An official website of the United States government
Three amidine-based ligands were used in the crystal design of a series of mononuclear Zn(II) complexes. Interaction of zinc chloride, ZnCl2, with N-2-pyridylimidoyl-2-pyridylamidine (Py2ImAm) resulted in complexes [Zn(Py2ImAm)2] (1) and [ZnCl2(Py2ImAm)] (2). In [Zn(Py2ImAm)2] (1, monoclinic, P21/c), the metal ion was coordinated with the bidentate pocket of the anionic form of Py2ImAm, while in [ZnCl2(Py2ImAm)] (2, monoclinic, P21/n), the tridentate coordination to a neutral Py2ImAm was completed by two chloride anions. This structural variation was achieved by a pH-controlling strategy using the weak base triethylamine (TEA). Otherwise, three ionic complexes were obtained with 2-amidinopyridine (PyAm) and Zinc(II), [ZnCl(PyAm)2]Cl (3, triclinic, P-1), [ZnCl(PyAm)2]2[ZnCl4]·C2H5OH (4, monoclinic, P21/n), and [ZnCl(PyAm)2]2Cl·CH3OH (5, triclinic, P-1). They comprised the same [ZnCl(PyAm)2]+ monocation with a butterfly-like shape provided by the bidentate chelate coordination of two PyAm neutral entities and a chloride ligand. In a similar butterfly shape, ionic complex [ZnCl(PmAm)2]2[ZnCl4] (6, monoclinic, C2/c) comprised the mononuclear [ZnCl(PmAm)2]+ cations with two bidentate chelate-coordinated 2-amidinopyrimidine (PmAm) as neutral ligands. The Zn(II) pentacoordinated arrangement in 3–6 was variable, from square pyramidal to trigonal bipyramidal. The reported compounds’ synthetic protocols, crystal structures and photoluminescence properties are discussed.
more »
« less
A Redox‐Active Tetrazine‐Based Pincer Ligand for the Reduction of N‐Oxyanions Using a Redox‐Inert Metal
Abstract The reaction chemistry of the bis‐tetrazinyl pyridine ligand (btzp) towards nitrogen oxyanions coordinated to zinc is studied in order to explore the reduction of the NOx−substrates with a redox‐active ligand in the absence of redox activity at the metal. Following syntheses and characterization of (btzp)ZnX2for X=Cl, NO3and NO2, featuring O−Zn linkage of both nitrogen oxyanions, it is shown that a silylating agent selectively delivers silyl substituents to tetrazine nitrogens, without reductive deoxygenation of NOx−1. A new synthesis of the highly hydrogenated H4btzp, containing two dihydrotetrazine reductants is described as is the synthesis and characterization of (H4btzp)ZnX2for X=Cl and NO3, both of which show considerable hydrogen bonding potential of the dihydrotetrazine ring NH groups. The (H4btzp)ZnCl2complex does not bind zinc in the pincer pocket, but instead H4btzp becomes a bridge between neighboring atoms through tetrazine nitrogen atoms, forming a polymeric chain. The reaction of AgNO2with (H4btzp)ZnCl2is shown to proceed with fast nitrite deoxygenation, yielding water and free NO. Half of the H4btzp reducing equivalents form Ag0and thus the chloride ligand remains coordinated to the zinc metal center to yield (btzp)ZnCl2. To compare with AgNO2, experiments of (H4btzp)ZnCl2with NaNO2result in salt metathesis between chloride and nitrite, highlighting the importance of a redox‐active cation in the reduction of nitrite to NO.
more »
« less
- PAR ID:
- 10268111
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- Volume:
- 27
- Issue:
- 45
- ISSN:
- 0947-6539
- Format(s):
- Medium: X Size: p. 11676-11681
- Size(s):
- p. 11676-11681
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
During the course of exploring crystallization conditions in generating metal–organic frameworks (MOFs) for use in the crystalline sponge method, two discrete metal–organic complexes, namely, aqua[2,4,6-tris(pyridin-4-yl)-1,3,5-triazine]zinc(II) bromide, [Zn(C18H12N6)(H2O)]Br2, and aqua[2,4,6-tris(pyridin-4-yl)-1,3,5-triazine]zinc(II) chloride, [Zn(C18H12N6)(H2O)]Cl2, were encountered. Structures in the orthorhombic space groupPnma(No. 62) for the bromide congener at 299 K and the chloride congener at 100 K were obtained. A phase transition for the bromide congener occurred upon cooling from 299 to 100 K, yielding a crystal polymorph with four domains that exhibits monoclinicP21/mspace-group symmetry (No. 11), which arises from conformational changes. The main intramolecular contacts that contribute to the crystal packing in all observed structures are H...H, Halide...H/H...Halide, C...H/H...C, and N...H/H...N. Intramolecular hydrogen bonding between the Zn-bound water and non-Zn-bound pyridyl N atoms is a prominent feature within the three-dimensional networks. Aromatic π-stacking between the non-Zn-bound pyridine rings and contacts involving the halide ligands further stabilize the crystal packing.more » « less
-
Structural analyses of the compounds di-μ-acetato-κ 4 O : O ′-bis{[2-methoxy- N , N -bis(quinolin-2-ylmethyl)ethanamine-κ 4 N , N ′, N ′′, O ]manganese(II)} bis(tetraphenylborate) dichloromethane 1.45-solvate, [Mn 2 (C 23 O 2 ) 2 (C 23 H 23 N 3 O) 2 ](C 24 H 20 B)·1.45CH 2 Cl 2 or [Mn(DQMEA)(μ-OAc) 2 Mn(DQMEA)](BPh 4 ) 2 ·1.45CH 2 Cl 2 or [1] (BPh 4 ) 2 ·1.45CH 2 Cl 2 , and (acetato-κ O )[2-hydroxy- N , N -bis(quinolin-2-ylmethyl)ethanamine-κ 4 N , N ′, N ′′, O ](methanol-κ O )manganese(II) tetraphenylborate methanol monosolvate, [Mn(CH 3 COO)(C 22 H 21 N 3 O)(CH 3 OH)](C 24 H 20 B)·CH 3 OH or [Mn(DQEA)(OAc)(CH 3 OH)]BPh 4 ·CH 3 OH or [2] BPh 4 ·CH 3 OH, by single-crystal X-ray diffraction reveal distinct differences in the geometry of coordination of the tripodal DQEA and DQMEA ligands to Mn II ions. In the asymmetric unit, compound [1] (BPh 4 ) 2 ·(CH 2 Cl 2 ) 1.45 crystallizes as a dimer in which each manganese(II) center is coordinated by the central amine nitrogen, the nitrogen atom of each quinoline group, and the methoxy-oxygen of the tetradentate DQMEA ligand, and two bridging-acetate oxygen atoms. The symmetric Mn II centers have a distorted, octahedral geometry in which the quinoline nitrogen atoms are trans to each other resulting in co-planarity of the quinoline rings. For each Mn II center, a coordinated acetate oxygen participates in C—H...O hydrogen-bonding interactions with the two quinolyl moieties, further stabilizing the trans structure. Within the crystal, weak π – π stacking interactions and intermolecular cation–anion interactions stabilize the crystal packing. In the asymmetric unit, compound [2] BPh 4 ·CH 3 OH crystallizes as a monomer in which the manganese(II) ion is coordinated to the central nitrogen, the nitrogen atom of each quinoline group, and the alcohol oxygen of the tetradentate DQEA ligand, an oxygen atom of OAc, and the oxygen atom of a methanol ligand. The geometry of the Mn II center in [2] BPh 4 ·CH 3 OH is also a distorted octahedron, but the quinoline nitrogen atoms are cis to each other in this structure. Hydrogen bonding between the acetate oxygen atoms and hydroxyl (O—H...O) and quinolyl (C—H...O and N—H...O) moieties of the DQEA ligand stabilize the complex in this cis configuration. Within the crystal, dimerization of complexes occurs by the formation of a pair of intermolecular O3—H3...O2 hydrogen bonds between the coordinated hydroxyl oxygen of the DQEA ligand of one complex and an acetate oxygen of another. Additional hydrogen-bonding and intermolecular cation–anion interactions contribute to the crystal packing.more » « less
-
Abstract There is a strong interest in finding highly soluble redox compounds to improve the energy density of redox flow batteries (RFBs). However, the performance of electrolytes is often negatively influenced by high solute concentration. Herein, we designed a high‐potential (0.5 V vs. Ag/Ag+) catholyte for RFBs, where the charged and discharged species are both gaseous nitrogen oxides (NOx). These species can be liberated from the liquid electrolyte and stored in a separate gas container, allowing scale‐up of storage capacity without increasing the concentration and volume of the electrolyte. The oxidation of NO in the presence of NO3−affords N2O3, and the reduction of N2O3regenerates NO and NO3−, together affording the electrochemical reaction: NO3−+3 NO⇌2 N2O3+e−with a low mass/charge ratio of 152 grams per mole of stored electron. A proof‐of‐concept NOxsymmetric H‐cell shows 200 stable cycles over 400 hours with >97 % Coulombic efficiency and negligible capacity decay.more » « less
-
The syntheses of (DIM)Ni(NO 3 ) 2 and (DIM)Ni(NO 2 ) 2 , where DIM is a 1,4-diazadiene bidentate donor, are reported to enable testing of bis boryl reduced N-heterocycles for their ability to carry out stepwise deoxygenation of coordinated nitrate and nitrite, forming O(Bpin) 2 . Single deoxygenation of (DIM)Ni(NO 2 ) 2 yields the tetrahedral complex (DIM)Ni(NO)(ONO), with a linear nitrosyl and κ 1 -ONO. Further deoxygenation of (DIM)Ni(NO)(ONO) results in the formation of dimeric [(DIM)Ni(NO)] 2 , where the dimer is linked through a Ni–Ni bond. The lost reduced nitrogen byproduct is shown to be N 2 O, indicating N–N bond formation in the course of the reaction. Isotopic labelling studies establish that the N–N bond of N 2 O is formed in a bimetallic Ni 2 intermediate and that the two nitrogen atoms of (DIM)Ni(NO)(ONO) become symmetry equivalent prior to N–N bond formation. The [(DIM)Ni(NO)] 2 dimer is susceptible to oxidation by AgX (X = NO 3 − , NO 2 − , and OTf − ) as well as nitric oxide, the latter of which undergoes nitric oxide disproportionation to yield N 2 O and (DIM)Ni(NO)(ONO). We show that the first step in the deoxygenation of (DIM)Ni(NO)(ONO) to liberate N 2 O is outer sphere electron transfer, providing insight into the organic reductants employed for deoxygenation. Lastly, we show that at elevated temperatures, deoxygenation is accompanied by loss of DIM to form either pyrazine or bipyridine bridged polymers, with retention of a BpinO − bridging ligand.more » « less
