The First Hexanuclear Copper(I) Carboxylate:  X-ray Crystal Structure and Reactivity in Solution and Gas-Phase Reactions

Abstract

The carboxylate ligand-exchange reaction of copper(I) trifluoroacetate by 3,5-difluorobenzoate yielded a new product, [Cu(O2C(3,5-F)2C6H3)] (1). Single crystals of 1 suitable for X-ray structural characterization were obtained by sublimation-deposition procedures at 230 degrees C. An X-ray diffraction study revealed a remarkable planar hexanuclear copper(I) core supported by bridging carboxylates, the first such structural type among other known copper(I) carboxylates. The Cu...Cu distances within the core range from 2.7064(8) to 2.8259(8) A and fall into the category of cuprophillic interactions. The hexacopper unit remains intact upon gas-phase deposition with a planar polyarene, coronene (C24H12), to give [Cu6(O2C(3,5-F)2C6H3)6](C24H12) (2). Density functional theory calculations suggest the latter compound to be a cocrystallization product having electrostatic interactions between the hexacopper complex and coronene. However, cocrystallization affects the photophysical properties of 2. While copper(I) 3,5-difluorobenzoate (1) exhibits photoluminescence at ca. 554 nm (lambda(ex) = 350 nm) in the solid state, compound 2 is nonluminescent at room temperature in the visible region. Gas-phase and solution reactions of 1 with alkyne ligands, diphenylacetylene (C14H10) and 1,4-bis(p-tolylethynyl)benzene (C24H18), result in the rupture of the [Cu6] core to afford dinuclear organometallic copper(I) complexes. The latter have a dimetal core cis-bridged by two carboxylate groups with acetylene ligands eta(2)-coordinated to each copper(I) center.

Breaking Infinite CuI Carboxylate Helix Held by Cuprophilicity into Discrete Cun Fragments (n = 6, 4, 2)

“…It was proven to be effective for the isolation of single crystalline products of electrophilic complexes without any exogenous ligands and interfering solvent effects. [7,[9][10][11] Thus, crystals of 1 in the form of colorless thin needles are readily accessible by the gas-phase sublimation of the crude powder in the temperature range of 140-190°C in a sealed evacuated Pyrex tube.…”

“…We have recently observed that co-deposition of the hexanuclear copper(I) carboxylate complex with coronene from the gas phase did not change the nuclearity of the copper(I) core in its crystalline adduct. [11] The choice of ligands, fluoranthene (L 1 = C 16 H 10 ), pyrene (L 2 = C 16 H 10 ), and coronene (L 3 = C 24 H 12 ) (Scheme 4), was based on their different volatility that covers a broad temperature range for co-deposition reactions (melting points are 105°C for fluoranthene, 146°C for pyrene, and 428°C for coronene). In addition, the copper(I) binding toward π-donor substrates has been long considered important in molecular recognition processes for many biological and artificial systems, [17] as well as in catalysis of aromatic cross-coupling reactions.…”

“…[10] Surprisingly, in contrast to the above-mentioned benzoate ligands that resulted in the tetracopper(I) clusters, 3,5-difluorobenzoate afforded a remarkable hexanuclear copper(I) complex, the first such example in the series. [11] At the same time, copper(I) pivalate was found to exhibit a unique double helical polymeric structure (Scheme 1, e). Its formation was explained by a delicate balance between the cuprophilicity and the steric effect of the bulky tBu groups.…”

“…(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) for crystal growth, we have recently accomplished the preparation and structural characterization of [Cu 2 (O 2 C(2,6-CF 3 ) 2 C 6 H 3 ) 2 ] ϱ [9] (Scheme 1, a), [Cu 4 (O 2 C(3-F)C 6 H 4 ) 4 ] and [Cu 4 (O 2 C(2,3,4-F) 3 (c), and [Cu 6 (O 2 C(3,5-F) 2 C 6 H 3 ) 6 ] [11] (d). Thus, the known structural types of copper(I) carboxylates range from discrete [6,10,11] to infinite motifs, [5,[7][8][9] based on mono-, [8] di-, [5,9] tetra-, [6,7,10] or hexanuclear [11] copper(I) units.…”

“…Thus, the known structural types of copper(I) carboxylates range from discrete [6,10,11] to infinite motifs, [5,[7][8][9] based on mono-, [8] di-, [5,9] tetra-, [6,7,10] or hexanuclear [11] copper(I) units. Such structural diversity is fascinating but not well rationalized so far.…”