Ferromagnetic Coupling in "Double-Bridged" Dihydrogenpyrophosphate Complexes of Cobalt(II) and Nickel(II).

Three isostructural compounds of the formula {[M(bipy)(H2O)(H2P2O7)]2·2H2O} [bipy = 2,2'-bipyridine; M = Ni (1), Co (2), Mn (3)] have been isolated from aqueous solutions containing the corresponding metal(II) chloride hydrate with a bipy and sodium pyrophosphate solution in a 1:1:2 molar ratio, and their structures were determined by single-crystal X-ray diffraction. The structures of 1-3 consist of neutral aqua(2,2'-bipyridine)metal(II) dinuclear units bridged by two dihydrogenpyrophosphate groups adopting a bidentate/monodentate mode. Each metal ion in 1-3 is six-coordinate in a distorted octahedral geometry, with the reduced value of the angle subtended by the chelating bipy at the metal ion [79.6(1)° (1), 77.32(7)° (2), and 72.9(1)° (3)] being the main source of this distortion. The values of the intramolecular metal-metal separation are 5.271(1) Å (1), 5.3065(8) Å (2), and 5.371(1) Å (3). Magnetic susceptibility measurements on polycrystalline samples of 1-3 in the temperature range 1.9-300 K shows weak intramolecular ferromagnetic [J = +1.86(2) cm(-1) (1) and +0.25(1) cm(-1) (2)] and antiferromagnetic [J = -0.48(1) cm(-1) (3)] coupling, with the spin Hamiltonian being defined as H = -JSM1·SM1a. This rarely observed coordination mode for dihydrogenpyrophosphate leads to ferromagnetic coupling in complexes of nickel(II) or cobalt(II).

Clinical isolates of Candida albicans, Candida tropicalis, and Candida krusei have different susceptibilities to Co(II) and Cu(II) complexes of 1,10-phenanthroline.

The minimal inhibitory concentrations (MICs) of copper and cobalt based dimeric pyrophosphate complexes with capping 1,10-phenanthroline groups on clinical isolates of C. albicans (28 isolates), C. krusei (20 isolates) and C. tropicalis (20 isolates) are reported. C. albicans was inhibited by the cobalt complex better than by the copper complex, while C. krusei demonstrated the opposite results. C. tropicalis showed similar sensitivities to both metals in terms of calculated MIC50 values but was more sensitive to cobalt when MIC90 values were noted. Knockout strains of C. albicans that had the copper efflux protein P-type ATPase (CRP1), the copper binding metallothionein CUP1 or both CRP1/CUP1 removed clearly demonstrate that the origins of copper resistant in C. albicans lies primarily in the P-type ATPase, with the MT playing an important secondary role in the absence of the efflux protein. This study suggests that certain strains of Candida have evolved to protect against particular metal ions and that in the case of C. albicans, a primary invasive fungal species, cobalt may be a good starting-point for new therapeutic development.