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The crystal structure of racemic and meso ‐diastereoisomers of aqua[2,6‐bis(3‐carboxy‐1,2‐dimethyl‐2‐azapropyl)pyridine]‐Co(III) · Hexafluorophosphate · Di‐ and monohydrate, respectively
Author(s) -
StoeckliEvans Helen,
Brehm Lotte,
Pousaz Philippe,
Bernauer Klaus,
Bürgi HansBeat
Publication year - 1985
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19850680123
Subject(s) - chemistry , triclinic crystal system , substituent , pyridine , hexafluorophosphate , diastereomer , ligand (biochemistry) , crystallography , crystal structure , molecule , orthorhombic crystal system , stereochemistry , octahedron , ring (chemistry) , medicinal chemistry , organic chemistry , biochemistry , ionic liquid , receptor , catalysis
Synthesis of the pentadentate ligand 2,6‐bis(3‐carboxy‐1,2‐dimethyl‐2‐azapropyl)pyridine yields a mixture of the racemic and meso ‐isomers which it was difficult to separate by column chromatography. When the cationic Co(III)‐complex of this ligand was crystallized with hexafluorophosphate as anion, two distinct crystalline forms were produced. The complex of the racemic ligand, 1 , has C 2 symmetry and is a dihydrate; a = 8.999(8), b = 12.047(6), c = 20.65(1) Å, orthorhombic, space group Peen , Z = 4, R = 0.074 for 1439 observed reflections. The complex of the meso ‐ligand, 2 , shows two independent molecules ( 2A and 2B ) per asymmetric unit, both monohydrates with a resolved disordered H 2 O molecule in 2A ; a = 10.109(4), b = 12.835(2), c = 16.651(3) Å, α = 89.5(1)°, β = 84.7(3)°, γ = 88.6(3)°, triclinic, space group P 1 , Z = 4, Rs = 0.054 for 4198 observed reflections. The coordination around the Co‐atom is distorted octahedral in both complexes, with the coordinated H 2 O molecule trans to the pyridine N‐atom. In the racemic form of the complex, 1 , the pyridine ring is twisted about the Co‐N(1) bond with respect to the plane defined by atoms Co, N(1), O(W1), N(2) and N(2P) by 17.2(2)°. In the meso ‐form of the complex, 2 , the CH 3 substituent C(8P) on atom C(4P), is now axial with respect to the 5‐membered chelate ring. As a result of steric hinderance between atom O(1) and CH 3 (8P), the pyridine ring has been displaced from the best mean‐plane formed by atoms Co, O(W1), N(2) and N(2P). The principal axis of the pyridine ring C(3)…N(1), makes an angle of 14.1(1)° (mean) with this plane. At the same time the pyridine ring is twisted about axis C(3)…N(1) with respect to this plane by 19.7(1)° (mean).