Metallosupramolecular Chemistry of Novel Chiral closo-o-Carboranylalcohol Pyridine and Quinoline Ligands: Syntheses, Characterization, and Properties of Cobalt Complexes

Abstract

The cobalt(II) complexes CoCl 2 (LOH) 2 (LOH = 1-[R(hydroxy)methyl]-2-R′-1,2-dicarba-closo-dodecaborane (R′ = H or Me; R = 2-pyridyl 3a or 4a, 3-pyridyl 3b or 4b, 4-pyridyl 3c or 4c, 2-quinolyl 3d or 4d, 4-quinolyl 3e or 4e)) and CoCl 2 (LOH) 4 (5, R′ = H; R = 4-pyridyl) were synthesized and characterized. Deprotonation of alcohol in 3a afforded the squareplanar complex Co II (LO) 2 (6) that oxidized slowly in solution and under air to give the cobaltacarborane complex Co III {(η 5 -C 2 B 9 H 10 )(CHOH)(η 1 -NC 5 H 4 )}(η 2 -NC 5 H 4 COO) (7). Crystal structures for 3a, 3a•2MeOH, 3b, 3e, 4c, 4e, 5, 6, and 7 have been determined by X-ray diffraction (XRD). Molecular structures show octahedral (3a, 3a•2MeOH, 5), tetrahedral (3b, 3e, 4c, 4e), and square-planar (6) coordination around Co II centers, whereas 2-pyridyl and quinolyl ligands favor a bidentate N,O-coordination mode and 3-and 4-pyridyl and quinolyl ligands favor a monodentate N-coordination. The supramolecular structures are dominated by intermolecular O−H•••Cl/O hydrogen bonds and π−π interactions in the case of tetrahedral complexes. The magnetic properties of 3a−c were investigated in the temperature range 2−300 K by means of χ M T, which corroborated coordination numbers and geometries as well as provided information on the supramolecular interactions among neighboring molecules for all three compounds. Complex 3a shows solvent accessible channels running parallel to the hydrogen bonding network and is able to uptake methanol vapors to convert into 3a•2MeOH. The structure of 3a is related to that for 3a•2MeOH by rotation of complex molecules within the 1D O−H•••Cl hydrogen bonding networks and insertion of methanol into it.

N,O-Type Carborane-Based Materials

“…Complex 17a seems to enable O2 activation, followed by transformation of the ligands and metal oxidation states affording a Co III carborane complex 18. The 3-and 4-pyridyl or quinolyl derivatives 1b-c, 1e and 2b-c, 2e also reacted with CoCl2•6H2O under the same reaction conditions, providing, in this case, the corresponding tetrahedral Co II complexes 15a and 16a, respectively (Scheme 6) [60]. Octahedral complex 21 was, however, formed in the presence of excess of 2c.…”

“…The solid-state, variable-temperature (2-300 K) magnetic susceptibility data were collected on polycrystalline samples of 16a, 20b and 20c (Figure 2) and the data agree well with their crystallographic data and stress the relevance of intermolecular interactions among neighboring molecules providing well-organized supramolecular 1 D systems (vide infra). The 3-and 4-pyridyl or quinolyl derivatives 1b-c, 1e and 2b-c, 2e also reacted with CoCl2•6H2O under the same reaction conditions, providing, in this case, the corresponding tetrahedral Co II complexes 15a and 16a, respectively (Scheme 6) [60]. Octahedral complex 21 was, however, formed in the presence of excess of 2c.…”

“…The 2-pyridyl derivatives 1a and 2a reacted with CoCl 2¨6 H 2 O in a 2:1 ratio under aerobic conditions to provide the corresponding Co II complexes 15a and 16a, respectively (Scheme 5) [60]. X-ray diffraction studies confirmed that 2a acts as a bidentate N,O-ligand, giving an octahedral-coordinated Co II complex.…”

A Distinct Tetradentate N2O2‐type Ligand: (o‐Carboranyl)bis(2‐hydroxymethyl)pyridine

“…The latter can be regarded as a hmpH ligand where one of the hydrogen atoms at the ‐CH 2 ‐ position of the alcohol arm has been replaced by a carboranyl ( closo‐ 1, 2‐C 2 B 10 H 10 ) fragment. The high thermal and chemical stability, hydrophobicity, acceptor character, ease of functionalization and three‐dimensional nature of the icosahedral carborane clusters make these new molecules valuable ligands in coordination chemistry and we recently published the first results on the metallosupramolecular chemistry of these ligands 6. Thus, oCB hmpH acts as a bidentate N , O ‐ligand, giving an octahedrally coordinated Co II complex [CoCl 2 ( oCB hmpH) 2 ] and providing an interesting intrinsically porous molecular material, which porosity is triggered by self‐assembly into the solid state and by the presence of the carboranyl fragment.…”

“…The presence of two chelating arms, provides two potentially bidentate {NO} or one tetradentate {N 2 O 2 } binding pockets. Following our first results on the metallosupramolecular chemistry of the monosubstituted o ‐carboranylalcohol ligands,6 we have already initiated a systematic study of the metallosupramolecular chemistry of all these new disubstituted ligands with several transition metals. In this paper we report the synthesis, characterization and molecular structure of the first metal complex with this new type of disubstituted o ‐carboranylalcohols ligand oCB (hmpH) 2 , which corresponds to a mononuclear octahedral Co II complex.…”