A series of diruthenium phosphine carbonyl complexes containing bridging nitro and nitrate groups, [Ru-2(CO)(4)-(mu-NO2)(2)L(2)] (1-4) and [Ru-2(CO)(4)(mu-NO3)(2)L(2)] (5-9), were cleanly prepared from the reactions of [Ru-2(CO)(4)-(NCMe)(4)L(2)][BF4](2) (L = PPh(3), PPh(2)(allyl), PPh(2)Me, PPhMe(2), or PMe(3)) with excess NaNO2 or NaNO3 in MeOH. Complexes 1-4 are present in two isomeric forms, A and B, with a head-to-head orientation of two bridging eta(2)-(N,O)-NO2 groups for form A and a head-to-tail arrangement of the groups for form B, in an approximate 3:1 ratio, but complexes 5-9 are present in only one isomeric form with an eta(2)-(O,O)-NO3 attachment. Crystal data : 1A, a = 12.452(2) Angstrom, b = 23.520(3) Angstrom, c = 13.441(2) Angstrom, beta = 98.280(1)degrees, monoclinic P2(1)/n, Z = 4; 5, a = 11.737(3) Angstrom, b = 23.496(5) Angstrom, c = 14.629(3) Angstrom, beta = 100.34(2)degrees, monoclinic P2(1)/n, Z = 4. The five-membered metallacycle {Ru-2(ONO)} in 5-9 is more reactive than the four-membered metallacycle {Ru-2(NO)} in 1-4, reflected by the different reactivity of [Ru-2(CO)(4)(mu-NO2)(2)(PPh(3))(2)] (1) and [Ru-2(CO)(4)(mu-NO3)(2)(PPh(3))(2)] (5) with various reagents to give [Ru-2(CO)(4)(mu-I)2(PPh3)(2)] (I), [Ru-2(CO)(4)(mu-N-3)(2)(PPh(3))(2)] (11), and [Ru-2(CO)(4)(eta(1)-NO3)(2)(mu-X)(2)(PPh(3))(2)] (X = Br (12), I (13)). Crystal data of 13 : a = 31.394(3) Angstrom, b = 9.761(1) Angstrom, c = 18.200(2) Angstrom, beta = 118.420(1)degrees, monoclinic C2/c, Z = 4. The intermolecular oxygen transfer from the ligated NO2 groups in 1 to exogenous PMe(3) is readily observed in MeCN at ambient temperature, apparently forming nitrosyl groups and free OPMe(3).