The complex Na-3[{Ni-II(nmp)}(3)S(3)BTA(alk))] (1) (nmp(2-) = deprotonated form of N-(2-mercaptoethyl)-picolinamide; H(3)S(3)BTA(alk) = N-1,N-3,N-5-tris(2-mercaptoethyl)-benzene-1,3,5-tricarboxamide, where H = dissociable protons), supported by the thiolate-benzenetricarboxamide scaffold (S(3)BTA(alk)), has been synthesized as a trimetallic model of nickel-containing superoxide dismutase (NiSOD). X-ray absorption spectroscopy (XAS) and H-1 NMR measurements on 1 indicate that the Ni(II)centers are square-planar with N2S2 coordination, and Ni-N and Ni-S distances of 1.95 and 2.16 A, respectively. Additional evidence from IR indicates the presence of H-bonds in 1 from the approximately-200 cm(-1) shift in v(NH) from free ligand. The presence of H-bonds allows for speciation that is temperature-, concentration-, and solvent-dependent. In unbuffered water and at low temperature, a dimeric complex (1(A); lambda = 410 nm) that aggregates through intermolecular NH center dot center dot center dot O=C bonds of BTA units is observed. Dissolution of 1 in pH 7.4 buffer or in unbuffered water at temperatures above 50 degrees C results in monomeric complex (1(M); lambda = 367 nm) linked through intramolecular NH center dot center dot center dot S bonds. DFT computations indicate a low energy barrier between 1A and 1M with nearly identical frontier MOs and Ni-ligand metrics. Notably, 1(A) and 1(M) exhibit remarkable stability in protic solvents such as MeOH and H2O, in stark contrast to monometallic [Ni-II(nmp)(SR)](-) complexes. The reactivity of 1 with excess OD H2O2, and O-2(center dot-) is species dependent. IR and UV-vis reveal that 1A in MeOH reacts with excess O-2 to yield an S-bound sulfinate, but does not react with O-2(center dot-). In contrast, 1M is stable to O-2 in pH 7.4 buffer, but reacts with O-2(center dot-) to yield a putative [Ni-II(nmp)(O-2)](-) complex from release of the BTA-thiolate based on EPR