1-Azabicyclo[3.2.0]hept-2-ene-2-carboxylic acid,6-(1-hydroxyethyl)-3-[7-[(2-imino-1(2H)-pyridinyl)methyl]-1-(1H-tetrazol-5-yl)-3-phenanthrenyl]-4-methyl-7-oxo-, monopotassium salt