Complexes pseudo-tetrahedral

Cobalt(i).— Anhydrous CoX (X - Cl,Br. or I) can be reduced by BH in the presence of MeC(CH2PPh2)3 to form [CoXL], which are non-electrolytes and isomorphous with the analogous Cu complexes. Pseudo-tetrahedral geometry is proposed. ... 

Cationic cyclopentadienyl complexes are not common in this group, but recent examples whose structures have been determined include [Nb ( j -C5H5)2Cl2]BF4< > and [Nb( j -C5H5)2L2](BF4)2 (L = CNMe and NCMe),< > which have pseudo-tetrahedral symmetry. 

The role of coordinated ethylene is evidenced by the recent ab initio calculation performed by Espelid and Borve [121-123], who have shown that ethylene may coordinate in two different ways to the reduced Cr(II) species, either as a molecular complex or covalently bound to chromium. At longer Cr-C distances (2.36-2.38 A) an ethylene-chromium zr-complex forms, in which the four d electrons of chromium remain high-spin coupled and the coordination interaction is characterized by donation from ethylene to chromium. Cr(II) species in a pseudo-tetrahedral geometry may adsorb up to two equivalents of ethylene. In the case of a pseudo-octahedral Cr(II) site a third ethylene molecule can also be present. The monoethylene complex on the pseudo-tetrahedral Cr(II) site was also found to undergo a transformation to covalently bound complex, characterized by shorter Cr-C distances (about... 

The bi- and tridentate phosphines dppp (l,3-bis(diphenylphosphino)propane) and dppep (bis (2-diphenylphosphinoethyl)phenylphosphine) have been complexed with Co and their divalent four- and five-coordinated thiophenolate complexes Co(dppp)(SPh)2 and Co(dppep)(SPh)2 have been isolated and structurally characterized.379 Somewhat related to dppp is the bidentate silane Ph2PCH2SiMe2CH2PPh2, which forms high-spin, pseudo-tetrahedral dihalocobalt(II) complexes.380... 

The complex has crystallographic ///-symmetry, the mirror plane bisecting the unique benzyl group, the nitrogen atom to which it is attached, and the ethylzinc moiety. The pseudo-tetrahedral zinc atom has a short (1.930(4) A) zinc-ethyl bond, but comparatively long (2.230(2) A) nitrogen-zinc donor bonds. 

N-Donor Ligands. CrOa forms a 1 1 complex with hexamethylenetetramine, the i.r. and electronic spectra of which indicate that the metal has a pseudo-tetrahedral (C3J environment. ... 

The potentially terdentate ligand, thiodiethanol (88), forms 1 1 complexes and 1 2 complexes with C0CI2. The former are five-co-ordinate and the latter octahedral. 1 1 Complexes of Co and diethylenetrithioacetic acid, ethylene-dithiodiacetic acid, and ethylidenetetrathiotetra-acetic acid have all been reported." " Potassium monothiobenzoate reacts with an equimolar quantity of CoSO in aqueous solution to yield green crystals of the pseudo-tetrahedral dinuclear complex [Co2(SOCPh)4 ], which contains both bidentate and bridging thiobenzoate ligands. ... 

Stretching frequencies used to assign the structures. Ni(N03)2 reacts with [Ni(R-salen)2] (R = Et or Pr ) to give trinuclear complexes (165) which contain two pseudo-tetrahedral and one octahedral nickel atoms. ... 

Brown, I. D. (1980a). On the prediction of angles in tetrahedral complexes and pseudo-tetrahedral complexes with stereoactive lone pairs. /. Amer. Chem. Soc. 102, 2112-3. 

In the presence of copper(I), 2,9-dianisyl-l,10-phenanthroline forms a very stable pseudo-tetrahedral complex in which the two ligands are intertwined around the metallic center. Because of its very special topography [66], this com-... 

Most of the bis adducts NiX2L2 (L = substituted imidazoles and pyrazoles) have pseudo-tetrahedral coordination, but some of the chloride and thiocyanato complexes can be six-coordinate in a polymeric structure. 

Bis(aminotroponeiminato)nickel(II) complexes (124) give rise to square planar pseudotetrahedral equilibria in solution.99 1000 The amount of the paramagnetic pseudo-tetrahedral species increases as the size of the substituents R becomes greater. 

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