Influence of anion on the solution and solid-state structures of some 1∶2 adducts of silver(I) salts with 1,3-bis(diphenylphosphino)propane

Abstract

Crystallization of 1∶2 silver(I) halide/pseudo halide∶1,3-bis(diphenylphosphino)propane (dppp) mixtures from acetonitrile have resulted in the isolation of a novel series of neutral complexes, [AgX(dppp-P,P′)(dppp-P)] (X = Cl, Br, I or CN) containing co-ordinated anion and uni- and bi-dentate dppp ligands. In contrast, the thiocyanate and nitrate complexes precipitate as ionic [Ag(dppp-P,P′) ₂ ]X with unco-ordinated anion and bidentate phosphine ligands, a structural type previously found for other 1∶2 silver(I)∶diphosphine complexes. The complexes have been characterized by single-crystal X-ray structure determinations and solid-state ³¹ P cross-polarization magic angle spinning (CP MAS) NMR spectroscopy. The salt [Ag(dppp-P,P′) ₂ ]SCN is obtained as crystals suitable for X-ray studies from pyridine, crystallizing as a sesqui-pyridine solvate in the monoclinic space group P2 ₁ /c with a = 10.691(2), b = 24.75(2), c = 22.360(4) Å, β = 108.38(1)°. The neutral AgXP ₃ complexes (X = Cl, Br, I or CN) are isomorphous, crystallizing in the monoclinic space group C2/c, with a ≈ 21.8, b ≈ 10.3, c ≈ 45 Å, β ≈ 95°. The solid-state ³¹ P CP MAS spectra are consistent with the structural results; the tetrahedral SCN and NO ₃ complexes give a similar broad complex multiplet centred at δ -6, whereas the spectra of the neutral AgXP ₃ complexes are interpretable as A ₂ BMX spin systems with signals assignable to the non-co-ordinated (δ -23), bidentate (δ ca. 13) and unidentate (δ ca. 3) phosphorus atoms. For the latter ¹ J(P–Ag) couplings are in the range 288 Hz (CN) to 367 Hz (Br). Solution ³¹ P NMR studies on these complexes show that both neutral and ionic complexes exist in equilibrium in solution, with the position of the equilibrium dependent on the nature of the anion X. The potential significance to the antitumour activity of bis-chelated 1∶2 silver(I)–diphosphine complexes is discussed.