FULL PAPER DOI: 10.1002/ejic.200800349 Synthesis and Characterization of Linear Trinuclear Pd, Co, and Pd/Co Pyrazolate Complexes Haralampos N. Miras, [a] Hong Zhao, [a] Radovan Herchel, [b] Carlos Rinaldi, [c] Soribel Pérez, [a] and Raphael G. Raptis* [a] Keywords: Heterometallic compounds / Nitrogen heterocycles / Magnetic properties / Palladium / Cobalt A family of dinuclear and linear trinuclear Co/Pd pyrazolate compounds, namely, [Bu 4 N] 2 [Co 2 (μ-4-Cl-3,5-Me 2 -pz) 2 Cl 4 ] (1), [Bu 4 N] 2 [Co 2 (μ-4-Br-3,5-Me 2 -pz) 2 Br 4 ](2), [Bu 4 N] 2 [Co 2 (4-I- 3,5-Me 2 -pz) 2 Cl 4 ] (3), [Et 4 N] 2 [Pd 2 Co(4-Br-3,5-Me 2 -pz) 4 Cl 4 ] (4), [Et 3 NH] 4 [PdCo 2 (4-Br-3,5-Me 2 -pz) 4 Cl 4 ][NO 3 ] 2 (5), [Et 3 NH] 2 - [Pd Co 2 (3-Me-5-Ph-pz) 4 Cl 4 ](6), [Et 3 NH] 2 [Pd 3 (4-Br-3,5-Me 2 - pz) 4 Cl 4 ](7), and [Co 3 (3,5-Me 2 -pz) 4 (3,5-Me 2 -pzH) 2 (CH 3 CO 2 ) 2 ] Introduction This work stems from our interest in exploring the struc- tural parallel between transition-metal pyrazolate and car- boxylate chemistry. [1] Polynuclear transition-metal carbox- ylate complexes have been widely investigated for the fol- lowing reasons: (i) Besides 1D, 2D, or 3D magnetic order- ing, [2–5] it has been shown that carboxylate complexes show single-molecule magnet (SMM) properties. (ii) Several car- boxylate complexes have been successfully used as biomi- metic models of metalloprotein polynuclear active cen- ters. [5d,5e] (iii) Metal carboxylates can be viewed as extended models of intermediates during the formation of geological sediments. [5f] (iv) A variety of unique organic reactions are efficiently catalyzed by polynuclear carboxylates due to the ability of polymetallic centers to coordinate and to activate several functional groups of a substrate. [5e,5g] (v) It has re- cently been demonstrated that polynuclear carboxylate complexes can be used as precursors for the preparation of nanosized magnetic oxide particles. [6–8] The synthesis and structural characterization of carbox- ylato-bridged complexes is now a well-developed field. [2–10] In our previously reported work we suggested that a wide class of polynuclear metal–pyrazolates with interesting re- [a] Department of Chemistry and the Institute of Functional Nan- omaterials, University of Puerto Rico, San Juan, PR 00931-3346, USA E-mail: raphael@adam.uprr.pr [b] Department of Inorganic Chemistry, Palacký University, Kr ˇíz ˇkovského 10, CZ-77147 Olomouc, Czech Republic. [c] Department of Chemical Engineering and the Institute of Functional Nanomaterials, University of Puerto Rico, Mayagüez, PR 00681-9046, USA Eur. J. Inorg. Chem. 2008, 4745–4755 © 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 4745 (8) was synthesized. The single-phase nature of the solids was established by single-crystal X-ray diffraction, thermal analysis, and spectroscopic techniques. Moreover, the mag- netic behavior is studied and a magnetostructural compari- son to the corresponding carboxylate analogues is made. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) dox and magnetic properties, which are structural ana- logues of known carboxylates of the same metals, remain to be fully explored. [1] Evidently, the field of metal–pyrazol- ates is significantly less developed than that of the analo- gous carboxylates. [9] Still, several oligonuclear metallocyclic pyrazolato complexes, from tri- to tetradecanuclear, are known. [1b,11–14] In contrast, only a limited number of non- cyclic metal–pyrazolate structural motifs have been re- ported so far. [11,12d,15] Studies of the exchange interaction between paramag- netic metal centers through multiatom bridging ligands are important to a variety of research areas, ranging from coor- dination chemistry to solid-state physics, biology, and bio- inorganic chemistry. [16–30] Chauduri et al., as well as others, have reported extensively on the exchange interactions be- tween paramagnetic metal centers bridged by three-atom bridges in di- and trinuclear, homo- and heterometallic complexes. [16–18,21–30] Analogous studies of systems involv- ing pyrazolate bridges have been hitherto lacking. Here we report the first part of our studies of linear tri- nuclear pyrazolato complexes, involving homometallic (Pd or Co) and heterobimetallic (Pd/Co) systems, including the syntheses, magnetic, thermal, spectroscopic, and X-ray structural characterization of [Bu 4 N] 2 [Co 2 (4-Cl-3,5-Me 2 - pz) 2 Cl 4 ](1), [Bu 4 N] 2 [Co 2 (4-Br-3,5-Me 2 -pz) 2 Br 4 ](2), [Bu 4 N] 2 - [Co 2 (4-I-3,5-Me 2 -pz) 2 Cl 4 ](3), [Et 4 N] 2 [Pd 2 Co(4-Br-3,5-Me 2 - pz) 4 Cl 4 ](4), [Et 3 NH] 4 [PdCo 2 (4-Br-3,5-Me 2 -pz) 4 Cl 4 ][NO 3 ] 2 (5), [Et 3 NH] 2 [PdCo 2 (3-Me-5-Ph-pz) 4 Cl 4 ] (6), [Et 3 NH] 2 [Pd 3 (4-Br-3,5-Me 2 -pz) 4 Cl 4 ](7), and [Co 3 (3,5-Me 2 -pz) 4 (3,5- Me 2 -pzH) 2 (CH 3 CO 2 ) 2 ](8), where 4-X-3,5-Me 2 -pzH and 4- X-3,5-Me 2 -pz represent the ligands 4-X-3,5-dimethylpyr- azole and 4-X-3,5-dimethylpyrazolate anion (X = Cl, Br, I).