STRUCTURES OF 2 SPIRO(CYCLOPROPANE-1,3'-INDOLINE)-CIS,SYN-1,3-DIMETHYLURACIL CYCLOBUTANE PHOTODIMERS

(1) 4a-(Spiro[cyclopropane-1,3'-indolin]-2'-yl)-1,3,6,8-tetramethyl-4a,4b,8a,8b-tetracyclobuta-[1,2-d:4,3-d']dipyrimidine-2,4,5,7(1H,3H,6H,8H)-tetraone, C22H25N5O4, M(r) = 423.52, monoclinic, P2(1)/c, a = 7.868 (4), b = 14.167 (4), c = 18.340 (6) angstrom, beta = 92.69 (4)-degrees, V = 2042 (1) angstrom 3, Z = 4, D(m) = 1.37, D(x) = 1.38 g cm-3, lambda(Mo K-alpha) = 0.71073 angstrom, mu(Mo K-alpha) = 0.91 cm-1, F(000) = 896, T = 298 K, R = 0.0548 for 2868 observed data [F0 > 3-sigma(F(o))] of 5805 unique data collected. (2) C22H25N5O4, M(r) = 423.52, orthorhombic, Pna2(1), a = 22.856 (12), b = 7.785 (4), c = 11.604 (3) angstrom, V = 2065 (1) angstrom 3, Z = 4, D(m) 1.36, D(x) = 1.36 g cm-3, lambda(Mo K-alpha) = 0.71073 angstrom, mu(Mo K-alpha) = 0.90 cm-1, F(000) = 896, T = 298 K, R = 0.0808 for 2172 observed data [F(o) > 3-sigma(F0)] of 4405 unique data collected. While differing only in configuration at the indoline C atom between the cyclobutyl group of the dimer and the N atom of the indoline, these two compounds exhibit markedly different dimer splitting efficiencies upon photochemical excitation of the indoline chromophore. For a given solvent, the splitting efficiency for (1) is twice that of (2).