The electronic spectra of some LM(CO)¡ compounds of Civ or related symmetry are reported in the range 5000-1900 Á in the vapor and solution phases. L may be CF3, CH3, H, Cl, Br, or I and M may be Mn or Re. The compounds have been classified according to the and properties of the ligand. Band assignments are made and qualitative molecular orbital energy diagrams are given to account for charge-transfer bands. The low-energy spectra of the tetracarbonyl dimers of Mn are reported and related to those of Civ compounds. ship to G. B. B.

amount of N-bonded product arising from nitrogen attack would account for the slight rate increase actually observed, or it could simply be due to a salt effect. In summary, a dependence upon the size of the reagent is consistent with the second mechanism but should not be a factor in the ring-opening mechanism.*l (21) A referee suggested that the strain on the bent SeCNgroup by the tridentate amine, without distortion of the Pd-amine bonds, is a more probable explanation of its special position among leaving groups; Le., a relatively weak interaction of the palladium-(11) with a potential entering group might be enough t o remove a strained -SeCN-. We do not find this explanation t o be compelling. Its logical extension suggests that the strained, angular Pd-SCN group should also be susceptible t o attack by an incoming group for it, too, is destabilized by the presence of the ethyl groups and isomerizes Registry No. [Pd(Et4dien)SCN] [B(C6H5)4], 22143-00-6; [Pd(Et4dien)NCS] [B(C6HS),] , 22 142-99-0; Br-, 24959-67-9; [Pd(Et4dien)SeCN] [B(C6Hs)4] , 19599-79-2; [Pd(Et4-dien)NCSe] [B(C6Hs)4] , 18024-40-3; I-, 2046-1 54-5; N; , 14343-69-2; CN-, 57-12-5; SeCN-, 5749-48-4.sincere appreciation to the National Science Foundation for the support of this research (Grants GP-8327 and GP-20607) and to Professor Harry Gray for supplying us with a copy of his paper prior to publication. at rates only slightly slower than those of the Pd-SeCN isomer. In point of fact, only the Pd-SeCN isomer exhibits the second-order pathway.Acknowledgment. The authors wish to express their Stability constants, Km-, for the complexation reaction ML + X * MLX have been determined from proton magnetic resonance chemical shift measurements for a series of complexes where M is cadmium or zinc, L is nitrilotriacetic acid (nta) or p, p', 0"-triaminotriethylamine (tren), and X is ethylenediamine (en), glycine (gly), malonic acid (ma), or iminodiacetic acid (ida). The log K m m~ values are as follows: 5.00, Zn(nta)(en)-; 5.05, Cd(nta)(en)-; 1.15, Zn(tren)(en)'+; 2.83, Cd(tren)(en)'+; 3.62, Zn(nta)(gly)'-; 2.93, Cd(nta)(gly)'-; 1 .OO, Zn(tren)(gly)+; 2.59, Cd(tren)(gly)+; 3.61, Zn(nta)(ida)'-; 4.01, Cd(nta)(ida)'-; 1.34, Z n (~~t a ) ( m a )~-. The stability constants of the monohydroxy complexes of Zn(nta)-and Zn(tren)'+ were also determined; the log K W the other complexes studied, suggesting that the structure of Zn(tren)" is different from the structures of the other 1 :1 complexes. The structures of the M(nta)(gly)'-, M(nta)(idaI3-, and M ( I I~~) ,~-complexes are discussed on the basis of the formation constants of the ternary complexes. values are 4.01 for Zn(nta)(OH)'-and 2.90 for Zn(tren)(OH)+. The results indicate the tendency of Zn(tren) 2 + U O H )to form mixed complexes with en and gly is significantly less than that of Introduction There has been considerable recent interest in the formation of mixed-ligand complexes in solution, in part due to the use of such complexes as models in studies of metalloenzyme-substrateIn the present work, th...

(1975).The lability of the metal-nitrogen bonds in the Cd(II), Zn(II), and Hg(I1) complexes of (H02CCH2)2N(CH2)nN(CH2C02H)2 (n = 2, 3, 4) has been investigated by proton magnetic resonance spectroscopy. The acetate methylenic protons of each of the complexes give rise t o AB multiplet patterns, indicating the metal-nitrogen bonds to be inert on the n.m.r. time scale. From the temperature dependence of the multiplet patterns, the relative lability of the metal-nitrogen bonds in each series of complexes has been established. In the Cd(I1) and Zn(I1) complexes, the metal-nitrogen bonds become more labile as the size of the internal chelate ring increases whereas it becomes more inert in the Hg(I1) complexes. Also, the mercury-proton coupling constants increase as n is increased from two to four, which is interpreted as evidence that the increased kinetic stability results from structural changes to a more linear N-Hg-N arrangement. The metal-nitrogen bonds in the Cd(I1) complexes havingn = 3 and4 is more labile than in the corresponding Zn(I1) complexes. The thermodynamic stability patterns of the complexes are discussed in terms of their relative kinetic stabilities. DALLASL. RIBENSTEIN, GEORGE BLAKNEY BRYAN J. FUHR. Can. J. Chem. 53,787 (1975). On aCtudiC, par r.m.p., la labiliti des liens metaux-azote dans des complexes du Cd(II), Zn(I1) et du Hg(II) avec (HO~CCHZ)ZN(CHZ)~N(CH~COZH)~ (n = 2, 3,4). Les protons methylCniques de I'acetate de chaque complexe donnent lieu des patrons de type AB sous forme de multiplets, indiquant que les liens metaux-azote sont inertes a I'echelle de temps de la r.m.n. Onapu etablir, grhce la dependance sur la temperature des patrons des multiplets, la labilite relative des liens metaux-azote dans chaque sene des complexes. Dans les complexes Cd(I1) et Zn(II), les liens metaux-azote deviennent plus labiles a mesure que la grandeur du cycle chelate interne augmente alors qu'ils deviennent plus inertes dans les complexes du Hg(I1). De plus les constantes d e couplage mercure-proton augmentent lorsque n augmente de 2 a 4; on interprete ces rksultats comme signifiant que la stabilite cinetique accrue resulte de changements structuraux menant a des arrangements N-Hg-N plus lineaires. Les liens mitaux-azote dans les complexes avec Cd(I1) dans lesquels n = 3 e t 4 sont plus labiles que dans les complexes Zn(I1) wrrespondants. O n discute des patrons de stabilite thermodynamique des complexes en terme de leur stabilitk cinktique relative.[Traduit par le journal]

PMR‐spektroskopische Untersuchungen zeigen, daß die Metall‐N‐Bindungen in den Zn‐ und Cd‐Komplexen (I) mit zunehmender Größe des Chelatringes, also mit wachsendem n, instabiler werden, während sie in den Hg(II)‐Komplexen aufgrund der Strukturänderung zu einer mehr linearen N‐Hg‐N‐Anordnung inerter werden.

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