Comparison of solid‐state and solution structures of (R 3 P) 2 CdX 2 , (Et 3 P) 2 Cd 2 X 4 and (Bu 3 P) 3 Cd 2 X 4 complexes

The cadmíum (II) phosphine complexes (Et 3 P) 2 Cd 2 X 4 , (R 3 P) 2 CdX 2 [R 3 P = Ph 3 ,P, Bu 3 P, Et 3 P, 1‐phenyldibenzophosphole (DBP), and 1‐phenyl‐3,4,‐dimethylphosphole (DMPP)] and (Bu 3 P) 3 Cd 2 X 4 (X = Cl, Br, I) have been prepared and their solution and solid state structures determined by a combination of elemental analyses, conductance, infrared and NMR spectroscopy. The structures of (Ph 3 P) 2 CdI 2 (1) and (DBP) 2 CdI 2 (2) have been determined from three‐dimensional X‐ray data collected by counter methods. Compound 1 crystallized in space group P2 1 ,/ a with a = 18.312 (9), b = 10.285 (5), c = 19.311 (9) Å, β = 115.53 (4)° and Z = 4. Compound 2 crystallized in space group P2 1 ,/ n with a = 12.698 (3), b = 15.302 (4), c = 17.477 (4) Å, β = 96.66 (2)° and Z = 4. The structures were refined by least‐squares methods with R F = 0.041 and 0.048 for 4157 and 3393 unique reflections with I/σ(I) ⩾ 2.0 for 1 and 2, respectively. Both molecules deviate from ideal C 2 v symmetry and have very slightly different Cd‐I (1; 2.724 (2), 2.731 (2); 2; 2.718 (1), 2.721 (1) Å) and Cd‐P (1, 2.631 (2), 2.653 (2); 2; 2.616 (3), 2.603 (3) Å) bond distances. The Cd‐P bond distance differences are sufficient to give rise to a second order ABX CP/MAS 31 P{ 1 H} NMR spectrum for 1 but for 2 the phosphorus nuclei of the two DBP ligands are chemical shift equivalent. The CP/MAS 113 Cd{ 1 H} NMR spectra of both compounds 1 and 2 show apparent first order triplets. The (Bu 3 P) 3 Cd 2 X 4 complexes are shown by variable temperature 31 P{ 1 H} NMR and conductance measurements to exist in solution as equilibrium mixtures of (Bu 3 P) 2 Cd 2 X 4 and (Bu 3 P) 2 CdX 2 . CP/MAS 31 P{ 1 H} and 113 Cd{ 1 H} NMR spectra suggest that these compounds exist as doubly halide bridged (R 3 P) 2 Cd(μ‐X) 2 CdX 2 (R 3 P) species containing four‐ and five‐coordinate cadmium in the solid state. Equilibrium and activation thermodynamics for the ligand exchange processes of representative complexes have been determined from variable temperature 31 P{ 1 H} NMR spectra in CDCl 3 /CH 2 Cl 2 (1:1) solutions.