The reduction of perrhenate, molybdate and pertechnetate with 2-hydrazinopyridine dihydrochloride in methanol has led to the preparation of a class of complexes containing the {M(eta(1)-NNC5H4NHx)(eta(2)-HNNHyC5H4N)} core, represented by [TcCl3(NNC5H4NH)(HNNC5H4N)] (2), [ReCl3(NNC5H4NH)(HNNC5H4N)] (3), and [MoCl3(NNC5H4NH)(HNNHC5H4N)] (6). The reaction of 3 with NEt3 results in the formation of [HNEt3][[ReCl3(NNC5H4N)(HNNC5H4N)] . H2O (4) by deprotonation of the pyridine nitrogen site. Similarly, the reduction of perrhenate with 2-hydrazino-2-imidazoline hydrobromide has led to the preparation of the analogous [ReCl3(NNC3H4N2H)(HNNHC3H4N2H)] (5). Reaction of 3 with pyridine-2-thiol and pyrimidine-2-thiol yields two structurally characterized derivatives with a modified {Re(eta(1)-NNC5H4N)(eta(2)-HNNC5H4N)} core, [Re(C5H4NS)(2)(NNC5H4N)(HNNC5H4N)] (8) and [Re(C4H3N2S)(2)(NNC5H4N)(HNNC5H4N)] (9), respectively. Reaction of 6 with pyrimidine-2-thiol led to the isolation of the analogous [Mo(C4H3N2S)(2)(NNC5H4N)(HNNHC5H4N)] (11) and the seven-coordinate monohydrazine core complex [Mo(C4H3N2S)(3)(NNC5H4N)]. CH2Cl2(12). In similar fashion, the reaction of 2 with pyridine-2-thiol yielded a complex structurally analogous to 8, [Tc(C5H4NS)(2)(NNC5H4N)(HNNC5H4N)] (7). Crystal data for 3, C10H10Cl3N6Re : triclinic, P (1) over bar, a = 7.527(2) Angstrom, b = 7.599(2) Angstrom, c = 13.118(3) Angstrom, or 106.55(3)degrees, beta = 90.28(3)degrees, gamma = 93.83(3)degrees, V = 717.4(4) Angstrom(3), Z = 2. For 4, C16H27Cl3N7ORe : orthorhombic, P2(1)2(1)2(1), a = 7.503(2) Angstrom, b = 10.3643(2) Angstrom, c = 30.1540(5) Angstrom, V = 2345.20(6) Angstrom(3), Z = 2. For 5, C6H12Cl3N8Re : monoclinic, P2(1)/n, a = 9.093(2) Angstrom, b = 11.105(2) Angstrom, c = 14.295(3) Angstrom, beta = 94.71(3)degrees, V = 1438.6(7) Angstrom(3), Z = 4. For 6, C10H11Cl3N6Mo : monoclinic, P2(1)/c, a = 15.366(3) Angstrom, b = 7.804(2) Angstrom, c = 12.378(3) Angstrom, beta = 95.92(3)degrees, V = 1476.4(5) Angstrom(3), Z = 4. For 7, C20H17N8S2Tc : monoclinic, P2(1), a = 8.827(2) Angstrom, b = 9.278(2) Angstrom, c = 13.304(3) Angstrom, beta = 98.92(3)degrees, V = 1076.5(5) Angstrom(3) Z = 2, 2564 reflections. For 8, C20H17N8S2Re : monoclinic, P2(1), a = 8.848(2) Angstrom, b = 9.190(2) Angstrom, c = 13.293(3) Angstrom, beta = 98.89(3)degrees, V = 1067.9(5) Angstrom(3), Z = 2. For 9, C18H15N10S2Re : monoclinic, P2(1), a = 8.796(2) Angstrom, b = 9.008(2) Angstrom, c = 13.208(3) Angstrom, beta = 97.90(3)degrees, V = 1036.6(5) Angstrom(3), Z = 2. For 12, C18H15N9S3Cl2Mo : monoclinic, P2(1)/n, a = 10.52900(10) Angstrom, b = 15.1116(3) Angstrom, c = 15.8193(3) Angstrom, beta = 108.4790(10)degrees, V = 2387.23(7) Angstrom(3), Z = 4. Complexes 2 and 3 serve as models for the binding of Tc(V)-oxo and Re(V)-oxo species to hydrazinonicotinamide (HYNIC)-conjugated chemotactic peptides. Furthermore, since the use of the pyrimidinethiol coligand in the {Tc-99m-HYNIC-peptide} radiochemical species results in favorable pharmacokinetics, the thiolate derivatives 8 and 9 provide models for possible modes of interaction of metal-hydrazine cores with coligands in the radiopharmaceutical reagents.