Facially Coordinating Triamine Ligands with a Cyclic Backbone: Some Structure−Stability Correlations

Di-μ-chlorido-bis(chlorido{8-[2-(dimethylamino)ethylamino]quinoline}cadmium) ethanol monosolvate

The title solvated bimetallic complex, [Cd2Cl4(C13H17N3)2]·C2H5OH, comprises two Cd2+ metal ions linked by a pair of μ2 Cl− ions. The coordination sphere around each Cd2+ ion is completed by three N atoms of a tridentate 8-[2-(dimethylamino)ethylamino]quinoline ligand and another chloride ion to form a distorted fac-CdN3Cl3 octahedron. The ethanol molecule is both an acceptor of an N—H...O and a donor of an O—H...Cl hydrogen bonds to its adjacent complex unit. In the crystal, weak aromatic π–π stacking is observed.

Structural, Spectroscopic, Electrochemical, and Magnetic Properties for Manganese(II) Triazamacrocyclic Complexes

We report the synthesis of [Mn(tacud)2](OTf)2 (1) (tacud = 1,4,8-triazacycloundecane), [Mn(tacd)2](OTf)2 (2) (tacd = 1,4,7-triazacyclodecane), and [Mn(tacn)2](OTf)2 (3) (tacn = 1,4,7-triazacyclononane). Electrochemical measurements on the MnIII/II redox couple show that complex 1 has the largest anodic potential of the set (E 1/2 = 1.16 V vs NHE, ΔE p = 106 mV) compared to 2 (E 1/2 = 0.95 V, ΔE p = 108 mV) and 3 (E 1/2 = 0.93 V, ΔE p = 96 mV). This is due to the fact that 1 has the fewest 5-membered chelate rings and thus is least stabilized. Magnetic studies of 1-3 revealed that all complexes remain high spin throughout the temperature range investigated (2 - 300 K). X-band EPR investigations in methanol glass indicated that the manganese(II) centers for 2 and 3 resided in a more distorted octahedral geometric configuration compared to 1. To ease spectral interpretation and extract ZFS parameters, we performed high-frequency high-field EPR (HFEPR) at frequencies above 200 GHz and a field of 7.5 T. Simulation of the spectral data yielded g = 2.0013 and D = -0.031 cm-1 for 1, g = 2.0008, D = -0.0824 cm-1, |E/D| = 0.12 for 2, and g = 2.00028, D = -0.0884 cm-1 for 3. These results are consistent with 3 possessing the most distorted geometry. Calculations (PBE0/6-31G(d)) were performed on 1-3. Results show that 1 has the largest HOMO-LUMO gap energy (6.37 eV) compared to 2 (6.12 eV) and 3 (6.26 eV). Complex 1 also has the lowest HOMO energies indicating higher stability.

Crystal structures of benzoxazolyl–copper(iii,ii,i) complexes and investigation of Cu(ii)-mediated aryl carbon–hydrogen bromination

We report three new copper complexes with different oxidation states based on the phenylbenzoxazole system.

Formation and base hydrolysis of oxidimethaneamine bridges in CoIII-amine complexes

cis-[CoL2](3+) (1a(3+)), trans-[CoL2](3+) (2a(3+)), cis-[Co(MeL)2](3+) (1b(3+)), and trans-[Co(MeL)2](3+) (2b(3+)), L = 1,4-diazepan-6-amine (daza) and MeL = 6-methyl-1,4-diazepan-6-amine (Medaza), were allowed to react as templates in acetonitrile with paraformaldehyde and triethylamine. Several Co(III) complexes, where two adjacent amino groups of two ligand moieties are interlinked by an oxidimethaneamine bridge, were obtained. Connection of a primary with a secondary amino group (prim-sec bridging) was found to be predominant. The singly and doubly bridged daza- and Medaza-derivatives 7a(3+), 9a(3+) and 7b(3+), 9b(3+) were characterized by crystal-structure analysis. The bridging process resulted in a slight lengthening of the mean Co-N distance, a red shift of the A1g-T1g transition, and an increase of the Co(III)/Co(II) reduction potential. Several minor components, which could be only partially separated by chromatographic methods, were also formed. The daza-derivatives 6a(3+) (prim-prim bridged) and 10a(3+) (bidentate coordination of one daza frame) formed in small quantities. The Medaza derivatives 3b(3+) and 4b(3+) (trans configuration of the Medaza frames, with additional pending carbinolamino groups), and 8b(3+) (with a methylideneimino group) represent intermediates of the condensation process. Their structure was again corroborated by X-ray diffraction. All bridged species (6a(3+), 7a(3+), 7b(3+), 8b(3+), 9a(3+), 9b(3+), and 10a(3+)) exhibited exclusively a cis orientation of the two diazepane frames, even if the trans configured 2a(3+) or 2b(3+) were used as starting materials. Molecular mechanics calculations indicate that in the bridged species with a trans configuration steric strain is substantially more pronounced. In alkaline aqueous media, 9a(3+) and 9b(3+) revealed a complete degradation of the bridges whereby the original 1a(3+) and 1b(3+) reformed. The pseudo-first-order rate constant k(obs) of the degradation reaction was found to depend linearly on OH(-) concentration. The degradation of the first bridge is about 100 times faster than the degradation of the second. The mechanism of formation and degradation of such oxidimethaneamine bridges is discussed.

Redetermination of 1,3-diammonio-1,2,3-tride-oxy-cis-inositol dichloride

The crystal structure of the title compound, C₆H₁₆N₂O₃²⁺·2Cl⁻, has been reported previously by Palm [Acta Cryst. (1967 ▶), 22, 209–216] from Weisenberg camera data, with R1 = 10.5%, isotropic refinement of non-H atoms and H atoms not located. We remeasured a data set of the title compound and present a more precise structure determination. The asymmetric unit contains two unique 1,3-diammonio-1,2,3-tride­oxy-cis-inositol cations and four Cl⁻ counter-ions. The cyclo­hexane rings of both inositol cations adopt chair conformations with two axial hy­droxy groups. An extended network of hydrogen bonds is formed. The four chloride counter ions are hydrogen bonded to the hydroxy and ammonium groups of the cations by N—H⋯Cl and O—H⋯Cl interactions. The cations are aligned into wavy layers by cation⋯cation interactions of the form N—H⋯O(ax), N—H⋯O(eq) and O(ax)—H⋯O(eq). Intramolecular hydrogen bonding between the axial hydroxy groups is, however, not observed.

1,3-Diammonio-1,2,3-tride-oxy-cis-inositol sulfate

In the crystal structure of the title compound, C(6)H(16)N(2)O(3) (2+)·SO(4) (2-), each cation forms three O-H⋯O and five N-H⋯O hydrogen bonds to six neighbouring sulfate anions. In addition, interlinking of the cations by N-H⋯O interactions is also observed. The cyclo-hexane ring adopts a chair conformation with two axial hy-droxy groups. Although the separation of 2.928 Å is almost ideal for a hydrogen bond, intra-molecular hydrogen bonding between these two hy-droxy groups is not observed.

fac-{2-[Bis(2-amino-eth-yl)amino]-ethanaminium}trichloridorhodium(III) chloride hemihydrate

The crystal structure of the title compound, [Rh(C₆H₁₉N₄)Cl₃]Cl·0.5H₂O, is isotypic with the previously reported Ru analogue. The structure contains two crystallographically independent [Rh(Htren)Cl₃]⁺ cations with a facial tridentate coordination of the monoprotonated tren ligand [tren = tris­(2-amino­eth­yl)amine], leading to an overall distorted octahedral coordination environment around the Rh(III) atom. In one of the two cations, the ethyl­ene groups of the two chelate rings as well as the non-coordinating ethyl­ammonium group are disordered over two sets of sites [0.579 (3):0.421 (3) occupancy ratio]. A series of N—H⋯Cl and O—H⋯Cl hydrogen bonds stabilizes the structure.