Bifunctional single amino acid chelates for labeling of biomolecules with the {Tc(CO)3}+ and {Re(CO)3}+ cores.: Crystal and molecular structures of [ReBr(CO)3(H2NCH2C5H4N)], [Re(CO)3{(C5H4NCH2)2NH}]Br, [Re(CO)3{(C5H4NCH2)2NCH2CO2H}]Br, [Re(CO)3{X(Y)NCH2CO2CH2CH3}]Br (X = Y=2-pyridylmethyl; X=2-pyridyimethyl, Y=2-(1-methylimidazolyl)methyl; X = Y=2-(1-methylimidazolyl)methyl), [ReBr(CO)3{(C5H4NCH2)NH(CH2C4H3S)}], and [Re(CO)3{(C5H4NCH2)N(CH2C4H3S)(CH2CO2)}]