Ab initio quantum mechanical methods were employed to study the periodic trends of transition metal (M Ti, V, and Cr) hydrides MH(2), dihydride dihydrogen complexes MH(2) . H-2, and-tetrahydrides MH(4). The configuration interaction with single and double excitations (CISD), coupled cluster including all single and double substitutions (CCSD) methods, and CCSD with the effects of connected triple excitation added perturbatively [CCSD(T)] were used with the TZP, TZP+f, and TZP(f,d) basis sets. The ground electronic states for TiH2 and VH2 were found to be B-3(1) and B-4(2), respectively. The bond angles for the TiH2 and VH2 molecules are predicted to be 142 degrees and 139 degrees, respectively, at the TZP(f,d) CISD level of theory. On the low-spin potential energy surfaces, the lowest lying electronic states for the TiH2, VH2, and CrH2 molecules are (1)A(1), (2)A(1), and B-3(2), respectively.