Synthesis, X-ray single crystal and magnetic study of new heteroleptic late transition metal alkoxdes with tetranuclear square planar metal core, Co<sub>4</sub>Cl<sub>2</sub(OC<sub>2</sub>H<sub>4</sub>OEt)<sub>6</sub>, Co<sub>4</sub>(O <sub>2</sub>(acac)<sub>6</sub>(MeOH)<sub>2</sub> and Zn<sub>4</sub>(OMe)<sub>2</sub>(acac)<sub>6</sub>(C<sub>7</sub>H<sub>8</sub>)