A ligand represented by the formula (1): R1R2N-Q1-X-Q2-NR3R4  (1) wherein R1, R2, R3 and R4 are each the same or different and represent a group represented by the formula (2): wherein Q3 is an optionally substituted alkylene group, an optionally substituted cycloalkylene group, an optionally substituted arylene group, or an optionally substituted divalent heterocyclic group, R5 is an optionally substituted alkyl group, an optionally substituted aryl group or an optionally substituted heterocyclic group and R6 is a substituent which may coordinate or bind to a metal atom, or R5 and R6, taken together, may form a ring, Q1 and Q2 are each the same or different and represent an optionally substituted alkylene group or a single bond, and X is a divalent spacer.