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Structural Diversity of Calcium, Strontium, and Barium Complexes with Reduced Forms of the 3,6‐Di‐ tert ‐butyl‐o‐benzoquinone Ligand
Author(s) -
Sinitsa Dmitry K.,
Sukhikh Taisiya S.,
Petrov Pavel A.,
Nadolinny Vladimir A.,
Konchenko Sergey N.,
Pushkarevsky Nikolay A.
Publication year - 2019
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201900678
Subject(s) - chemistry , crystallography , metal , pentagonal bipyramidal molecular geometry , tetrahydrofuran , barium , ligand (biochemistry) , quinone , dissociation (chemistry) , stereochemistry , benzoquinone , trigonal bipyramidal molecular geometry , semiquinone , electron paramagnetic resonance , crystal structure , inorganic chemistry , organic chemistry , biochemistry , receptor , solvent , physics , nuclear magnetic resonance
Molecular complexes of Ca, Sr, and Ba with the reduced forms of 3,6‐di‐ tert ‐butyl‐o‐benzoquinone as ligands (catecholate, 3,6‐Cat 2– , or semiquinone 3,6‐SQ –‧ ) were synthesized and structurally characterized. Trinuclear complexes [M 3 (3,6‐Cat) 3 (thf) 6 ] ( 1 , M = Ca; 2 , M = Sr) or tetranuclear complex [Ba 4 (3,6‐Cat) 4 (thf) 6 ] ( 3 ) crystallize from tetrahydrofuran (thf) solutions. In the structures of 1 and 2 metal atoms form a nearly right triangle with two µ 3 ‐bridging 3,6‐Cat ligands; in 3 , the metal atoms form a tetrahedron contracted along a twofold axis, and all the catecholates are µ 3 ‐bridging. In nonpolar media the complexes 1 – 3 lose coordinated thf, upon which 1 is converted into complex [Ca 4 (3,6‐Cat) 4 (thf) 4 ] ( 4 ), structurally similar to 3 . Complex 1 is oxidized by one equivalent of the quinone to yield mixed‐ligand complex [Ca 3 (3,6‐SQ) 2 (3,6‐Cat) 2 (thf) 4 ] ( 5 ), structurally similar to 1 . Successive oxidation by the quinone leads to dissociation to mononuclear species, [Ca(3,6‐SQ) 2 (thf) 3 ] ( 5 ), which possesses pentagonal‐bipyramidal coordination with two semiquinolate ligands lying in an equatorial plane. Solution behavior of the complexes is studied by NMR (for catecholates) and EPR (for semiquinolates) spectroscopy.