SINGLE-CRYSTAL, SOLID-STATE, AND SOLUTION CD-113 NMR-STUDIES OF [CD(SR)2(N-DONOR)2] COMPLEXES - STRUCTURAL AND SPECTROSCOPIC ANALOGS FOR BIOLOGICALLY OCCURRING [M(S-CYS)2(HIS)2] CENTERS

A series of compounds of the formula [Cd(SR)2(N-donor)2] has been synthesized, characterized by X-ray crystallography, and studied by solid-state and solution 113Cd NMR spectroscopy to serve as analogues for biologically occurring [M(5-Cys)2(His)2] centers. The compounds include [Cd(S-2,4,6-(-Pr3-C6H2)2(bpy)] (1), [Cd(S-2,4,6-i-Pr3-C6H2)2(phen)]2 (2), [Cd(S-2,4,6-i-Pr3-C6H2)2(1-Me-imid)2] (3), and [Cd(S-2,4,6-i-Pr3-C6H2)2(1,2-Me2-imid)2] (4). Compounds 1-3 have been characterized by X-ray crystallography. The unit cell parameters are as follows. For I: a = 15.081 (9)Å, b = 14.716 (9) Å, c = 17.72 (1) Å, β = 100.36 (5)°, V= 3868 (8) Å3, Z = 4, P21/c. For 2: a = 10.12 (2) Å, b = 16.56 (1) Å, c = 23.50 (2) Å, β = 92.1 (5)°, V = 3934 (14) Å3, Z = 2, P21/n. For 3: a = 16.541 (7) Å, b = 15.887 (6) Å, c = 16.36 (1) Å, β = 108.91 (5)°, V = 4068 (7) Å3, Z = 4, P21/c. Compounds 1-4 have been characterized by solution and CP/MAS 113Cd spectroscopy. The 13Cd shielding tensors of 1 have been obtained from a single-crystal study (σ11 = 814 σ22 = 630 ppm, σ33 = 32 ppm). Similar large chemical shielding anisotropies (CSA) were also observed for 2-4. The solution 113Cd NMR spectra arc consistent with monomeric [Cd(SR)2(N)2] structures. The large difference in the 113Cd chemical shift for 2 in the solution and solid state is explained by the weak dimeric structure of 2 in the solid state. The implications of the large CSA to solution and solid-state measurements of related centers in proteins are discussed. © 1990, American Chemical Society. All rights reserved.