Structures of pentacarbonyltriphenylphosphinechromium and pentacarbonyl(triphenyl phosphite)chromium

Abstract

Sir:Yellow or brown diamagnetic planar and blue-violet paramagnetic octahedral are both well-established forms for nickel(I1). With certain polyamine complexes, both conformations exist in solution in detectable concentrations. Thus, blue aqueous solutions containing Ni(trien)(HzO)z2+, Ni(en)n(HzO)z2+, or Ni(pn)z-(Hz0)22+ turn brownish yellow on heating. The absorption band at -440 mp characteristic of tetragonal nickel(I1) is developed, and the original color returns on cooling the so1ution.ls2 Aqueous solutions of the nickel complex of the quadridentate ligand NH2(CH&-NH(CH2)3NH(CH2)2NH2 (abbreviated 2,3,2-tet) are already brown3 and thus contain substantial amounts of the planar form at room t e m p e r a t~r e .~ Information on the rate at which such equilibria as (L = trien, or 2,3,2-t et) octahedral-Ni(L)(HzO)?2f e planar-Ni(L)z-+ 2 H i 0 are established is lacking, but the system is amenable to the relaxation method of rate measurement.j Sizable absorbance changes at 440 mp with a small temperature rise, 2.5-6.5 O, particularly with the 2,3,2-tet complex, allowed work at low amplification and thus at the shortest time ranges of the temperature-jump apparatus.j It was found, however, that with the 1 : l nickel(I1)-trien and nickel(II)-2,3,2-tet systems, the establishment of the yellow-blue equilibria was complete at 5" within 10 psec which was the shortest time we could reach with our equipment. The first-order rate constant for the conformation change must be >lo5 sec-l. Only a slight "electronic ripple" was observed when solutions of Ni(tren)(H.O)?*f or K N 0 3 were used in the temperature-jump cell. The amine tren, N(CH2CH2NH2)3, can only coordinate to leave two cis positions in the octahedron.We believe that with 2,3,2-tet the fast transition observed is between the Trans-octahedral and the planar complex. Of relevance are the reactions of the complex with EDTA and oxalate which indicate that there are at least two blue isomers of Ni(2,3,2-tet)(H20)22+ present in solution. Upon mixing EDTA and Ni-2,3,2-tet (1 : l ) complex there is an absorbance jump at 380 mp corresponding to about 40% of the total complex present. the remainder, both blue and yellow forms, reacting by a slow first-order process (k = 9.3 X sec-l at pH 8.34).6 The fast transition with the trien complex may be due to a trans-octahedral-planar equilibrium although Ni(trien)(H20)2?+ is believed to have predominantly the cis-octahedral structure in aqueous(1) C. I<. Jprgensen, Acta Chem. aqueous solution (25", p = 0.5 M ) the yellow form of Ni (2,3,2-tet)Z+ cannot be more than 25 % of the total Ni(2,3,2-tet)?' as opposed to 50% suggested in a n earlier report.3 This estimate is based on spectral measurements, using a n approximate value for the molar absorptivity of the yellow form at 440 m p of 67 (obtained in high electrolyte concentration, 7.4 M NaCIO1). The planar yellow form is at most 2 ' % of the total Ni(trien)'+ under the conditions p = 0.5 M , 25 ^. ( 5 ) M . Eigen and L. work in progress.solution. The high rate constant resembles...

Ligand properties of N-heterocyclic and Bertrand carbenes: A density functional study

“…Our predicted geometrical parameters of the Cr(CO) 5 L complexes of 1c and of Cr(CO) 6 are in fine agreement with the X-ray data [26,[46][47][48]. The experimentally determined bond distances are slightly underestimated by DFT.…”

The chromium–heavy group 5 donor bond: a comparison of structural changes within the series [Cr(CO)5(XPh3)](X = P, As, Sb, or Bi)via their X-ray crystal structures

“…l ~~ However observation (a) may be due to the tendency (Bent's rule) for s-orbital character to accumulate in the phosphorus donor orbital as the electronegativity of the substituents on phosphorus increase^^^^ and there is now evidence that a difference of 0.02-0.04 A between metalphosphine and metal-phosphite bond lengths may be due to an intrinsic CT effect independent of metal oxidation state. 6 We now report accurate X-ray data for [Cr(CO),-(XPh,)] (X = As, Sb, or Bi) for coinparison with [Cr(CO),PPh,]. The results are pertinent not only to sorbital participation in chromium-group 5 ligaiid bonding but also to structural features of transition metal-heavy atom donor co-ordination chemistry in general.…”

Structure of 3-(2-pyridyl)-2-(2-tolyl)-1,3-thiazolidin-4-one, C15H14N2OS

“…Compounds: A : 2-Amino-5-phenyl-1,3-thiazolin-4-one (Plastas & Stewart, 1969;Mornon & Raveau, 1971). B: 2-Amino-5-phenyl-l,3-thiazolin-4-one, ~ccond form (Mornon & Bally.…”