Angular expression within an ng-repeat

When trying to include an angular expression within ng-repeat, I am getting an Error. I’m being able to use {{val}} which is being passed by state.params outside the ng-repeat, but not inside it.

.factory('Chats', function($http) {
    var data = $http.get('https://oom-hgt.firebaseio.com/.json');
    return {
        oom1: function() {
            return data;
        }
    };   

.controller('OOM', function($scope, $state, Chats) {
  Chats.oom1().then(function successCallback(response) {
      $scope.oom = response.data, 
      });
      $scope.val = $state.params.val;
}); 

<ion-list ng-repeat = "(key,val) in  oom">
  <ion-item href="#/app/a1/{{key}}">
      <div>{{key}}
      </div>
    </div>
  </ion-item>
</ion-list>

  <ion-item ng-show='item.NAME.length > 0' ng-repeat="item in oom.{{val}}">
    <span>
      <div class="row">
        <div class="col">{{item.RANK}}
        </div>
        <div class="col col-75">{{item.NAME}}
        </div>
        <div class="col">{{item.PLAYED}}
        </div>
        <div class="col">{{item.POINTS}}
        </div>
      </div>
    </span>
  </ion-item>