The dicopper(II) complex with the ligand N,N,N',N',N"-pentakis[(1-methyl-2-benzimidazolyl)methyl]dipropylenetriamine (LB5) has been synthesized and structurally characterized. The small size and the quality of the single crystal required that data be collected using synchrotron radiation at 276 K. [Cu(2)(LB5)(H(2)O)(2)][ClO(4)](4): platelet shaped, P&onemacr;, a = 11.028 Å, b = 17.915 Å, c = 20.745 Å, alpha = 107.44 degrees, beta = 101.56 degrees, gamma = 104.89 degrees, V = 3603.7 Å(3), Z = 2; number of unique data, I >/= 2sigma(I) = 3447; number of refined parameters = 428; R = 0.12. The ligand binds the two coppers nonsymmetrically; Cu1 is coordinated through five N donors and Cu2 through the remaining three N donors, while two water molecules complete the coordination sphere. Cu1 has distorted TBP geometry, while Cu2 has distorted SP geometry. Voltammetric experiments show quasireversible reductions at the two copper centers, with redox potential higher for the CuN(3) center (0.40 V) and lower for the CuN(5) center (0.17 V). The complex binds azide in the terminal mode at the CuN(3) center with affinity lower than that exhibited by related dinuclear polyaminobenzimidazole complexes where this ligand is bound in the bridging mode. The catechol oxidase activity of [Cu(2)(LB5)](4+) has been examined in comparison with that exhibited by [Cu(2)(L-55)](4+) (L-55 = alpha,alpha'-bis{bis[(1-methyl-2-benzimidazolyl)methyl]amino}-m-xylene) and [Cu(2)(L-66)](4+) (L-66 = alpha,alpha'-bis{bis[2-(1-methyl-2-benzimidazolyl)ethyl]amino}-m-xylene) by studying the catalytic oxidation of 3,5-di-tert-butylcatechol in methanol/aqueous buffer pH 5.1. Kinetic experiments show that [Cu(2)(L-55)](4+) is the most efficient catalyst (rate constant 140 M(-1) s(-1)), followed by [Cu(2)(LB5)](4+) (60 M(-1) s(-1)), in this oxidation, while [Cu(2)(L-66)](4+) undergoes an extremely fast stoichiometric phase followed by a slow and substrate-concentration-independent catalytic phase. The catalytic activity of [Cu(2)(L-66)](4+), however, is strongly promoted by hydrogen peroxide, because this oxidant allows a fast reoxidation of the dicopper(I) complex during turnover. The activity of [Cu(2)(LB5)](4+) is also promoted by hydrogen peroxide, while that of [Cu(2)(L-55)](4+) is little affected. The phenol monooxygenase activity of [Cu(2)(LB5)](2+) has been compared with that of [Cu(2)(L-55)](2+) and [Cu(2)(L-66)](2+) by studying the ortho hydroxylation of methyl 4-hydroxybenzoate to give methyl 3,4-dihydroxybenzoate. The LB5 complex is much more selective than the other complexes since its reaction produces only catechol, while the main product obtained with the other complexes is an addition product containing a phenol residue condensed at ring position 2 of the catechol.

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Solid and circular cone angles and ligand profiles have been calculated for some sulfoxides, showing that S-bonded ligands are markedly bulkier than 0-bonded ligands. An application of the cone angles to complexes of Ru" and Ruii' showed that the bonding mode of sulfoxides appears to be the result of a balance between electronic and steric effects. The complex mer-[RuCl,(dpso),] (dpso = Ph,SO) has been synthesized and structurally characterized: triclinic, space group P i , Z = 2 with a = 10.315(3), b = 13.093(4), c = 15.692(5) A, a = 102.98(2), p = 106.79(1), y = 102.17(2)". TWO of the three sulfoxides are 0and one is S-bonded. One dpso-0 is trans to dpso-S, while the other is trans to CI. The co-ordination bond distances are consistent with the trans-influence order 0 < CI < S. Strain-energy and conformational-entropy terms of three isomers of mer-[RuCl,(dpso),] have been evaluated through molecular mechanics calculations. The energy difference of 7.6 kcal mol-' between the characterized complex and the linkage isomer with two trans dpso-S ligands indicates that the isomer isolated is probably favoured thermodynamically and suggests that the interligand steric interactions play an important role in the isomer stability.

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