pubs.acs.org/IC Published on Web 01/12/2010 r 2010 American Chemical Society 1626 Inorg. Chem. 2010, 49, 1626–1633 DOI: 10.1021/ic9020367 Reversible Cu 4 T Cu 6 Core Interconversion and Temperature Induced Single-Crystal-to-Single-Crystal Phase Transition for Copper(I) Carboxylate Alexander S. Filatov, † Oleksandr Hietsoi, † Yulia Sevryugina, † Nikolay N. Gerasimchuk, ‡ and Marina A. Petrukhina* ,† † Department of Chemistry, University at Albany, 1400 Washington Avenue, Albany, New York 12222 and ‡ Department of Chemistry, Missouri State University, 901 South National Avenue, Springfield, Missouri, 65897 Received October 14, 2009 The first example of a reversible [Cu 4 ] T [Cu 6 ] interconversion for polynuclear copper(I) complexes under controlled experimental settings is reported. It illustrates the key role of specific crystal growth conditions for accessing the target cluster nuclearity that consequently determines physical properties of the resulting solid state products. Thus, when copper(I) benzoate crystallizes from a 1,2-dichlorobenzene solution at room temperature, it forms [Cu 4 ]-core based crystalline material, [Cu 4 (O 2 CC 6 H 5 ) 4 ](1). In contrast, crystal growth by deposition from the gas phase at elevated temperatures results in the exclusive formation of [Cu 6 (O 2 CC 6 H 5 ) 6 ](2). Complexes 1 and 2 have been isolated in pure form, fully characterized, and reversibly interconverted into each other. The effect of a core structure on the spectroscopic properties of 1 and 2, such as IR, Raman, and photoluminescence, has been investigated. Additionally, a combination of X-ray powder and single crystal diffraction methods has been used to discover the temperature induced phase transition in the hexanuclear copper(I) system. Two modifications of 2 exhibiting slightly different solid state packing of the [Cu 6 (O 2 CC 6 H 5 ) 6 ] units have been identified at room and low temperature. Moreover, reversible single-crystal-to-single- crystal transitions between these polymorphic forms have been confirmed. The important role of weak intermolecular interactions between polynuclear copper(I) units in the solid state has also been revealed and discussed. Introduction Polynuclear complexes of copper(I), silver(I), and gold(I) are subjects of considerable research activity focused on the inter- play between their geometric and electronic structures, 1 as well as size-reactivity relationships for practical optoelectronic, 2 catalytic, 3 and biochemical applications. 4 Specifically, interac- tions between closed d 10 shells in various clusters attract broad attention, since the number and arrangement of metal centers in close proximity affect stability, chemical, and photophysical behavior of the resulting systems. However, target preparation of a desired cluster core with tailored properties remains a significant synthetic challenge. We have recently turned to investigation of polynuclear copper(I) complexes supported by various carboxylate groups since they exhibit a remarkable structural diversity and that should be the key factor allowing tuning of their physical properties and chemical reactivity. Among a rather limited number of the structurally confirmed examples, there are discrete complexes with tetra- 5 and hexa- nuclear cores, 6 as well as with extended structures formed by di- and tetranuclear copper units held by additional Cu 333 O intermolecular interactions. 7,8 Additionally, two new examples of extended helical chains held by cuprophilic Cu 333 Cu inter- actions in the solid state have been reported for copper(I) pivalate 9 and 3,5-bis(trifluoromethyl)benzoate. 10 Analyzing *Corresponding author. E-mail: marina@albany.edu. (1) (a) Balch, A. L. Struct. Bonding (Berlin) 2007, 123,1–40. (b) Balch, A. L. Angew. Chem., Int. Ed. 2009, 48, 2641–2644. (2) (a) Ford, P. C.; Cariati, E.; Bourassa, J. Chem. 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