An organometallic complex represented by Formula IA: wherein: the dashed line represents a coordinative bond; M is zinc or magnesium; X is a monoanionic ligand; A is a bridging moiety having a general Formula A1, A2 or A3: -C 1 R 5 R 6 - Formula A1 -C 1 (R 7 R 8)-C 2 (R 9 R 10)- Formula A2 -C 1 (R 11 R 12)-C 2 (R 13 R 14)-C 3 (R 15 R 16)- Formula A3 wherein R 5 -R 12, R 15 and R 16 are each independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl, heteroaryl and heteroalicyclic, R 13 and R 14 are each independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, heteroalicyclic, hydroxyl, alkoxy, thiol, thioalkoxy, aryloxy, and amine or, alternatively, at least two of R 1, R 2 and R 6 -R 6 in Formula A1, or at least two of R 1, R 2 and R 7 -R 10 in Formula A2 or at least two of R 1, R 2 and R 11 -R 16 in Formula A3 form a 5 to 7-membered alicyclic, heteroalicyclic, aromatic or heterocyclic ring; m is an integer of from 1 to 6, or from 1 to 4, or from 1 to 2; Ra and Rb are each independently hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, heteroalicyclic, hydroxyl, alkoxy, thiol, thioalkoxy, aryloxy, and amine, wherein when m is other than 1, Ra and Rb in each (CRaRb) unit can be the same or different, and one or both Ra and Rb in one unit can form a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring with one or both Ra and Rb of an adjacent unit; n is an integer of from 1 to 6, or from 1 to 4, or from 1 to 2; Rc and Rd are each independently hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, heteroalicyclic, hydroxyl, alkoxy, thiol, thioalkoxy, aryloxy, and amine, wherein when n is other than 1, Rc and Rd in each (CRcRd) unit can be the same or different, and one or both Rc and Rd in one unit can form a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring with one or both Rc and Rd of an adjacent unit; R 1 and R 2 are each independently hydrogen, alkyl, cycloalkyl, aryl or alternatively, one or both of R 1 and R 2 form together, optionally with one or more carbon atoms in A, a heteroalicyclic or heteroaromatic, 5-membered, 6-membered or 7-membered ring; andR 23 -R 30 are each independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl, halo, alkoxy, aryloxy, trialkylsilyl, heteroalicyclic, heteroaryl and amine. the dashed line represents a coordinative bond; M is zinc or magnesium; X is a monoanionic ligand; A is a bridging moiety having a general Formula A1, A2 or A3: -C 1 R 5 R 6 - Formula A1 -C 1 (R 7 R 8)-C 2 (R 9 R 10)- Formula A2 -C 1 (R 11 R 12)-C 2 (R 13 R 14)-C 3 (R 15 R 16)- Formula A3 wherein R 5 -R 12, R 15 and R 16 are each independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl, heteroaryl and heteroalicyclic, R 13 and R 14 are each independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, heteroalicyclic, hydroxyl, alkoxy, thiol, thioalkoxy, aryloxy, and amine or, alternatively, at least two of R 1, R 2 and R 6 -R 6 in Formula A1, or at least two of R 1, R 2 and R 7 -R 10 in Formula A2 or at least two of R 1, R 2 and R 11 -R 16 in Formula A3 form a 5 to 7-membered alicyclic, heteroalicyclic, aromatic or heterocyclic ring; m is an integer of from 1 to 6, or from 1 to 4, or from 1 to 2; Ra and Rb are each independently hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, heteroalicyclic, hydroxyl, alkoxy, thiol, thioalkoxy, aryloxy, and amine, wherein when m is other than 1, Ra and Rb in each (CRaRb) unit can be the same or different, and one or both Ra and Rb in one unit can form a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring with one or both Ra and Rb of an adjacent unit; n is an integer of from 1 to 6, or from 1 to 4, or from 1 to 2; Rc and Rd are each independently hydrogen, alkyl, cycloalkyl, aryl, heteroaryl, heteroalicyclic, hydroxyl, alkoxy, thiol, thioalkoxy, aryloxy, and amine, wherein when n is other than 1, Rc and Rd in each (CRcRd) unit can be the same or different, and one or both Rc and Rd in one unit can form a 5-membered, 6-membered or 7-membered alicyclic, heteroalicyclic, aromatic or heteroaromatic ring with one or both Rc and Rd of an adjacent unit; R 1 and R 2 are each independently hydrogen, alkyl, cycloalkyl, aryl or alternatively, one or both of R 1 and R 2 form together, optionally with one or more carbon atoms in A, a heteroalicyclic or heteroaromatic, 5-membered, 6-membered or 7-membered ring; andR 23 -R 30 are each independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl, halo, alkoxy, aryloxy, trialkylsilyl, heteroalicyclic, heteroaryl and amine.