Syntheses, structures, and magnetic properties of diphenoxo-bridged M(II)Ln(III) complexes derived from N,N'-ethylenebis(3-ethoxysalicylaldiimine) (M = Cu or Ni; Ln = Ce-Yb): observation of surprisingly strong exchange interactions

A series of heterodinuclear Cu(II)Ln(III) and Ni(II)Ln(III) complexes, [M(II)L(1)Ln(III)(NO(3))(3)] (M = Cu or Ni; Ln = Ce-Yb), with the hexadentate Schiff base compartmental ligand N,N'-ethylenebis(3-ethoxysalicylaldiimine) (H(2)L(1)) have been synthesized and characterized. The X-ray crystal structure determinations of 13 of these compounds reveal that they are all isostructural. All of these complexes crystallize with the same orthorhombic P2(1)2(1)2(1) space group with closely similar unit cell parameters. Typically, the structure consists of a diphenoxo-bridged 3d-4f dinuclear core, self-assembled to two dimensions due to the intermolecular nitrate...copper(II) or nitrate...nickel(II) semicoordination and weak C-H...O hydrogen bonds. Despite that, the metal centers of the neighboring units are well separated (the ranges of the shortest intermolecular contacts (A) are (M...M) 7.46-7.60, (Ln...Ln) 8.56-8.69, and (M...Ln) 6.12-6.20). Variable-temperature (5-300 K) magnetic susceptibility measurements of all the complexes have been made. The nature of exchange interactions in the Cu(II)Ln(III) systems has been inferred from the Deltachi(M)T versus T plots, where Deltachi(M)T is the difference between the values of chi(M)T for a Cu(II)Ln(III) system and its corresponding Ni(II)Ln(III) analogue. Ferromagnetic interactions seem to be exhibited by the Cu(II)Gd(III), Cu(II)Tb(III), Cu(II)Dy(III), Cu(II)Ho(III), Cu(II)Tm(III), and Cu(II)Yb(III) complexes, while, for the Cu(II)Er(III) complex, no definite conclusion could be reached. On the other hand, among the lower members of the series, the complexes of Ce(III), Nd(III), and Sm(III) exhibit antiferromagnetic interactions, while the Cu(II)Pr(III) and Cu(II)Eu(III) analogues behave as spin-uncorrelated systems. The observations made here vindicate the proposition of Kahn (Inorg. Chem. 1997, 36, 930). The Deltachi(M)T versus T plots also suggest that, for most of the Cu(II)Ln(III) complexes, the exchange interactions are fairly strong, which probably could be related to the small dihedral angle (ca. 4 degrees) between the CuO(2) and LnO(2) planes.     

Intramolecular O-H...O hydrogen-bond-mediated reversal in the partitioning of conformationally restricted triplet 1,4-biradicals and amplification of diastereodifferentiation in their lifetimes

The photoreactivity and nanosecond transient phenomena have been investigated for a rationally designed set of ketones 4-9 in order to gain comprehensive insights concerning the influence of intramolecular hydrogen bonding on (i) the lifetimes of triplet 1,4-biradicals and (ii) the partitioning of the latter between cyclization and elimination. Comparisons of the photochemical results and lifetime data for the biradicals of ketones 6 versus 8 and 7 versus 9 revealed a remarkable influence of hydrogen bonding when superimposed upon steric factors: while 6 and 7 yielded cyclobutanols in poor yields, cyclization was found to be overwhelmingly predominant for 8-anti and moderately so for 9-anti, with a high stereoselectivity in the formation of cyclobutanols (>95% for 8-anti). The diastereochemistry in the case of 8 permitted the occurrence of fragmentation or cyclization almost exclusively (>90% cyclization for 8-anti and >75% elimination for 8-syn). Significantly, the intramolecular hydrogen bonding in the biradicals of 8 and 9 was found to reverse their partitioning between cyclization and elimination compared with the behavior of the biradicals of ketones 3; the ketones 8-anti and 9-anti underwent cyclization in benzene, predominantly leading to cyclobutanols with syn stereochemistry between the C2 and C3 substituents. In accordance with photoproduct profiles, an unprecedented approximately 2-fold difference in the lifetimes of the intermediate diastereomeric triplet biradicals of ketones 8 in nonpolar solvents (e.g., tau(syn) = 123 ns and tau(anti) = 235 ns in cyclohexane) was observed via nanosecond laser flash photolysis, while no such difference in lifetimes was found for the triplet biradicals of acetoxy ketones 9. The intriguing diastereodifferentiation in the lifetimes of the diastereomeric triplet 1,4-biradicals of 8 and the product profiles of ketones 6, 7, and 9 are best reconciled via a unified mechanistic picture in which superposition of steric factors over varying magnitudes of O-H...O hydrogen bonding selectively facilitates a particular pathway. In particular, the diastereodifferentiation in the photochemical outcomes for the diastereomers of ketone 8 and in the lifetimes of their triplet biradicals can be understood on the basis of rapid deactivation of the 8-syn triplet biradical via fragmentation and slow cyclization of the 8-anti triplet biradical from chair- and twist-boat-like hydrogen-bonded conformations, respectively. The photolysis in polar aprotic solvents such as DMSO and pyridine was found to reverse the chemoselectivity, yielding reactivity paralleling that of ketones 3, for which the steric factors between the C2 and C3 substituents control the photochemical outcome.     

Oxo-vanadium(IV) dihydrogen phosphate: preparation, magnetic study, and heterogeneous catalytic epoxidation

A layered oxo-vanadium(IV) dihydrogen phosphate, {VO(H2PO 4)2} n has been synthesized hydrothermally and characterized by several physicochemical methods. Single-crystal X-ray analysis (crystal system, tetragonal; space group, P4/ ncc; unit cell dimensions, a = b = 8.9632(4), c = 7.9768(32) A) of {VO(H2PO4) 2} n reveals that the compound has an extended two-dimensional structure. The VO2+ moieties are connected through bridging H 2PO4 (-) ions, and this type of connection propagates parallel to the crystallographic ab plane which gives rise to a layered structure. The layers are staked parallel to the crystallographic c axis with a separation between the layers of ca. 4.0 A. Magnetic susceptibility of {VO(H2PO4)2} n has been measured in the temperature range 2-300 K on a SQUID magnetometer. The magnetic property of {VO(H2PO4)2} n is explicable in the light of a two-dimensional quantum Heisenberg antiferromagnet model. Magnetic pathways are available through the dihydrogen-phosphato bridges within the layer and provide for weak antiferromagnetic interactions. Notably {VO(H2PO4)2} n catalyzes the epoxidation reaction of alkenes with tert-BuOOH in acetonitrile medium under heterogeneous condition.     

Interplay of Anion-π+ and π+-π+ Interactions in Novel Pyrido[2,1-a]isoquinolinium-Based AIEgens - Substituent- and Counterion-Dependent Fluorescence Modulation and Applications in Live Cell Mitochondrial Imaging**

Recently, the concept of anion-π⁺ interactions has witnessed unique applications in the field of AIEgen development. In this contribution, we disclose a consolidated study of a library of N-doped ionic AIEgens accessed through silver-mediated cyclization of pyridino-alkynes. A thorough photophysical, computational and crystallographic study has been conducted to rationalize the observed substituent- and counterion-dependent fluorescence properties of these luminogens. We further elucidate the prominent role of anion-π⁺ interactions, π⁺-π⁺ interactions and other non-covalent interactions, in inhibiting the undesired ACQ effect. Finally, we have also demonstrated the application of selected AIEgens for imaging of mitochondria in live cells.     

Multicomponent One‐pot Reactions Towards the Synthesis of Stereoisomers of Dipicolylamine Complexes

Reported are multi‐component one‐pot syntheses of chiral complexes [M(L^ROR′)Cl₂] or [M(L^RSR′)Cl₂] from the mixture of an N‐substituted ethylenediamine, pyridine‐2‐carboxaldehyde, a primary alcohol or thiol and MCl₂ utilizing in‐situ formed cyclized Schiff bases where a C?O bond, two stereocenters, and three C?N bonds are formed (M=Zn, Cu, Ni, Cd; R=Et, Ph; R′=Me, Et, nPr, nBu). Tridentate ligands L^ROR′ and L^RSR′ comprise two chiral centers and a hemiaminal ether or hemiaminal thioether moiety on the dipicolylamine skeleton. Syn‐[Zn(L^PhOMe)Cl₂] precipitates out readily from the reaction mixture as a major product whereas anti‐[Zn(L^PhOMe)Cl₂] stays in solution as minor product. Both syn‐[Zn(L^PhOMe)Cl₂] and anti‐[Zn(L^PhOMe)Cl₂] were characterized using NMR spectroscopy and mass spectrometry. Solid‐state structures revealed that syn‐[Zn(L^PhOMe)Cl₂] adopted a square pyramidal geometry while anti‐[Zn(L^PhOMe)Cl₂] possesses a trigonal bipyramidal geometry around the Zn centers. The scope of this method was shown to be wide by varying the components of the dynamic coordination assembly, and the structures of the complexes isolated were confirmed by NMR spectroscopy, mass spectrometry, and X‐ray crystallography. Syn complexes were isolated as major products with Zn^II and Cu^II, and anti complexes were found to be major products with Ni^II and Cd^II. Hemiaminals and hemiaminal ethers are known to be unstable and are seldom observed as part of cyclic organic compounds or as coordinated ligands assembled around metals. It is now shown, with the support of experimental results, that linear hemiaminal ethers or thioethers can be assembled without the assistance of Lewis acidic metals in the multi‐component assembly, and a possible pathway of the formation of hemiaminal ethers has been proposed.     

Ar+ ArH+ Reactive Collisions of Astrophysical Interest: The Case of 36Ar

The reactive collision between ³⁶Ar and the ³⁶ArH⁺ species has been investigated by means of quantum mechanical (QM), quasiclassical trajectories (QCT) and statistical quantum mechanical (SQM) approaches. Reaction probabilities, cross sections as a function of the energy and rate constants in terms of the temperature have been obtained. Cumulative distributions as a function of the collision time and the inspection of selected QCT corresponding to specific dynamical mechanisms have been analysed. Predictions by means of the SQM method are in good agreement with the QM results, thus supporting the complex-forming nature of the process.     

Structural and Morphological Transformations of Covalent Organic Nanotubes

Covalent organic nanotubes (CONTs) are porous one-dimensional frameworks connected through imine bonds via Schiff base condensation between aldehydes and amines. The presence of two amine groups at the ortho position in the structurally demanding tetraaminotriptycene (TAT) building block leads to multiple reaction pathways between the ditopic aldehyde and the tetratopic amine. We have synthesized five different monomers of CONT-1 by the Schiff base condensation reaction between TAT and o-anisaldehyde. The conversion of imine to imidazole bonding in a monomer is probed using NMR, mass spectrometry, and X-ray diffraction techniques. Solid-state NMR provide insights into the CONTs’ structural connectivity. A theoretical investigation suggests that the π-π stacking could be the driving force for rapid imine to imidazole conversion within the CONT-1. Microscopic imaging sheds further light on the self-assembly process of the CONTs, indicating both head-to-head and side-by-side assembly.     

Structural and magnetic studies on copper(II) azido complexes

The azide ligand has been receiving intense attention in the rapid growth of literature in the field of molecular magnetism. Primarily, azide ion functions as a bridging ligand and magnetic coupler of paramagnetic metal ions. This review is centered on the study of diverse structural and magnetic properties of copper(II) azido complexes. Some of the trends identified could serve as a privileged starting point for the further development of this promising area.