Do paramagnetic platinum metal hydrides really exist? A reinvestigation of the synthesis and magnetochemical properties of Ir(H)x(Cl)2(P-i-Pr3)2 (1). Syntheses and crystal structure determinations of trans-Ir(H)(Cl)2(CO)(P-i-Pr3)2 (2), cis-Ir(H)(Cl)2(CO)(P-i-Pr3)2 (4) and trans-Ir(Cl)(CO)(P-i-Pr3)2 (5)

Abstract

As further studies of our samples of Ir(H)x(Cl)2(P-i-Pr3)2 (1) led us to suspect that their paramagnetism was due to cooperative surface phenomena we decided a through reinvestigation of the system 1. The reaction of ethanolic solution of H2[IrCl6] with P-i-Pr3, in the presence of concentrated HCl, gave compound 1 in 70% yield. The magnetic moment of this sample does not exceed 0.5 BM. Washing the sample with water or with organic solvents and crushing it with a platinum spatula gave an increase in μeff. 1H spin-lattice relaxation (T1) measurement on solid samples of 1 at different μeff values (0.5, 1.5 BM) suggest that the paramagnetism is due to cooperative surface phenomena and the bulk of 1 is diamagnetic. As found in the complex prepared starting from (NH4)2[IrCl6], the above sample shows two weak bands at 2116 and 2002 cm−1. These, however, are not due to νIrH but to the presence of small amounts of two carbonyl complexes. By bubbling CO gas into an ethanolic solution of 1, the trans-Ir(H)(Cl)2(CO)(P-i-Pr3)2 (2) compound is obtained. This carbonyl complex shows an extremely strong band at 2002 cm−1. Trans-2, both in solution and in the solid state, isomerizes into cis-Ir(H)(Cl)2(CO) (P-i-Pr3)2 (4). By reacting an ethanolic solution of H2[IrCl6] with P-i-Pr3, without addition of HCl, a mixture of 1 and another complex, trans-Ir(Cl)(CO)(P-i-Pr3)2 (5), is obtained, characterized by a strong band at 1930 cm−1. Subsequent refluxing of the mother liquor of the above synthesis gave pure 5. This new complex is responsible for the very strong band at 1930 cm−1. Thus, the νIrH of complex 1 does not occur in the unusual region, and may be masked by the H2) absorption at ca. 1700−1600 cm−1. Crystallographic data: for trans-2 (at 298 K), a = 15.515(6), b = 8.633(4), c = 19.521(9) Å, β = 104.34(3)° in space group la (Z = 4). For cis-4 (at 298 K), a 16.488(1), b = 27.118(2), c = 11.384(1) Å in space group Pbca (Z = 8). For trans-5 (at 298 K), a = 8.152(3), b = 8.918(3), c = 16.639(6) Å, β = 93.50(3)° in space group