Alcoholysis of 2,2′-Pyridil, (2-C 5 H 4 N)C(O)C(O)(2-C 5 H 4 N), in the Presence of Copper(II): A Family of Planar Pentanuclear Copper(II) Complexes Stabilized by [(2-C 5 H 4 N)C(O)(OR)C(O)(OR)(2-C 5 H 4 N)] 2- and Carboxylate Ligands Giannis S. Papaefstathiou, ² Catherine P. Raptopoulou, ‡ Alexandros Tsohos, ‡ Aris Terzis,* ,‡ Evangelos G. Bakalbassis,* ,§ and Spyros P. Perlepes* ,² Department of Chemistry, University of Patras, 265 00 Patras, Greece, Institute of Materials Science, NCSR “Demokritos”, 153 10 Aghia Paraskevi Attikis, Greece, and Laboratory of Applied Quantum Chemistry, Department of Chemistry, Aristotle University of Thessaloniki, 540 06 Thessaloniki, Greece ReceiVed October 4, 1999 Introduction The development 1 of routes and strategies for the synthesis of high-nuclearity complexes of 3d metals in moderate oxidation states is of great importance because these species have provided substantial impetus for developments in several different fields, including bioinorganic chemistry, magnetochemistry, material chemistry, and solid-state physics. We have been pursuing studies 2,3 of polynuclear complexes of the later 3d metals because such clusters may display unusual structures and interesting magnetic properties. One of our routes 2 takes advantage of the observation that the reactions between metal carboxylates and di-2-pyridyl ketone [(2-C 5 H 4 N)C(O)- (2-C 5 H 4 N); see Chart 1] lead to incomplete replacement of the carboxylate ligands and the formation of large polynuclear arrays of metal ions. The structural diversity of the resultant species stems from the ability of the singly and doubly deprotonated anions of the gem-diol form of (2-C 5 H 4 N)C(O)(2-C 5 H 4 N) to adopt a variety of coordination modes, sometimes two different modes in the same complex. Restricting further discussion to copper(II) chemistry, we note that the synthetic investigation of the [Cu 2 (O 2 CMe) 4 (H 2 O) 2 ]/(2-C 5 H 4 N)C(O)(2-C 5 H 4 N)/ClO 4 - reaction mixture in H 2 O has led to the isolation of the remarkable octanuclear complex 2a [Cu 8 {(2-C 5 H 4 N)C(O)(OH)- (2-C 5 H 4 N)} 8 (O 2 CMe) 4 ](ClO 4 ) 4 , whereas the reaction of [Cu 2 (O 2 - CMe) 4 (H 2 O) 2 ] with (2-C 5 H 4 N)C(O)(2-C 5 H 4 N) in MeCN, in the absence of counterions, gave the novel molecules 2b [Cu 7 (OH) 2 - {(2-C 5 H 4 N)CO 2 (2-C 5 H 4 N)} 3 (O 2 CMe) 6 ] and [Cu 12 {(2-C 5 H 4 N)- CO 2 (2-C 5 H 4 N)} 6 (O 2 CMe) 12 ]. More recently, our efforts have turned toward the use of 2,2′- pyridil [(2-C 5 H 4 N)C(O)C(O)(2-C 5 H 4 N); Chart 1], which pre- sents chemical similarities to (2-C 5 H 4 N)C(O)(2-C 5 H 4 N) but contains an extra donor group, to see how incorporation of this ligand type might affect the structures and physical properties of the products. Here we report a study of a simple reaction involving a “blend” of (2-C 5 H 4 N)C(O)C(O)(2-C 5 H 4 N) and carboxylate ligands in alcohols, which produces a series of planar pentanuclear copper(II) complexes. The structures of three members of this family and the magnetic properties of one representative complex are described. This work can also be regarded as a contribution to the almost unexplored coordination chemistry of 2,2′-pyridil. 4 Experimental Section Syntheses. All manipulations were performed under aerobic conditions using materials and solvents as received (Aldrich Co.). The compound Cu(O 2 CPh) 2 ‚EtOH was prepared as described elsewhere. 5 [Cu 5 (OH) 2 {(2-C 5 H 4 N)C(O)(OEt)C(O)(OEt)(2-C 5 H 4 N)} 2 - (O 2 CMe) 4 (EtOH) 2 ]‚2EtOH (1). To a solution of (2-C 5 H 4 N)C- (O)C(O)(2-C 5 H 4 N) (0.12 g, 0.56 mmol) in EtOH (10 mL) was added a solution of [Cu 2 (O 2 CMe) 4 (H 2 O) 2 ] (0.28 g, 0.70 mmol) in the same solvent (30 mL). The blue solution obtained was stirred at ambient temperature for 30 min and allowed to stand undisturbed for 3 d. Well-formed, X-ray-quality crystals of 1 slowly appeared. The blue prismatic crystals were collected by filtration, washed with EtOH, and dried in air. The yield was ∼45% based on copper. Anal. Calcd for C 48 H 74 Cu 5 N 4 O 22 : C, 41.87; H, 5.41; N, 4.07; Cu, 23.07. Found: C, 41.70; H, 5.36; N, 4.22; Cu, 22.47. Selected IR data (cm -1 ) (KBr pellet): 3444 (m, br), 1590 (s), 1474 (m), 1408 (s), 1124 (m), 1092 (s), 1022 (m), 772 (m), 656 (m). [Cu 5 (OH) 2 {(2-C 5 H 4 N)C(O)(OPr n )C(O)(OPr n )(2-C 5 H 4 N)} 2 - (O 2 CMe) 4 (Pr n OH) 2 ]‚0.8Pr n OH (2). To a stirred solution of [Cu 2 (O 2 CMe) 4 (H 2 O) 2 ] (0.14 g, 0.35 mmol) in Pr n OH (20 mL) was added a solution of (2-C 5 H 4 N)C(O)C(O)(2-C 5 H 4 N) (0.06 g, 0.28 mmol) in the same solvent (10 mL). Layering of Et 2 O ² University of Patras. ‡ NCSR “Demokritos”. § Aristotle University of Thessaloniki. 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