(1))(2)(μ(1,1)-N(3))(N(3))(H(2)O)]·CH(3)CH(2)OH (1) and [Ni(II)(2)(L(2))(2)(μ(1,1)-N(3))(CH(3)CN)(H(2)O)](ClO(4))·H(2)O·CH(3)CN (2), where HL(1) and HL(2) are the [1+1] condensation products of 3-methoxysalicylaldehyde and 1-(2-aminoethyl)-piperidine (for HL(1))/4-(2-aminoethyl)-morpholine (for HL(2)), along with density functional theoretical magneto-structural correlations of μ-phenoxo-μ(1,1)-azido dinickel(II) systems. Compounds 1 and 2 crystallize in orthorhombic (space group Pbca) and monoclinic (space group P2(1)/c) systems, respectively. The coordination environments of both metal centers are distorted octahedral. The variable-temperature (2-300 K) magnetic susceptibilities at 0.7 T of both compounds have been measured. The interaction between the metal centers is moderately ferromagnetic; J = 16.6 cm(-1), g = 2.2, and D = -7.3 cm(-1) for 1 and J = 16.92 cm(-1), g = 2.2, and D(Ni1) = D(Ni2) = -6.41 cm(-1) for 2. Broken symmetry density functional calculations of exchange interaction have been performed on complexes 1 and 2 and provide a good numerical estimate of J values (15.8 cm(-1) for 1 and 15.35 cm(-1) for 2) compared to experiments. The role of Ni-N bond length asymmetry on the magnetic coupling has been noted by comparing the structures and J values of complexes 1 and 2 together with previously published dimers 3 (Eur. J. Inorg. Chem. 2009, 4982), 4 (Inorg. Chem. 2004, 43, 2427), and 5 (Dalton Trans. 2008, 6539). Our extensive DFT calculations reveal an important clue to the mechanism of coupling where the orientation of the magnetic orbitals seems to differ with asymmetry in the Ni-N bond lengths. This difference in orientation leads to a large change in the overlap integral between the magnetic orbitals and thus the magnetic coupling. DFT calculations have also been extended to develop several magneto-structural correlations in this type of complexes and the correlation aim to focus on the asymmetry of the Ni-N bond lengths reveal that the asymmetry plays a proactive role in governing the magnitude of the coupling. From a completely symmetric Ni-N bond length, two behaviors have been noted: with a decrease in bond length there is an increase in the ferromagnetic coupling, while an increase in the bond lengths leads to a decrease in ferromagnetic interaction. The later correlation is supported by experiments. The magnetic properties of 1, 2, and three previously reported related compounds have been discussed in light of the structural parameters and also in light of the theoretical correlations determined here.

Syntheses and crystal structures of CuIIBiIII, CuIIBaIICuII, [CuIIPbII]2 and cocrystallized (UVIO2)2.4CuII complexes: structural diversity of the coordination compounds derived from N,N′-ethylenebis(3-ethoxysalicylaldiimine)

Syntheses, characterization and structures of heterodinuclear compound [CuIIL1BiIII(NO3)3] (1), sandwich type heterotrinuclear compound [(CuIIL1)2BaII(NO3)2]·0.2H2O (2), heterotetranuclear compound [{CuIIL1PbII(µ-NO3)(NO3)}2] (3) and heterohexanuclear [2 × 1 + 1 × 4] cocrystal [(UVIO2)2(µ-H2O)2(NO3)4]·4[CuIIL1⊂(H2O)] (4) are described in this investigation (H2L1 = N,N′-ethylenebis(3-ethoxysalicylaldiimine)). Compounds 1 and 4 crystallize in orthorhombic P212121 and triclinic Pī systems, respectively, while the space group of compounds 2 and 3 is monoclinic P21/c. The structure of 1 consists of a diphenoxo-bridged CuIIBiIII dinuclear core containing three chelating nitrates and a 10-coordinate bismuth(III) centre. The dinuclear cores are self-assembled to two dimensions through intermolecular nitrate oxygen⋯copper(II) semicoordination and weak C–H⋯O hydrogen bonds. Compound 2 is a double-decker CuIIBaIICuII system in which a barium(II) ion is sandwiched between two mononuclear [CuIIL1] moieties. The barium(II) centre is 11-coordinate, four phenoxo and four ethoxy oxygen atoms and one chelating and one monodentate nitrate ions. Compound 3 is a tetranuclear system (dimer of two dinuclear moieties) in which one nitrate is chelating, while the second nitrate behaves as both a chelating and bridging ligand. The lead(II) centre is 9-coordinate in this compound. Compound 4 is a [2 × 1 + 1 × 4] cocrystal of one diaqua-bridged diuranyl(VI) moiety, containing two chelating nitrates and 8-coordinated hexagonal bipyramidal uranium(VI) centres and four inclusion species [CuIIL1⊂(H2O)]. The governing factor for the self-assembled cocrystallization in 4 are the C–H⋯·π and C–H⋯O hydrogen bonds. The compounds reported in this investigation and other heteronuclear systems derived from N,N′-ethylenebis(3-ethoxysalicylaldiimine) indicate that this ligand system is an important example which gives rise to structurally diverse heteronuclear compounds. In addition to the structural diversity, the structural resemblance of bismuth(III) with lanthanides(III) and utilization of noncovalent interactions to form self-assembly and cocrystals are the major outcomes of the present investigations.

A unique example of a three component cocrystal of metal complexes

The synthesis, characterization and structure of a [3 × 1 + 2 × 1 + 1 × 2] cocrystal [(NiIIL1)2NaI(NO3)]·[{NiIIL1NaI(H2O)2}{NiIIL1}2(NO3)] derived from the hexadentate Schiff base compartmental ligand N,N′-ethylenebis(3-ethoxysalicylaldimine) (H2L1) are described. The compound crystallizes in the monoclinic system (space group C2/c). The structure consists of one trinuclear double-decker [(NiIIL1)2NaI]+ cation, one dinuclear [NiIIL1NaI(H2O)2]+ cation and two mononuclear [NiIIL1] moieties. Each of the two coordinated water molecules of the dinuclear unit is encapsulated in the O4 cavities of the two mononuclear [NiIIL1] moieties resulting in the formation of a tetranuclear self-assembly, which is further interlinked with the trinuclear sandwich species due to Ni⋯Ni interaction to result in an overall one-dimensional topology in the title compound. A unique example of a three component cocrystal of metal complexes, existence of NaI in two entirely different environments in spite of being surrounded by the same blocking ligand and structural resemblance of sodium(I) with 3d metal ions are the major outcomes of the present investigation.

Syntheses and crystal structures of dinuclear, trinuclear [2 × 1 + 1 × 1] and tetranuclear [2 × 1 + 1 × 2] copper(II)–d10 complexes (d10 ⇒ ZnII, CdII, HgII and AgI) derived from N,N′-ethylenebis(3-ethoxysalicylaldimine)

Syntheses, characterization and crystal structures of heterotetranuclear [2 × 1 + 1 × 2] co-crystals [{CuIILZnII(H2O)2}{CuIIL}2](ClO4)2 (1) and [{CuIILCdII(H2O)2(CH3CN)}{CuIIL}2](ClO4)2 (2), dinuclear compound [CuIILHgII(CH2COCH3)](ClO4) (3) and heterotrinuclear [2 × 1 + 1 × 1] co-crystal [{CuIILAgI(H2O)}{CuIIL}](ClO4) (4) derived from N,N′-ethylenebis(3-ethoxysalicylaldimine) (H2L) are reported herein. Compounds 3 and 4 crystallize in the orthorhombic Pbca and monoclinic P21/c systems, respectively, while the space group of compounds 1 and 2 is monoclinic C2/c. The structure of 3 consists of a monophenoxo-bridged CuIIHgII dinuclear core in which the mercury(II) centre is dicoordinated by the bridging phenoxo oxygen atom and the CH2 carbon atom of the mono-deprotonated acetone anion. The coordination environment of HgII in this compound is almost linear. In the CuII2AgI compound 4, one diphenoxo-bridged [CuIILAgI(H2O)]+ cation is co-crystallized with one mononuclear [CuIIL] moieties. On the other hand, the structures of the CuII3MII compounds 1 (M = Zn) and 2 (M = Cd) consist of one diphenoxo-bridged dinuclear CuIIMII unit and two mononuclear [CuIIL] moiety; the composition of the dinuclear unit being [CuIILZnII(H2O)2]2+ and [CuIILCdII(H2O)2(CH3CN)]2+ for 1 and 2, respectively. The AgI (in 4), ZnII (in 1) and CdII (in 2) ions in the diphenoxo-bridged dinuclear cores are tri-, tetra- and heptacoordinated, respectively. The metal ions are coordinated to two bridging phenoxo oxygen atoms, with the silver(I) and zinc(II) centres being additionally coordinated to one and two water molecules, respectively. While in the case of cadmium(II), the additional five coordination positions are occupied by two ethoxy oxygen atoms, two water oxygen atoms and one acetonitrile nitrogen atom. The coordination environment of silver(I) in 4 is pyramidal with a scalene O3 triangle as the base, whereas those of zinc(II) and cadmium(II) in 1 and 2 are distorted tetrahedral and distorted pentagonal bipyramidal, respectively. The coordinated water molecule in 4 and each of the two coordinated water molecules in 1 and 2 are encapsulated into the O4 compartment of a [CuIIL] moiety resulting in the [2 × 1 + 1 × 1] (for 4) or [2 × 1 + 1 × 2] (for 1 and 2) cocrystallization and self-assemblies. Clearly, the encapsulation of the coordinated water molecule(s) is the governing force for the formation of dinuclear-mononuclear co-crystals in 1, 2 and 4. In addition all four compounds 1–4 have π–π stacking interactions which form dimers between pairs of adjacent molecules in the structure of 3 consisting of CuIIHgII dimers, while one-dimensional stacks are formed in the CuII3ZnII (1), CuII3CdII (2) and CuII2AgI (4) complexes. The compositions of the title compounds are compared with the related systems derived from the same ligand. The [2 × 1 + 1 × 1] co-crystal, 4, is a new type of system in terms of the number of components. Again, in spite of the tri-, tetra- and hepta-coordinated nature of the second metal ion in the dinuclear cores, co-crystallization in 1, 2 and 4, respectively, are new observations. The accommodation/coordination of varieties of metal ions by the O4 compartment of H2L has also been highlighted in the present investigation.

A tale of crystal engineering of metal complexes derived from a special ligand family having a cosmopolitan compartment

The journey of the syntheses and studies of the structures and properties of metal complexes derived from double-compartment 3-ethoxysalicylaldehyde-diamine (H2LOEt) ligands was started in 1995, as per the CSD version 1.15 (2012) record. After dealing with mainly mononuclear complexes in the early years, the “metallo-ligand as reactant” approach was started in 2002 with the reporting of a CuIIGdIII compound, with the aim to explore the magnetic properties of 3d–4f systems. It was realized within a few years that the O(phenoxo)2O(ethoxy)2 compartment has strong potential to interact with water molecule(s) due to the formation of bifurcated hydrogen bonds, resulting in the stabilization of the mononuclear inclusion products and two-component and even three-component cocrystals. “Metallo-ligand as reactant” was reacted with several metal ions from various parts of the periodic table (s, p, 3d, d10, 4f, 5f) as well as with possible hydrogen bond donors, such as an ammonium ion, diprotonated diamines, dicarboxylic acids and aquated proton (perchloric acid). A number of cocrystals, supramolecular dimers, a new type of hydrate isomerism, systems with interesting topologies and systems showing resemblances of entirely different types of metal ions have been obtained. Eventually, we can call the H2LOEt a special ligand family and the O(phenoxo)2O(ethoxy)2 compartment a cosmopolitan compartment. This highlight deals with the metal complexes derived from 3-ethoxysalicylaldehyde-diamine ligands from a crystal engineering perspective.

Crystal structures of discrete, one-dimensional and cocrystalline copper(II)–uranyl(VI) systems: the influence of the reactant ratio in the competition between hydrogen bonds and coordinate bonds

This paper presents the syntheses and crystal structures of four copper(II)–uranyl(VI) compounds [{CuIILOEt–en}2·{(UVIO2)(NO3)2(H2O)2}] (1), [CuII(MeCN)LOEt–pn(UVIO2)(NO3)2] (2), [(UVIO2)2(μ-H2O)2(NO3)4]∙4[CuIILOEt–py(H2O)]∙2MeCN (3) and {[CuIILOMe–en(UVIO2)(NO3)]2[(UVIO2)2(μ-HO)2(NO3)4]}n (4), where H2LOEt–en, H2LOEt–pn, H2LOEt–py and H2LOMe–en are 3-ethoxysalicylaldehyde-diamine (H2LOEt) or 3-methoxysalicylaldehyde-diamine (H2LOMe) ligands in which the diamine functionality are ethylenediamine, 1,3-diaminopropane, 2,3-diaminopyridine and ethylenediamine, respectively. Compound 1 is a [1 × 2 + 1 × 1] trinuclear cocrystal containing two mononuclear [CuIILOEt–en] and one mononuclear [(UVIO2)(NO3)2(H2O)2] moiety; two coordinated water molecules interact with two O4 compartments by forming hydrogen bonds. Compound 2 is a dinuclear system in which two phenoxo oxygen atoms coordinate with the uranium(VI) centre. Compound 3 is a [2 × 1 + 1 × 4] hexanuclear cocrystal of four mononuclear [CuIILOEt–py(H2O)] units and one dinuclear [(UVIO2)2(μ-H2O)2(NO3)4] moiety; O–H⋯O and C–H⋯O interactions interlink the five units here. In 4, there are two dinuclear [CuIILOMe–en(UVIO2)(NO3)]+ cations and one dinuclear [(UVIO2)2(μ-HO)2(NO3)4]2− anion, which are self-assembled to generate a one-dimensional topology. Interesting structural aspects including the weak interaction directed self-assemblies and most importantly, the competition between hydrogen bond and coordinate bond formation and the influence of the reactant ratio in governing that competition are discussed. The diffuse reflectance or solution transmission spectra (for the d–d band) of 1–4 and the corresponding mononuclear copper(II) precursors are also described.

Syntheses, crystal structures and supramolecular topologies of nickel(II)–s/p/d10/NH4+ complexes derived from a compartmental ligand

The syntheses, characterization and crystal structures of ten complexes of composition [{NiIILLiI(H2O)2}{NiIIL}2](ClO4) (1), [NiIILNaI(ClO4)(CH3OH)] (2), [(NiIIL)2NaI](BPh4)·CH3COCH3 (3), [(NiIIL)2RbI](BPh4)·CH3COCH3 (4), [(NiIIL)2CsI](ClO4)·CH3CN (5), [{NiIILMgII(H2O)3}{NiIIL}2](ClO4)2 (6), [NiIILCaII(NO3)2(H2O)]·1.5H2O (7), [NiIILCdII(NO3)2]·CH3CN (8), [NiIILPbII(NO3)2] (9) and [(NiIIL)2(NH4)](PF6) (10) are reported, where H2L = N,N′-ethylenebis(3-ethoxysalicylaldimine). The crystal systems and space groups are: triclinic Pī for 1, 4, 5 and 8, monoclinic P21/c for 2, 3, 7 and 9, monoclinic C2/c for 6 and monoclinic P21/n for 10. In 1–10, the salen type N2O2 compartment of [L]2− is occupied by a NiII ion, while the larger and open O(phenoxo)2O(ethoxy)2 compartment interacts with LiI in 1, NaI in 2 and 3, RbI in 4, CsI in 5, MgII in 6, CaII in 7, CdII in 8, PbII in 9 and NH4+ in 10. Compounds 1 and 6 are [2 × 1 + 1 × 2] tetrametallic cocrystals of one diphenoxo-bridged dinuclear NiIILiI (for 1) and NiIIMgII (for 6) unit and two mononuclear [NiIIL] moieties. Compounds 2, 7, 8 and 9 are diphenoxo-bridged dinuclear NiIINaI, NiIICaII and NiIICdII and NiIIPbII systems, respectively. On the other hand, compounds 3, 4 and 5 are trinuclear NiII2NaI, NiII2RbI and NiII2CsI systems, respectively, in which each of the two adjacent pairs of metal ions is diphenoxo-bridged. The rubidium(I) and cesium(I) analogues are also double-decker sandwich systems. The ammonium ion in [(NiIIL)2(NH4)](PF6) (10) is sandwiched in between two [NiIIL] moieties due to hydrogen bonds between ammonium hydrogen atoms and O4 compartments. Weak interaction assisted following self-assemblies are observed: dimeric in 1 and one-dimensional in 10 due to Ni⋯Ni weak interaction; one-dimensional in 2 due to C–H⋯π and O–H⋯O hydrogen bonds; nice cyclic topology in 5 due to Ni⋯Ni interaction and C–H⋯O hydrogen bonds; one-dimensional in 6 due to Ni⋯Ni interaction and C–H⋯O hydrogen bond; one-dimensional in 8 due to π···π stacking.

Syntheses, characterizations, and crystal structures of 3d–s/d10 metal complexes derived from two compartmental Schiff base ligands

The present investigation reports the syntheses, characterizations, and crystal structures of nine copper(II)/nickel(II)–s/d10 complexes, [CuIIL1NaI(ClO4)(CH3CN)] (1), [CuIIL1KI(ClO4)(CH3COCH3)] (2), [CuIIL2ZnIICl2]·CH3CN (3), [(CuIIL2)2NaI](ClO4)·CH3COCH3 (4), [(NiIIL1)2KI](ClO4) (5), [(CuIIL1)2CsI(ClO4)]·2CH3CN (6), [(NiIIL1)2CsI(ClO4)]·2H2O (7), [(CuIIL2)2SrII(H2O)2](NO3)2 (8), and [{CuIIL2LiI(H2O)}2(μ-H2O)](ClO4)2 (9), where H2L1 and H2L2 are two 3-methoxysalicylaldehyde-diamine (H2LOMe) ligands in which the diamine moieties are o-phenylenediamine and trans-1,2-diaminocyclohexane, respectively. Among these nine compounds, three (1, 2, and 3) are dinuclear, five (4, 5, 6, 7, and 8) are trinuclear, and 9 is tetranuclear. Trinuclear 6 and 7 are double-decker sandwich systems. Some (in 3 and 9) or all (in 1, 2, and 4–8) of the four oxygens of the O(phenoxo)2O(methoxy)2 compartment(s) are coordinated to the second metal ion (NaI in 1 and 4, KI in 2 and 5, ZnII in 3, CsI in 6 and 7, SrII in 8, and LiI in 9). The di/tri/tetranuclear molecules in 2–9 are self-assembled by weak attractions, such as hydrogen bonds/cation (KI) π/C–H π interactions. The following self-assemblies are observed: 1-D in 3, 7, and 9, 1-D ladder in 4, 2-D in 8, and 3-D in 2 and 5.

Slow magnetic relaxation and electron delocalization in an S = 9/2 iron(II/III) complex with two crystallographically inequivalent iron sites

The magnetic, electronic, and Mössbauer spectral properties of [Fe(2)L(μ-OAc)(2)]ClO(4), 1, where L is the dianion of the tetraimino-diphenolate macrocyclic ligand, H(2)L, indicate that 1 is a class III mixed valence iron(II∕III) complex with an electron that is fully delocalized between two crystallographically inequivalent iron sites to yield a [Fe(2)](V) cationic configuration with a S(t) = 9∕2 ground state. Fits of the dc magnetic susceptibility between 2 and 300 K and of the isofield variable-temperature magnetization of 1 yield an isotropic magnetic exchange parameter, J, of -32(2) cm(-1) for an electron transfer parameter, B, of 950 cm(-1), a zero-field uniaxial D(9∕2) parameter of -0.9(1) cm(-1), and g = 1.95(5). In agreement with the presence of uniaxial magnetic anisotropy, ac susceptibility measurements reveal that 1 is a single-molecule magnet at low temperature with a single molecule magnetic effective relaxation barrier, U(eff), of 9.8 cm(-1). At 5.25 K the Mössbauer spectra of 1 exhibit two spectral components, assigned to the two crystallographically inequivalent iron sites with a static effective hyperfine field; as the temperature increases from 7 to 310 K, the spectra exhibit increasingly rapid relaxation of the hyperfine field on the iron-57 Larmor precession time of 5 × 10(-8) s. A fit of the temperature dependence of the average effective hyperfine field yields |D(9∕2)| = 0.9 cm(-1). An Arrhenius plot of the logarithm of the relaxation frequency between 5 and 85 K yields a relaxation barrier of 17 cm(-1).