Tetrahedral molecular geometry

About: Tetrahedral molecular geometry is a research topic. Over the lifetime, 1795 publications have been published within this topic receiving 30706 citations.

On the Composition and Crystal Structure of the New Quaternary Hydride Phase Li4BN3H10

Abstract: X-ray data on single crystals of the quaternary metal hydride near the composition LiB0.33N0.67H2.67, previously identified as “Li3BN2H8”, reveal that its true composition is Li4BN3H10. The structure has body-centered-cubic symmetry [space group I213, cell parameter a = 10.679(1)−10.672(1) A] and contains an ordered arrangement of BH4- and NH2- anions in the molar ratio 1:3. The borohydride anion has an almost ideal tetrahedral geometry (∠H−B−H ∼ 108−114°), while the amide anion has a nearly tetrahedral bond angle (∠H−N−H ∼ 106°). Three symmetry-independent Li atom sites are surrounded by BH4- and NH2- anions in various distorted tetrahedral configurations, one by two B and two N atoms, another by four N atoms, and the third by one B and three N atoms. The Li configuration around B is nearly tetrahedral, while that around N resembles a distorted saddlelike configuration, similar to those in LiBH4 and LiNH2, respectively.

β-Diketiminate aluminium complexes: synthesis, characterization and ring-opening polymerization of cyclic esters

Abstract: A series of aluminium alkyl complexes (BDI)AlEt2 (3a–m) bearing symmetrical or unsymmetrical β-diketiminate ligand (BDI) frameworks were obtained from the reaction of triethyl aluminium and the corresponding β-diketimine. The monomeric structure of the aluminium complex 3k was confirmed by an X-ray diffraction study, which shows that the aluminium center is coordinated by both of the nitrogen donors of the chelating diketiminate ligand and the two ethyl groups in a distorted tetrahedral geometry. Attempt to synthesize β-diketiminate aluminium alkoxide complexes by the reactions of monochloride complex “(BDI-2a)AlMeCl” (4) with alkali salts of 2-propanol gave unexpectedly an aluminoxane [(BDI-2a)AlMe]2(μ-O) (7) as characterized by X-ray diffraction methods. Complexes 3a–m and [(2,6-iPr2C6H3NCMe)2HC]AlEt2 (8) were found to catalyze the ring-opening polymerization (ROP) of e-caprolactone with moderate activities. The steric and electronic characteristics of the ancillary ligands have a significant influence on the polymerization performance of the corresponding aluminium complexes. The introduction of electron-donating substituents at the para-positions of the aryl rings in the ligand resulted in an apparent decrease in catalytic activity. Complex 3h showed the highest activity among the investigated aluminium complexes due to the high electrophilicity of the metal center induced by the meta-trifluoromethyl substituents on the aryl rings. The increase of steric hindrance of the ligand by introducing ortho-substituents onto the phenyl moieties also resulted in a decrease in the catalytic activity. Although the viscosity average molecular weights (Mη) of the obtained poly(caprolactone)s increased with the enhancement of monomer conversion, the ROPs of e-caprolactone initiated by complexes 3a–m and 8 were not well-controlled, as judged from the broad molecular weight distributions (PDI = 1.66–3.74, Mw/Mn) of the obtained polymers and the nonlinear relationship of molecular weight versus monomer conversion.

Novel Single‐Crystal‐to‐Single‐Crystal Anion Exchange and Self‐Assembly of Luminescent d10 Metal (CdII, ZnII, and CuI) Complexes Containing C3‐Symmetrical Ligands

Abstract: Ligands L1 and L2' (L1 = N,N',N"-tris(4-pyridyl)trimesic amide, L2'=N,N',N"-tris(3-pyridinyl)-1,3,5-benzenetricarboxamide) belonging to an interesting family of tripyridyltriamides with C 3 -symmetry have been utilized to construct 3D porous or hydrogen-bonded frameworks. Through a novel single-crystal-to-single-crystal anion-exchange process, [Cd(L1) 2 -(ClO 4 ) 2 ] n (1c) can be obtained from [Cd(L1) 2 Cl 2 ] n (1b) in the presence of ClO 4 - anions. This anion-exchange process is highly selective and only the substitution of Cl - by ClO 4 - or PF 6 - could be realized; Cl - was found not to be substituted by BPh 4 - . This demonstrates that the exchange process depends on the size of the anions in relation to the size of the cavities in the host material (ca. 7.5 A). In addition, the anion-exchange properties of 1b have also been investigated by means of powder X-ray diffraction (PXRD), elemental analysis (EA), and infrared absorption spectroscopy (IR). Structurally, [Zn(L1)(NO 3 ) 2 ] n (2) consists of a 2D coordination network with five-coordinate Zn II ions. Surprisingly, different trigonal-bipyramidal Zn II ions propagate to form distinct respective sheet structures, A and B, which are packed in an A-B-A-B manner in the crystal lattice, and these are hydrogen-bonded to give a 3D extended framework. The molecular structure of [CuI-(L2')] n (3) shows that the CU 1 ion adopts a distorted tetrahedral geometry, and 3 also forms a 2D coordination network. Significantly, this 2D coordination network is further assembled into a remarkable 3D homochiral framework through triple hydrogen bonding and π···π interactions. All of these 3D coordination polymers and/or hydrogen-bonded frameworks are luminescent in the solid state, and their solid-state luminescent properties have been investigated at room temperature and/or at 77 K.

Change of coordination from tetrahedral gold–ammonium to square-pyramidal gold–arsonium cations

Abstract: RECENT work1–5 has shown that gold-based ligands in compounds of carbon and nitrogen can induce novel molecular structures with coordination numbers at C and N as high as 5 and 6. These phenomena must be ascribed to metal–metal interactions (Au…Au), which can overrule bonding in classical configurations. Here we describe a study of the molecular structures of tetra(auro)ammonium ((LAu)4N+) and tetra(auro)arsonium ((LAu)4As+) cations (where L is a ligand). We find that the classical tetrahedral structure in these four-coordinate compounds is abandoned in favour of a square-pyramidal geometry once the radius of the central element is too large to allow for metal–metal bonding in a tetrahedral geometry. Thus, whereas the nitrogen compounds adopt a tetrahedral structure, for the larger arsenic atom an arsenic-capped square of gold atoms represents a more favourable core geometry. We have not yet been able to prepare the intermediate phosphorus compound, but we expect it also to have the square-pyramidal structure.