Synthesis and Structural Study of Tris( -pyrazolyl)hexakis(pyrazole)dicobalt(III) Nitrate

The new (Hpyz)3Co(μ2-pyz)3Co complex has been isolated as the nitrate salt through a reaction of Co(II) nitrate, Hpyz (pyrazole), triethylamine, and oxygen. The salt crystallizes in the monoclinic space group P21/m with a = 12.5977(3)？？, b = 15.3387(4)？？, c = 14.0800(3)？？, β = 93.0868(15)°, and = 1.464？g/cm3 at 150(1)？K. The complex, with pseudo-octahedral coordination about the equivalent cobalt centers, has shorter Co–N distances for the bridging anionic pyz ligands as compared to the neutral Hpyz ligands, with the averages being 1.918(2) and 1.966(4), respectively. The Co–Co separation is 3.568？？, reflecting the absence of any significant metal-metal interaction. 1. Introduction Although numerous approaches for the syntheses of heterobimetallic complexes have been developed, most of these either involve organometallic complexes or utilize ligands such as bridging phosphides, which could be detrimental to potential catalytic applications [1]. It would therefore appear advantageous to construct the heterobimetallic species using more traditional coordination chemistry. Ligands such as 1,8-naphthyridine or pyridazine could potentially be utilized, but their lack of negative charge appears often to lead to the more strongly Lewis acidic metal ion abstracting the ligand from the weaker acid [2, 3]. Hence, more basic species such as the pyrazolyl ion, 1,2- (1, Figure 1), appear more useful for the stabilization of the desired bimetallics. Indeed, we recently reported a cobalt/ruthenium complex [1] in which the two metal centers were united via three -pyrazolyl anions. Though other heterobimetallics had been isolated previously with this same linking agent [4–7], they had all been organometallic complexes. Herein we report a homobimetallic complex involving two cobalt centers, linked by three -pyrazolyl ligands, that was isolated as part of our general bimetallic studies. Figure 1 2. Materials and Methods 2.1. Synthesis All reactions were carried out in Schlenk apparatus under a nitrogen atmosphere. THF was dried by distillation from sodium benzophenone ketyl under nitrogen. All reagents were obtained commercially. Hexakis(pyrazole)tris( 2–pyrazolyl)dicobalt(III) nitrate, [(Hpyz)3Co( 2-pyz)3Co(Hpyz)3](NO3)3, 2 [NO3]3. To a solution of 1.00？g (14.7？mmol) of pyrazole and 0.63？mL (4.5？mmol) of NEt3 in 10？mL of THF was added dropwise 5？mL of a THF solution containing 0.45？g (1.5？mmol) of Co(NO3)2·6H2O. Upon mixing, much pink crystalline solid precipitated from the light red solution over the course of several minutes. The mixture was then stirred at room