Bicompartmental Schiff Base Research Articles

Molecular architecture, characterization, and applications of homoleptic heteronuclear 3d/4f metals’ complexes derived from bi-compartmental Schiff-base

A series of homoleptic heterotrinuclear 3d/4f metal complexes (2-6) of general formula [Zn2Ln(salopn)2(NO3)3H2O].CH3CN.H2O; where Ln = La (2), Nd (3), Sm (4), Gd (5) and Dy (6); have been synthesized by using tetradentate bi-compartmental Schiff base ligand, [2-((E)-(2-((E)-2-hydroxybenzylideneamino)phenylimino)methyl)phenol], and Zn(salopn) precursor (1). The unequivocal evidence of their structural motifs is obtained by characterizing the compounds through FT-IR spectroscopic, and single crystal XRD data, besides the elemental analyses. The trinuclear complex 6 shows that the ligand attached to the metals’ centers, Zn(II) and Dy(III) through N, O and O, O sites respectively. The zinc center is pentacoordinated having distorted square pyramidal geometry and to which Zn-O and Zn-N bond lengths lie in range 2.006-2.035 Å and 2.044-2.060 Å respectively. The dysprosium center is octa-coordinated which is attached to four oxygen atoms from salopn−2 and four oxygens from bidentate nitrate moieties, where Dy-O bond length is in range 2.292-2.517 Å. The photoluminescence (PL) data described that the heteronuclear complexes show characteristic luminescence properties and sensitization across the bi-compartmental ligand. The magnetic parameters for (2-6) are determined and their room temperature χm T and µeff values are found in range 0.18-15.12 emu.mole−1.K and 1.20-10.96 µB respectively that describe the paramagnetic nature.

Water inclusion mediated structural diversity and the role of H-bonds in molecular assemblies of manganese(III) bicompartmental Schiff-base complexes

Six new manganese(III) derivatives using the ligand H2MeOsalen: N,N′-ethylenebis(3-methoxysalicylaldiimine), have been synthesized and structurally characterized. In all cases the manganese ion is six-coordinated and occupies the internal cavity of the bicompartmental salen ligand. The manganese ion completes its coordination environment with one axial water molecule and one additional ligand, either water, ethanol or one acetate anion. The molecular unit is dimerized by the insertion of the coordinated water molecule into the external MeOsalen cavity of one neighbouring complex. This supramolecular dimer constitutes the structural basis for these compounds, the differences arising from the intermolecular hydrogen bonds involving the counter anions and crystallization solvent molecules. In this way, examples of pseudopolymorphism, cocrystallization and water/anion tapes held by the interaction with the complex dimers are described. The compound [{Mn(MeOsalen)K(H2O)0.5}2(μ-OOCMe)](PF6)3·HOCH2CH2OH is a heterometallic Mn/K derivative where the potassium ion occupies the external cavity, while the coordination of the manganese ion is completed by bridging acetate and ethyleneglycol ligands. The formation of ethyleneglycol is attributed to a stoichiometric oxidation of the ethanol solvent, attributed to the presence of the potassium ion in the complex.

Binuclear CuLn complexes (LnIII = Gd, Tb, Dy) of alcohol-functionalized bicompartmental Schiff-base ligand. Hydrogen bonding and magnetic behaviors

Preparation, crystal structures and magnetic properties of a series of four binuclear Cu–Ln complexes are reported (Ln=GdIII, TbIII, and DyIII). These are based on a bicompartmental Schiff-base ligand formed by condensation of 1,3-diaminopropan-2-ol with ortho-vanillin. This Schiff-base is known to usually involve its deprotonated alcohol group in metal coordination, which is not the case here. Instead the OH unit is engaged in H-bonding interactions. Intra- and inter-molecular H-bonds are formed when the alcohol group is located in axial position of the six-member ring formed by the diamino moiety and the Cu atom. In equatorial position, this group is only involved in intermolecular bonding. The corresponding Cu–Tb derivative is shown to behave as a Single Molecule Magnet with ΔkB=24.6K and τ0=2.1×10−8s (HDC=1.5kOe).

Oligomeric and polymeric organizations of potassium salts with compartmental Schiff-base complexes as ligands

The complexation of K+ ions by mono-metallated bicompartmental Schiff-base complexes in double-decker-type arrangement was found to yield various supramolecular organizations as a function of the associated anions. A series of four [{LMK}n{LM}]n+ aggregates with n = 1, 2, 3, and ∞ are reported (M = Ni2+ or Cu2+; L stands for the Schiff-base). Assembling KNCS with the metallo-ligand led to 1-D [L3CCuK(NCS)]n whereas KOH yielded the simplest possible case, [(L2CNi)2KOH]·H2O. Oligomeric organizations containing two or three alkali ions were achieved in the presence of the [Mo(NCS)6]3− anion. Such stacks have not been found with Na2+ due to a different local arrangement with the metallo-ligand. The crystal packing for [(L2CNi)2KOH]·H2O yields an open-framework structure with a void volume of 20%.

First binuclear Cr(III)–Mn(III) oxalato-bridged complexes: Synthesis, crystal structures and magnetic properties

Two Cr(III)–Mn(III) binuclear complexes, with the general formula [{Mn(H 2O)(valen)}{Cr(AA)(C 2O 4) 2}] · 3H 2O, have been obtained by assembling [Mn((H 2O)(CH 3CN)(valen)] + and [Cr(AA)(C 2O 4) 2] − ions [H 2valen is a bicompartmental Schiff-base proligand, resulting from the 2:1 condensation of 3-methoxysalicyladehyde with ethylenediamine; AA = 2,2′-bipyridine (bipy) 1; 1,10-phenahroline (phen) 2]. In the two compounds the [Cr(AA)(C 2O 4) 2] − ions coordinate through one oxalato oxygen atom into one apical position of the manganese(III) ions, which exhibit an elongated octahedral stereochemistry. The other apical position is occupied by an aqua ligand. The intramolecular distances between the metal centers are 5,329 and 5.442 Å, for 1 and 2, respectively. The packing of the molecules in the crystal (the interactions at the supramolecular level) are governed by the self-complementarity of the {Mn(valen)(H 2O)} moieties. The aqua ligand of one moiety is hydrogen bonded to the oxygen atoms from the { O 2 O 2 ′ } compartment of a second complex yielding head-to-teal dimeric species. The magnetic properties of the two complexes have been investigated and reveal weak antiferromagnetic interactions mediated by the oxalato bridge (2 J = −2.12, and −2.02 cm −1 for 1 and 2, respectively). The zero-field-splitting effects for the two metal ions have been taken into account.