Crystal Structure of a Lantern-type Dirhodium(II) Complex with Axial Pyridine Molecules cis-[Rh2(4-Me-pf )2(O2CCMe3)2(py)2], 4-Me-pf− = N,N′-Di-p-tolylformamidinate Anion

The complexes [M2(O2CR)4] (m = 0 – 2), in which two transition metal ions are bridged with four μ-carboxylato bidentate ligands, are called lantern-type (or paddlewheel type) diuclear complexes from the view point of their molecular structures.1 The axial sites of the dinuclear complexes are coordinated by linkage ligands, such as pyrazine, to produce the assembled polymer complexes. The polymer complexes have been attracting many chemists concerning their interesting properties. For instance, nitrogen gas occulusion properties have been found for polymer complexes [Cu2(O2CPh)4(pyz)]n and [Rh2(O2CPh)4(pyz)]n. N,N′-Diarylformamidinato ions (R-pf–) also work as bidentate ligands for metal ions to give lantern-type dinuclear complexes. We have reported on the polymer complexes [Rh2(4-Me-pf )4(1,4-dib)]n (4-Me-pf– = N,N′-di-p-tolylformamidinate anion; 1,4-dib = 1,4-diisocyanobenzene) and cis-[Rh2(4-Me-pf )2(O2CR)2(L)]n (R = CF3 and CMe3; L = pyz and 4,4′-bipyridine (4,4′-bpy)).4,5 We also reported on the bis-adduct complexes 4-phenylpyridine (4-phpy) cis-[Rh2(4-Me-pf )2(O2CR)4(4-phpy)2] (R = CF3 and CMe3) and cis-[Rh2(4-Me-pf )2(O2CCMe3)2(4-phpy)2]BF4. A pyridine adduct complex, cis-[Rh2(4-Me-pf )2(O2CCF3)4(py)2], has been synthesized, but not reported concerning its crystal structure.6 In this report, we here report on the synthesis and crystal structure of cis-[Rh2(4-Me-pf )2(O2CCMe3)4(py)2] (1). The chemical structure of the title compound 1 is depicted in Fig. 1. The starting material, cis-[Rh2(4-Me-pf )2(O2CCMe3)2], was prepared according to a method described in the literature.7 To a solution of cis-[Rh2(4-Me-pf )2(O2CCMe3)2] (96.0 mg (0.11 mmol) in chloroform (5.0 mL) and methanol (15.0 mL) was added pyridine (1.0 mL), and the mixture was stirred for 3 h at room temperature. To the resultant solution was added water (1.0 mL), and the reaction mixture was evaporatd to ca. 3 mL. The evapotated solution was left at room temperature until red microcrystals were deposited. The deposited microcrytals were collected by suction, washed with a small portion of water, and dried over P2O5 in a vaccum desicater for 3 h. The yield was 76.3 mg (68.2% base on cis-[Rh2(4-Mepf )2(O2CCMe3)2]). Anal. Found: C, 59.12; H, 5.34; N, 8.26. Calcd for C50H58N6O4Rh2: C, 59.29; H, 5.77; N, 8.30%. IR (KBr, cm–1): 2983 w, 2917 w, 2859 w (CH), 1622 s, 1592 s (Ar), 1504 s, 1480 m, 1412 s, 1333 m (COO), 1222 s (Ar). X-ray quality crystals of 1 were obtained by recrystallization from dichlroromethane solution with several drops of pyridine. X-ray crystallographic data (Table 1) were collected for a single crystal of 1 at 150 K on a RIGAKU HyPix6000 CCD system equipped with a Mo rotating-anode X-ray generator (λ = 2021 © The Japan Society for Analytical Chemistry