Gary L. Simon

Synthesis and structural characterization of acetatobis(triphenylphosphine)dicarbonylmanganese(I), (CH3CO2)Mn(CO)2[P(C6H5)3]2: An organometallic complex containing a chelating acetate ligand

The accidental but intriguing synthesis of acetatobis(triphenylphosphine)dicarbonylmanganese(I), (CH 3 CO 2 )Mn(CO) 2 [P(C 6 H 5 ) 3 ] 2 , has been accomplished by the reaction of NaMn(CO) 5 with (CH 3 ) 3 SiCl followed by the addition of triphenylphosphine and acetic acid. A three-dimensional single-crystal X-ray diffraction analysis has shown an octahedral-like molecule containing a symmetrically oxygen-chelating acetate group, the first such group to be reported in a metal carbonyl complex. The two triphenylphosphine ligands occupy mutually trans positions with the two carbonyl ligands possessing the remaining cis sites in the octahedral complex. The compound crystallizes with four molecules in a monoclinic unit cell of space group symmetry and of dimensions a = 17.744(2) A, b = 9.692(1) A, c = 20.004(2) A, and β = 106.195(4)°. The relatively long MnO(acetate) bond lengths [2.066(6) and 2.069(7) A] and the relatively short MnCO bond lengths [1.701(12) and 1.760(13) A] and the relatively short MnP(C 6 H 5 ) 3 bond lengths [2.260(3) and 2.275(3) A], compared to the corresponding MnCO and MnP(C 6 H 5 ) 3 bond lengths in other manganese carbonyl triphenylphosphine complexes, are rationalized on the basis that the acetate ligand in this molecule functions primarily as a σ-donor.

Crystal structure of 25-hydroxy-vitamin D3 monohydrate: a stereochemical analysis of vitamin D molecules

A three-dimensional X-ray diffraction study on the monohydrate of the 25-hydroxy-vitamin D3, the predominant metabolite of vitamin D3 in the blood and the immediate precursor of 1α,25-dihydroxy-vitamin D3, has provided the first high-precision molecular parameters for this class of molecules. A detailed comparative analysis of the solid state conformations of the rings and side-chain is made with those of other stucturally known vitamin D molecules, and the resulting stereochemical implications are discussed with respect to biological activities of various metabolites and active analogues. Crystals are monoclinic with Z= 2 in a unit cell of space group P21 and dimensions a= 10.600(1), b= 6.798(1), c= 18.142(2)A, β= 103.75(2)°. The structure was solved by direct methods and refined to R 3.4% based on 2 012 independent intensities.