The room-temperature electronic absorption spectra of [Rh(CNR)4]+ (R = Ph, i-Pr, cyclohexyl, t-Bu, vinyl) in solution do not follow Beer's law. This behavior has been attributed to oligomerization of Rh(CNR)4+ units to form species of the type [Rhn(CNR)4n]n+. Band maxima attributable to oligomers are as follows: R = Ph, 568 nm (n = 2), 727 nm (n = 3), in acetonitrile solution; R = t-Bu, 490 nm (n = 2), 622 nm (n = 3), in aqueous solution; R = i-Pr, 495 nm (n = 2), 610 nm (n = 3), in aqueous solution; R = cyclohexyl, 516 nm (n = 2), in acetonitrile solution; R = vinyl, 555 nm (n = 2), 715 nm (n = 3), 962 nm (n = 4), in aqueous solution. The molar extinction coefficients (εn) and formation constants Kn-1 have been obtained for R = Ph in acetonitrile solution and R = t-Bu in aqueous solution. Parameter values are as follows: for R = Ph, K1 = 35 (15) M-1, ε2 = 1.05 (20) × 104, ε3K2 = 1.83 (40) × 105 M-1; for R = t-Bu, K1 = 250 (125) M-1, ε2 = 1.69 (34) × 104. The x-ray crystal structure of Rh(CNPh)4BPh4 has been completed (final R = 0.057). The compound crystallizes in the Pbcn space group (a = 23.80 (1), b = 19.23 (1), c = 19.08 (1) Å) with four discrete cationic [Rh2(CNPh)8]2+ units and eight BPh4- anions. The dimeric cation has idealized D4d symmetry; the two [Rh(CNPh)4]+ units are bonded face to face so as to give a staggered configuration of ligands. The Rh-Rh distance is 3.193 Å. The electronic absorption spectra of D4d [Rh2(CNR)8]2+ and assumed D4h [Rh3(CNR)12]3+ complexes are interpreted in terms of the interactions expected between the occupied a1g(dz2) and unoccupied a2u[pz, π*(CNR)] monomer orbitals. The lowest band in each of the [Rh2(CNR)8]2+ complexes is assigned to the allowed 1b2 → 2a1 transition. In the spectra of [Rh3(CNR)12]3+ complexes, the lowest band is attributed to 2a1g → 2a2u.
|Number of pages||7|
|Publication status||Published - 1978|
ASJC Scopus subject areas
- Inorganic Chemistry