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2,5‐Dioxido‐1,4‐benzoquinonediimine (H 2 L 2− ), A Hydrogen‐Bonding Noninnocent Bridging Ligand Related to Aminated Topaquinone: Different Oxidation State Distributions in Complexes [{(bpy) 2 Ru} 2 (μ‐H 2 L)] n ( n =0,+,2+,3+,4+) and [{(acac) 2 Ru} 2 (μ‐H 2 L)] m ( m =2−,−,0,+,2+)
Author(s) -
Kar Sanjib,
Sarkar Biprajit,
Ghumaan Sandeep,
Janardanan Deepa,
van Slageren Joris,
Fiedler Jan,
Puranik Vedavati G.,
Sunoj Raghavan B.,
Kaim Wolfgang,
Lahiri Goutam Kumar
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200500202
Subject(s) - bridging (networking) , bridging ligand , hydrogen bond , chemistry , hydrogen , ligand (biochemistry) , state (computer science) , crystallography , crystal structure , organic chemistry , molecule , computer science , computer network , receptor , algorithm , biochemistry
The symmetrically dinuclear title compounds were isolated as diamagnetic [(bpy) 2 Ru(μ‐H 2 L)Ru(bpy) 2 ](ClO 4 ) 2 ( 1 ‐(ClO 4 ) 2 ) and as paramagnetic [(acac) 2 Ru(μ‐H 2 L)Ru(acac) 2 ] ( 2 ) complexes (bpy=2,2′‐bipyridine; acac − =acetylacetonate=2,4‐pentanedionato; H 2 L=2,5‐dioxido‐1,4‐benzoquinonediimine). The crystal structure of 2⋅ 2 H 2 O reveals an intricate hydrogen‐bonding network: Two symmetry‐related molecules 2 are closely connected through two NH(H 2 L 2− )⋅⋅⋅O(acac − ) interactions, while the oxygen atoms of H 2 L 2− of two such pairs are bridged by an (H 2 O) 8 cluster at half‐occupancy. The cluster consists of cyclic (H 2 O) 6 arrangements with the remaining two exo ‐H 2 O molecules connecting two opposite sides of the cyclo ‐(H 2 O) 6 cluster, and oxido oxygen atoms forming hydrogen bonds with the molecules of 2 . Weak antiferromagnetic coupling of the two ruthenium( III ) centers in 2 was established by using SQUID magnetometry and EPR spectroscopy. Geometry optimization by means of DFT calculations was carried out for 1 2+ and 2 in their singlet and triplet ground states, respectively. The nature of low‐energy electronic transitions was explored by using time‐dependent DFT methods. Five redox states were reversibly accessible for each of the complexes; all odd‐electron intermediates exhibit comproportionation constants K c >10 8 . UV‐visible‐NIR spectroelectrochemistry and EPR spectroscopy of the electrogenerated paramagnetic intermediates were used to ascertain the oxidation‐state distribution. In general, the complexes 1 n + prefer the ruthenium( II ) configuration with electron transfer occurring largely at the bridging ligand (μ‐H 2 L n − ), as evident from radical‐type EPR spectra for 1 3+ and 1 + . Higher metal oxidation states ( iii, iv ) appear to be favored by the complexes 2 m ; intense long‐wavelength absorption bands and Ru III ‐type EPR signals suggest mixed‐valent dimetal configurations of the paramagnetic intermediates 2 + and 2 − .