Infrared evidence is presented for the formation of a three-co-ordinate species, [Co(CO),(NO)], on the U.V. photolysis of [Co(CO),(NO)] in argonand methane matrices,andfortheforniation of four-co-ordinate species, [Co(CO),-(N,)(N@)] and probably [Co(CQ)(N,),(NO)],in nitrogen matrices a t 20 K. The primary photolysis steps are readily reversed by irradiation withvisible light and by annealing the matrix in the case of the reaction of [Co(CO),-(N@)] with CO. The results are discussed in reletion to the postulate of co-ordinatively unsaturated and expandedco-ordination-shell species as intermediates in the thermal substitution reactions of [Co(CO), (NOj]. THE thermal substitution reactionsof the pseudo-first stage in the decomposition of [Ni(CO)J both [Ni(CO),] series of complexes [M(CO),-,(NO),] have been thermally and photochemically also involves CO loss, extensively studied.l Tetracarbonylnickel undergoes slow fast substitution and exchanges CO by a dissociative "i(CO)d ---t [~i(CO),] -"i(CO)&I mechanism, (l), with a first-order rate law (2).2 The Southampton SO9 5NH.

Dihydrogen has been codeposited with alkali halides in argon matrices at -10 K. The presence of the alkali halide induces infrared activity which is assigned to the H-H stretching vibration that is red-shifted by as much as 114 cm-l from the position of the Q branch vibration of O-H2 in argon. The observations suggest that it is the anion of the alkali halide ion pair which is responsible for the perturbation of H2. Thus, the largest perturbations have been recorded for KF and CsF while the perturbation due to RbNO3 is not nearly as great as that for RbCl. Moreover, the position of the perturbed H-H stretch is quite insensitive to the size of the cation in the series of alkali chlorides. The extent of perturbation on the H-H stretch has been found to be greater for alkali halide monomers than for aggregates.

evidence, including *H labelling, is presented to show that photolysis of [(q5-C5R5)M(C0),] complexes (M = Rh, R = Me; M = Ir, R = H, Me) in CH4 matrices at 12 K leads primarily to [(q5-C,R5)M(CO)(H)(Me)] species whereas in Ar and N2 matrices only small yields of {(q5-C5R5)M(CO)] species are observed. One of the most important goals in the petrochemicals [(q5-C5R5)M(CO)2] [(r5-CsMes>Ir(Co)(H)(Me)l (4) industry is to find catalysts which will activate saturated hydrocarbons, particularly CH4, so as to enable their use as feedstocks.' The recent discoveries that [ ( T ~-C ~R ~) I ~( C O ) ~] complexes [R = H (l), Me (2)] would photochemically activate C-H bonds in CH4,2a neopentane,zb cyclohexane72b and benzene,2b and that [ (q5-C5Me5)M(PMe3)H2] (M = Rh,3 Ir4) could similarly activate C-H bonds in alkanes have (

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C4H4) (CO) 31 and [Fe(C(CHJ 3HCO) 31 * [711472