Tetranuclear Zn/4f coordination clusters as highly efficient catalysts for Friedel-Crafts alkylation

A series of custom-designed, high yield, isoskeletal tetranuclear Zn/4f coordination clusters showing high efficiency as catalysts with low catalytic loadings in Friedel-Crafts alkylation are described for the first time. The possibility of altering the 4f centers in these catalysts without altering the core topology allows us to further confirm their stability via EPR and NMR, as well to gain insights into the plausible reaction mechanism, showcasing the usefulness of these bimetallic systems as catalysts

Assembly of Near‐Infrared Luminescent Lanthanide Host(Host–Guest) Complexes With a Metallacrown Sandwich Motif

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87095/1/9834_ftp.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/87095/2/ange_201103851_sm_miscellaneous_information.pd

In search for molecules displaying ferromagnetic exchange: multiple-decker Ni12 and Ni16 complexes from the use of pyridine-2-amidoxime

The use of pyridine-2-amidoxime (pyaoxH2) in Ni chemistry has provided access to a dodecanuclear complex and a hexadecanuclear Ni cluster, namely [Ni12(pyaox)6(pyaoxH)6(MeOH)2Cl2]Cl4·5MeOH (1·5MeOH) and [Ni16(pyaox)8(pyaoxH)8(MeOH)4](SO4)4·10H2O·26MeOH (2·10H2O·26MeOH). Complex 1·5MeOH was isolated by the reaction of NiCl2·6H2O, pyaoxH2 and NaOMe in a 1 : 1 : 2 molar ratio in MeOH in 60% yield. Treatment of NiSO4·6H2O with pyaoxH2 and NEt3 in a 1 : 1 : 2 molar ratio in MeOH afforded 2·10H2O·26MeOH in good yield (65%). The two compounds display a multi-decker configuration based on stacked Ni4 layers, {Ni4(pyaox)2(pyaoxH)2}2+x (x = 3, 1·5MeOH; x = 4, 2·10H2O·26MeOH); each deck consists of two square planar and two octahedral NiII centres. The number of decks observed in 1·5MeOH and 2·10H2O·26MeOH depends on the nature of the inorganic anion that is present in the reaction system, which provides elements of synthetic control towards new high nuclearity NiII species. 2·10H2O·26MeOH is the first structurally characterized complex of any metal displaying a quadruple-decker configuration, being also the highest nuclearity metal cluster bearing pyaoxH2 and the highest nuclearity NiII cluster with any type of 2-pyridyl oxime. Each cluster cation displays ferromagnetic exchange between the octahedral NiII ions resulting in a spin ground state of S = 6 for 1 and S = 8 for 2. Magnetothermal studies have been performed and discussed for both clusters.CP and CE thank the School of Chemistry, NUI Galway, for the financial support. RI thanks the Royal Society of Edinburgh and ME thanks Spanish MINECO (MAT2015-68204-R) for funding. LCS acknowledges the financial support by FEDER (Fundo Europeu de Desenvolvimento Regional) through PT2020, by FCT (Fundação para a Ciência e a Tecnologia) for the research centre REQUIMTE/LAQV (UID/QUI/50006/2013) and for the grant SFRH/BPD/111899/2015.Peer Reviewe

Voltammetric Characterization of Redox-Inactive Guest Binding to Ln III [15-Metallacrown-5] Hosts Based on Competition with a Redox Probe

A novel competitive binding assay was implemented to monitor the binding of a redox inactive substrate to a redox inactive metallacrown host based on its competition with ferrocene carboxylate (FcC − ) using cyclic voltammetry (CV). First, the binding of FcC − to Ln III [15-MC Cu II ,N,L-pheHA -5] (LnMC) hosts was characterized by cyclic voltammetry. It was shown that the voltammetric half wave potentials, E 1/2 , shifted to more positive potentials upon the addition of LnMC. The explicit dependence of E 1/2 with the concentration of LnMC was used to determine the association constants for the complex. The FcC − binding strength decreased with larger central lanthanide metals in the LnMC hosts, and substantially weaker binding was observed with La III . X-ray crystallography revealed that the hydrophobic host cavity incompletely encapsulated FcC − when the guest was bound to the nine-coordinate La III , suggesting the LnMC’s ligand side chains play a substantial role in guest recognition. With knowledge of the MC-FcC − solution thermodynamics, the binding affinity of a redox inactive guest was then assessed. Addition of sodium benzoate to a LnMC and FcC − mixture resulted in E 1/2 shifting back to the value observed for FcC − in the absence of LnMC. The association constants between benzoate and LnMC’s were calculated via the competitive binding approach. Comparison with literature values suggests this novel assay is a viable method for determining association constants for host–guest systems that exhibit the proper electrochemical behavior. Notably, this CV competitive binding approach does not require the preparation of a modified electrode or a tethered guest, and thus can be generalized to a number of host–guest systems.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77442/1/chem_200903015_sm_miscellaneous_information.pd

Photoelectron and threshold photoelectron valence spectra of pyridine

The pyridine molecule has been examined by the means of photoelectron and threshold photoelectron spectroscopies. Ionization energies were determined for both outer and inner valence orbitals and new adiabatic values were also resolved. Vibronic structure associated with several states was assigned mainly to be due to C-C stretches and ring bends. Additionally a Rydberg state converging to 7b2 state was ascribed. The data shown here are in a good agreement with previous results and brings some new insights into the electronic structure of this biologically and astrochemically relevant and important molecule

Using the Structural Versatility of Lanthanide Metallacrowns to Tune Anion Recognition, Self-Assembly, and Luminescence Properties.

Natural and artificial supramolecular systems utilize weak, reversible interactions to control the organization of matter and facilitate separations, catalysis, and materials design. Metallacrowns are metal dense macrocycles assembled through dative bonds. This thesis explores how structural changes to the building blocks can enhance the solid state organization, anion recognition, structure, and physical properties of the metallacrown. A systematic crystallographic study was performed to assess how the side chain and central metal influences the size and selectivity of dimeric Ln(III)[15-MC-5] compartments. Phenyl side chains with 0-2 methylene spacers generate dimeric compartments ranging from 9.7 to 15.2 Å in height that selectively encapsulate 4.3 to 9.2 Å long dicarboxylate guests. Up to five carboxylate guests can be encapsulated based on considerations of side chain sterics and the coordination number of the central metal. Solution studies were performed with a novel voltammetric binding assay. Chiral Gd(III)[15-MCCu(II),L-pheHA-5]Cl3 metallocavitands bind alpha-amino acid analogs with affinity constants ranging from 70 +/- 7 to 3260 +/- 70 M-1 in 50% aqueous methanol for N-acetyl-R-phenylalanine and S-mandelate, respectively. Increasing the methylene spacers in the phenyl side chain from 0 to 2 increases the binding constant for benzoate from 800 +/- 100 to 3000 +/- 300 M-1 in 40% aqueous acetonitrile. Mandelate enantioselectivity is enhanced (KS/KR up to 2.2 +/- 0.6) by changing the phenyl side chain. Optically transparent lanthanide metallacrowns with Zn(II) ring metals were assembled for their luminescence properties. Six distinct metallacrown motifs were assembled from picoline hydroxamic acid, Zn(II), Ln(III) through a strict solvent dependence and structurally characterized: Zn(II)[12-MC-4], Ln(III)[12-MC-4], Ln(III)[15-MC-5], Ln(III)[12-MC-4]2, Ln(III)[12-MC-4]2[24-MC-8], and Ln(III)2Zn¬9. The Yb(III)[12-MC-4]2[24-MC-8] is luminescent in methanol, emitting at 980 nm upon excitation at 325 nm with a quantum yield of 0.89 % and lifetime of 14 microseconds. This complex is the brightest near-infrared emitting lanthanide coordination complex in protic solvents due to reduced vibrational quenching through the removal of C-H oscillators from the proximity of the lanthanide ion by the metallacrown. These results reveal that the unique topology and structural versatility of metallacrowns create great promise for chiral separations, catalysis, and molecular materials.PHDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/93877/1/jankolov_1.pd

Crystal structure of bis(μ- N

The title compound, [Na2(C6H5N2O2)2(C6H6N2O2)4], is a centrosymmetric coordination dimer based on the sodium(I) salt of N-hydroxypicolinamide. The molecule has an {Na2O6(μ-O)2} core with two bridging carbonyl O atoms and two hydroxamate O atoms of two mono-deprotonated residues of N-hydroxypicolinamide, while two neutral N-hydroxypicolinamide molecules are coordinated in a monodentate manner to each sodium ion via the carbonyl O atoms [the Na—O distances range from 2.3044 (2) to 2.3716 (2) Å]. The pentacoordinated sodium ion exhibits a distorted trigonal–pyramidal coordination polyhedron. In the crystal, the coordination dimers are linked into chains along the c axis via N—H...O and N—H...N hydrogen bonds; the chains are linked into a two-dimensional framework parallel to (100) via weak C—H...O and π–π stacking interactions